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Semin Reprod Med. Author manuscript; available in PMC 2009 August 17. Published in final edited form as: Published online 2008 October 24. doi: 10.1055/s-0028-1096128. | PMCID: PMC2728121 NIHMSID: NIHMS121242 |
MicroRNA Signature and Regulatory Functions in the Endometrium during Normal and Disease States Qun Pan, M.D., Postdoctoral Associate and Nasser Chegini, Ph.D., Professor Division of Reproductive Endocrinology and Infertility, Department of Obstetrics and Gynecology, University of Florida, Gainesville, Florida During the menstrual cycle, human endometrium undergoes extensive cyclic morphologic and biochemical modifications in preparation for embryo implantation. These processes are highly regulated by ovarian steroids and various locally expressed gene products and involve inflammatory reaction, apoptosis, cell proliferation, angiogenesis, differentiation (tissue formation), and tissue remodeling. MicroRNAs (miRNAs) have emerged as key regulators of gene expression, and their altered and/or aberrant expression has been associated with establishment and progression of various disorders, including tumorigenesis. This review highlights the endometrial expression of miRNAs and their potential regulatory functions under normal and pathologic conditions such as endometriosis, dysfunctional uterine bleeding, and endometrial cancer. Given the key regulatory function of miRNAs on gene expression stability, understanding the underlying mechanisms of how endometrial miRNAs are regulated and identifying their specific target genes and their functions might lead to the development of preventive and therapeutic strategies by regulating specific target genes associated with such reproductive disorders. Keywords: MicroRNA, endometrium, gene expression, gene regulation, endometrial disorders During the menstrual cycle, endometrium undergoes extensive cyclic morphologic and biochemical modifications in preparation for embryo implantation that are remarkably consistent during each cycle throughout the reproductive years. This process, which begins with degenerative signals resulting in menstrual bleeding and endometrial shedding, integrates many overlapping and dynamic events to regenerate and become receptive. The endometrial regenerative process is initiated by an inflammatory reaction followed by a rapid cell proliferation, angiogenesis, differentiation (tissue formation), and tissue remodeling. 1–7 If conception is not established, endometrium is ready to begin the next cycle. Ovarian sex steroids are central to endometrial regenerative and receptive processes. Accumulative evidence also suggests that endometrial expression of various autocrine/paracrine regulators, including many growth factors, cytokines, chemokines, proteases, and extracellular matrix, serve as key components of these processes. 1–7 The endometrial expression of these molecules must be optimal, precise, and synchronized to generate a timely progression of their signaling pathways. Any alterations in the expression of these mediators seem to be responsible for inappropriate tissue regeneration, embryo implantation failure, and other uterine abnormalities, including dysfunctional uterine bleeding, endometriosis, and endometrial cancer. 8–11miRNA AND GENE EXPRESSION STABILITY Whether regulated independently or through an ovarian steroid-dependent manner, expression of endometrial genes is subjected to transcriptional and translational regulation that establishes the framework of their biological functions throughout the menstrual cycle. Since their discovery less than a decade ago, microRNAs (miRNAs) have emerged as key regulators of gene expression stability. 12,13 These small, non–protein-coding RNAs are transcribed from specific genes with primary transcripts (pri-miRNAs) of several kilobases in length. The pri-miRNAs undergo substantial processing that results in generation of a 70- to 90-nucleotide (nt) stem-loop precursor miRNA (pre-miRNA) in the nucleus. After transportation into the cytoplasm, the pre-miRNAs undergo a second cleavage by Dicer generating a double-stranded miRNA duplex containing 2-nt-long 3′ overhangs that unwind and form a single-strand, mature miRNA. 14–16 The mature miRNAs incorporate into the RNA-induced silencing complex (RISC) and through complementary interaction with target genes regulate their expression mostly, but not always through translational repression. 13,17 The miRNA-induced translational repression is considered to involve two distinct mechanisms: the inhibition of translation initiation and/or inhibition of a “postinitiation” step in translation, which also elicits co-translational degradation of the nascent peptide. 18–20 Through this mechanism, miRNAs influence the outcome of various cellular activities under normal and disease conditions. Many putative miRNAs have been identified and/or predicted in the genome of different species, including in mammals, with potential of targeting the expression of a large number of protein-coding and possibly non–protein-coding genes. 21,22 In the human, around 580 miRNAs have been identified and more than 1000 predicted. Because the specificity of miRNAs is dictated by 6 to 7 nt that bind to the 3′ untranslated region (3′ UTR) of their target mRNAs, a single miRNA can potentially target hundreds of genes, or a single gene could be a potential target of many different miRNAs. 23–25 Although the biological significance of such diversity is unclear, it appears that binding of several miRNAs may be required to achieve adequate regression of a specific target gene. Because the extent of miRNA-induced gene regression depends on the degree of complementary sequence homology with the target gene, 13,24 the level of regression may vary significantly and, to date, only 70 to 100 specific target genes have been experimentally confirmed as targets of several miRNAs. POTENTIAL REGULATORY FUNCTION OF miRNAs IN THE ENDOMETRIUM Upon the establishment of regular ovulatory cycles, the endometrium under the influence of sex steroids undergoes substantial cyclic morphologic and biochemical changes. Estrogen acts as a mitogen for various endometrial cells, and progesterone acting on the estrogen-primed endometrium induces differentiation and secretory changes in the glandular epithelial cells. Although the mid–luteal phase rise in estrogen is not essential for successful embryo implantation, 26,27 the uterus retains its responsiveness to sex steroid hormones, and endometrial cycles can be induced to become receptive for embryo implantation even after menopause. 28 Progesterone also causes stromal decidualization and prepares the endometrium for embryo implantation, and a sudden decline in sex steroids production at the end of luteal phase initiates normal menstrual bleeding. 6,29,30 Estrogen and progesterone mediate their actions through estrogen receptors (ERs) and progesterone receptors (PRs), respectively. These receptors are ligand-activated transcription factors, and their activation leads to regulation of expression of their target genes in cell- and promoter-specific manners in ovarian steroid sensitive tissues, including the endometrium. Accumulated evidence supports the expression and regulatory function of many gene products in the endometrium throughout the menstrual cycle under normal and pathologic conditions. 5,6,11,28,31–34 The expression of these genes, which include many inflammatory and immune mediators, fibrinolytic and proteolytic enzymes, cell-cycle and apoptotic regulators, extracellular matrix, adhesion molecules, and angiogenic factors and their receptors, are differentially regulated during the menstrual cycle as part of preparation for endometrial degenerative and reparative processes. 1–7 These intrinsic molecules are expressed and released by activated platelets, inflammatory and immune-related cells infiltrating into the endometrium, as well as by endometrial epithelial, stromal, and vascular endothelial cells. Altered endometrial expression of these molecules seems to be responsible for inappropriate tissue regeneration, resulting in dysfunctional uterine bleeding, failure in embryo implantation, as well as many other endometrial disorders. 1,5,6,8–11,31,34–39 Gene expression is regulated at multiple levels, including at transcriptional and translational levels and influenced by miRNA regulatory functions. Although the field of miRNA research has rapidly evolved during the past few years, only limited information is currently available for their expression and functions in human reproductive tract tissues. Given the key regulatory function of miRNAs in gene expression, it is pivotal to define their expression and their underlying mechanism of actions and regulation in these tissues. It is also essential to identify the specific genes relevant to endometrium targeted by these miRNAs at various stages of normal menstrual cycle and associated abnormalities. We have recently reported the expression profile of a few hundred miRNAs in human endometrium and endometrial stromal and epithelial cells. 40 Of the 287 human miRNAs profiled, we identified the expression of 65 miRNAs in the endometrium, of which 32 were differentially expressed in endometrial stromal and glandular epithelial cells isolated from the same tissues. Such a sharp reduction in expression of a large number of miRNAs in isolated endometrial cells implies the importance of endometrial microenvironment on regulation of miRNA expression. The decline in the number of miRNAs expressed in the endometrial cells compared with their original tissues also reflects possible regulatory function of ovarian steroids or many locally expressed mediators on the expression of these miRNAs by various endometrial cells. However, our study was limited to endometrial tissues of the early to mid luteal phase of the menstrual cycle to draw any specific conclusion, as the profile of miRNA expression most likely differs in endometrium from other phases of the menstrual cycle. To provide support for the influence of ovarian steroids, we used isolated endometrial cells cultured under defined conditions and identified the regulatory action of ovarian steroids on the expression of a selected number of these miRNAs. 40Among the miRNAs regulated by 17β estradiol and progesterone in the endometrial epithelial and stromal cells are miR-20a, miR-21, miR-23, miR-26a, miR-18a, miR-181a, miR-206, and miR-142-5p. 40 These miRNAs have been predicted to target the expression of a large number of genes, including transforming growth factor, β (TGF-β), TGF-β receptors, ERs, PRs, and CYP-19A1 (aromatase), many of which are known to play critical roles in endometrial activities. 40 We are further investigating the expression of specific genes targeted by these miRNAs in the endometrial cells with the aim of identifying the mechanism by which these miRNAs regulate gene expression relevant to the endometrium. Accumulated evidence has been generated in support of the expression of miRNAs in various cells and tissues under normal and disease conditions. 15,40–44 Recent functional analysis of several miRNAs has revealed their key regulatory influence of the expression of target genes involved in various cellular activities under normal physiologic and disease conditions, more specifically developmental processes and tumorigenesis. 15,40–43 In particular, miRNAs target the expression of genes involved in cell-cycle progression, differentiation, apoptosis, inflammatory and immune response, and angiogenesis (). 42,44–48 These cellular processes are integrated in parts of the endometrial regeneration throughout the menstrual cycle that are regulated by sex steroids and a vast number of gene products whose expression may be the target of miRNA regulatory functions. miRNAs AND ENDOMETRIAL INFLAMMATORY RESPONSE The onset of menstruation is associated with the expression of a network of highly active substances with inflammatory- and immune-related activities. 6,35 The endometrial expression of these inflammatory and immune mediators is necessary for progression of tissue degeneration during menses. It is also necessary for the progression of tissue repair mechanisms after menses as deficiency in inflammatory response results in wound impairment. 49 The mechanisms that control the expression of these mediators and terminate their activities are complex and regulated at different levels, including at the level of gene expression stability. Several miRNAs have been identified to influence the expression of inflammatory and immune response mediators, more specifically let7, miR-17–5p, miR-20a, miR-106a, miR-125b, miR-146, and miR-155 ( Table 1; ). 50–55 Of particular importance to these processes are recent studies showing that expression of miR-125b and miR-155 is necessary for proper development of T, B, and dendritic cells. 52–55 It was revealed that exposure of macrophages to endotoxin, proinflammatory cytokines, such as tumor necrosis factor α (TNF-α), and increase in nuclear factor of kappa light polypeptide gene enhancer in B cells (NF-κB) activity altered the expression of these miRNAs. The authors suggested the direct involvement of NF-κB transcriptional activity, a key element in inflammatory response, in regulating the expression of these miRNAs. 53 Interestingly, miR-155 targeted the expression of several proteins involved in lipopolysaccharide (LPS) signaling and enhanced TNF-α translation, and miR-125b downregulated TNF-α expression. Because exposure of Emu-miR-155 transgenic mice to endotoxin resulted in elevated production of TNF-α, this study provided further evidence for interactive regulatory functions between inflammatory response and miR-155 and miR-125b expression. | Table 1A List* of Some miRNAs Whose Expression Has Been Identified in Human Endometrial and Endometriosis Implants23 as well as in Several Other Cells and Tissues |
The endometrial expression of these miRNAs 40 along with expression of several proinflammatory cytokines, including TNF-α and increased NF-κB activity, 56–61 raised the possibility that miR-125b and miR-155 may function in similar manners regulating the endometrial inflammatory and immune response. This regulatory function is specifically relevant to endometrial activities during menses and dysfunctional uterine bleeding, characterized by an increased expression of proinflammatory mediators, including TNF-α and increased NF-κB activity. However, it remains unclear if inflammation causes the expression of specific miRNAs or if unregulated expression of miRNAs results in activation of inflammation-associated genes during an inflammatory response. If the endometrial expression of these miRNAs differs in women experiencing normal menstruation compared with those with dysfunctional uterine bleeding, unregulated expression of specific miRNAs and their target genes may account for manifestation of this disorder. We have identified and are currently analyzing such a relationship between the expression of a selective number of these miRNAs and the target genes with specific reference to dysfunctional endometrial bleeding. The expression of miR-125b and miR-155 and their response to TNF-α has also been found to be cell lineage dependent. 53 Tili et al suggested that differential expression of miR-125b is specific to cells of the immune system limiting the level and duration of the immune response before it becomes detrimental, and in breast cancer MCF7 cells it may regulate cell homeostasis and proliferation. 53 In this respect, a selective expression of miRNAs not only in endometrial epithelial and stromal cells but also in inflammatory- and immune-related cells and the vasculature may influence the outcome of gene expression with multiple activities in a cell-dependent and/or menstrual cycle–dependent manner. Infiltrating macrophages and T cells and an increase in their populations is critical to various endometrial activities, specifically during menses and dysfunctional uterine bleeding, and may be regulated in similar manners in the endometrium. The inflammatory activation of monocytes has also been reported to cause NF-κB–dependent induction of miR-146, resulting in inhibition of TNF-α receptor-associated factor 6 (TRAF6) and interleukin-1 receptor associated kinase 1 (IRAK1) expression. 62 TRAF6 and IRAK1 act downstream from Toll-like receptor (TLR) and cytokine signaling, 62 whose expression has been identified in human endometrium. 5,31 Interestingly, miR-146a expression is triggered by cell surface and not by intracellular TLR, which mainly senses viral nucleic acids, and is suggested to function in response to bacterial rather than viral infection. 52,62,63 This raises the possibility that miRNAs such as miR-146a could function in a similar fashion in the endometrium of women with dysfunctional uterine bleeding experiencing endometritis with altered endometrial expression of inflammatory-related genes. 64–67 Dysfunctional uterine bleeding and bacterial infection resulting in an inflammatory environment is also associated with an increased expression of proteolytic enzymes such as matrix metalloproteinases (MMPs). 6,65,66 Increased expression and elevated activity of MMPs is observed at the onset of menstruation and linked to wound-healing impairment. 66,68,69 However, there is no evidence to suggest the regulatory function of miRNAs on the expression of MMPs and their physiological inhibitors, tissue inhibitor of MMPs (TIMPs), although several miRNAs including miR-20, miR-23a, and miR-222 are predicted to target their genes. 40 For instance, TIMP-3 mRNA levels increased significantly during the late secretory and menstrual phases when compared with the proliferative and early secretory phases 70 and was reported to be the target of miR-222. 71Resolution of the endometrial inflammatory response is necessary for reparative mechanisms to take place. In the endometrium, the conclusion of menses is associated with a reduction in inflammatory- and immune-related cell populations, expression of proinflammatory mediators, and proteolytic enzyme activities. 6 Whether the endometrial expression of miRNAs during this period reflects an anti-inflammatory regulatory function awaits investigation; however, several miRNAs including overexpression of miR-17–5p, miR-20a, and miR-106a have been reported to inhibit the differentiation and maturation of monocytes. 72 These miRNAs are expressed in the endometrium, and endometrial cells and several genes, including TGF-β and TGF-β receptors family, proteases and their inhibitors, and cell-cycle–related and apoptosis-related genes are among their predicted targets. 40 Various components of the TGF-β family are expressed and regulated in human endometrium throughout the menstrual cycle where they serve as key regulators of various cellular activities. TGF-β is a major cytokine with anti-inflammatory activities and differentially regulates proteases, extracellular matrix, and adhesion molecules expression resulting in the progression of tissue repair. 49 In addition, miR-181a expression is increased in mature T cells 73 and found to regulate the expression of antiapoptotic proteins, such as B cell lymphoma 2 (Bcl2) and the cell surface regulator CD69. 63 We identified the expression of miR-181a in the endometrium and showed that it is differentially regulated by the ovarian steroids along with miR-17–5p and miR-20a expression in endometrial epithelial and stromal cells. 40 Because the endometrium expresses many anti-inflammatory and antiapoptotic genes during the menstrual cycle, their differential expression may be regulated by miRNAs for the purpose of promoting transition from an inflammatory phase into a reparative stage. miRNAs AND ENDOMETRIAL CELLULAR APOPTOSIS The resolution of endometrial inflammatory reaction also parallels increased apoptotic activities to remove the damaged cells after the conclusion of menstruation. 9,74 Apoptosis is a complex process and is regulated by several multifunctional mediators. These mediators control the activation of pathways that help remove the unwanted damaged cells and act to minimize cellular damage and sustain cell growth and differentiation. In normal human endometrium, apoptosis has been reported to appear in the mid secretory phase, increasing in the late secretory phase, and is maximal during the menstrual phase. 9,74 The concordant endometrial expression of many genes that trigger the activation of apoptotic and cell-cycle signaling has been identified. 9,31,74 Many miRNAs have been identified and/or predicted to regulate the expression of genes with functions in apoptosis and cell-cycle regulation of several cancer cells. 46,7–78 However, limited evidence exists to support the regulatory functions of miRNAs in proliferative response of normal, differentiated quiescent cells. Among the miRNAs functionally associated with events leading to apoptosis are miR-10a, miR-28, miR-196a, and miR-337, as well as miR-96, miR-145, miR-150, miR-155, and miR-188 (), which differentially regulate the activation of caspase-3, respectively. 79 TNF-α is a key regulator of apoptotic processes and TNF-related apoptosis-inducing ligand (TRAIL, Apo-2L), which activates caspase-dependent apoptotic machinery, associated with altered expression of several miRNAs. 80 TRAIL-resistant cells displayed different levels of miRNAs profile with increased expression of miR-221 and miR-222 targeting c-Kit and p27 (kip1) expression and maintain TRAIL-resistant phenotype. 80 TRAIL induced apoptosis via the formation of a death-inducing signaling complex consisting of Fas-associated death domain protein (FADD) and activated procaspase-8 is also triggered by miR-155. 52,53 Cyclin A/cdk1, E/cdk2, and D1/cdk4 as well as cyclin-dependent kinases and cyclin-dependent kinase inhibitors such as p16 (INK4A), p21 (WAF-1/CIP-1), p27, p53, and p57 and other cell-cycle regulators and caspases are expressed and play a central role in endometrial transition from the inflammatory to reparative stage. 2,6,9,23,81–83 The expression of several of these regulators has been identified or predicted as targets of several miRNAs, more specifically let-7 and miR-17–192 clusters, miR-20, and miR-21. 50,76,77,84 For instance, the E2F transcription factors E2F1, E2F2, and E2F3, which play a central role in cell-cycle progression and apoptosis, target the promoters of several caspases and other proapoptotic targets of p53. The expression of E2F1 has been found to be inhibited by miR-17a and miR-20a, which are part of the miR-17–92 cluster. 85–89 Overexpression of miR-20a inhibited prostate cancer cell line from apoptosis possibly through regulation of E2F2 and E2F3 expression and the direct binding of E2F1–3 to the promoter of the miR-17–92 cluster. 52,77,88 The miR-17–92 cluster also promoted cell proliferation by shifting E2F transcriptional balance away from proapoptotic E2F1 and toward the proliferative E2F3 transcriptional network. 90 Over-expression of miR-21 in breast tumors and malignant cholangiocytes has been associated with increased cell growth, and inhibition of miR-21 with anti-miR enhanced their apoptosis and decreased their proliferation. 76,84 Recent studies have also implicated the miR-34 family as part of the p53 tumor suppressor network because overexpression of miR-34 resulted in apoptosis or cellular senescence. 85–87,89 Apoptosis is also controlled by the Bcl2 family of proteins, and miR-15a and miR-16-1 appear to play a central role in regulating their expression. 1,91,92Several studies indicated that ovarian steroids may control endometrial apoptosis through differential regulation of proapoptotic and antiapoptotic genes. 82 Whether the ovarian steroids differentially trigger the expression of specific miRNAs that target proapoptotic and antiapoptotic genes in the endometrium throughout the menstrual cycle is open to investigation. However, the expression of miRNAs such as miR-17–192 cluster, miR-20, miR-21, and miR-181 and their differential regulation by ovarian steroids in the endometrial cells support their potential influence on endometrial genes associated with cell-cycle progression and apoptotic processes. 40miRNAs AND ENDOMETRIAL ANGIOGENESIS In the healthy adult, angiogenesis occurs only in the corpus luteum, and during placental development, cyclic endometrium, and wound healing. 4,93 Angiogenesis is a self-limiting and strictly regulated event. It occurs in a sequential manner involving degradation of the vascular basement membrane and interstitial matrix by endothelial cells, migration and proliferation of endothelial cells, and finally tubulogenesis and formation of capillary loops. Many factors with angiogenic and antiangiogenic properties are known to regulate these events. An optimal and timely production of many proteolytic enzymes in response to angiogenic factors, which include various growth factors, cytokines, and chemokines and a balance between the expression of their inhibitors, is critical to the outcome of angiogenesis. 4,93 Human endometrium expresses many angiogenic mediators and their specific receptors. 4,93 Although the potential role of ovarian steroids in angiogenesis and neovascularization in the early stage of endometrial regeneration may be limited, they become active participants after the conclusion of menstruation. The vascular endothelial cells, including those in the endometrium, contain receptors for ovarian steroids implicating their regulatory actions on vascular activities. Because of the importance of angiogenic modifiers in endometrial reparative processes, the stability of their expression is critical specifically during dysfunctional uterine bleeding in which the endometrium undergoes repetitive breakdown and repair. The regulatory function of miRNAs in angiogenesis has been illustrated in several in vitro and in vivo models. During embryogenesis in Dicerex1/2 homozygous mouse embryos, defective blood vessel formation/maintenance and severely compromised yolk sacs has been reported. 94 Defective angiogenesis in this model was associated with altered expression of vascular endothelial growth factor (VEGF), fms-related tyrosine kinase 1 (FLT1), kinase insert domain receptor (KDR), and tyrosine kinase with immunoglobulin and epidermal growth factor homology domains 1 (TIE1) in mutant embryos. These defects were possibly due to altered regulatory function of Dicer, which is required for miRNA processing that regulates the expression of these genes. 94 Dicer expression silencing in human endothelial cells also resulted in altered expression of several key regulators of angiogenesis, such as TEK/TIE-2, KDR/VEGFR2, TIE1, endothelial nitric oxide synthase, and IL-8. 95 More specifically, miR-221 and miR-222 were found to regulate the expression of endothelial nitric oxide synthase after Dicer silencing. 95 In human umbilical vein endothelial cells (HUVECs), the expression of 15 miRNAs was associated with the expression of angiogenic factors and their receptors, with miR-221 and miR-222 affecting the expression of c-Kit and its ligand stem cell factor (SCF). 96 Silencing of Dicer and Drosha was associated with reduced capillary sprouting and tube-forming activity through a mechanism involving deceased migration of endothelial cells. 47,97 Inhibition of let-7f and miR-27b expression reduced sprout formation, suggesting their possible regulatory function in angiogenesis by targeting antiangiogenic genes. 47,97 Furthermore, miR-130a has been found to regulate the angiogenic phenotype of vascular endothelial cells largely through modulating the expression of growth arrest homeobox transcription factor (GAX) and homeobox A5 (HOXA5), 98 and miR-378 enhanced cell survival, reduced caspase-3 activity, and promoted angiogenesis. 99 Although the expression of several of these miRNAs has been identified in human endometrium 40 and in preimplantation mouse uterus, 100 their regulatory functions on endometrial angiogenic and antiangiogenic genes expression remains to be investigated (). However, the existing evidence obtained in other systems strongly supports the role of miRNAs in regulating the expression of genes involved in various aspects of angiogenesis. miRNA AND ENDOMETRIAL EMBRYO IMPLANTATION Human embryo implantation is an extremely complex process, and the underlying mechanisms involved in this process and the establishment of maternal tolerance to the embryo remains incompletely understood. 1,5,7,28,38,101–104 It is clear that ovarian steroids and their receptors are essential for adequate endometrial receptivity. Evidence also indicates the requirement for several endometrium-derived autocrine/paracrine mediators for the establishment of an environment to allow for embryo implantation. Although the precise nature of the endometrial mediator(s) that distinguish this period is unknown, conventional and large-scale gene expression profiling has identified many candidate genes considered to play pivotal roles in this process. 1,5,7,38,101,102,104Specific numbers of adhesion molecules and their receptors (integrins) important for the establishment of a direct dialogue between the embryo and the endometrium and several cytokines, growth factors, and chemokines are among these candidate genes. Although mice with targeted deletion of many of these genes do not exhibit any profound alterations in embryo implantation, lack of expression of some of these genes may influence other stages of embryo development. Functional redundancy among the biological actions of some of these factors may account for the mechanism of such activities. However, interruption in leukemia inhibitory factor (LIF) gene results in the failure of blastocyst implantation. In addition to adequate preparation of receptive endometrium, the establishment and maintenance of a viable embryo prior to reaching endometrium is essential for successful implantation. This is shown in part by the significant percentage of the embryos that reach the endometrium and do not implant. To gain insight into endometrial gene regulation during the embryo implantation period, many in vitro and in vivo animal models have been used. The results of these studies indicate to a complex microenvironment involving many specific genes highly regulated at transcriptional and translational levels. 1,5,7,38,101,102,104 Because of miRNA regulatory function in gene expression stability, a recent study by Chakrabarty et al illustrated the expression of a specific number of miRNAs during peri-implantation and preimplantation periods in mice, suggesting to serve as potential candidates relevant to embryo implantation. 100 Among the 32 miRNAs identified as relevant to embryo implantation, hsa-miR-101, hsa-miR-144, and hsa-miR-199a* are predicted to target cyclooxygenase-2 (COX-2) gene, which is considered to participate in events leading to peri-implantation and preimplantation embryo in mice. 100 The expression of these miRNAs correlated with the expression of COX-2 in the uterus during delayed implantation, further suggesting the potential regulatory function of these miRNAs on gene expression relevant to embryo implantation. The expression of COX-2 is regulated by a large number of growth factors, cytokines, and chemokines such as TNF-α and ovarian steroids. The expression of many of these mediators is targeted by miRNAs such as miR-125b and miR-155, 53 of which miR-155 expression was upregulated in day 4 (receptive) uteri. 100 Whether a feedback regulatory mechanism exists in coregulating the expression of miRNA-155 and target genes in the endometrium is yet to be determined; however, an increased endometrial expression of COX-2 and miR155 accompanied by a decrease in TNF-α expression during the receptive period support such interactions. In addition, TNF-α expression is targeted by miR-125b. 105 Other miRNAs whose profiles were identified as differentially expressed during peri-implantation and in day 4, day 5, and day 6 pregnant uteri in mice included hsa-let-7b, hsa-miR-19a, hsa-miR-127, hsa-miR-20a, hsa-miR-103, hsa-miR-199b, mmu-miR-201, hsa-miR-144, hsa-miR-512–3p, hsa-miR-195, hsa-miR-101, hsa-miR-199a*, hsa-miR-186, hsa-miR-17–3p, mmu-miR-291-5p, hsa-miR-181b, hsa-miR-96, hsa-miR-516–3p, hsa-miR-137, rno-miR-20*, hsa-miR-9*, mmu-miR-291-3p, and hsa-miR-302b. 100 Although many of these miRNAs are of human origin, their functional association during embryo implantation and early pregnancy in humans could only be predicted; however, because of their conserved homology among various species, they may function in similar manners. We have identified the expression of several of these miRNAs in human endometrium during the early to mid luteal phase, including the expression of let-7b, miR-19a, miR-20a, miR-199b, miR-101, miR-17-3p, miR-181b, as well as miR-125, miR-155, miR-26a, and miR-26b. 40 The miR-26 family has been predicted to target the expression of LIF among other genes. 106,107 Furthermore, the expression of miR-20a, miR-26a, miR-17–5p, miR-181, and miR-206 was the target of ovarian steroid regulatory actions in the endometrial epithelial and stromal cells. 40 These observations suggest that differential regulation of subsets of miRNAs may be required to stabilize the endometrial expression of specific genes critical for embryo implantation. However, detailed studies are needed to identify the specific endometrial genes targeted by these miRNAs and their associations with embryo implantation. miRNAs AND ENDOMETRIAL DISORDERS Considerable evidence exists implicating the altered expression of subsets of endometrial genes as hallmarks of establishment and progression of endometrial cancer, endometriosis, and dysfunctional uterine bleeding (). They include ovarian steroid receptors, oncogenic and tumor suppressor genes, proinflammatory-and immune-related genes, angiogenic factors, progression cell-cycle related genes, and adhesion molecules and their receptors. 6,8,10,11,28–30,34,37,108 We provided evidence that the expression of subsets of miRNAs is altered in ectopic endometrium compared with paired eutopic or endometrium of women without endometriosis. Currently, there is no evidence indicating whether the expression of miRNAs in endometrial cancer differ from normal endometrium. However, considering the existence of different miRNA profiles in endometrium of women with endometriosis, it raises the possibility of differential expression profile in endometrial cancer compared with normal endometrium. Comparative analysis of the miRNAs expression among different endometrial abnormalities may allow for identification of specific miRNAs and their targeted genes associated with each disorder. Results of expression profiling generated from several cancer cells and tissues indicate considerable alterations in the expression of a large number of miRNAs compared with their normal cells and tissue counterparts. 44,109–116 In these studies, several oncogenes and tumor suppressor genes were identified and/or predicted as potential target of several miRNAs. 111 In most cases, association of miRNAs expression with tumorigenesis has been identified to be due to their ability to differentially regulate the expression tumor suppressor genes or oncogenes. 111,117 The expression of many of these oncogenes and tumor suppressor genes have also been associated with establishment and progression of endometrial cancer, 10 implying that miRNAs may serve in regulating their expression. Additionally, miRNA genes are frequently located at fragile sites and regions of loss of heterozygosity or common breakpoint regions. 109,111 Common fragile sites are large, genomically unstable regions, which are hot spots for deletions and other alterations, especially in cancer cells, including endometrial cancer cells. 118 In addition to oncogenes and tumor suppressor genes, miRNAs also target the expression of gene function as proinflammatory- and immune-related response, angiogenesis, cell-cycle progression, and adhesion molecule response. These processes are known to play a central role in various cellular activities critical to tumorigenesis, including endometrial cancer; they are also involved in pathogenesis of endometriosis and dysfunctional uterine bleeding. A considerable number of miRNAs predicted to target the expression of genes functioning as proinflammatory- and immune-related response, angiogenesis, cell-cycle progression, and adhesion molecules were expressed in eutopic and ectopic endometrium of women with endometriosis. The level of expression of these miRNAs in most instances was down regulated in the eutopic and ectopic endometrium of women with endometriosis as without endometriosis. 40 Although the expression of the genes targeted by specific miRNAs must be validated, the results suggest that ectopic endometrial tissues are programmed differently with respect to their gene expression regulation. Women with endometrial cancer, endometriosis, and more specifically contraceptive users often experience dysfunctional endometrial bleeding, which similar to normal menstruation is characterized by an increased inflammatory reaction and increased production of angiogenic mediators as well as excess production of proteolytic enzymes. 6,29,67,119 A detailed study involving miRNA expression profile at different stages of endometrial cancer and endometriosis as well as in women with dysfunctional bleeding would allow for better understating of the genes involved and establish the lineage and state of progression of these disorders. In addition, it would be of interest to determine whether the expression of miRNAs differs in normal menstruation compared with that in women experiencing dysfunctional uterine bleeding associated with contraceptive use. To provide some prospective of potential regulatory function of several miRNAs identified in normal endometrium and ectopic endometrium, we selected those whose expressions were confirmed in these tissues and isolated endometrial cells for further discussion. 40 Among these miRNAs, several are predicted to regulate the expression of angiogenic and proinflammatory- and immune-related genes, including let-7, miR-15, miR16, and miR-125. The expression of let7 family has been reported to be downregulated in several tumors and considered to serve as tumor suppressor. 120–122 Let-7 family clusters with miR-99/miR-100 and miR-125 family and is predicted to regulate inflammatory- and immune-related genes, cell-cycle progression, and apoptosis. 53 Additionally, miR-15a and miR-16–1 cluster is located at 13q14.3, a region that is deleted and/or downregulated in several disorders, with germ-line mutation identified in miR-16–1 precursor associated with low level of miR-16–1 expression in chronic lymphocytic leukemia. 123 The expression of miR-15a and miR-16–1 was also inversely correlated with Bcl-2 expression, 92 which is expressed in endometriosis and endometrial cancer tissues and may be the target of these miRNAs. Several studies have implicated ovarian steroids as regulators of endometrial cellular apoptosis through differential regulation of Bcl-2 and Bax expression. 6 Although ovarian steroids through differential regulation of miR-15 and miR-16–1 and other miRNAs could target the expression of apoptotic and antiapoptotic genes, it is also possible that differential regulation of inflammatory-related genes and their associated miRNAs account for promotion of apoptotic and antiapoptotic activities. Ovarian steroids regulate the expression and activation of c-myc in human endometrium and endometrial cancer, 124 and c-myc activation has been shown to increase the expression of the miR-17–92 cluster. 125,126 These observations have led to the suggestion that the miR-17–92 cluster in cooperation with increased c-myc expression results in accelerated tumor development. 125,126 These tumors established and developed earlier, were more aggressive, and had increased mitotic rate and less apoptosis compared with tumors generated with c-myc alone. The transcription factor E2F1 is also predicted as a target of the miR-17–92 cluster and transcriptionally regulated by c-myc. Regression of E2F1 expression has been shown to influence cell-cycle progression, and despite oncogenic activity, the miR-17-92 cluster can serve as tumor suppressor by decreasing E2F1 expression. 90 Unregulated expression of miR-221 and miR-222 promote cell growth by inhibiting p27, 127 and miR-27a suppresses the cdc2/cyclin B inhibitor Myt-1 in MDA-MB-231 cells promoting cell proliferation. 78In the study of Kim et al, 128 they provided evidence that overexpression of miR-206 promotes cellular differentiation in C2C12 myoblasts. Detailed information implicating the regulatory function of miR-206 in gene expression is reviewed by Adams et al. 129 Interestingly, miR-206 also targets the expression of ERα in ER-positive breast cancer cells. 129 Altered expression of ERα as well as ERβ has been associated with several endometrial disorders, including endometrial caner, endometriosis, and dysfunctional uterine bleeding. 130–132 We demonstrated that ovarian steroids regulate the expression of miR-206 in endometrial epithelial and stromal cells and their actions were in part altered by estrogen and progesterone antagonists ICI-182780 and RU486, respectively. Selective estrogen and progesterone receptor modulators and estrogen and progesterone antagonists have been demonstrated to effectively regress the growth of endometrial implants in animal models of endometriosis, in clinical trials in humans, and of endometrial cell growth in vitro. These observations suggest that estrogen and progesterone antagonists may target the endometrial expression of miRNAs resulting in a reprogramming of their target genes expression. Detailed studies are needed to determine the molecular mechanisms by which these agents influence the expression of miRNAs and their target genes. The unprecedented advancements in molecular biological approaches during the past decade have led to the identification of the expression of many genes in the endometrium under normal and diseased conditions. The product of some of these genes acting in an autocrine/paracrine and interactive manners are known to regulate many events such as inflammatory and immune responses, cell-cycle progression, differentiation, apoptosis, and tissue remodeling. Precise regulation of the expression of these genes is fundamental in directing these processes for normal endometrial functions. Unregulated expression of some of these genes appears to account for various endometrial abnormalities including infertility, endometriosis, and endometrial cancer. Clearly, ovarian steroids through their ability to regulate the expression of many of these genes at transcriptional and translational levels play central roles in endometrial biological and physiologic integrity. Micro-RNAs have emerged as important regulators of gene expression. These small, non–protein-coding RNAs through complementary interactions with their predicted target genes regulate their expression mostly through transcriptional and translational regression. 133 Expression profiling and cloning strategies have identified a large number of miRNAs in various cells and tissues under normal and disease conditions. Functional analysis also revealed that miRNAs can potentially target the expression of a third or possibly more of the genes in humans. Current evidence for the expression, regulation, and function of miRNAs in human reproductive tract tissues is limited to a few studies. The expression profile of a few hundred miRNAs in the endometrium and endometrial cells and their aberrant expression in ectopic endometrium in women with endometriosis support their key biological relevance. Additionally, ovarian steroids appear to regulate the expression of miRNAs in endometrial cells; however, the specific pattern of their expression throughout the menstrual cycle remains to be elucidated. It is also necessary to verify and correlate the expression of genes targeted by differentially expressed miRNAs in the endometrium and to determine whether their profiles and targeted genes expression differ in endometrial disorders such as endometrial cancer and dysfunctional uterine bleeding compared with that of normal endometrium. This is particularly important because expression profiling of miRNAs appears to be far more superior to mRNA expression profiling to differentiate normal from diseased tissues. If such a pattern of miRNA expression could differentiate normal endometrium from diseased conditions, the result may have a significant impact on prognostics and diagnostics approach as a useful tool for assessing response to various treatment strategies. In addition, miRNAs that are aberrantly expressed in any of the endometrial disorders could be effectively targeted by their complementary anti-miR and/or pri-miR oligonucleotides for loss of function and gain of function. As such, evidence generated in other cell and in vivo systems supports their experimental use for therapeutic application and management of disorders such as lowering of plasma cholesterol (miR-122), cancer therapy (miR-21), cardiac hypertrophy (miR-21), and cardiac arrhythmia (miR-1). Collectively, extensive basic and transitional research is needed to improve our basic knowledge of endometrial miRNAs expression, regulation, and functions under normal and diseased conditions to allow for identification of potent therapeutic applications for miRNAs. We apologize to those whose work could not be discussed in this article due to space constraints. This work is supported in part by grant HD37432 from the National Institutes of Health. | | 3′ UTR | 3′ untranslated region | | | Bcl2 B | cell lymphoma 2 | | | COX-2 | cyclooxygenase-2 | | | ERs | estrogen receptors | | | FADD | Fas-associated death domain protein | | | FLT1 | fms-related tyrosine kinase 1 | | | GAX | growth arrest homeobox transcription factor | | | HOXA5 | homeobox A5 | | | HUVEC | human umbilical vein endothelial cell | | | IRAK1 | interleukin-1 receptor associated kinase 1 | | | KDR | kinase insert domain receptor | | | LIF | leukemia inhibitory factor | | | LPS | lipopolysaccharide | | | miRNA | microRNA | | | MMP | matrix metalloproteinase | | | NF-κB | nuclear factor of kappa light polypeptide gene enhancer in B cells | | | PR | progesterone receptor | | | RISC | RNA-induced silencing complex | | | SCF | stem cell factor | | | TGF-β | transforming growth factor β | | | TIE1 | tyrosine kinase with immunoglobulin and epidermal growth factor homology domains 1 | | | TIMPs | tissue inhibitior of metrix metalloproteinases | | | TLR | Toll-like receptor | | | TNF-α | tumor necrosis factor α | | | TRAF6 TNF | receptor-associated factor 6 | | | TRAIL | TNF-related apoptosis-inducing ligand | | | VEGF | vascular endothelial growth factor |
1. Achache H, Revel A. Endometrial receptivity markers, the journey to successful embryo implantation. Hum Reprod Update. 2006;12:731–746. [PubMed] 2. Chegini N, Williams RS. Cytokine networks in human endometrium from menstruation to implantation. In: Hill J, editor. Cytokines in Human Reproduction. Hoboken, NJ: John Wiley & Sons; 2000. pp. 93–132. 3. Du H, Taylor HS. Contribution of bone marrow-derived stem cells to endometrium and endometriosis. Stem Cells. 2007;25:2082–2086. [PubMed] 4. Girling JE, Rogers PA. Recent advances in endometrial angiogenesis research. Angiogenesis. 2005;8:89–99. [PubMed] 5. Horcajadas JA, Pellicer A, Simon C. Wide genomic analysis of human endometrial receptivity: new times, new opportunities. Hum Reprod Update. 2007;13:77–86. [PubMed] 6. Jabbour HN, Kelly RW, Fraser HM, et al. Endocrine regulation of menstruation. Endocr Rev. 2006;27:17–46. [PubMed] 7. Makker A, Singh MM. Endometrial receptivity: clinical assessment in relation to fertility, infertility, and antifertility. Med Res Rev. 2006;26:699–746. [PubMed] 8. Ferenczy A. Pathophysiology of endometrial bleeding. Maturitas. 2003;45:1–14. [PubMed] 9. Harada T, Taniguchi F, Izawa M, et al. Apoptosis and endometriosis. Front Biosci. 2007;12:3140–3151. [PubMed] 10. Abal M, Planaguma J, Gil-Moreno A, et al. Molecular pathology of endometrial carcinoma: transcriptional signature in endometrioid tumors. Histol Histopathol. 2006;21:197–204. [PubMed] 11. Prat J, Gallardo A, Cuatrecasas M, et al. Endometrial carcinoma: pathology and genetics. Pathology. 2007;39:72–87. [PubMed] 12. Ambros V, Chen X. The regulation of genes and genomes by small RNAs. Development. 2007;134:1635–1641. [PubMed] 13. Bartel DP. MicroRNAs: genomics, biogenesis, mechanism, and function. Cell. 2004;116:281–297. [PubMed] 14. Bernstein E, Caudy AA, Hammond SM, et al. Role for a bidentate ribonuclease in the initiation step of RNA interference. Nature. 2001;409:363–366. [PubMed] 15. Paroo Z, Liu Q, Wang X. Biochemical mechanisms of the RNA-induced silencing complex. Cell Res. 2007;17:187–194. [PubMed] 16. Bernstein E, Kim SY, Carmell MA, et al. Dicer is essential for mouse development. Nat Genet. 2003;35:215–217. [PubMed] 17. Zamore PD, Haley B. Ribo-gnome: the big world of small RNAs. Science. 2005;309:1519–1524. [PubMed] 18. Jackson RJ, Standart N. How do microRNAs regulate gene expression? Sci STKE. 2007;2007:rel. 19. Nilsen TW. Mechanisms of micro RNA-mediated gene regulation in animal cells. Trends Genet. 2007;23:243–249. [PubMed] 20. Pillai RS, Bhattacharyya SN, Filipowicz W. Repression of protein synthesis by miRNAs: how many mechanisms? Trends Cell Biol. 2007;17:118–126. [PubMed] 21. Berezikov E, van Tetering G, Verheul M, et al. Many novel mammalian microRNA candidates identified by extensive cloning and RAKE analysis. Genome Res. 2006;16:1289–1298. [PubMed] 22. Yu Z, Jian Z, Shen SH, et al. Global analysis of microRNA target gene expression reveals that miRNA targets are lower expressed in mature mouse and Drosophila tissues than in the embryos. Nucleic Acids Res. 2007;35:152–164. [PubMed] 23. Brennecke J, Stark A, Russell RB, et al. Principles of microRNA-target recognition. PLoS Biol. 2005;3:e85. [PubMed] 24. Grimson A, Farh KK, Johnston WK, et al. MicroRNA targeting specificity in mammals: determinants beyond seed pairing. Mol Cell. 2007;27:91–105. [PubMed] 25. Lai EC. Micro RNAs are complementary to 3′ UTR sequence motifs that mediate negative post-transcriptional regulation. Nat Genet. 2002;30:363–364. [PubMed] 26. Ghosh D, De P, Sengupta J. Luteal phase ovarian oestrogen is not essential for implantation and maintenance of pregnancy from surrogate embryo transfer in the rhesus monkey. Hum Reprod. 1994;9:629–637. [PubMed] 27. Smitz J, Bourgain C, Van Waesberghe L, et al. A prospective randomized study on oestradiol valerate supplementation in addition to intravaginal micronized progesterone in buserelin and HMG induced superovulation. Hum Reprod. 1993;8:40–45. [PubMed] 28. Groothuis PG, Dassen HH, Romano A, et al. Estrogen and the endometrium: lessons learned from gene expression profiling in rodents and human. Hum Reprod Update. 2007;13:405–417. [PubMed] 29. Smith OP, Critchley HO. Progestogen only contraception and endometrial break through bleeding. Angiogenesis. 2005;8:117–126. [PubMed] 30. Smith OP, Jabbour HN, Critchley HO. Cyclooxygenase enzyme expression and E series prostaglandin receptor signalling are enhanced in heavy menstruation. Hum Reprod. 2007;22:1450–1456. [PubMed] 31. Kao LC, Tulac S, Lobo S, et al. Global gene profiling in human endometrium during the window of implantation. Endocrinology. 2002;143:2119–2138. [PubMed] 32. Lee K, Jeong J, Tsai MJ, et al. Molecular mechanisms involved in progesterone receptor regulation of uterine function. J Steroid Biochem Mol Biol. 2006;102:41–50. [PubMed] 33. Sherwin R, Catalano R, Sharkey A. Large-scale gene expression studies of the endometrium: what have we learnt? Reproduction. 2006;132:1–10. [PubMed] 34. Taylor RN, Mueller MD. Anti-angiogenic treatment of endometriosis: biochemical aspects. Gynecol Obstet Invest. 2004;57:54–56. [PubMed] 35. Chegini N, Ma C, Roberts M, et al. Differential expression of interleukins (IL) IL-13 and IL-15 throughout the menstrual cycle in endometrium of normal fertile women and women with recurrent spontaneous abortion. J Reprod Immunol. 2002;56:93–110. [PubMed] 36. Chegini N, Roberts M, Ripps B. Differential expression of interleukins (IL)-13 and IL-15 in ectopic and eutopic endometrium of women with endometriosis and normal fertile women. Am J Reprod Immunol. 2003;49:75–83. [PubMed] 37. Fujimoto J, Toyoki H, Jahan I, et al. Sex steroid-dependent angiogenesis in uterine endometrial cancers. J Steroid Biochem Mol Biol. 2005;93:161–165. [PubMed] 38. Hannan NJ, Salamonsen LA. Role of chemokines in the endometrium and in embryo implantation. Curr Opin Obstet Gynecol. 2007;19:266–272. [PubMed] 39. Vitiello D, Kodaman PH, Taylor HS. HOX genes in implantation. Semin Reprod Med. 2007;25:431–436. [PubMed] 40. Pan Q, Luo X, Toloubeydokhti T, et al. The expression profile of micro-RNA in endometrium and endometriosis and the influence of ovarian steroids on their expression. Mol Hum Reprod. 2007;13:797–806. [PubMed] 41. Ambros V. The functions of animal micro RNAs. Nature. 2004;431:350–355. [PubMed] 42. Li SC, Tang P, Lin WC. Intronic microRNA: discovery and biological implications. DNA Cell Biol. 2007;26:195–207. [PubMed] 43. Lim LP, Lau NC, Garrett-Engele P, et al. Microarray analysis shows that some microRNAs downregulate large numbers of target mRNAs. Nature. 2005;433:769–773. [PubMed] 44. Carleton M, Cleary MA, Linsley PS. MicroRNAs and cell cycle regulation. Cell Cycle. 2007;6:2127–2132. [PubMed] 45. Harfe BD, McManus MT, Mansfield JH, et al. The RNaseIII enzyme Dicer is required for morphogenesis but not patterning of the vertebrate limb. Proc Natl Acad Sci USA. 2005;102:10898–10903. [PubMed] 46. Jovanovic M, Hengartner MO. miRNAs and apoptosis: RNAs to die for. Oncogene. 2006;25:6176–6187. [PubMed] 47. Kuehbacher A, Urbich C, Dimmeler S. Targeting micro-RNA expression to regulate angiogenesis. Trends Pharmacol Sci. 2008;29:12–15. [PubMed] 48. Linsley PS, Schelter J, Burchard J, et al. Transcripts targeted by the micro RNA-16 family cooperatively regulate cell cycle progression. Mol Cell Biol. 2007;27:2240–2252. [PubMed] 49. Chegini N. Peritoneal molecular environment, adhesion formation and clinical implication. Front Biosci. 2002;7:E91–E115. [PubMed] 50. Meng F, Henson R, Wehbe-Janek H, et al. The MicroRNA let–7a modulates interleukin-6-dependent STAT-3 survival signaling in malignant human cholangiocytes. J Biol Chem. 2007;282:8256–8264. [PubMed] 51. Meng F, Wehbe-Janek H, Henson R, et al. Epigenetic regulation of microRNA-370 by interleukin-6 in malignant human cholangiocytes. Oncogene. 2008;27:378–386. [PubMed] 52. O’Connell RM, Taganov KD, Boldin MP, et al. MicroRNA-155 is induced during the macrophage inflammatory response. Proc Natl Acad Sci U S A. 2007;104:1604–1609. [PubMed] 53. Tili E, Michaille JJ, Cimino A, et al. Modulation of miR-155 and miR-125b levels following lipopolysaccharide/ TNF-alpha stimulation and their possible roles in regulating the response to endotoxin shock. J Immunol. 2007;179:5082–5089. [PubMed] 54. Rodriguez A, Vigorito E, Clare S, et al. Requirement of bic/microRNA-155 for normal immune function. Science. 2007;316:608–611. [PubMed] 55. Costinean S, Zanesi N, Pekarsky Y, et al. Pre-B cell proliferation and lymphoblastic leukemia/high-grade lymphoma in E(mu)-miR155 transgenic mice. Proc Natl Acad Sci U S A. 2006;103:7024–7029. [PubMed] 56. Bergqvist A, Bruse C, Carlberg M, et al. Interleukin 1beta, interleukin-6, and tumor necrosis factor-alpha in endometriotic tissue and in endometrium. Fertil Steril. 2001;75:489–495. [PubMed] 57. Cao WG, Morin M, Sengers V, et al. Tumour necrosis factor-alpha up-regulates macrophage migration inhibitory factor expression in endometrial stromal cells via the nuclear transcription factor NF-kappaB. Hum Reprod. 2006;21:421–428. [PubMed] 58. Chegini N, Dou Q, Williams RS. An inverse relation between the expression of tumor necrosis factor alpha (TNF-alpha) and TNF-alpha receptor in human endometrium. Am J Reprod Immunol. 1999;42:297–302. [PubMed] 59. Cork BA, Tuckerman EM, Li TC, et al. Expression of interleukin (IL)-11 receptor by the human endometrium in vivo and effects of IL-11, IL-6 and LIF on the production of MMP and cytokines by human endometrial cells in vitro. Mol Hum Reprod. 2002;8:841–848. [PubMed] 60. Kayisli UA, Aksu CA, Berkkanoglu M, et al. Estrogenicity of isoflavones on human endometrial stromal and glandular cells. J Clin Endocrinol Metab. 2002;87:5539–5544. [PubMed] 61. Khan KN, Masuzaki H, Fujishita A, et al. Interleukin-6-and tumour necrosis factor alpha-mediated expression of hepatocyte growth factor by stromal cells and its involvement in the growth of endometriosis. Hum Reprod. 2005;20:2715–2723. [PubMed] 62. Taganov KD, Boldin MP, Baltimore D. MicroRNAs and immunity: tiny players in a big field. Immunity. 2007;26:133–137. [PubMed] 63. Neilson JR, Zheng GX, Burge CB, et al. Dynamic regulation of miRNA expression in ordered stages of cellular development. Genes Dev. 2007;21:578–589. [PubMed] 64. Chegini N, Luo X, Pan Q, et al. Endometrial expression of epithelial neutrophil-activating peptide-78 during the menstrual cycle or in progestin-only contraceptive users with breakthrough bleeding and the influence of doxycycline therapy. Hum Reprod. 2007;22:427–433. [PubMed] 65. Li R, Luo X, Pan Q, et al. Doxycycline alters the expression of inflammatory and immune-related cytokines and chemokines in human endometrial cells: implication in irregular uterine bleeding. Hum Reprod. 2006;21:2555–2563. [PubMed] 66. Li R, Luo X, Archer DF, et al. Doxycycline alters the expression of matrix metalloproteases in the endometrial cells exposed to ovarian steroids and pro-inflammatory cytokine. J Reprod Immunol. 2007;73:118–129. [PubMed] 67. Rhoton-Vlasak A, Chegini N, Hardt N, et al. Histological characteristics and altered expression of interleukins (IL) IL-13 and IL-15 in endometria of levonorgestrel users with different uterine bleeding patterns. Fertil Steril. 2005;83:659–665. [PubMed] 68. Clark IM, Swingler TE, Sampieri CL, et al. The regulation of matrix metalloproteinases and their inhibitors. Int J Biochem Cell Biol. 2008;40:1362–1378. [PubMed] 69. Gill SE, Parks WC. Metalloproteinases and their inhibitors: regulators of wound healing. Int J Biochem Cell Biol. 2008;40:1334–1347. [PubMed] 70. Goffin F, Munaut C, Frankenne F, et al. Expression pattern of metalloproteinases and tissue inhibitors of matrix-metalloproteinases in cycling human endometrium. Biol Reprod. 2003;69:976–984. [PubMed] 71. Dalmay T, Edwards DR. MicroRNAs and the hallmarks of cancer. Oncogene. 2006;25:6170–6175. [PubMed] 72. Fontana L, Pelosi E, Greco P, et al. MicroRNAs 17–5p-20a-106a control monocytopoiesis through AML1 targeting and M-CSF receptor upregulation. Nat Cell Biol. 2007;9:775–787. [PubMed] 73. Li QJ, Chau J, Ebert PJ, et al. miR-181a is an intrinsic modulator of T cell sensitivity and selection. Cell. 2007;129:147–161. [PubMed] 74. Brosens JJ, Gellersen B. Death or survival—progesterone-dependent cell fate decisions in the human endometrial stroma. J Mol Endocrinol. 2006;36:389–398. [PubMed] 75. Meng F, Henson R, Lang M, et al. Involvement of human micro-RNA in growth and response to chemotherapy in human cholangiocarcinoma cell lines. Gastroenterology. 2006;130:2113–2129. [PubMed] 76. Si ML, Zhu S, Wu H, et al. miR-21-mediated tumor growth. Oncogene. 2007;26:2799–2803. [PubMed] 77. Matsubara H, Takeuchi T, Nishikawa E, et al. Apoptosis induction by antisense oligonucleotides against miR-17–5p and miR-20a in lung cancers overexpressing miR-17–92. Oncogene. 2007;26:6099–6105. [PubMed] 78. Mertens-Talcott SU, Chintharlapalli S, Li X, et al. The oncogenic microRNA-27a targets genes that regulate specificity protein transcription factors and the G2-M checkpoint in MDA-MB-231 breast cancer cells. Cancer Res. 2007;67:11001–11011. [PubMed] 79. Ovcharenko D, Kelnar K, Johnson C, et al. Genome-scale microRNA and small interfering RNA screens identify small RNA modulators of TRAIL-induced apoptosis pathway. Cancer Res. 2007;67:10782–10788. [PubMed] 80. Garofalo M, Quintavalle C, Di Leva G, et al. MicroRNA signatures of TRAIL resistance in human non-small cell lung cancer. Oncogene. 2008;27:3845–3855. [PubMed] 81. Jones RK, Searle RF, Bulmer JN. Apoptosis and bcl-2 expression in normal human endometrium, endometriosis and adenomyosis. Hum Reprod. 1998;13:3496–3502. [PubMed] 82. Selam B, Kayisli UA, Mulayim N, et al. Regulation of Fas ligand expression by estradiol and progesterone in human endometrium. Biol Reprod. 2001;65:979–985. [PubMed] 83. Watanabe H, Kanzaki H, Narukawa S, et al. Bcl-2 and Fas expression in eutopic and ectopic human endometrium during the menstrual cycle in relation to endometrial cell apoptosis. Am J Obstet Gynecol. 1997;176:360–368. [PubMed] 84. Meng F, Henson R, Wehbe-Janek H, et al. MicroRNA-21 regulates expression of the PTEN tumor suppressor gene in human hepatocellular cancer. Gastroenterology. 2007;133:647–658. [PubMed] 85. He X, He L, Hannon GJ. The guardian’s little helper: microRNAs in the p53 tumor suppressor network. Cancer Res. 2007;67:11099–11101. [PubMed] 86. He L, He X, Lowe SW, et al. microRNAs join the p53 network—another piece in the tumour-suppression puzzle. Nat Rev Cancer. 2007;7:819–822. [PubMed] 87. Raver-Shapira N, Marciano E, Meiri E, et al. Transcriptional activation of miR-34a contributes to p53-mediated apoptosis. Mol Cell. 2007;26:731–743. [PubMed] 88. Sylvestre Y, De G, Querido E, et al. An E2F/miR-20a autoregulatory feedback loop. J Biol Chem. 2007;282:2135–2143. [PubMed] 89. Welch C, Chen Y, Stallings RL. MicroRNA-34a functions as a potential tumor suppressor by inducing apoptosis in neuroblastoma cells. Oncogene. 2007;26:5017–5022. [PubMed] 90. Woods K, Thomson JM, Hammond SM. Direct regulation of an oncogenic micro-RNA cluster by E2F transcription factors. J Biol Chem. 2007;282:2130–2134. [PubMed] 91. Adams JM, Cory S. Life-or-death decisions by the Bcl-2 protein family. Trends Biochem Sci. 2001;26:61–66. [PubMed] 92. Cimmino A, Calin GA, Fabbri M, et al. miR-15 and miR-16 induce apoptosis by targeting BCL2. Proc Natl Acad Sci USA. 2005;102:13944–13949. [PubMed] 93. Smith SK. Angiogenesis and reproduction. BJOG. 2001;108:777–783. [PubMed] 94. Yang WJ, Yang DD, Na S, et al. Dicer is required for embryonic angiogenesis during mouse development. J Biol Chem. 2005;280:9330–9335. [PubMed] 95. Suarez Y, Fernandez-Hernando C, Pober JS, et al. Dicer dependent microRNAs regulate gene expression and functions in human endothelial cells. Circ Res. 2007;100:1164–1173. [PubMed] 96. Poliseno L, Tuccoli A, Mariani L, et al. MicroRNAs modulate the angiogenic properties of HUVECs. Blood. 2006;108:3068–3071. [PubMed] 97. Kuehbacher A, Urbich C, Zeiher AM, et al. Role of Dicer and Drosha for endothelial microRNA expression and angiogenesis. Circ Res. 2007;101:59–68. [PubMed] 98. Chen Y, Gorski DH. Regulation of angiogenesis through a microRNA (miR-130a) that down-regulates antiangiogenic homeobox genes GAX and HOXA5. Blood. 2008;111:1217–1226. [PubMed] 99. Lee DY, Deng Z, Wang CH, et al. MicroRNA-378 promotes cell survival, tumor growth, and angiogenesis by targeting SuFu and Fus-1 expression. Proc Natl Acad Sci USA. 2007;104:20350–20355. [PubMed] 100. Chakrabarty A, Tranguch S, Daikoku T, et al. MicroRNA regulation of cyclooxygenase-2 during embryo implantation. Proc Natl Acad Sci U S A. 2007;104:15144–15149. [PubMed] 101. Fanchin R, Gallot V, Rouas-Freiss N, et al. Implication of HLA-G in human embryo implantation. Hum Immunol. 2007;68:259–263. [PubMed] 102. Giudice LC. Microarray expression profiling reveals candidate genes for human uterine receptivity. Am J Pharmacogenomics. 2004;4:299–312. [PubMed] 103. Hamatani T, Ko MS, Yamada M, et al. Global gene expression profiling of preimplantation embryos. Hum Cell. 2006;19:98–117. [PubMed] 104. Laird SM, Tuckerman EM, Li TC. Cytokine expression in the endometrium of women with implantation failure and recurrent miscarriage. Reprod Biomed Online. 2006;13:13–23. [PubMed] 105. Lodish HF, Zhou B, Liu G, et al. Micromanagement of the immune system by microRNAs. Nat Rev Immunol. 2008;8:120–130. [PubMed] 106. Lewis BP, Shih IH, Jones-Rhoades MW, et al. Prediction of mammalian microRNA targets. Cell. 2003;115:787–798. [PubMed] 107. Lewis BP, Burge CB, Bartel DP. Conserved seed pairing, often flanked by adenosines, indicates that thousands of human genes are microRNA targets. Cell. 2005;120:15–20. [PubMed] 108. Laschke MW, Menger MD. In vitro and in vivo approaches to study angiogenesis in the pathophysiology and therapy of endometriosis. Hum Reprod Update. 2007;13:331–342. [PubMed] 109. Calin GA, Croce CM. Chromosomal rearrangements and microRNAs: a new cancer link with clinical implications. J Clin Invest. 2007;117:2059–2066. [PubMed] 110. Cho WC. OncomiRs: the discovery and progress of microRNAs in cancers. Mol Cancer. 2007;6:60. [PubMed] 111. Croce CM. Oncogenes and cancer. N Engl J Med. 2008;358:502–511. [PubMed] 112. Huppi K, Volfovsky N, Mackiewicz M, et al. MicroRNAs and genomic instability. Semin Cancer Biol. 2007;17:65–73. [PubMed] 113. Ma L, Teruya-Feldstein J, Weinberg RA. MicroRNAs in malignant progression. Cell Cycle. 2008;7:570–572. [PubMed] 114. Rajalingam K, Schreck R, Rapp UR, et al. Ras oncogenes and their downstream targets. Biochim Biophys Acta. 2007;1773:1177–1195. [PubMed] 115. Sen CK, Roy S. miRNA: licensed to kill the messenger. DNA Cell Biol. 2007;26:193–194. [PubMed] 116. Wu W, Sun M, Zou GM, et al. MicroRNA and cancer: current status and prospective. Int J Cancer. 2007;120:953–960. [PubMed] 117. Chang TC, Yu D, Lee YS, et al. Widespread microRNA repression by Myc contributes to tumorigenesis. Nat Genet. 2008;40:43–50. [PubMed] 118. McAvoy S, Ganapathiraju SC, Ducharme-Smith AL, et al. Non-random inactivation of large common fragile site genes in different cancers. Cytogenet Genome Res. 2007;118:260–269. [PubMed] 119. Jones RL, Findlay JK, Farnworth PG, et al. Activin A and inhibin A differentially regulate human uterine matrix metalloproteinases: potential interactions during decidualization and trophoblast invasion. Endocrinology. 2006;147:724–732. [PubMed] 120. Esquela-Kerscher A, Trang P, Wiggins JF, et al. The let-7 microRNA reduces tumor growth in mouse models of lung cancer. Cell Cycle. 2008;7:759–764. [PubMed] 121. Johnson CD, Esquela-Kerscher A, Stefani G, et al. The let-7 microRNA represses cell proliferation pathways in human cells. Cancer Res. 2007;67:7713–7722. [PubMed] 122. Lee YS, Dutta A. The tumor suppressor microRNA let-7 represses the HMGA2 oncogene. Genes Dev. 2007;21:1025–1030. [PubMed] 123. Calin GA, Ferracin M, Cimmino A, et al. A microRNA signature associated with prognosis and progression in chronic lymphocytic leukemia. N Engl J Med. 2005;353:1793–1801. [PubMed] 124. Bircan S, Ensari A, Ozturk S, et al. Immunohistochemical analysis of c-myc, c-jun and estrogen receptor in normal, hyperplastic and neoplastic endometrium. Pathol Oncol Res. 2005;11:32–39. [PubMed] 125. Rinaldi A, Poretti G, Kwee I, et al. Concomitant MYC and microRNA cluster miR-17-92 (C13orf25) amplification in human mantle cell lymphoma. Leuk Lymphoma. 2007;48:410–412. [PubMed] 126. Lu Y, Thomson JM, Wong HY, et al. Transgenic over-expression of the microRNA miR-17–92 cluster promotes proliferation and inhibits differentiation of lung epithelial progenitor cells. Dev Biol. 2007;310:442–453. [PubMed] 127. le Sage C, Nagel R, Egan DA, et al. Regulation of the p27(Kip1) tumor suppressor by miR-221 and miR-222 promotes cancer cell proliferation. EMBO J. 2007;26:3699–3708. [PubMed] 128. Kim HK, Lee YS, Sivaprasad U, et al. Muscle-specific microRNA miR-206 promotes muscle differentiation. J Cell Biol. 2006;174:677–687. [PubMed] 129. Adams BD, Furneaux H, White BA. The micro-ribonucleic acid (miRNA) miR-206 targets the human estrogen receptor-alpha (ERalpha) and represses ERalpha messenger RNA and protein expression in breast cancer cell lines. Mol Endocrinol. 2007;21:1132–1147. [PubMed] 130. Singh M, Zaino RJ, Filiaci VJ, et al. Relationship of estrogen and progesterone receptors to clinical outcome in metastatic endometrial carcinoma: a Gynecologic Oncology Group Study. Gynecol Oncol. 2007;106:325–333. [PubMed] 131. Bukulmez O, Hardy DB, Carr BR, et al. Inflammatory status influences aromatase and steroid receptor expression in endometriosis. Endocrinology. 2008;149:1190–1204. [PubMed] 132. Gleeson NC, Gonsalves R, Bonnar J. Plasminogen activator inhibitors in endometrial adenocarcinoma. Cancer. 1993;72:1670–1672. [PubMed] 133. Lim LP, Glasner ME, Yekta S, et al. Vertebrate microRNA genes. Science. 2003;299:1540. [PubMed] 134. Boren T, Xiong Y, Hakam A, et al. MicroRNAs and their target messenger RNAs associated with endometrial carcinogenesis. Gynecol Oncol. 2008;110:206–215. [PubMed] 135. Daikoku T, Hirota Y, Tranguch S, et al. Conditional loss of uterine Pten unfailingly and rapidly induces endometrial cancer in mice. Cancer Res. 2008;68:5619–5627. [PubMed] 136. Hong X, Luense LJ, McGinnis LK, Nothnick WB, Christenson LK. Dicer1 is essential for female fertility and normal development of the female reproductive system. Endocrinology. 2008 Aug 14; Epub ahead of print. 137. Nagaraja AK, Andreu-Vieyra C, Franco HL, et al. Deletion of dicer in somatic cells of the female reproductive tract causes sterility. Mol Endocrinol. 2008;22:2336–2352. [PubMed] 138. Hu SJ, Ren G, Liu JL, et al. MicroRNA expression and regulation in mouse uterus during embryo implantation. J Biol Chem. 2008;283:23473–23484. [PubMed]
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