• We are sorry, but NCBI web applications do not support your browser and may not function properly. More information
Logo of nihpaAbout Author manuscriptsSubmit a manuscriptNIH Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
Cancer Genomics Proteomics. Author manuscript; available in PMC Jan 2, 2008.
Published in final edited form as:
PMCID: PMC2170889
NIHMSID: NIHMS35760

Non-coding MicroRNAs hsa-let-7g and hsa-miR-181b are Associated with Chemoresponse to S-1 in Colon Cancer

Abstract

Background

MicroRNAs (miRNAs) are small non-coding RNAs (~22 nucleotides) that regulate gene expression at a post-transcriptional level via imperfect base pairing to the 3’-UTR of their target mRNAs. Previous studies from our group identified a number of deregulated miRNAs due to the loss of p53 tumor suppressor in colon cancer cell lines. To further investigate the in vivo biological significance of these miRNAs, the expressions of hsa-let-7g, hsa-miR-143, hsa-miR-145, hsa-miR-181b and hsa-miR-200c were investigated using formalin-fixed paraffin-embedded (FFPE) colon cancer specimens to evaluate the potential relationship with chemosensitivity and tumorigenesis.

Patients and Methods

Forty-six patients with recurrent or residual colon cancer lesions were treated with the 5-fluorouracil-based antimetabolite S-1. This includes twenty-one pairs of tumor and normal samples. Total RNAs were isolated and the expression level of each particular miRNA was quantified using real time qRT-PCR analysis.

Results

The expression levels of hsa-let-7g, hsa-miR-181b and hsa-miR-200c were over-expressed in tumor tissues compared to normal tissues. The expression levels of hsa-let-7g (p=0.03; Mann-Whitney test) and hsa-miR-181b (p=0.02; Mann-Whitney test) were strongly associated with clinical response to S-1. Although hsa-let-7g and hsa-miR-181b are strongly associated with patient’s response to S-1 treatment, they are not significant prognostic factors for predicting survival.

Conclusion

hsa-let-7g, hsa-miR-181b and hsa-miR-200c may be associated with tumorigenesis in colon cancer. In addition, hsa-let-7g and hsa-miR-181b may be potential indicators for chemoresponse to S-1 based chemotherapy.

Keywords: miRNA, colon cancer, S-1

5-Fluorouracil (5-FU) has been one of the main anti-neoplastic drugs for treating various solid tumors for nearly a half century (1). The response rate for colorectal cancer, however, is only 14% with bolus 5-FU infusion and 22%, despite continuous infusion (2). Extensive effects have been focused on improving the response rate and survival by enhancing 5-FU cytotoxicity through various modulations. The recent standard regimen, 5-FU/leucovorin, generated higher response rate (23%) compared to 5-FU alone (11%) (3). 5-FU/leucovorin/oxaliplatin has now become one of the standard treatments for advanced colorectal cancer with improved response rate (4). S-1 (TS-1; Taiho Pharmaceutical, Tokyo, Japan) is a fourth-generation 5-FU based oral drug developed to improve the drug efficacy, to reduce side-effects and improve quality of life (5). It is the first-line therapy for treating advanced colon cancer in Japan and the administration of S-1 alone has shown better response rate of 24.3~39.5% in several phase II studies for colorectal cancer (6-8). The most recent multi-center phase II clinical trial also showed a great promise for S-1 plus cisplatin in treating advanced gastric or gastroesophageal junction adenocarcinoma (9). S-1 is composed of 5-FU prodrug tegafur (FT), a dihydropyrimidine dehydrogenase inhibitor gimestat (CDHP) and an inhibitor of orotate phosphoribosyltransferase otastat potassium (Oxo) in a molar ratio of 1:0.4:1, based on the biochemical modulation of 5-FU. Oxo has the potential to reduce 5-FU related gastrointestinal toxicity through its inhibition of orotate phosphoribosyl transferase and 5-FU phosphorylation (10). Over the past decade, extensive efforts have been focused on further improving patient response to 5-FU-based therapy using biomarkers to predict chemoresponse and disease prognosis. The expression levels of several mRNAs, such as thymidylate synthase (TS), dihydroprymidine dehydrogenase (DPD), thymidine phosphorylase (TP), were shown to be significant predictors for 5-FU-based therapy (11-13). However, due to the complexity of the disease, additional biomarkers are clearly needed to further improve the accuracy of the prediction.

Previous studies from our laboratory have identified a number of deregulated microRNAs (miRNAs) due to p53 deletion using a colon cancer cell line model (14). Over 64% of miRNA promoters contain putative p53 consensus binding site(s). A number of deregulated miRNAs were discovered due to the loss of p53 tumor suppressor in colon cancer cell lines. It was well established that the tumor suppressor p53 is one of the most frequently mutated genes in colorectal and other types of solid tumors (15, 16). It is reasonable to speculate that p53 may act through some of these miRNAs to mediate its down stream gene expression.

miRNAs have recently emerged as new players to regulate gene expression at the level of mRNA translation. miRNAs are non-coding RNAs that regulate gene expression by suppressing their target mRNAs at the post-transcriptional level. At present, over 300 mammalian miRNAs have been identified (17-23) and some of them have been shown to play important roles in the regulation of cell differentiation, proliferation and apoptosis (24-30). Each individual miRNA can potentially regulate mRNA translation for up to several hundred genes via imperfect base pairing based on bioinformatics analysis. We reasoned that certain miRNAs may be a better class of biomarkers because of their broad regulatory function and since they are far less noisy than mRNAs. In addition, these miRNAs are relatively stable due to its stem-loop structure in formalin-fixed paraffin-embedded (FFPE) samples for easy quantification.

To further evaluate the in vivo significance of deregulated miRNAs in relationship with chemosensitivity to S-1 treatment, the expression levels of hsa-let-7g, hsa-miR-143, hsa-miR-145, hsa-miR-181b and hsa-miR-200c were investigated. They were chosen because they were highly over-expressed due to the loss of p53 gene and the critical roles of their down stream mRNA targets (e.g., Ras, cyclin-D, E2F, c-myc, cytochrome C, ECIP-1, MAPPKKK1, TEM6, E2F5, GATA6, PP2B and eIF5A). Our results showed that the expressions of hsa-let-7g, hsa-miR-181b and hsa-miR-200c were over-expressed in colorectal cancer. In addition, the expressions of hsa-let-7g (p=0.03) and hsa-miR-181b (p=0.02) were significantly associated with patient response to S-1-based chemotherapy.

Patients and Methods

Patients and samples

The paraffin sections of the colorectal cancer samples were obtained from the Department of Surgery, Institute of Gastroenterology, Tokyo Women’s Medical University, Japan. Informed consent forms from all patients were obtained before conducting the treatment or study. Forty-six patients had undergone surgical removal from 1996 to 2002. Among the 46 patient samples, 21 normal samples were also obtained. Patients who had recurrence or residual colorectal cancer lesions were treated with S-1 alone or S-1 plus cisplatin (CDDP). The dose of S-1 was determined based on patient’s body surface area (BSA) as follows: <1.25 m2; 80 mg/day, ≥1.25 and < 1.5 m2; 100 mg/day, >1.5 m2; 120 mg/day. The regimen of the treatment was the following: S-1 alone: S-1 was administered twice a day orally for 28 consecutive days, followed by a two-week drug-free interval; S-1/CDDP: S-1 was administered twice-daily via oral administration, followed by 2-weeks rest, while CDDP (30 mg/m2) was injected intravenously on day 1 and 8.

FFPE tissues were prepared using the standard method of the Department of Pathology, Tokyo Women’s Medical University, Japan. The paraffin blocks were cut into 10-μm sections. The patients’ characteristics are summarized in Table I.

Table I
Patient characteristics.

Total RNA extraction

The archived colorectal cancer FFPE specimens (contained either >90% tumor or >90% normal tissues) were dissected and placed in nuclease-free microcentrifuge tubes. The deparaffinization was performed by adding 1 ml of Xylene and vortexing for 5 min at room temperature. The samples were incubated for 3 min at 60°C. After incubation, samples were centrifuged at 14,000 rpm for 7 min at room temperature. The supernatants were removed and 1 ml of 100% ethanol was added with vortexing for 7 min at room temperature. The samples were centrifuged at 14,000 rpm for 7 min at room temperature. After the supernatants were removed, ethanol washes were repeated. After centrifugation, the samples were air dried and 180 μl of digestion buffer (30 mM Tris-HCl, 20 mM EDTA, 1% SDS and nuclease-free water) were added to the samples followed by homogenization. After homogenization, 20 μl of Proteinase K (QIAGEN Inc., Valencia, CA, USA) solution were added and the samples were incubated for additional 3 h at 56°C. Subsequently, 500 μl of TRIzol® (Invitrogen Inc., Carlsbad, CA, USA) were added and folowed by vortexing for 5 min at room temperature. Fifty μl of 1-bromo-3-chloropropane (BCP) solution was added and vortexed for 2 min. The samples were incubated for 3 min at room temperature. After centrifugation at 14,000 rpm for 7 min at 4°C, the upper aqueous phase containing extracted RNA was transferred to the new microcentrifuge tube. One hundred μg of glycogen were added and mixed by vortexing. Samples were precipitated with 500 μl of 100% isopropanol and were incubated for 60 min at −20°C. The RNA samples were centrifuged at 14,000 rpm for 7 min at 4°C. After removing the supernatant, 1 ml of 75% ethanol was added and the samples were centrifuged at 14,000 rpm for 7 min at 4°C. Upon removal the supernatant, the RNA pellet was air dried and resuspended with nuclease-free water.

Reverse transcription (RT)

mirVana™ qRT-PCR miRNA Detection Kit and mirVana™ qRT-PCR Primer Sets (Ambion Inc., Austin, TX, USA) for hsa-let-7g, hsa-miR-143, hsa-miR-145, hsa-miR-200c and 5S ribosomal RNA as an internal control specific reverse transcription were utilized based on the manufactures’ protocol. Briefly, the reaction mixture containing mirVana™ 5x RT Buffer, 1x mirVana™ RT Primer, ArrayScript™ Enzyme Mix and nuclease-free water were mixed with 20 ng of each total RNA. The mixture was incubated for 30 min at 37°C and then for 10 min at 95°C. TaqMan® MicroRNA Assay (Applied Biosystems Inc., Foster City, CA, USA) was used for hsa-miR-181b based on the manufacturer’s protocol. Briefly, the reaction master mix containing 10x RT Buffer, 5x RT Primer for hsa-miR-181 and RNU6B as an internal control, MultiScribe Reverse Transcriptase, RNase Inhibitor and nuclease-free water were mixed with 20 ng of total RNA.

Quantitative real-time PCR

Quantitative real-time PCR was carried out using Applied Biosystems 7500 Real-Time PCR System (Applied Biosystems Inc.). For hsa-let-7g, hsa-miR-143, hsa-miR-145 and hsa-miR-200c, the PCR master mix of a total reaction volume of 25 μl for each reaction containing mirVana™ 5x PCR Buffer (with SYBR® Green I), 50x ROX, SuperTaq™ Polymerase, mirVana™ PCR Primers for each target, nuclease-free water and RT products was prepared. The PCR condition was as follows: 95°C for 3 min, followed by 40 cycles of 95°C for 15 sec and 60°C for 35 sec. For hsa-miR-181b, the PCR master mix of total reaction volume of 20 μl for each reaction containing TaqMan 2x Universal PCR Master Mix (No AmpErase UNG), hsa-miR-181b and RNU6B 10x TaqMan Assay, nuclease-free water and 1.33 μl of RT products was prepared. PCR conditions were 95°C for 10 min, followed by 40 cycles of 95°C for 15 sec and 60°C for 60 sec.

Data analysis

The threshold cycle (CT) value for each target was determined by SDS software v1.2 (Applied Biosystems Inc.). Expression levels of each miRNAs were normalized by calculating the ΔCT values based on subtracting the CT value of target miRNA from the CT value of the internal control 5S ribosomal RNA or RNU6B. The sample with the highest expression levels of miRNAs was used as 100% to generate relative expression values. The statistical studies were performed using MedCalc® for Windows, version 8.1.1.0 (MedCalc software, Mariakerke, Belgium). The statistical differences of the expression level between tumor and normal tissues for each target were calculated by Wilcoxon test. The Mann-Whitney test was performed for comparison of chemoresponse data for hsa-let-7g and hsa-miR-181b. The Log-rank test for Kaplan-Meier curve was generated to evaluate the association between the expression level of each miRNA and survival rate. Statistical significance was set as a p≤0.05.

Results

Median miRNA expression levels of normal and tumor samples

The tumor tissues from 46 patients were divided into the response group (n=27, including the patients evaluated as complete remission, partial response and stable disease after treatment with S-1) and the disease progression patient group (n=19) according to their response to S-1 treatment. The expression levels of five mature miRNAs in these samples were screened via miRNA specific real time qRT-PCR analysis. Based on the real time qRT-PCR analysis, there was no significant difference in expression levels of hsa-miR-143 and hsa-miR-145 between tumor tissues and corresponding normal samples (p=0.1219; p=0.0853, respectively) (Figure 1). In contrast, the expression level of hsa-miR-200c was significantly over-expressed by nearly 6-fold in tumor tissues compared to the corresponding normal samples (p=0.0001; Figure 2). Hsa-let-7g was also significantly over-expressed in tumor tissues compared to corresponding normal colorectal samples (p=0.0037; Figure 3). The expression level of hsa-miR-181b was elevated in tumors compared to the corresponding normal samples (p=0.0005; Figure 4).

Figure 1
Hsa-miR-143 (A) and hsa-miR-145 (B) expressions in colorectal cancer and normal tissue specimens. Relative gene expression values were calculated using samples with the highest expression level of miRNA as 100% (see Materials and Methods). Hsa-miR-143 ...
Figure 2
Hsa-miR-200c expression in colorectal cancer and normal tissue specimens. Relative gene expression values were calculated using sample with the highest expression level of miRNA as 100% (see Materials and Methods). P=0.0001; Wilcoxon test.
Figure 3
Hsa-let-7g expression in colorectal cancer and normal tissue specimens. Relative gene expression values were calculated using sample with the highest expression level of miRNA as 100% (see Materials and Methods). P=0.0037; Wilcoxon test.
Figure 4
hsa-miR-181b expression in colorectal cancer and normal tissue specimens. Relative gene expression values were calculated using sample with the highest expression level of miRNA as 100% (Details see Materials and Methods). (p=0.0005; Wilcoxon test).

Correlation of patient pathological responses with the level of miRNA expression

To evaluate the potential association of certain miRNAs with patient clinical responses, the expression levels of each miRNAs in the response group was compared to the levels in patients with disease progression. Patients who responded to S-1 treatment tend to have lower expression level of hsa-let-7g compared to the disease progression group (p=0.0305; Figure 5). However, the expression of hsa-let-7g was not associated with better survival based on the Kaplan-Meier survival analysis (p=0.9166; Figure 6). On the other hand, the expression of hsa-miR-181b was strongly associated with patient response (Figure 7). Patients who responded to S-1 treatment also displayed a lower expression level of hsa-miR-181b compared to the disease progression group (p=0.0209; Figure 7). However, this parameter was not associated with patient survival based on Kaplan-Meier survival analysis (p=0.1203; Figure 8).

Figure 5
Response based on hsa-let-7g expression (p=0.0305; Mann-Whitney test). CR=complete response; PR=partial response; NC=no change; PD=progressive disease.
Figure 6
Kaplan-Meier overall survival curve based on hsa-let-7g expression (p=0.9166; Log-rank test).
Figure 7
Response based on hsa-miR-181b expression (p=0.0209; Mann-Whitney test). CR=complete response; PR=partial response; NC=no change; PD=progressive disease.
Figure 8
Kaplan-Meier overall survival curve based on hsa-miR-181b expression (p=0.1203; Log-rank test).

Discussion

We evaluated the in vivo significance of several mature miRNAs using FFPE colorectal cancer patient specimens treated with the oral 5-FU drug S-1. S-1 has been widely used as an oral 5-FU-based drug in Japan for treating advanced colorectal cancer. S-1 was also evaluated in both Europe and the United States recently in clinical trials for treatment of advanced gastric and colorectal cancer with promising results (8, 9, 31, 32). Therefore, it is important to discover new biomarkers that can be used for disease prognosis with S-1-based chemotherapy. Here we focused on small non-coding miRNAs that may be associated with chemoresponse and disease progression. Recent studies from our group identified a number of miRNAs that were found to be deregulated in colon cancer due to the loss of p53 function (14). As mentioned above, there are several advantages of using miRNAs as biomarkers instead of mRNAs. First, there are only over 300 known mammalian miRNAs discovered to date and they can potentially regulate up to 30% of the total genes at the translational level. It is relatively easier to discover reliable biomarkers from approximately 300 miRNA candidates than from over 50,000 genes. As a translational regulator, miRNAs can mediate a number of genes in response to acute cellular stress caused by drug treatment. Another advantage is that due to their small size and stem-loop structure, they are less subjected to degradation, fixation and sample processing. This will be a big advantage for archived FFPE patient samples. The real-time miRNA-specific qRT-PCR assays are very sensitive and require only 10~25 ng of total RNA from archived FFPE patient samples.

We profiled 5 mature miRNAs utilizing real time qRT-PCR analysis on 46 FFPE colorectal cancer patient samples that were treated with S-1. The rationale in part, is that the mRNA targets (e.g., RAS, cyclin D, c-myc, cytochrome C, ECIP-1, MAPPKKK1, TEM6, E2F5, GATA6, PP2B, eIF5A and E2F) regulated by some of these miRNAs have been shown to play critical roles in cell cycle check point control and apoptosis. Because one miRNA can potentially regulate several hundred mRNA targets at the post-transcriptional level, even a small expression change of key miRNA may have a large impact on cell cycle control and chemosensitivity.

The expression levels of hsa-miR-143 and hsa-miR-145 were not significantly different in tumor samples compared to their corresponding normal samples. This was a bit surprising since it had been reported by Michael et al. that the expression of hsa-miR-143 and hsa-miR-145 in human colorectal cancers decreased compared to normal samples (33). Based on our results, the reduction of the expression level in tumor tissue compared to corresponding normal sample was observed in only seven (33%) for hsa-miR-143 and eight (38%) for hsa-miR-145 out of twenty-one pairs (Figure 1). These observetions could be due to the genetic differences between the Japanese patients and European patients.

The expression level of hsa-miR-200c was significantly over-expressed in our colorectal tumor samples compared to the corresponding normal samples (Figure 2), in corroboration with the report from the Michael et al. study in colorectal tumor cells (33). The expression of hsa-let-7g was highly over-expressed in colorectal cancer samples compared to the corresponding normal samples (Figure 3). Based on the bioinformatics analysis, hsa-let-7g can potentially interact with more than 200 mRNA targets. This includes several critical cell cycle control genes such as RAS, cyclin D, c-myc and E2F family members. It’s known that E2F family proteins are key transcription factors for regulating the expression of enzymes involved in DNA synthesis, such as TS and TK (34).

Based on our knowledge, this is the first report to demonstrate that hsa-let-7g is associated with chemosensitivity to S-1 based chemotherapy (Figure 5). Our results were consistent with the finding from a recent report by Johnson SM that the let-7 family regulates the expression of the oncogene RAS in C. elegans and human lung tumors (35). Let-7 interacts with multiple interaction sites at the 3’-UTR of RAS mRNA to regulate its translation. Previous reports have shown that there is a strong link between the chemosensitivity vs. RAS status (36, 37). We speculate that chemotherapeutic sensitivity of S-1 is potentially affected by the hsa-let-7g-mediated target transcripts such as E2F, cyclin D and c-myc (38-40). Although the expression level of hsa-let-7g was significantly associated with patient response to S-1 (Figure 5), there was no discernible benefit in predicting patient survival (Figure 6). This is not surprising because the response and survival markers are two different entities and often there is no connection between the two. Nonetheless, it is still important to be able to predict which patient will respond to a particular therapy. The expression of hsa-miR-181b was strongly associated with patient response to S-1 (Figure 7). Many genes, such as cytochrome C, ECIP-1, MAPPKKK1, TEM6, E2F5, GATA6, PP2B and eIF5A, are predicted to be regulated by hsa-miR-181b. These genes have been shown to be important for cell signaling, cell cycle control and chemosensitivity. We speculate that the miRNAs can modulate the expression of a number of genes at the translational level in a quick and energy-efficient control process. Clearly the detailed molecular and cellular mechanisms of miRNA-mediated translational control will be required in future studies to establish the direct link of hsa-miR-181b and chemosensitivity to fluoropyrimidine based drugs. Although hsa-miR-181b was associated with patient clinical response, the expression of hsa-miR-181b was not significant for patient survival (Figure 8).

In conclusion, the in vivo significance of 5 mature miRNAs was evaluated in colorectal cancer patient samples treated with S-1. Hsa-let-7g, hsa-miR-181b and hsa-miR-200c were over-expressed in colorectal cancer patients and may be useful as tumor markers. Hsa-let-7g and hsa-miR-181b may be significant indicators for chemoresponse to S-1-based chemotherapy.

Acknowledgments

We appreciate the critical review of the manuscript by Ms. Elaine Gavin. This research was supported by Mitchell Cancer Institute Start-up fund (J. Ju), U.S.A.

References

1. Heidelberger C, Chaudhuri NK, Danneberg P, Mooren D, Griesbach L, Duschinsky R, Schnitzer RJ, Pleven E, Scheiner J. Fluorinated pyrimidines, a new class of tumour-inhibitory compounds. Nature. 1957;179:663–666. [PubMed]
2. Piedbois P, Rougier P, Buyse M, Pignon JP, Ryan L, Hansen R, Zee B, Weinerman B, Pater J, Leichman C, Macdonald J, Benedetti J, Lokich J, Fryer J, Brufman G, Isacson R, Laplanche A, Levy E. Efficacy of intravenous continuous infusion of fluorouracil compared with bolus administration in advanced colorectal cancer. Meta-analysis Group In Cancer. J Clin Oncol. 1998;16:301–308.
3. Piedbois P, Buyse M, Rustum Y, Machover D, Erlichman C, Carlson RW, Valone F, Labianca R, Doroshow JH, Petrelli N. Modulation of fluorouracil by leucovorin in patients with advanced colorectal cancer: evidence in terms of response rate. Advanced Colorectal Cancer Meta-analysis Project. J Clin Oncol. 1992;10:896–903. [PubMed]
4. O’Connell MJ. Current status of adjuvant therapy for colorectal cancer. Oncology (Williston Park) 2004;18:751–755. discussion 755-758. [PubMed]
5. Schoffski P. The modulated oral fluoropyrimidine prodrug S-1, and its use in gastrointestinal cancer and other solid tumors. Anticancer Drugs. 2004;15:85–106. [PubMed]
6. Ohtsu A, Baba H, Sakata Y, Mitachi Y, Horikoshi N, Sugimachi K, Taguchi T. Phase II study of S-1, a novel oral fluorophyrimidine derivative, in patients with metastatic colorectal carcinoma. S-1 Cooperative Colorectal Carcinoma Study Group. Br J Cancer. 2000;83:141–145. [PMC free article] [PubMed]
7. Shirao K, Ohtsu A, Takada H, Mitachi Y, Hirakawa K, Horikoshi N, Okamura T, Hirata K, Saitoh S, Isomoto H, Satoh A. Phase II study of oral S-1 for treatment of metastatic colorectal carcinoma. Cancer. 2004;100:2355–2361. [PubMed]
8. Van den Brande J, Schoffski P, Schellens JH, Roth AD, Duffaud F, Weigang-Kohler K, Reinke F, Wanders J, de Boer RF, Vermorken JB, Fumoleau P. EORTC Early Clinical Studies Group early phase II trial of S-1 in patients with advanced or metastatic colorectal cancer. Br J Cancer. 2003;88:648–653. [PMC free article] [PubMed]
9. Ajani JA, Lee FC, Singh DA, Haller DG, Lenz HJ, Benson AB, 3rd, Yanagihara R, Phan AT, Yao JC, Strumberg D. Multicenter phase II trial of S-1 plus cisplatin in patients with untreated advanced gastric or gastroesophageal junction adenocarcinoma. J Clin Oncol. 2006;24:663–667. [PubMed]
10. Takechi T, Nakano K, Uchida J, Mita A, Toko K, Takeda S, Unemi N, Shirasaka T. Antitumor activity and low intestinal toxicity of S-1, a new formulation of oral tegafur, in experimental tumor models in rats. Cancer Chemother Pharmacol. 1997;39:205–211. [PubMed]
11. McDermott U, Longley DB, Johnston PG. Molecular and biochemical markers in colorectal cancer. Ann Oncol. 2002;13(Suppl 4):235–245. [PubMed]
12. Salonga D, Danenberg KD, Johnson M, Metzger R, Groshen S, Tsao-Wei DD, Lenz HJ, Leichman CG, Leichman L, Diasio RB, Danenberg PV. Colorectal tumors responding to 5-fluorouracil have low gene expression levels of dihydropyrimidine dehydrogenase, thymidylate synthase, and thymidine phosphorylase. Clin Cancer Res. 2000;6:1322–1327. [PubMed]
13. Vallbohmer D, Kuramochi H, Shimizu D, Danenberg KD, Lindebjerg J, Nielsen JN, Jakobsen A, Danenberg PV. Molecular factors of 5-fluorouracil metabolism in colorectal cancer: analysis of primary tumor and lymph node metastasis. Int J Oncol. 2006;28:527–533. [PubMed]
14. Xi Y, Shalgi R, Fodstad O, Pilpel Y, Ju J. Differentially regulated micro-RNAs and actively translated messenger RNA transcripts by tumor suppressor p53 in colon cancer. Clin Cancer Res. 2006;12:2014–2024. [PubMed]
15. Elsaleh H, Powell B, Soontrapornchai P, Joseph D, Goria F, Spry N, Iacopetta B. p53 gene mutation, microsatellite instability and adjuvant chemotherapy: impact on survival of 388 patients with Dukes’ C colon carcinoma. Oncology. 2000;58:52–59. [PubMed]
16. Hollstein M, Sidransky D, Vogelstein B, Harris CC. p53 mutations in human cancers. Science. 1991;253:49–53. [PubMed]
17. Lau NC, Lim LP, Weinstein EG, Bartel DP. An abundant class of tiny RNAs with probable regulatory roles in Caenorhabditis elegans. Science. 2001;294:858–862. [PubMed]
18. Lee RC, Ambros V. An extensive class of small RNAs in Caenorhabditis elegans. Science. 2001;294:862–864. [PubMed]
19. Lagos-Quintana M, Rauhut R, Lendeckel W, Tuschl T. Identification of novel genes coding for small expressed RNAs. Science. 2001;294:853–858. [PubMed]
20. Lagos-Quintana M, Rauhut R, Yalcin A, Meyer J, Lendeckel W, Tuschl T. Identification of tissue-specific microRNAs from mouse. Curr Biol. 2002;12:735–739. [PubMed]
21. Mourelatos Z, Dostie J, Paushkin S, Sharma A, Charroux B, Abel L, Rappsilber J, Mann M, Dreyfuss G. miRNPs: a novel class of ribonucleoproteins containing numerous microRNAs. Genes Dev. 2002;16:720–728. [PMC free article] [PubMed]
22. Reinhart BJ, Weinstein EG, Rhoades MW, Bartel B, Bartel DP. MicroRNAs in plants. Genes Dev. 2002;16:1616–1626. [PMC free article] [PubMed]
23. Lagos-Quintana M, Rauhut R, Meyer J, Borkhardt A, Tuschl T. New microRNAs from mouse and human. Rna. 2003;9:175–179. [PMC free article] [PubMed]
24. Schratt GM, Tuebing F, Nigh EA, Kane CG, Sabatini ME, Kiebler M, Greenberg ME. A brain-specific microRNA regulates dendritic spine development. Nature. 2006;439:283–289. [PubMed]
25. Chen JF, Mandel EM, Thomson JM, Wu Q, Callis TE, Hammond SM, Conlon FL, Wang DZ. The role of microRNA-1 and microRNA-133 in skeletal muscle proliferation and differentiation. Nat Genet. 2005;38(2):228–233. [PMC free article] [PubMed]
26. Xu P, Vernooy SY, Guo M, Hay BA. The Drosophila microRNA Mir-14 suppresses cell death and is required for normal fat metabolism. Curr Biol. 2003;13:790–795. [PubMed]
27. Brennecke J, Hipfner DR, Stark A, Russell RB, Cohen SM. Bantam encodes a developmentally regulated microRNA that controls cell proliferation and regulates the proapoptotic gene hid in Drosophila. Cell. 2003;113:25–36. [PubMed]
28. Reinhart BJ, Slack FJ, Basson M, Pasquinelli AE, Bettinger JC, Rougvie AE, Horvitz HR, Ruvkun G. The 21-nucleotide let-7 RNA regulates developmental timing in Caenorhabditis elegans. Nature. 2000;403:901–906. [PubMed]
29. Lee RC, Feinbaum RL, Ambros V. The C. elegans heterochronic gene lin-4 encodes small RNAs with antisense complementarity to lin-14. Cell. 1993;75:843–854. [PubMed]
30. Chen JF, Mandel EM, Thomson JM, Wu Q, Callis TE, Hammond SM, Conlon FL, Wang DZ. The role of microRNA-1 and microRNA-133 in skeletal muscle proliferation and differentiation. Nat Genet. 2006;38:228–233. [PMC free article] [PubMed]
31. Baba H, Kohnoe S, Endo K, Ikeda Y, Toh Y, Nakashima H, Okamura T. State of the treatment for gastrointestinal cancer. Gan To Kagaku Ryoho. 2000;27:1233–1246. [PubMed]
32. Shirasaka T, Tsukuda M, Inuyama Y, Taguchi T. New oral anticancer drug, TS-1 (S-1)–from bench to clinic. Gan To Kagaku Ryoho. 2001;28:855–864. [PubMed]
33. Michael MZ, OC SM, van Holst Pellekaan NG, Young GP, James RJ. Reduced accumulation of specific microRNAs in colorectal neoplasia. Mol Cancer Res. 2003;1:882–891. [PubMed]
34. Banerjee D, Mayer-Kuckuk P, Capiaux G, Budak-Alpdogan T, Gorlick R, Bertino JR. Novel aspects of resistance to drugs targeted to dihydrofolate reductase and thymidylate synthase. Biochim Biophys Acta. 2002;1587:164–173. [PubMed]
35. Johnson SM, Grosshans H, Shingara J, Byrom M, Jarvis R, Cheng A, Labourier E, Reinert KL, Brown D, Slack FJ. RAS is regulated by the let-7 microRNA family. Cell. 2005;120:635–647. [PubMed]
36. Klampfer L, Huang J, Sasazuki T, Shirasawa S, Augenlicht L. Oncogenic Ras promotes butyrate-induced apoptosis through inhibition of gelsolin expression. J Biol Chem. 2004;279:36680–36688. [PubMed]
37. Klampfer L, Swaby LA, Huang J, Sasazuki T, Shirasawa S, Augenlicht L. Oncogenic Ras increases sensitivity of colon cancer cells to 5-FU-induced apoptosis. Oncogene. 2005;24:3932–3941. [PubMed]
38. Arango D, Corner GA, Wadler S, Catalano PJ, Augenlicht LH. c-myc/p53 interaction determines sensitivity of human colon carcinoma cells to 5-fluorouracil in vitro and in vivo. Cancer Res. 2001;61:4910–4915. [PubMed]
39. Elliott MJ, Farmer MR, Atienza C, Jr, Stilwell A, Dong YB, Yang HL, Wong SL, McMasters KM. E2F-1 gene therapy induces apoptosis and increases chemosensitivity in human pancreatic carcinoma cells. Tumour Biol. 2002;23:76–86. [PubMed]
40. Akervall J, Brun E, Dictor M, Wennerberg J. Cyclin D1 overexpression versus response to induction chemotherapy in squamous cell carcinoma of the head and neck–preliminary report. Acta Oncol. 2001;40:505–511. [PubMed]
PubReader format: click here to try

Formats:

Related citations in PubMed

See reviews...See all...

Cited by other articles in PMC

See all...

Links

  • MedGen
    MedGen
    Related information in MedGen
  • PubMed
    PubMed
    PubMed citations for these articles

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...