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J Biol Chem. 2010 Jan 1;285(1):216-25. doi: 10.1074/jbc.M109.041640. Epub 2009 Nov 10.

NFkappaB p50-CCAAT/enhancer-binding protein beta (C/EBPbeta)-mediated transcriptional repression of microRNA let-7i following microbial infection.

Author information

1
Division of Gastroenterology and Hepatology, Miles and Shirley Fiterman Center for Digestive Diseases, Mayo Clinic, Rochester, Minnesota 55905, USA. ohara.steven@mayo.edu

Abstract

MicroRNAs, central players of numerous cellular processes, regulate mRNA stability or translational efficiency. Although these molecular events are established, the mechanisms regulating microRNA function and expression remain largely unknown. The microRNA let-7i regulates Toll-like receptor 4 expression. Here, we identify a novel transcriptional mechanism induced by the protozoan parasite Cryptosporidium parvum and Gram(-) bacteria-derived lipopolysaccharide (LPS) mediating let-7i promoter silencing in human biliary epithelial cells (cholangiocytes). Using cultured cholangiocytes, we show that microbial stimulus decreased let-7i expression, and promoter activity. Analysis of the mechanism revealed that microbial infection promotes the formation of a NFkappaB p50-C/EBPbeta silencer complex in the regulatory sequence. Chromatin immunoprecipitation assays (ChIP) demonstrated that the repressor complex binds to the let-7i promoter following microbial stimulus and promotes histone-H3 deacetylation. Our results provide a novel mechanism of transcriptional regulation of cholangiocyte let-7i expression following microbial insult, a process with potential implications for epithelial innate immune responses in general.

PMID:
19903813
PMCID:
PMC2804168
DOI:
10.1074/jbc.M109.041640
[Indexed for MEDLINE]
Free PMC Article
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