Transcriptional Suppression of mir-29b-1/mir-29a Promoter by c-Myc, Hedgehog, and NF-kappaB

MicroRNAs regulate pathways contributing to oncogenesis, and thus the mechanisms causing dysregulation of microRNA expression in cancer ate of significant interest Mature mir-29b levels are decreased in malignant cells, and this alteration promotes the malignant phenotype. including apoptosis resistance However, the mechanism responsible for mir-29b suppression is unknown. Here, we examined mir-29 expression front chromosome 7q32 using cholangiocarcinoma cells as a model for mir-29b downregulation using 5' rapid amplification of cDNA ends, the transcriptional start site was identified for this microRNA locus Computational analysis revealed the presence or two putative E-box (Myc-binding) sites, a Oh-binding site, and four NW-kappa B-binding sues in the region flanking the transcriptional start site Promoter activity in cholangiocarcinoma cells was repressed by transfection with c-Myc. consistent with reports in other cell types Treatment with the hedgehog inhibitor cyclopamme. which blocks smoothened signaling, Increased the activity of (he promoter and expression of mature mir-29b Mutagenesis analysis and gel shift data are consistent with a direct binding of Gli to the mir-29 promoter Finally, activation of NF-kappa B signaling. via ligation of Toll-like receptors. also repressed mir-29b expression and promoter function Of note, activation of hedgehog. Toll-like receptor, and c-Myc signaling protected cholangiocytes from TRAIL-induced apoptosis Thus, in addition to c-Myc, mir-29 expression can be suppressed by hedgehog signaling and inflammatory pathways. both commonly activated in the genesis of human malignancies. J. Cell Biochem 110, 1155-1164, 2010. (C) 2010 Wiley-Liss. Inc