Transcriptional suppression of mir‐29b‐1/mir‐29a promoter by c‐Myc, hedgehog, and NF‐kappaB

Abstract

MicroRNAs regulate pathways contributing to oncogenesis, and thus the mechanisms causing dysregulation of microRNA expression in cancer are 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 from 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 of two putative E-box (Myc-binding) sites, a Gli-binding site, and four NF–κB-binding sites 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 cyclopamine, which blocks smoothened signaling, increased the activity of the 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–κB 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.

Protective Role of Estrogen-induced miRNA-29 Expression in Carbon Tetrachloride-induced Mouse Liver Injury

“…3). The inverse relationship between the NF-B activity and the expression of miR-29a/b also confirms the previous report that the NF-B pathway negatively regulates miR-29 expression (31).…”

“…It has been well established that E 2 is involved in modulation of transcriptional factors such as NF-B and STAT-1 (29,30). Interestingly, previous studies also showed that NF-B served as a negative regulator for expression of miR-29a and miR-29b (31). To determine whether NF-B is involved in the E 2 -mediated up-regulation of miR-29a and miR-29b, we assayed the levels of NF-B p65 in nuclei of IAR20 cells with or without E 2 treatment.…”

MicroRNA-29b is involved in the Src-ID1 signaling pathway and is dysregulated in human lung adenocarcinoma

“…microRNA-29b in lung cancer SI Rothschild et al miR-29b by hedgehog signaling and NF-kB activation was also reported (Mott et al, 2010). Our data support the negative regulation of miR-29b and ID1 by c-Myc because forced expression of c-Myc in lung cancer cells suppressed miR-29b levels and induced the expression of ID1.…”

The role of miR-29 family members in malignant hematopoiesis

“…Increased miR-29b expression suggested constitutive hedgehog signaling in cholangiocarcinoma cells and demonstrated that this pathway repressed miR-29b expression. The data also supported the role of NF-κB activation through TLR signaling as a suppressor of miR29b-1/a promoter function and expression of mature miR29b through recognition of NF-κB binding sites located in the miR29b-1/a promoter region 11 . CCAAT/enhancer binding protein α (CEBPA) binding site was identified in miR-29b-1/a promoter 12 .…”