Abstract
Altered expression of microRNA (miRNA) is strongly implicated in cancer, and recent studies have shown that, in cancer, expression of some miRNAs cells is silenced in association with CpG island hypermethylation. To identify epigenetically silenced miRNAs in colorectal cancer (CRC), we screened for miRNAs induced in CRC cells by 5-aza-2'-deoxycytidine (DAC) treatment or DNA methyltransferase knockout. We found that miRNA-34b (miR-34b) and miR-34c, two components of the p53 network, are epigenetically silenced in CRC; that this down-regulation of miR-34b/c is associated with hypermethylation of the neighboring CpG island; and that DAC treatment rapidly restores miR-34b/c expression. Methylation of the miR-34b/c CpG island was frequently observed in CRC cell lines (nine of nine, 100%) and in primary CRC tumors (101 of 111, 90%), but not in normal colonic mucosa. Transfection of precursor miR-34b or miR-34c into CRC cells induced dramatic changes in the gene expression profile, and there was significant overlap between the genes down-regulated by miR-34b/c and those down-regulated by DAC. We also found that the miR-34b/c CpG island is a bidirectional promoter which drives expression of both miR-34b/c and B-cell translocation gene 4 (BTG4); that methylation of the CpG island is also associated with transcriptional silencing of BTG4; and that ectopic expression of BTG4 suppresses colony formation by CRC cells. Our results suggest that miR-34b/c and BTG4 are novel tumor suppressors in CRC and that the miR-34b/c CpG island, which bidirectionally regulates miR-34b/c and BTG4, is a frequent target of epigenetic silencing in CRC.
Highlights
MicroRNAs are a group of noncoding small RNAs that negatively regulate the translation and stability of partially complementary target mRNAs [1, 2], and it is clear that they play pivotal roles in a wide array of biological processes, including cell proliferation and differentiation and apoptosis [1, 2]
To screen for epigenetically silenced miRNAs, we initially examined a panel of 157 miRNAs in three colorectal cancer (CRC) cell lines (HCT116, DLD-1, and RKO) treated with or without DAC
Among the 37 www.aacrjournals.org miRNAs up-regulated by DNA methyltransferase (DNMT) inhibition, we focused on miR34b/c because recent studies have shown that miR-34 family members are direct targets of p53 [15,16,17, 29,30,31]
Summary
MicroRNAs (miRNA) are a group of noncoding small RNAs that negatively regulate the translation and stability of partially complementary target mRNAs [1, 2], and it is clear that they play pivotal roles in a wide array of biological processes, including cell proliferation and differentiation and apoptosis [1, 2] Consistent with their role in these processes, a number of studies have shown widespread alteration of miRNA expression patterns in. The DNA encoding both miR-127 and miR-124a is embedded within CpG islands that are hypermethylated in cancer cells This suggests that, as with other tumor suppressor genes, DNA methylation is a major mechanism by which miRNA expression is silenced in cancer
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
