Genetic Variation Of Mirna Sequence In Pancreatic Cancer

Objective: MicroRNAs (miRNAs) are small non-coding RNAs of 20–22 nucleotides (nts) and constitute a novel class of gene regulators that negatively regulate gene expression at the post-transcriptional level. They regulate diverse biological processes. Recent studies have shown that genetic variations or mutations of miRNA were identified in various human cancers besides mis-expression and indicate that miRNAs might play an important role in tumorigenesis. Alterations in miRNA sequence may be an important contributor to the development of pancreatic carcinoma. We hypothesized that genetic variations in miRNA genes were associated with pancreatic carcinoma.Methods: We analyzed genomic sequences coding for the precursors of 8 microRNA genes in both 20 pancreatic carcinoma tissues and 6 cancer cell lines. When a mutation was identified, we use TaqMan? MicroRNA Assays to analyze the expression level of the miRNA in both cancer cell lines and pancreatic carcinoma tissues. Promoter assay and prediction of secondary structure of miRNA precursor were performed to determine the molecular mechanism underlying the aberrant expression of miRNA.Results: 4 novel mutations in primary miRNA (pri-miRNA) transcripts were identified. TaqMan microRNA assays showed that miR-21 was significantly overexpressed in 20 pancreatic carcinomas and 6 cancer cell lines compared with paired benign tissues and normal pancreas (P<0.05). Two mutations of miR-21 did not notably alter the activity of the promoter of the miRNA gene (P>0.05). Although most of these mutations seem to have no effect on microRNA processing, an A to G mutation at 29 nt downstream of pre-miR-21 led to a conformational change of the secondary structure close to the stem reaching into the pre-miR-21, and a relatively reduction of the mature miR-21 expression in vivo.Conclusion: These results suggested that miRNA might play an important role in pancreatic tumorigenesis, but the molecular mechanism underlying the particular sequence variations in miRNA that can cause aberrant expression remains to be determined.