Abstract

MicroRNAs (miRNAs) are small non-codingRNAs of 20-22 nucleotides (nts) and constitute a novel class of gene regulatorsthat negatively regulate gene expression at the post-transcriptional level. Theexpression of miRNA is deregulated in many types of cancers. Alterations inmiRNA expression may be an important contributor to the development ofpancreatic carcinoma. We hypothesized that genetic variations in miRNA geneswere associated with pancreatic carcinoma and analyzed genomic sequences codingfor the precursors of eight miRNA genes in both pancreatic carcinoma tissuesand cancer cell lines. Four novel mutations in primary miRNA transcripts wereidentified. TaqMan miRNA assays showed that miR-21 was significantlyoverexpressed in 20 pancreatic carcinomas and 6 cancer cell lines compared withpaired benign tissues and normal pancreas. Two mutations of miR-21 did notnotably alter the activity of the promoter of the miRNA gene. Although most ofthese mutations seem to have no effect on miRNA processing, an A-G mutation at29-nt downstream of pre-miR-21 led to a conformational change of the secondarystructure close to the stem reaching into the pre-miR-21 and a relativereduction of the mature miR-21 expression in vivo. These results suggested thatmiRNA might play an important role in pancreatic tumorigenesis, but themolecular mechanism underlying the particular sequence variations in miRNA thatcan cause aberrant expression remains to be determined.