Department of Molecular and Cellular Biochemistry, University of Kentucky, College of Medicine, Lexington, 40536, USA.
MicroRNAs (miRNAs) are small noncoding ribonucleotides that bind mRNAs and function mainly as translational repressors in mammals. MicroRNAs have been implicated to play a role in many diseases, including diabetes. Several reports indicate an important function for miRNAs in insulin production as well as insulin secretion. We have recently carried out a screen in the pancreatic beta-cell line MIN6 to identify miRNAs with altered abundance in response to changes in glucose concentrations. This screen resulted in identification of 61 glucose-regulated miRNAs from a total of 108 miRNAs detectable in MIN6 cells. Many of the identified miRNAs, including miR-124a, miR-107, and miR-30d were up-regulated in the presence of high glucose. Only a few of the miRNAs, including miR-296, miR-484, and miR-690 were significantly down-regulated by high glucose treatment. Interestingly, we found that overexpression of miR-30d, one of the miRNAs up-regulated by glucose, increased insulin gene expression, while inhibition of miR-30d abolished glucose-stimulated insulin gene transcription. Overexpression or inhibition of miR-30d did not have any effect on insulin secretion. These data suggest that the putative target genes of miR-30d may be negative regulators of insulin gene expression.