Regulation of the expression of components of the exocytotic machinery of insulin-secreting cells by microRNAs

Abstract

Fine-tuning of insulin secretion from pancreatic b-cells participates in blood glucose homeostasis. Defects in this process can lead to chronic hyperglycemia and diabetes mellitus. Several proteins controlling insulin exocytosis have been identified, but the mechanisms regulating their expression remain poorly understood. Here, we show that two non-coding microRNAs, miR124a and miR96, modulate the expression of proteins involved in insulin exocytosis and affect secretion of the b-cell line MIN6B1. miR124a increases the levels of SNAP25, Rab3A and synapsin-1A and decreases those of Rab27A and Noc2. Inhibition of Rab27A expression is mediated by direct binding to the 39-untranslated region of Rab27A mRNA. The effect on the other genes is indirect and linked to changes in mRNA levels. Overexpression of miR124a leads to exaggerated hormone release under basal conditions and a reduction in glucose-induced secretion. miR96 increases mRNA and protein levels of granuphilin, a negative modulator of insulin exocytosis, and decreases the expression of Noc2, resulting in lower capacity of MIN6B1 cells to respond to secretagogues. Our data identify miR124a and miR96 as novel regulators of the expression of proteins playing a critical role in insulin exocytosis and in the release of other hormones and neurotransmitters.

Identification of microRNAs with a role in glucose stimulated insulin secretion by expression profiling of MIN6 cells

“…Previous studies have reported mir-375, mir-9, mir-124a and mir-96 to play a role in regulation of insulin secretion in rodent pancreatic beta cell lines MIN6, INS-IE and MIN6 B1 cells [1][2][3][4]; however, in this study, mir-375, mir-9, mir-124a and mir-96…”

“…In recent years, miRNAs have been implicated to play a role in regulation of insulin secretion [1][2][3][4], pancreatic islet development and cell differentiation [5][6][7][8][9][10][11], insulin resistance [12][13][14][15], and have been associated with secondary complications of diabetes, such as diabetic nephropathy [16,17] and cardiovascular disease [18,19].…”

“…Overexpression of mir-124a leads to increased Ca 2+ levels within MIN6 cells, possibly due to dysregulation of Kir6.2 and sur1 subunits [2]. Overexpression of mir-124a in MIN6 B1 cells led to increased insulin secretion in response to basal ACCEPTED MANUSCRIPT 4 glucose concentrations and reduced secretion in response to stimulatory glucose concentrations [4]. Mir-124a affects the expression of a number of other exocytosis related proteins in MIN6 B1 cells including SNAP25, Rab3A, synapsin-1A, Rab27A and Noc2; although only Rab27A is a direct target of mir-124a [4].…”

“…Overexpression of mir-124a in MIN6 B1 cells led to increased insulin secretion in response to basal ACCEPTED MANUSCRIPT 4 glucose concentrations and reduced secretion in response to stimulatory glucose concentrations [4]. Mir-124a affects the expression of a number of other exocytosis related proteins in MIN6 B1 cells including SNAP25, Rab3A, synapsin-1A, Rab27A and Noc2; although only Rab27A is a direct target of mir-124a [4]. These exocytosisrelated proteins also have predicted binding sites for regulation by other miRNAs, but these still remain to be experimentally validated [22].…”

MicroRNAs as regulators of death receptors signaling

“…1 They negatively regulate mRNA expression by repressing translation or directly cleaving the targeted mRNA. 2 In the past few years, our understanding of the role of miRNA has expanded from the initially identified functions in the development of round worms to it becoming a highly expressed and ubiquitous regulator implicated in a wide array of critical processes, including proliferation, cell death and differentiation, 3 metabolism 4 and, importantly, tumorigenesis. 5 MiRNAs are thought to regulate about 30% of the protein-coding genes of the human genome, and individual miRNAs typically target several transcripts rather than just one specific gene.…”