MicroRNA-9 controls the expression of Granuphilin/Slp4 and the secretory response of insulin-producing cells.
Insulin release from pancreatic beta-cells plays an essential role in blood glucose homeostasis. Several proteins controlling insulin exocytosis have been identified, but the factors determining the expression of the components of the secretory machinery of beta-cells remain largely unknown. MicroRNAs are newly discovered small non-coding RNAs acting as repressors of gene expression. We found that overexpression of mir-9 in insulin-secreting cells causes a reduction in exocytosis elicited by glucose or potassium. We show that mir-9 acts by diminishing the expression of the transcription factor Onecut-2 and, in turn, by increasing the level of Granuphilin/Slp4, a Rab GTPase effector associated with beta-cell secretory granules that exerts a negative control on insulin release. Indeed, electrophoretic mobility shift assays, chromatin immunoprecipitation, and transfection experiments demonstrated that Onecut-2 is able to bind to the granuphilin promoter and to repress its transcriptional activity. Moreover, we show that silencing of Onecut-2 by RNA interference increases Granuphilin expression and mimics the effect of mir-9 on stimulus-induced exocytosis. Our data provide evidence that in insulin-producing cells adequate levels of mir-9 are mandatory for maintaining appropriate Granuphilin levels and optimal secretory capacity.
Plaisance
Valérie
V
Department of Cell Biology and Morphology, University of Lausanne, and Department of Internal Medicine, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland.
Abderrahmani
Amar
A
Perret-Menoud
Véronique
V
Jacquemin
Patrick
P
Lemaigre
Frédéric
F
Regazzi
Romano
R
D001483:Base Sequence; D005089:Exocytosis; D005786:Gene Expression Regulation; D020868:Gene Silencing; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000378:metabolism; D035683:MicroRNAs; D008969:Molecular Sequence Data; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000096:biosynthesis* / Q000378:metabolism
D007328:Insulin; D035683:MicroRNAs; D034741:RNA, Small Interfering; C512779:SYTL4 protein, human; D033921:Vesicular Transport Proteins