The Effect of RGS4 on Autophagic Flux in Min6 Pancreatic Beta Cells

Defective autophagy can lead to dysregulation of metabolic homeostasis. Previous studies in our laboratory have shown that RGS4-overexpressing HEK cells show increased autophagic activity. Herein, we study the potential role of RGS4 as a regulator of autophagy in the Min6 mouse pancreatic beta cell line, via inhibition of Gαi3, an established attenuator of autophagy. Min6 cells exposed to nutrient-deprived conditions undergo autophagic initiation demonstrated by increased expression of autophagy markers. When RGS4-YFP is ectopically expressed in Min6 cells, confocal microscopy imaging revealed colocalization between RGS4-YFP (both wild type and loss-of-function mutants), Gαi3 (RC)-CFP, and autophagy markers including Beclin1-DsRed and Atg12-RFP on intracellular punctae. Despite its colocalization with known regulators of autophagy, RGS4 was apparently unable to modulate the activity of known mediators and markers of autophagic activity (phospho-p76S6K, LC3 II, phospho-Bcl-2). We conclude that Gαi3 and RGS4 are not major factors in the regulation of autophagic flux in Min6 cells.M.Sc.2017-11-20 00:00:0

RGS4-Deficiency Alters Intracellular Calcium and PKA-Mediated Control of Insulin Secretion in Glucose-Stimulated Beta Islets

A number of diverse G-protein signaling pathways have been shown to regulate insulin secretion from pancreatic β-cells. Accordingly, regulator of G-protein signaling (RGS) proteins have also been implicated in coordinating this process. One such protein, RGS4, is reported to show both positive and negative effects on insulin secretion from β-cells depending on the physiologic context under which it was studied. We here use an RGS4-deficient mouse model to characterize previously unknown G-protein signaling pathways that are regulated by RGS4 during glucose-stimulated insulin secretion from the pancreatic islets. Our data show that loss of RGS4 results in a marked deficiency in glucose-stimulated insulin secretion during both phase I and phase II of insulin release in intact mice and isolated islets. These deficiencies are associated with lower cAMP/PKA activity and a loss of normal calcium surge (phase I) and oscillatory (phase II) kinetics behavior in the RGS4-deficient β-cells, suggesting RGS4 may be important for regulation of both Gαi and Gαq signaling control during glucose-stimulated insulin secretion. Together, these studies add to the known list of G-protein coupled signaling events that are controlled by RGS4 during glucose-stimulated insulin secretion and highlight the importance of maintaining normal levels of RGS4 function in healthy pancreatic tissues