SAD-A Promotes Glucose-Stimulated Insulin Secretion Through Phosphorylation and Inhibition of GDI? in Male Islet ? Cells.

ABSTRACT: Rho GDP-dissociation inhibitor (GDI?) inhibits glucose-stimulated insulin secretion (GSIS) in part by locking Rho GTPases in an inactive GDP-bound form. The onset of GSIS causes phosphorylation of GDI? at Ser174, a critical inhibitory site for GDI?, leading to the release of Rho GTPases and their subsequent activation. However, the kinase regulator(s) that catalyzes the phosphorylation of GDI? in islet ? cells remains elusive. We propose that SAD-A, a member of AMP-activated protein kinase-related kinases that promotes GSIS as an effector kinase for incretin signaling, interacts with and inhibits GDI? through phosphorylation of Ser174 during the onset GSIS from islet ? cells. Coimmunoprecipitation and phosphorylation analyses were carried out to identify the physical interaction and phosphorylation site of GDI? by SAD-A in the context of GSIS from INS-1 ? cells and primary islets. We identified GDI? directly binds to SAD-A kinase domain and phosphorylated by SAD-A on Ser174, leading to dissociation of Rho GTPases from GDI? complexes. Accordingly, overexpression of SAD-A significantly stimulated GDI? phosphorylation at Ser174 in response to GSIS, which is dramatically potentiated by glucagonlike peptide-1, an incretin hormone. Conversely, SAD-A deficiency, which is mediated by short hairpin RNA transfection in INS-1 cells, significantly attenuated endogenous GDI? phosphorylation at Ser174. Consequently, coexpression of SAD-A completely prevented the inhibitory effect of GDI? on insulin secretion in islets. In summary, glucose and incretin stimulate insulin secretion through the phosphorylation of GDI? at Ser174 by SAD-A, which leads to the activation of Rho GTPases, culminating in insulin exocytosis.

SUBMITTER: Nie J 

PROVIDER: S-EPMC6693047 | biostudies-literature | 2018 Aug

REPOSITORIES: biostudies-literature