BAG3 regulates formation of the SNARE complex and insulin secretion.

V Iorio,V De Laurenzi,A Rosati,M Festa,M Capunzo,M C Turco,M Hahne,C Tiberti

doi:10.1038/cddis.2015.53

Abstract

Insulin release in response to glucose stimulation requires exocytosis of insulin-containing granules. Glucose stimulation of beta cells leads to focal adhesion kinase (FAK) phosphorylation, which acts on the Rho family proteins (Rho, Rac and Cdc42) that direct F-actin remodeling. This process requires docking and fusion of secretory vesicles to the release sites at the plasma membrane and is a complex mechanism that is mediated by SNAREs. This transiently disrupts the F-actin barrier and allows the redistribution of the insulin-containing granules to more peripheral regions of the β cell, hence facilitating insulin secretion. In this manuscript, we show for the first time that BAG3 plays an important role in this process. We show that BAG3 downregulation results in increased insulin secretion in response to glucose stimulation and in disruption of the F-actin network. Moreover, we show that BAG3 binds to SNAP-25 and syntaxin-1, two components of the t-SNARE complex preventing the interaction between SNAP-25 and syntaxin-1. Upon glucose stimulation BAG3 is phosphorylated by FAK and dissociates from SNAP-25 allowing the formation of the SNARE complex, destabilization of the F-actin network and insulin release.

Highlights

Received 23.9.14; revised 24.1.15; accepted 27.1.15; Edited by J Chipuk sites at the plasma membrane. This is mediated by a core machinery of membrane-associated soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs), which can be classified into two subfamilies: vesicle SNAREs (v-SNAREs) found on the vesicles and target SNAREs (t-SNAREs) found on the target membranes.[29]
Earlier studies have demonstrated that isolated insulin-containing granules co-sediment with filamentous actin (F-actin),[33] which is organized as a dense web beneath the plasma membrane, blocking access of secretory vescicles to the t-SNARE complex at cell membrane.[33,34,35,36]
Glucose stimulation of beta cells leads to focal adhesion kinase (FAK) phosphorylation, which acts on the Rho family proteins (Rho, Rac and Cdc42) that direct F-actin remodeling.[28,37]

Summary

Introduction

Received 23.9.14; revised 24.1.15; accepted 27.1.15; Edited by J Chipuk sites at the plasma membrane. Using a mouse insulinoma β-TC-6 cell model here we show that BAG3 silencing affects F-actin polymerization state resulting in increased insulin secretion.

Results

Conclusion