The exocyst complex regulates insulin-stimulated glucose uptake of skeletal muscle cells

Abstract

Skeletal muscle handles ~80–90% of the insulin-induced glucose uptake. In skeletal muscle, insulin binding to its cell surface receptor triggers redistribution of intracellular glucose transporter GLUT4 protein to the cell surface, enabling facilitated glucose uptake. In adipocytes, the eight-protein exocyst complex is an indispensable constituent in insulin-induced glucose uptake, as it is responsible for the targeted trafficking and plasma membrane-delivery of GLUT4. However, the role of the exocyst in skeletal muscle glucose uptake has never been investigated. Here we demonstrate that the exocyst is a necessary factor in insulin-induced glucose uptake in skeletal muscle cells as well. The exocyst complex colocalizes with GLUT4 storage vesicles in L6-GLUT4myc myoblasts at a basal state and associates with these vesicles during their translocation to the plasma membrane after insulin signaling. Moreover, we show that the exocyst inhibitor endosidin-2 and a heterozygous knockout of Exoc5 in skeletal myoblast cells both lead to impaired GLUT4 trafficking to the plasma membrane and hinder glucose uptake in response to an insulin stimulus. Our research is the first to establish that the exocyst complex regulates insulin-induced GLUT4 exocytosis and glucose metabolism in muscle cells. A deeper knowledge of the role of the exocyst complex in skeletal muscle tissue may help our understanding of insulin resistance in type 2 diabetes.

Deregulation of Exo70 Facilitates Innate and Acquired Cisplatin Resistance in Epithelial Ovarian Cancer by Promoting Cisplatin Efflux

“…As a critical member of the exocyst, Exo70 was reported to promote invasion via enhancing MMPs secretion in tumor cells [25,26,32], and increased glucose uptake by accelerating inter-endosomal GLUT4 traffic to the plasma membrane in adipocytes [33,34]. In the present study, we reported for the first time that Exo70 promotes cisplatin efflux in EOC cells.…”

Disrupted glucose homeostasis and skeletal-muscle-specific glucose uptake in an exocyst knockout mouse model

“…Previously, we demonstrated that the exocyst subunit EXOC5 is essential for insulin-stimulated GLUT4 exocytosis and glucose uptake in cultured rat skeletal myoblasts ( 17 ). To study the consequences of in vivo disruption of Exoc5 and the exocyst, we generated skeletal-muscle-specific Exoc5 conditional knockout ( Exoc5 -SMKO) mice.…”

“…There have been very few studies directly examining the role of the exocyst complex in skeletal muscle tissues. We have previously demonstrated that chemical inhibition of the exocyst complex and the heterozygous knockout of Exoc5 lead to a reduction in insulin-stimulated GLUT4 membrane delivery and glucose uptake in rat skeletal myoblasts ( 17 ).…”

“…Our previous study demonstrated that reducing the amount of EXOC5 impairs the ability of mouse skeletal muscle cells to uptake glucose in response to insulin ( 17 ). This was due to a failure to increase the amount of GLUT4 transporters at the plasma membrane.…”

Complexin-2 redistributes to the membrane of muscle cells in response to insulin and contributes to GLUT4 translocation

“…Insulin stimulation promotes re-localization of endogenous complexin-2 to the PM L6 myoblasts and myotubes modified to stably express a chimeric GLUT4 protein tagged with a myc-epitope at its first exofacial loop (L6-GLUT4myc) have been widely used to study insulin-dependent signals and GLUT4 translocation in a muscle background [33,34,39]. Indeed, L6-GLUT4myc myoblasts and L6 myoblasts stably transfected with untagged or HA-tagged GLUT4 represent useful cellular paradigms that retains the main features of GLUT4 traffic, such as significant GLUT4 segregation away from recycling proteins and responsiveness to insulin [32,[40][41][42][43][44][45]. In unstimulated L6-GLUT4myc myoblasts and myotubes (basal condition), endogenous complexin-2 displayed mixed diffuse and punctate distribution throughout the cytosol (Figure 1E).…”