Disruption of Cortical Actin in Skeletal Muscle Demonstrates an Essential Role of the Cytoskeleton in Glucose Transporter 4 Translocation in Insulin-sensitive Tissues

Abstract

Cell culture work suggests that signaling to polymerize cortical filamentous actin (F-actin) represents a required pathway for the optimal redistribution of the insulin-responsive glucose transporter, GLUT4, to the plasma membrane. Recent in vitro study further suggests that the actin-regulatory neural Wiskott-Aldrich syndrome protein (N-WASP) mediates the effect of insulin on the actin filament network. Here we tested whether similar cytoskeletal mechanics are essential for insulin-regulated glucose transport in isolated rat epitrochlearis skeletal muscle. Microscopic analysis revealed that cortical F-actin is markedly diminished in muscle exposed to latrunculin B. Depolymerization of cortical F-actin with latrunculin B caused a time-and concentration-dependent decline in 2-deoxyglucose transport. The loss of cortical F-actin and glucose transport was paralleled by a decline in insulin-stimulated GLUT4 translocation, as assessed by photolabeling of cell surface GLUT4 with Bio-LC-ATB-BMPA. Although latrunculin B impaired insulin-stimulated GLUT4 translocation and glucose transport, activation of phosphatidylinositol 3-kinase and Akt by insulin was not rendered ineffective. In contrast, the ability of insulin to elicit the cortical F-actin localization of N-WASP was abrogated. These data provide the first evidence that actin cytoskeletal mechanics are an essential feature of the glucose transport process in intact skeletal muscle. Furthermore, these findings support a distal actin-based role for N-WASP in insulin action in vivo.

Modulation of the Actin Cytoskeleton via Gelsolin Regulates Vacuolar H+-ATPase Recycling

“…Although a similar stimulation of exocytosis was observed upon moderate actin depolymerization in pancreatic acinar cells, severe depletion of Factin inhibited exocytosis in these cells (18), indicating the need for a minimal amount of polymerized actin. In intact muscle, the insulin-stimulated cell-surface mobilization of GLUT4 is inhibited after disruption of cortical F-actin (24). In contrast, accumulation of the water channel AQP2 in the plasma membrane of primary cultured kidney collecting duct principal cells occurs after disruption of the actin cytoskeleton (25).…”

Ceramide- and Oxidant-Induced Insulin Resistance Involve Loss of Insulin-Dependent Rac-Activation and Actin Remodeling in Muscle Cells

“…Insulin induces actin filament remodeling in mature skeletal muscle (3) and muscle cells in culture (4) that manifest as mesh-like structures beneath the plasma membrane. Actin filament-disrupting drugs (e.g., cytochalasin D and latrunculin B) and actin-stabilizing drugs (e.g., jasplakinolide) inhibit GLUT4 translocation and its consequent glucose uptake in muscle (4,5) and adipose (6,7) cells, as do toxins that inhibit Rho family GTPases that control actin dynamics (8).…”

Myo1c Regulates Glucose Uptake in Mouse Skeletal Muscle

“…Insulin causes actin filament (F-actin) formation in L6 skeletal muscle cells (15,16), and in rat epitrochlearis muscle, F-actin has been observed as mesh-like structures beneath the inner face of the sarcolemma membrane (14). Disruption of the actin network by latrunculin B, an actin monomer-binding compound, inhibited insulin-stimulated glucose uptake and GLUT4 translocation in rat epitrochlearis muscle without affecting proximal insulin signaling (14). Furthermore, F-actin staining was decreased in epitrochlearis muscles isolated from insulin-resistant hyperinsulinemic Zucker fatty rats (17), muscles that are characterized by reduced insulin-stimulated GLUT4 translocation.…”

“…Actin and microtubule networks are the major components of the cytoskeleton and have been reported to play roles in GLUT4 translocation in cultured 3T3-L1 adipocytes, whereas only the actin network has been shown to be involved in glucose uptake in rat skeletal muscle (13,14). Insulin causes actin filament (F-actin) formation in L6 skeletal muscle cells (15,16), and in rat epitrochlearis muscle, F-actin has been observed as mesh-like structures beneath the inner face of the sarcolemma membrane (14). Disruption of the actin network by latrunculin B, an actin monomer-binding compound, inhibited insulin-stimulated glucose uptake and GLUT4 translocation in rat epitrochlearis muscle without affecting proximal insulin signaling (14).…”

“…Actin and microtubule networks are the major components of the cytoskeleton and have been reported to play roles in GLUT4 translocation in cultured 3T3-L1 adipocytes, whereas only the actin network has been shown to be involved in glucose uptake in rat skeletal muscle (13,14). Insulin causes actin filament (F-actin) formation in L6 skeletal muscle cells (15, 16),…”