Cortactin, an actin binding protein, regulates GLUT4 translocation via actin filament remodeling

Abstract

Insulin regulates glucose uptake into fat and skeletal muscle cells by modulating the translocation of GLUT4 between the cell surface and interior. We investigated a role for cortactin, a cortical actin binding protein, in the actin filament organization and translocation of GLUT4 in Chinese hamster ovary (CHO-GLUT4myc) and L6-GLUT4myc myotube cells. Overexpression of wild-type cortactin enhanced insulin-stimulated GLUT4myc translocation but did not alter actin fiber formation. Conversely, cortactin mutants lacking the Src homology 3 (SH3) domain inhibited insulin-stimulated formation of actin stress fibers and GLUT4 translocation similar to the actin depolymerizing agent cytochalasin D. Wortmannin, genistein, and a PP1 analog completely blocked insulin-induced Akt phosphorylation, formation of actin stress fibers, and GLUT4 translocation indicating the involvement of both PI3-K/Akt and the Src family of kinases. The effect of these inhibitors was even more pronounced in the presence of overexpressed cortactin suggesting that the same pathways are involved. Knockdown of cortactin by siRNA did not inhibit insulin-induced Akt phosphorylation but completely inhibited actin stress fiber formation and glucose uptake. These results suggest that the actin binding protein cortactin is required for actin stress fiber formation in muscle cells and that this process is absolutely required for translocation of GLUT4-containing vesicles to the plasma membrane.

Signaling of the p21-activated kinase (PAK1) coordinates insulin-stimulated actin remodeling and glucose uptake in skeletal muscle cells

“…Studies are underway to investigate the role and placement of p41ARC and N-WASP in the PAK1-dependent insulin signaling pathway in skeletal muscle cells. Additionally, PAK1 signaling to other downstream factors such as cortactin, Myo1c and Filamin A should be investigated, since these targets are known to bind to PAK1 in non-muscle cells and have been implicated as indirect effectors of glucose uptake [52–56]. …”

Comparative Transcriptome and Methylome Analysis in Human Skeletal Muscle Anabolism, Hypertrophy and Epigenetic Memory

“…TIAM1 has been associated with skeletal muscle glucose uptake 52 . CTTN (cortactin) contributes to the organization of the actin cytoskeleton 53 and is also important in actin filament remodelling in L6 myotubes 30 . The abundance of FN1 (fibronectin) is blunted in elderly human skeletal muscle following muscle damage evoked via eccentric muscle contraction, compared to young healthy controls 54 .…”

The actin-related p41ARC subunit contributes to p21-activated kinase-1 (PAK1)–mediated glucose uptake into skeletal muscle cells

“…Cortactin and N-WASP can synergistically activate the ARP2/3 complex via cortactin binding to ARP3 and N-WASP binding to p41ARC and ARP2 (43). Although both scenarios involve cortactin, and cortactin is reportedly required for insulin-induced GLUT4 translocation and glucose uptake in skeletal muscle cells (29), validation of the role of cortactin in primary skeletal muscle will require new antibodies; at present, the requisite antibodies are not commercially available. In addition, although IPA3 and WISK are considered highly selective for their targets, it remains possible that either drug could impact Rac1 activation via an unknown feed-back signal; this requires testing over a thorough time course given the cyclic nature of the remodeling process.…”

“…Cortactin is an actin nucleation-promoting factor that mediates the assembly and organization of actin cytoskeletal meshwork (28). Cortactin is required for insulin-induced GLUT4 translocation and glucose uptake in skeletal muscle cells (29). In Hep2b clonal hepatocytes, phosphorylation of cortactin by PAK1 specifically at Ser-405 and Ser-418 increased the affinity of cortactin for a known enhancer of actin polymerization, neuronal Wiskott-Aldrich syndrome protein (N-WASP) (27).…”