title: Signaling of the p21-activated kinase (PAK1) coordinates insulin-stimulated actin remodeling and glucose uptake in skeletal muscle cells.
abstract: Skeletal muscle accounts for ∼ 80% of postprandial glucose clearance, and skeletal muscle glucose clearance is crucial for maintaining insulin sensitivity and euglycemia. Insulin-stimulated glucose clearance/uptake entails recruitment of glucose transporter 4 (GLUT4) to the plasma membrane (PM) in a process that requires cortical F-actin remodeling; this process is dysregulated in Type 2 Diabetes. Recent studies have implicated PAK1 as a required element in GLUT4 recruitment in mouse skeletal muscle in vivo, although its underlying mechanism of action and requirement in glucose uptake remains undetermined. Toward this, we have employed the PAK1 inhibitor, IPA3, in studies using L6-GLUT4-myc muscle cells. IPA3 fully ablated insulin-stimulated GLUT4 translocation to the PM, corroborating the observation of ablated insulin-stimulated GLUT4 accumulation in the PM of skeletal muscle from PAK1(-/-) knockout mice. IPA3-treatment also abolished insulin-stimulated glucose uptake into skeletal myotubes. Mechanistically, live-cell imaging of myoblasts expressing the F-actin biosensor LifeAct-GFP treated with IPA3 showed blunting of the normal insulin-induced cortical actin remodeling. This blunting was underpinned by a loss of normal insulin-stimulated cofilin dephosphorylation in IPA3-treated myoblasts. These findings expand upon the existing model of actin remodeling in glucose uptake, by placing insulin-stimulated PAK1 signaling as a required upstream step to facilitate actin remodeling and subsequent cofilin dephosphorylation. Active, dephosphorylated cofilin then provides the G-actin substrate for continued F-actin remodeling to facilitate GLUT4 vesicle translocation for glucose uptake into the skeletal muscle cell.
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Ragadeepthi
authors.initials: R
authors.lastname: Tunduguru
authors.affiliation: Cell Biology Program, The Hospital for Sick Children, Toronto, ON, Canada.
authors.forename: Tim T
authors.initials: TT
authors.lastname: Chiu
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, USA; Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Latha
authors.initials: L
authors.lastname: Ramalingam
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, USA; Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Elmendorf
authors.affiliation: Cell Biology Program, The Hospital for Sick Children, Toronto, ON, Canada.
authors.forename: Amira
authors.initials: A
authors.lastname: Klip
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, USA; Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN, USA; Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, IN, USA. Electronic address: dthurmon@iu.edu.
authors.forename: Debbie C
authors.initials: DC
authors.lastname: Thurmond
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D051379:Mice; D018345:Mice, Knockout; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D032448:Myoblasts, Skeletal / Q000187:drug effects / Q000201:enzymology*; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D054462:p21-Activated Kinases / Q000378:metabolism*
chemical_list: D000199:Actins; D007328:Insulin; C515905:Pak1 protein, mouse; D054462:p21-Activated Kinases; D005947:Glucose
keywords: Diabetes; F-actin remodeling; GLUT4 vesicle exocytosis; L6-GLUT4myc muscle cells; PAK1; Rac1; Skeletal muscle; Small Rho family GTPase