Reduced expression of focal adhesion kinase disrupts insulin action in skeletal muscle cells.
Integrins mediate interactions between cells and extracellular matrix proteins that modulate growth factor signaling. Focal adhesion kinase (FAK) is a key multifunctional integrin pathway protein. We recently reported that disruption of FAK impairs insulin-mediated glycogen synthesis in hepatocytes. To test the hypothesis that FAK regulates skeletal muscle insulin action, we reduced FAK expression in L6 myotubes using FAK antisense. In untransfected myotubes, insulin stimulated both FAK tyrosine phosphorylation and kinase activity. Cells treated with antisense FAK showed 78 and 53% reductions in FAK mRNA and FAK protein, respectively, whereas insulin receptor substrate 1/2 and paxillin abundance were unaffected. Insulin-stimulated U-(14)C-glucose incorporation into glycogen was abolished by FAK antisense, and 2-deoxy-glucose uptake and glucose transporter 4 (GLUT4) translocation were both markedly attenuated. Antisense FAK did not alter GLUT1 or GLUT3 protein abundance. Immunofluorescence staining showed decreased FAK Tyr(397) phosphorylation and reduced actin stress fibers. Thus, in skeletal myotubes, FAK regulates the insulin-mediated cytoskeletal rearrangement essential for normal glucose transport and glycogen synthesis. Integrin signaling may play an important regulatory role in muscle insulin action.
Division of Endocrinology, Diabetes and Hypertension, Diabetes Center, David Geffen School of Medicine at University of California, Los Angeles, 90095, USA.
Danshan
D
Huang
Michelle
M
Khoe
Dusko
D
Ilic
Michael
M
Bryer-Ash
D000199:Actins / Q000378:metabolism; D000818:Animals; D003599:Cytoskeleton / Q000378:metabolism; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000096:biosynthesis* / Q000502:physiology; D005947:Glucose / Q000378:metabolism; D051272:Glucose Transporter Type 1 / Q000378:metabolism; D051274:Glucose Transporter Type 3 / Q000378:metabolism; D051275:Glucose Transporter Type 4 / Q000378:metabolism; D007328:Insulin / Q000378:metabolism*; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D018482:Muscle, Skeletal / Q000166:cytology* / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D015398:Signal Transduction
D000199:Actins; D051272:Glucose Transporter Type 1; D051274:Glucose Transporter Type 3; D051275:Glucose Transporter Type 4; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; C526295:Irs1 protein, mouse; C526298:Irs2 protein, mouse; D010750:Phosphoproteins; D051416:Focal Adhesion Protein-Tyrosine Kinases; D005947:Glucose