Skeletal muscle cells and adipocytes differ in their reliance on TC10 and Rac for insulin-induced actin remodeling.
Insulin causes distinct cortical actin remodeling in muscle and fat cells, and interfering with actin dynamics halts glucose transporter 4 (GLUT4) translocation to the membrane. Phosphatidylinositol 3-kinase (PI3-K) and the small G protein Rac govern myocyte actin remodeling, whereas TC10 alpha contributes to adipocyte actin dynamics downstream of Cbl-associated protein (CAP) and Cbl, independently of PI3-K. Given the importance of insulin action in both cell types, it is paramount to determine whether signaling pathways and actin manifestations are cell type specific. We found CAP expression and insulin-mediated Cbl phosphorylation in differentiated myotubes but not in myoblasts. Unlike adipocytes, Cbl is phosphorylated on Y774 and Y731 in myotubes. TC10 alpha and beta-transcripts are amplified by RT-PCR in muscle cells, but the endogenous proteins are barely detectable using two unrelated antibodies. TC10 alpha transfected into myoblasts is activated by insulin despite the lack of CAP expression and Cbl phosphorylation. Moreover, dominant-negative TC10 alpha mutants do not prevent insulin-induced actin remodeling in either myoblasts or myotubes and do not interfere with insulin-mediated recruitment of c-myc epitope-tagged GLUT4 to the cell surface. In contrast to TC10 alpha, endogenous Rac is readily detectable in both muscle cells and adipocytes and binds GTP after insulin in a PI3-K-dependent manner. These data suggest that whereas individual components of the CAP to TC10 pathway are regulated by insulin, a functional TC10-dependent signaling pathway leading to actin remodeling and GLUT4 translocation may not operate in myocytes, as it does in adipocytes.
JeBailey
Lellean
L
Programme in Cell Biology, Hospital for Sick Children, 555 University Ave, Toronto, Ontario, Canada M5G 1X8. amira@sickkids.ca.
Rudich
Assaf
A
Huang
Xudong
X
Di Ciano-Oliveira
Caterina
C
Kapus
András
A
Klip
Amira
A
D000199:Actins / Q000187:drug effects / Q000378:metabolism*; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins / Q000187:drug effects / Q000378:metabolism; D051275:Glucose Transporter Type 4; D006160:Guanosine Triphosphate / Q000378:metabolism; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D009124:Muscle Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D021381:Protein Transport; D011518:Proto-Oncogene Proteins / Q000187:drug effects / Q000378:metabolism; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases / Q000187:drug effects / Q000378:metabolism; D020744:rac GTP-Binding Proteins / Q000187:drug effects / Q000378:metabolism*; D020741:rho GTP-Binding Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
D000199:Actins; D003598:Cytoskeletal Proteins; D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D011518:Proto-Oncogene Proteins; C495693:Slc2a4 protein, mouse; D006160:Guanosine Triphosphate; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; D019869:Phosphatidylinositol 3-Kinases; C503260:Rhoq protein, mouse; D020744:rac GTP-Binding Proteins; D020741:rho GTP-Binding Proteins; C493849:Cbl protein, mouse