Insulin stimulates the tyrosine phosphorylation of caveolin.
The specialized plasma membrane structures termed caveolae and the caveolar-coat protein caveolin are highly expressed in insulin-sensitive cells such as adipocytes and muscle. Stimulation of 3T3-L1 adipocytes with insulin significantly increased the tyrosine phosphorylation of caveolin and a 29-kD caveolin-associated protein in caveolin-enriched Triton-insoluble complexes. Maximal phosphorylation occurred within 5 min, and the levels of phosphorylation remained elevated for at least 30 min. The insulin-dose responses for the tyrosine phosphorylation of caveolin and the 29-kD caveolin-associated protein paralleled those for the phosphorylation of the insulin receptor. The stimulation of caveolin tyrosine phosphorylation was specific for insulin and was not observed with PDGF or EGF, although PDGF stimulated the tyrosine phosphorylation of the 29-kD caveolin-associated protein. Increased tyrosine phosphorylation of caveolin, its associated 29-kD protein, and a 60-kD protein was observed in an in vitro kinase assay after incubation of the caveolin-enriched Triton-insoluble complexes with Mg-ATP, suggesting the presence of an intrinsic tyrosine kinase in these complexes. These fractions contain only trace amounts of the activated insulin receptor. In addition, these complexes contain a 60-kD kinase detected in an in situ gel kinase assay and an approximately 60 kD protein that cross-reacts with an antibody against the Src-family kinase p59Fyn. Thus, the insulin-dependent tyrosine phosphorylation of caveolin represents a novel, insulin-specific signal transduction pathway that may involve activation of a tyrosine kinase downstream of the insulin receptor.
Mastick
C C
CC
Department of Signal Transduction, Parke-Davis Pharmaceutical Research Division, Warner-Lambert Company, Ann Arbor, Michigan 48105, USA.
Brady
M J
MJ
Saltiel
A R
AR
D016475:3T3 Cells; D000255:Adenosine Triphosphate / Q000378:metabolism; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D051242:Caveolin 1; D022461:Caveolins; D004815:Epidermal Growth Factor / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000302:isolation & purification / Q000378:metabolism*; D051379:Mice; D008970:Molecular Weight; D010766:Phosphorylation; D019000:Phosphotyrosine; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D011092:Polyethylene Glycols; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D014443:Tyrosine / Q000031:analogs & derivatives / Q000032:analysis
C495541:Cav1 protein, mouse; D051242:Caveolin 1; D022461:Caveolins; D007328:Insulin; D046911:Macromolecular Substances; D008565:Membrane Proteins; D010982:Platelet-Derived Growth Factor; D019000:Phosphotyrosine; D011092:Polyethylene Glycols; D014443:Tyrosine; D004815:Epidermal Growth Factor; D000255:Adenosine Triphosphate; D011505:Protein-Tyrosine Kinases