Specificity of insulin-like growth factor I and insulin on Shc phosphorylation and Grb2 recruitment in caveolae.
Caveolae are lipid raft microdomains that regulate endocytosis and signal transduction. IGF-I receptor (IGF-IR) localizes in caveolae and tyrosine phosphorylates caveolin 1, supporting a role for these subcellular regions in the compartmentalization of IGF-I signaling. Src homology 2/alpha-collagen related protein (Shc) is the main mediator of IGF-I mitogenic action, coupling IGF-IR phosphorylation to Ras-MAPK activation. Here we show that IGF-I induces Shc tyrosine phosphorylation in the caveolae with a time course significantly different from that observed in the nonraft cellular fractions. In the same time, IGF-I recruits growth factor receptor bound protein 2 (Grb2) to caveolae and activates p42/p44 MAPKs in these microdomains. Src family kinases regulate IGF-I action through an Shc-dependent mechanism. In R-IGF-IRWT cells, IGF-I causes Fyn enrichment in the caveolae with a time course consistent with Shc phosphorylation and Grb2 recruitment in these regions. Finally, we have observed that after IGF-I stimulation, IGF-IR and Fyn colocalize in lipid raft caveolin 1-enriched microdomains. As insulin and IGF-I share common substrates, the effect of insulin on these cellular processes was measured. Here we show that insulin also induces Shc phosphorylation and Grb2 recruitment to caveolae, but with a significantly different time course compared with IGF-I. Our results suggest that 1) IGF-I causes the colocalization of signaling proteins in caveolae through a phosphorylation-regulated mechanism; and 2) the time course of phosphorylation and recruitment of substrates in caveolae by insulin receptor and IGF-IR could determine the specific actions of these receptors.
Biedi
Claudia
C
Di.S.E.M., Viale Benedetto XV 6, 16132 Genova, Italy. record@unige.it.
Panetta
Danilo
D
Segat
Daniela
D
Cordera
Renzo
R
Maggi
Davide
D
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D021941:Caveolae / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology; D051380:GRB2 Adaptor Protein; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D051379:Mice; D010766:Phosphorylation; D011506:Proteins / Q000378:metabolism*; D011940:Receptor Aggregation / Q000187:drug effects / Q000502:physiology; D017526:Receptor, IGF Type 1 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D018909:src Homology Domains / Q000502:physiology*
D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; C495949:Grb2 protein, mouse; D007004:Hypoglycemic Agents; D007328:Insulin; D011506:Proteins; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1