Dynamic association of human insulin receptor with lipid rafts in cells lacking caveolae.
Cholesterol-sphingolipid rich plasma membrane domains, known as rafts, have emerged as important regulators of signal transduction. The adipocyte insulin receptor (IR) is localized to and signals via caveolae that are formed by polymerization of caveolins. Caveolin binds to IR and stimulates signalling. We report that, in liver-derived cells lacking caveolae, autophosphorylation of the endogenous IR is dependent on raft lipids, being compromised by acute cyclodextrin-mediated cholesterol depletion or by antibody clustering of glycosphingolipids. Moreover, we provide evidence that IR becomes recruited to detergent-resistant domains upon ligand binding and that clustering of GM2 ganglioside inhibits IR signalling apparently by excluding the ligand-bound IR from these domains. Our results indicate that, in cells derived from liver, an important insulin target tissue, caveolae are not required for insulin signalling. Rather, the dynamic recruitment of the ligand-bound IR into rafts may serve to regulate interactions in the initiation of the IR signalling cascade.
Vainio
Saara
S
Department of Molecular Medicine, National Public Health Institute, Biomedicum Helsinki, PO Box 104, Haartmaninkatu 8, 00251 Helsinki, Finland.
Heino
Sanna
S
Mansson
Jan-Eric
JE
Fredman
Pam
P
Kuismanen
Esa
E
Vaarala
Outi
O
Ikonen
Elina
E
D021941:Caveolae / Q000502:physiology*; D002784:Cholesterol / Q000097:blood / Q000378:metabolism; D006028:Glycosphingolipids / Q000378:metabolism; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D008099:Liver / Q000166:cytology / Q000378:metabolism; D021962:Membrane Microdomains / Q000502:physiology*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011972:Receptor, Insulin / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D014407:Tumor Cells, Cultured
D006028:Glycosphingolipids; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins; D002784:Cholesterol; D011972:Receptor, Insulin