title: Colocalization of insulin receptor and insulin receptor substrate-1 to caveolae in primary human adipocytes. Cholesterol depletion blocks insulin signalling for metabolic and mitogenic control.
abstract: Caveolae are plasma membrane invaginations with several functions, one of which appears to be to organize receptor mediated signalling. Here we report that in primary human subcutaneous adipocytes the insulin receptor was localized to caveolae by electron microscopy/immunogold detection and by isolating caveolae from plasma membranes. Part of insulin receptor substrate 1 (IRS1), the immediate downstream signal mediator, was colocalized with the insulin receptor in the plasma membrane and caveolae, as demonstrated by immunofluorescence microscopy, immunogold electron microscopy, and immunogold electron microscopy of transfected recombinant HA-IRS1. In contrast, rat epididymal adipocytes lacked IRS1 at the plasma membrane. Depletion of cholesterol from the cells using beta-cyclodextrin blocked insulin stimulation of glucose uptake, insulin inhibition of perilipin phosphorylation in response to isoproterenol, and insulin stimulation of protein kinase B and Map-kinases extracellular signal-related kinase (ERK)1/2 phosphorylation. Insulin-stimulated phosphorylation of the insulin receptor and IRS1 was not affected, indicating that caveolae integrity is required downstream of IRS1. In conclusion we show that insulin receptor and IRS1 are both caveolar proteins and that caveolae are required for both metabolic and mitogenic control in human adipocytes. Our results establish caveolae as foci of insulin action and stress the importance of examining human cells in addition to animal cells and cell lines.
authors.affiliation: Department of Cell Biology and Diabetes Research Centre, University of Linköping, Sweden.
authors.forename: Margareta
authors.initials: M
authors.lastname: Karlsson
authors.forename: Hans
authors.initials: H
authors.lastname: Thorn
authors.forename: Anna
authors.initials: A
authors.lastname: Danielsson
authors.forename: Karin G
authors.initials: KG
authors.lastname: Stenkula
authors.forename: Anita
authors.initials: A
authors.lastname: Ost
authors.forename: Johanna
authors.initials: J
authors.lastname: Gustavsson
authors.forename: Fredrik H
authors.initials: FH
authors.lastname: Nystrom
authors.forename: Peter
authors.initials: P
authors.lastname: Strålfors
mesh_terms: D000273:Adipose Tissue / Q000166:cytology*; D000328:Adult; D000368:Aged; D000818:Animals; D002352:Carrier Proteins; D021941:Caveolae / Q000378:metabolism* / Q000648:ultrastructure; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism*; D005260:Female; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D055504:Insulin Receptor Substrate Proteins; D008297:Male; D008875:Middle Aged; D000070778:Perilipin-1; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D011972:Receptor, Insulin / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D002352:Carrier Proteins; C526292:IRS1 protein, human; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526296:Irs1 protein, rat; D000070778:Perilipin-1; D010750:Phosphoproteins; D002784:Cholesterol; D011972:Receptor, Insulin