Characterization of a cytosolic heat-shock protein-caveolin chaperone complex. Involvement in cholesterol trafficking.
Caveolin is a 22-kDa protein that appears to play a critical role in regulating the cholesterol concentration of caveolae. Even though caveolin is thought to be a membrane protein, several reports suggest that this peculiar protein can traffic independently of membrane vesicles. We now present evidence that a cytosolic pool of caveolin is part of a heat-shock protein-immunophilin chaperone complex consisting of caveolin, heat-shock protein 56, cyclophilin 40, cyclophilin A, and cholesterol. Treatment of NIH 3T3 cells with 1 microM cyclosporin A or 100 nM rapamycin disrupted the putative transport complex and prevented rapid (10-20 min) transport of cholesterol to caveolae. The lymphoid cell line, L1210-JF, does not express caveolin, does not form an immunophilin-caveolin complex, and does not transport newly synthesized cholesterol to caveolae. Transfection of caveolin cDNA into L1210-JF cells allowed the assembly of a transport complex identical to that found in NIH 3T3 cells. In addition, newly synthesized cholesterol in transfected cells was rapidly (10-20 min) and specifically transported to caveolae. These data strongly suggest that a caveolin-chaperone complex is a mechanism by which newly synthesized cholesterol is transported from the endoplasmic reticulum through the cytoplasm to caveolae.
Uittenbogaard
A
A
University of Kentucky Medical School, Department of Physiology, MS 508, Lexington, Kentucky 40536, USA.
Ying
Y
Y
Smart
E J
EJ
D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D051242:Caveolin 1; D022461:Caveolins; D002451:Cell Compartmentation; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism*; D000081406:Peptidyl-Prolyl Isomerase F; D021983:Cyclophilins; D016572:Cyclosporine / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D018832:Molecular Chaperones / Q000378:metabolism*; D019696:Peptidylprolyl Isomerase / Q000378:metabolism*; D011090:Polyenes / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D020123:Sirolimus; D022021:Tacrolimus Binding Proteins
D002352:Carrier Proteins; C495541:Cav1 protein, mouse; D051242:Caveolin 1; D022461:Caveolins; D000081406:Peptidyl-Prolyl Isomerase F; D004268:DNA-Binding Proteins; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D018832:Molecular Chaperones; C000631446:PPIF protein, mouse; D011090:Polyenes; D016572:Cyclosporine; D002784:Cholesterol; D021983:Cyclophilins; D022021:Tacrolimus Binding Proteins; D019696:Peptidylprolyl Isomerase; D020123:Sirolimus