CHARACTERIZATION OF A CYTOSOLIC HEAT-SHOCK-PROTEIN CAVEOLIN CHAPERONECOMPLEX - INVOLVEMENT IN CHOLESTEROL TRAFFICKING

Caveolin is a 22-kDa protein that appears to play a critical role in r egulating the cholesterol concentration of caveolae, Even though caveo lin 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 caveo lin, heat-shock protein 56, cyclophilin 40, cyclophilin A, and cholest erol. Treatment of MH 3T3 cells with 1 mu m cyclosporin A or 100 nM ra pamycin disrupted the putative transport complex and prevented rapid ( 10-20 min) transport of cholesterol to caveolae, The lymphoid cell lin e, 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 allowe d the assembly of a transport complex identical to that found in NIH 3 T3 cells, In addition, newly synthesized cholesterol in transfected ce lls was rapidly (10-20 min) and specifically transported to caveolae, These data strongly suggest that a caveolin-chaperone complex is a mec hanism by which newly synthesized cholesterol is transported from the endoplasmic reticulum through the cytoplasm to caveolae.