A caveolin dominant negative mutant associates with lipid bodies and induces intracellular cholesterol imbalance

Recent studies have indicated a role for caveolin in regulating cholesterol -dependent signaling events. In the present study we have analyzed the role of caveolins in intracellular cholesterol cycling using a dominant negativ e caveolin mutant. The mutant caveolin protein, cav-3(DGV) specifically ass ociates with the membrane surrounding large lipid droplets. These structure s contain neutral lipids, and are accessed by caveolin 1-3 upon overexpress ion. Fluorescence, electron, and video microscopy observations are consiste nt with formation of the membrane-enclosed lipid rich structures by maturat ion of subdomains of the ER. The caveolin mutant causes the intracellular a ccumulation of free cholesterol (FC) in late endosomes, a decrease in surfa ce cholesterol and a decrease in cholesterol efflux and synthesis. The amph iphile U18666A acts synergistically with cav(DGV) to increase intracellular accumulation of FC. Incubation of cells with oleic acid induces a signific ant accumulation of full-length caveolins in the enlarged lipid droplets. W e conclude that caveolin can associate with the membrane surrounding lipid droplets and is a key component involved in intracellular cholesterol balan ce and lipid transport in fibroblasts.