Distinction between signaling mechanisms in lipid rafts vs. caveolae

The relative importance of lipid rafts vs. specialized rafts termed caveola e to influence signal transduction is not known. Here we show that in cells lacking caveolae, the dually acylated protein, endothelial nitric oxide sy nthase (eNOS), localizes to cholesterol-rich lipid raft domains of the plas ma membrane. In these cells, expression of caveolin-1 (cav-1) stimulates ca veolae biogenesis, promotes the interaction of cav-1 with eNOS, and the inh ibition of NO release from cells. Interestingly, in cells where cav-1 does not drive caveolae assembly, despite equal levels of cav-1 and eNOS and loc alization of both proteins to raft domains of the plasmalemma, the physical interaction of eNOS with cav-1 is dramatically less resulting in less inhi bition of NO release. Thus, cav-1 concentrated in caveolae, not in rafts, i s in closer proximity to eNOS and is necessary for negative regulation of e NOS function, thereby providing the first clear example of spatial regulati on of signaling in this organelle that is distinct from raft domains.