Caveolae and intracellular trafficking of cholesterol.

Caveolae, free cholesterol (FC)-rich microdomains of the plasma membrane, are both a terminus for the intracellular transit of newly synthesized and recycling cellular FC, and a site for FC efflux to the extracellular medium. The same domains play key roles as locations for the assembly of signaling complexes and for the endocytosis of selected ligands. Caveolin, the major structural protein of caveolae, plays a regulatory role in growth, the cell cycle, and cell adhesion. Each of these functions is FC-dependent. Caveolae appear to act as both sensors and regulators of cellular FC content, and in this way mediate an array of membrane-dependent cell functions.