CAVEOLIN MOVES FROM CAVEOLAE TO THE GOLGI-APPARATUS IN RESPONSE TO CHOLESTEROL OXIDATION

Caveolae are a membrane specialization used to internalize molecules b y potocytosis. Caveolin, an integral membrane protein, is associated w ith the striated coat present on the cytoplasmic surface of the caveol ae membrane. We now report that oxidation of caveolar cholesterol with cholesterol oxidase rapidly displaces the caveolin from the plasma me mbrane to intracellular vesicles that colocalize with Golgi apparatus markers. After the enzyme is removed from the medium, caveolin returns to caveolae. When untreated cells are gently homogenized, caveolin on the plasma membrane is accessible to both anti-caveolin IgG and tryps in. After cholesterol oxidase treatment, however, Golgi-associated cav eolin is inaccessible to both of these molecules. Brefeldin A, which i nhibits ER to Golgi trafficking, blocks the appearance of caveolin in the Golgi apparatus but does not prevent caveolin from leaving the pla sma membrane. Indirect immunogold localization experiments show that i n the presence of cholesterol oxidase caveolin leaves the plasma membr ane and becomes associated with endoplasmic reticulum and Golgi compar tments. Surprisingly, the loss of caveolin from the plasma membrane do es not affect the number or morphology of the caveolae.