Identification of caveolin-1 in lipoprotein particles secreted by exocrinecells

Caveolin-1 is a protein component (of relative molecular mass 22,000) of th e striated coat that decorates the cytoplasmic surface of caveolae membrane s. Previous biochemical and molecular tests have indicated that caveolin-1 is an integral membrane protein that is cc-translationally inserted into en doplasmic-reticulum membranes of fibroblast and epithelial cells such that its carboxy- and amino-terminal ends are in the cytoplasm. Here we identify caveolin-1 in the secretory pathway of exocrine cells. Secretion of caveol in-1 from pancreatic acinar cells and a transfected exocrine cell line, but not from Chinese hamster ovary cells, is stimulated by the secretagogues s ecretin, cholecystokinin and dexamethasone. The secreted caveolin-1 co-frac tionates with apolipoproteins, indicating that it may be secreted in a comp lex with lipids.