Caveolin binds independently to claudin-2 and occludin

Treatment of epithelial and endothelial cells with proinflammatory cytokines can stimulate tight junction protein endocytosis, with associated loss of physiologic barrier function. In some instances, the endocytic scaffolding protein, caveolin-1, has been implicated in the cytokine-dependent retrieval of the tight junction proteins occludin and claudins. How caveolin-1 interacts with these proteins, however, remains undefined. Using co-immunoprecipitation assays, we found that caveolin-1 separately interacts with claudin-2 and occludin, but not with ZO-1, ZO-2, or claudin-4. Further, we found that the interactions of caveolin-1 with claudin-2 and occludin were not disrupted by cholesterol removal, suggesting that they were not dependent on co-localization to cholesterol-rich lipid rafts. Co-immunoprecipitation of caveolin-1 with chimeras between claudin-2 and -4 indicated that the C-terminal cytoplasmic domain of claudin-2 is required for association with caveolin-1; similar analysis showed that the ZO-1 binding region of occludin is not required for its interaction with caveolin-1. The finding that caveolin-1 interacts with claudin-2 and occludin, but not with claudin-4 or ZO-1, suggests a potential mechanism for selective retrieval of tight junction components.