SRBC/cavin-3 is a caveolin adapter protein that regulates caveolae function

Caveolae are a major membrane domain common to most cells. One of the defining features of this domain is the protein caveolin. The exact function of caveolin, however, is not clear. One possible function is to attract adapter molecules to caveolae in a manner similar to how clathrin attracts molecules to coated pits. Here, we characterize a candidate adapter molecule called SRBC. SRBC binds PKCδ and is a member of the STICK ( s ubstrates t hat i nteract with C ‐ k inase) superfamily of PKC‐binding proteins. We also show it co‐immunoprecipitates with caveolin‐1. A leucine zipper in SRBC is essential for both co‐precipitation with caveolin and localization to caveolae. SRBC remains associated with caveolin when caveolae bud to form vesicles (cavicles) that travel on microtubules to different regions of the cell. In the absence of SRBC, intracellular cavicle traffic is markedly impaired. We conclude that SRBC ( s dr‐ r elated gene product that b inds to c ‐kinase) and two other family members [PTRF ( P ol I and t ranscription r elease f actor) and SDPR] function as caveolin adapter molecules that regulate caveolae function.