In vivo interaction of the adapter protein CD2-associated protein with thetype 2 polycystic kidney disease protein, polycystin-2

We identified a developmentally regulated gene from mouse kidney whose expr ession is up-regulated in metanephrogenic mesenchyme cells when they are in duced to differentiate to epithelial cells during kidney organogenesis. The deduced 70.5-kDa protein, originally named METS-1 (mesenchyme-to-epitheliu m transition protein with SH3 domains), has since been cloned as a CD2-asso ciated protein (CD2AP). CD2AP is strongly expressed in glomerular podocytes , and the absence of CD2AP in mice results in congenital nephrotic syndrome . We have found that METS-1/CD2AP thereafter referred to as CD2AP) is expre ssed at lower levels in renal tubular epithelial cells in the adult kidney, particularly in distal nephron segments. Independent yeast two-hybrid scre ens using the COOH-terminal region of either CD2AP or polycystin-2 as bait identified the COOH termini of polycystin-2 and CD2AP, respectively, as str ong interacting partners. This interaction was confirmed in cultured cells by eo-immunoprecipitation of endogenous polycystin-2 with endogenous CD2AP and vice versa. CD2AP shows a diffuse reticular cytoplasmic and perinuclear pattern of distribution, similar to polycystin-2, in cultured cells, and t he two proteins co-localize by indirect double immunofluorescence microscop y. CD2AP is an adapter molecule that associates with a variety of membrane proteins to organize the cytoskeleton around a polarized site. Such a funct ion fits well with that hypothesized for the polycystin proteins in renal t ubular epithelial cells, and the present findings suggest that CD2AP has a role in polycystin-2 function.