CHARACTERIZATION AND CELL DISTRIBUTION OF POLYCYSTIN, THE PRODUCT OF AUTOSOMAL-DOMINANT POLYCYSTIC KIDNEY-DISEASE GENE-1

Background: In a majority of cases, autosomal dominant polycystic kidn ey disease (ADPKD) is caused by mutations within a putative open readi ng frame of the PKD1 gene. The encoded protein, polycystin, is predict ed to span the plasma membrane several times and contains extracellula r domains, suggestive of a role in cell adhesion. The cellular distrib ution and function of polycystin is not known. Materials and Methods: We selected as immunogens two conserved 15 amino acid peptides: P1, lo cated in a predicted extracellular region of polycystin, and P2, locat ed in the C-terminal putative cytoplasmic tail. The anti-peptide antib odies from immunized rabbits were affinity purified on peptide-coupled resins and their specificity confirmed by their selective binding to recombinant polycystin fusion proteins. Western blotting and immunohis tochemistry were used to characterize the size, tissue, and cell distr ibution of polycystin. Results: A high-molecular mass protein (about 6 42 kD) was detected by Western blotting in rat brain tissue. A few add itional bands, in the 100- to 400-kD range, probably representing tiss ue-specific variants and/or proteolytic fragments, were recognized in human and rat tissues. Polycystin was abundantly expressed in fetal ki dney epithelia, where it displayed basolateral and apical membrane dis tribution in epithelial cells of the ureteric buds, collecting ducts, and glomeruli. In normal human adult kidney, polycystin was detected a t moderate levels and in a cell surface-associated distribution in cor tical collecting ducts and glomerular visceral epithelium. Expression of polycystin was significantly increased in cyst-lining epithelium in ADPKD kidneys, but was primarily intracellular. Conclusions: Polycyst in appears to be a developmentally regulated and membrane-associated g lycoprotein. Its intracellular localization in the cyst-lining epithel ium of ADPKD kidneys suggests an abnormality in protein sorting in thi s disease.