Mutations in autosomal dominant polycystic kidney disease 2 gene: Reduced expression of PKD2 protein in lymphoblastoid cells

The polycystic kidney disease 2 (PKDP) gene, encoding a 968-amino acid inte gral membrane protein with six predicted membrane-spanning domains and intr acellular NH2 and COOH termini, is mutated in approximately 15% of the case s of autosomal dominant polycystic kidney disease (ADPKD), a common genetic disease frequently resulting in renal failure. For a better understanding of the cause of this disorder, we searched for mutations in the PKD2 gene i n two PKD2-linked families characterized by different clinical phenotypes. A common polymorphism, a nonsense mutation, and a frameshift mutation were found. Both mutations are predicted to produce truncated proteins of 314 an d 386 amino acids, arrested at the first extracellular loop of the protein. Restriction enzyme analysis of polymerase chain reaction (PCR) and reverse transcriptase (RT)-PCR products, respectively, showed that mutations coseg regated with the disease and mutated alleles were expressed at the messenge r RNA level in lymphoblastoid cell lines. However, in these cells, Western blot analysis showed only PKD2 normal protein, and it was expressed at a lo wer level than that found in cells without the PKDP mutation. These finding s suggest that in lymphoblastoid cells, the truncated protein product of th e mutant allele may not be stable. (C) 1999 by the National Kidney Foundati on, Inc.