Abnormal polycyst1n expression in type 1 autosomal dominant polycystic kidney disease

Mutations of one allele of the recently described gene, PKD 1, result in the phenotype of type 1 autosomal dominant polycystic disease (ADPKD 1). The protein product of this gene, which has been named Polycystin, has a predicted molecular weight of ~460kDa, and is of unknown distribution and function. Over two thirds of its amino acid sequence, beginning at the N-terminus, is duplicated in a group of three or more homologous genes located telomeric lo PKD I on chromosome 16. To investigate the possibility that polycystin is expressed abnormally in ADPKD 1 we designed a group of four synthetic peptide antigens derived from the predicted sequence of the non-duplicated, C-terminal portion of polycystin.The peptides sequences used were: GNQSSPELGPPRLRQVRLQEALYPDPPGPR (a.a residues 3736-3765) GPRVHTCSAAGGFSTSDYDVGWESPHNGSGT (a.a. residues 3763-3793) KVRFEGMEPLPSRSSRGSKVSPDVPPPSAGSDAS (a.a. residues 4151-4184) LQGRRSSRAPAGSSRGPSRGLR (a.a. residues 4245-4266) These antigens, coupled to KLH, were used to raise a panel of polyclonal rabbit antisera. These antisera were used for immunohistochemical staining of paraffin embedded samples of normal human tissues, kidney and liver specimens from individuals with ADPKD 1, the genetically distinct disorder ADPKD 2 and acquired renal cystic disease (ARCD).These studies demonstrated strong staining of normal and cystic epithelial celis of the kidney and liver in ADPKD 1 but not in ADPKD 2, ARCD or non-cystc adult tissue. Of the glomerular, interstitial and vascular compartments within affected kidney, only glomerular parietal epithelial cells were positive. In affected liver, hepatocytes showed moderate staining. All antisera gave similar staining patterns with varying intensity. Prehnmune serum and immune serum pre-adsorbed with peptide antigen were consistently negative or, with the tatter, gave greatly diminished staining. We conclude that polycystin is overexpressed in both normal and cystic epithelium in ADPKD 1 compared to normal appearing adult kidney and liver. This overexpression is not a feature of ADPKD 2 or acquired cystic disease.