Cystin gene mutations cause autosomal recessive polycystic kidney disease associated with altered Myc expression

Abstract Mutation of the Cys1 gene underlies the renal cystic disease in the Cys1cpk/cpk (cpk) mouse that phenocopies human autosomal recessive polycystic kidney disease (ARPKD). Cystin, the protein product of Cys1, is expressed in the primary apical cilia of renal ductal epithelial cells. In previous studies, we showed that cystin regulates Myc expression via interaction with the tumor suppressor, necdin. Here, we demonstrate rescue of the cpk renal phenotype by kidney-specific expression of a cystin-GFP fusion protein encoded by a transgene integrated into the Rosa26 locus. In addition, we show that expression of the cystin-GFP fusion protein in collecting duct cells down-regulates expression of Myc in cpk kidneys. Finally, we report the first human patient with an ARPKD phenotype due to homozygosity for a predicted deleterious splicing defect in CYS1. These findings suggest that mutations in the Cys1 mouse and CYS1 human orthologues cause an ARPKD phenotype that is driven by overexpression of the Myc proto-oncogene. Translational StatementThe cystin-deficient cpk mouse is a model for the study of autosomal recessive polycystic kidney disease (ARPKD). We show that the cpk mouse phenotype is associated with altered Myc expression. To date, the clinical relevance of cystin deficiency to human disease was unclear, due to the absence of ARPKD cases associated with CYS1 mutations. We report the first case of ARPKD linked to a CYS1 mutation disrupting normal splicing. These findings confirm the relevance of cystin deficiency to human ARPKD, implicate Myc in disease initiation or progression, and validate the cpk mouse as a translationally relevant disease model.