A polycystin-2 protein with modified channel properties leads to an increased diameter of renal tubules and to renal cysts

Mutations in the PKD2 gene cause autosomal-dominant polycystic kidney disease but the physiological role of polycystin-2, the protein product of PKD2, remains elusive. Polycystin-2 belongs to the transient receptor potential (TRP) family of non-selective cation channels. To test the hypothesis that altered ion channel properties of polycystin-2 compromise its putative role in a control circuit controlling lumen formation of renal tubular structures, we generated a mouse model in which we exchanged the pore loop of polycystin-2 with that of the closely related cation channel polycystin-2L1 (encoded by PKD2L1), thereby creating the protein polycystin-2(poreL1). Functional characterization of this mutant channel in Xenopus laevis oocytes demonstrated that its electrophysiological properties differed from those of polycystin-2 and instead resembled the properties of polycystin-2L1, in particular regarding its permeability for Ca(2+) ions. Homology modeling of the ion translocation pathway of polycystin-2(poreL1) argues for a wider pore in polycystin-2(poreL1) than in polycystin-2. In Pkd2(poreL1) knock-in mice in which the endogenous polycystin-2 protein was replaced by polycystin-2(poreL1) the diameter of collecting ducts was increased and collecting duct cysts developed in a strain-dependent fashion.