Functionally conserved Pkd2, mutated in autosomal dominant polycystic kidney disease, localizes to the endoplasmic reticulum and regulates cytoplasmic calcium homeostasis in fission yeast

Mutations in PKD1 or PKD2 genes lead to autosomal dominant polycystic kidney disease (ADPKD) that is the most frequent family inherited renal disorder. These genes encode polycystin-1/PC-1 and polycycstin-2/PC-2, respectively. Although the genetic basis of ADPKD is well established, the crucial functions of polycystins underlying onset and development of cyst formation remain elusive. Fission yeast Schizosaccharomyces pombe has a single polycystin homolog, Pkd2, which is essential for cell growth. In this study, the truncation analyses of Pkd2 reveal that Pkd2 localizes to not only the plasma membrane but also the endoplasmic reticulum (ER) and regulates cytoplasmic calcium signaling in fission yeast. Internal transmembrane domains within Pkd2 are sufficient for these processes. Surprisingly, more than half of Pkd2 is not required for cell viability. Cytoplasmic calcium levels are mainly regulated through C-terminus of Pkd2. Importantly, human Pkd2 also localizes to the ER and furthermore, fully complements the loss of fission yeast Pkd2. As the functions of polycystin-2 are conserved, fission yeast provides a suitable model to study the mechanism of ADPKD as well as polycystins.