Background: Polycystin-2 (PC2), encoded by the gene that is mutated in autosomal dominant polycystic kidney\r\ndisease (ADPKD), functions as a calcium (Ca2+) permeable ion channel. Considerable controversy remains regarding\r\nthe subcellular localization and signaling function of PC2 in kidney cells.\r\nMethods: We investigated the subcellular PC2 localization by immunocytochemistry and confocal microscopy in\r\nprimary cultures of human and rat proximal tubule cells after stimulating cytosolic Ca2+ signaling. Plasma membrane\r\n(PM) Ca2+ permeability was evaluated by Fura-2 manganese quenching using time-lapse fluorescence microscopy.\r\nResults: We demonstrated that PC2 exhibits a dynamic subcellular localization pattern. In unstimulated human or rat\r\nproximal tubule cells, PC2 exhibited a cytosolic/reticular distribution. Treatments with agents that in various ways affect\r\nthe Ca2+ signaling machinery, those being ATP, bradykinin, ionomycin, CPA or thapsigargin, resulted in increased PC2\r\nimmunostaining in the PM. Exposing cells to the steroid hormone ouabain, known to trigger Ca2+ oscillations in kidney\r\ncells, caused increased PC2 in the PM and increased PM Ca2+ permeability. Intracellular Ca2+ buffering with BAPTA,\r\ninositol 1,4,5-trisphosphate receptor (InsP3R) inhibition with 2-aminoethoxydiphenyl borate (2-APB) or Ca2+/Calmodulindependent\r\nkinase inhibition with KN-93 completely abolished ouabain-stimulated PC2 translocation to the PM.\r\nConclusions: These novel findings demonstrate intracellular Ca2+-dependent PC2 trafficking in human and rat kidney\r\ncells, which may provide new insight into cyst formations in ADPKD.
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