Polycystin-1 Activates the Calcineurin/NFAT (Nuclear Factor of Activated T-cells) Signaling Pathway

Regulation of intracellular Ca(2+) mobilization has been associated with the functions of polycystin-1 (PC1) and polycystin-2 (PC2), the protein products of the PKD1 and PKD2 genes. We have now demonstrated that PC1 can activate the calcineurin/NFAT (nuclear factor of activated T-cells) signaling pathway through Galpha(q) -mediated activation of phospholipase C (PLC). Transient transfection of HEK293T cells with an NFAT promoter-luciferase reporter demonstrated that membrane-targeted PC1 constructs containing the membrane proximal region of the C-terminal tail, which includes the heterotrimeric G protein binding and activation domain, can stimulate NFAT luciferase activity. Inhibition of glycogen synthase kinase-3beta by LiCl treatment further increased PC1-mediated NFAT activity. PC1-mediated activation of NFAT was completely inhibited by the calcineurin inhibitor, cyclosporin A. Cotransfection of a construct expressing the Galpha(q) subunit augmented PC1-mediated NFAT activity, whereas the inhibitors of PLC (U73122) and the inositol trisphosphate and ryanodine receptors (xestospongin and 2-aminophenylborate) and a nonspecific Ca(2+) channel blocker (gadolinium) diminished PC1-mediated NFAT activity. PC2 was not able to activate NFAT. An NFAT-green fluorescent protein nuclear localization assay demonstrated that PC1 constructs containing the C-tail only or the entire 11-transmembrane spanning region plus C-tail induced NFAT-green fluorescent protein nuclear translocation. NFAT expression was demonstrated in the M-1 mouse cortical collecting duct cell line and in embryonic and adult mouse kidneys by reverse transcriptase-PCR and immunolocalization. These data suggest a model in which PC1 signaling leads to a sustained elevation of intracellular Ca(2+) mediated by PC1 activation of Galpha(q) followed by PLC activation, release of Ca(2+) from intracellular stores, and activation of store-operated Ca(2+) entry, thus activating calcineurin and NFAT.