Altered store operated calcium entry increases cAMP production and ERK1/2 phosphorylation in Polycystin-2 defective cholangiocytes

Mutations in polycystins (PC1 or PC2/TRPP2) cause progressive polycystic liver disease (PLD). In PC2 defective mice, cAMP/PKA-dependent activation of ERK/mTOR signaling stimulates cyst growth. We investigated the mechanisms connecting PC2 dysfunction to altered Ca(2+) and cAMP production and inappropriate ERK signaling in PC2-defective cholangiocytes. Cystic cholangiocytes were isolated from PC2 conditional-KO mice (Pkd2(flox/-) :pCxCreER(TM) - hence called Pkd2KO) and compared to cholangiocytes from Wild Type mice (WT). Our results show that, compared to wild type cells, in PC2 -defective cholangiocytes (Pkd2KO) cytoplasmic and ER-Ca(2+) (measured with Fura-2 and Mag-Fluo4) levels are decreased, store-operated Ca(2+) entry (SOCE) is inhibited, while the expression of Ca(2+) -sensor STIM1 and of store-operated Ca(2+) channels (Orai1 channel) are unchanged. In Pkd2KO cells, ER-Ca(2+) depletion increases [cAMP] and PKA-dependent ERK1/2 activation and both are inhibited by STIM1 inhibitors or by silencing of adenylyl cyclase 6 (AC6). CONCLUSION: these data suggest that PC2 plays a key role in SOCE activation and inhibits the STIM-dependent activation of AC6 by ER Ca(2+) depletion. In PC2-defective cells, the interaction of STIM-1 with Orai channels is uncoupled, while coupling to AC6 is maximized. The resulting overproduction of cAMP, in turn, potently activates the PKA/ERK pathway. PLD due to PC2-deficiency represents the first example of human disease linked to inappropriate activation of "Store-operated cAMP production" (SOcAMP).