Prostaglandin F2alpha stimulates CFTR activity by PKA- and PKC-dependent phosphorylation

The cystic fibrosis transmembrane conductance regulator (CFTR) can be activated by protein kinase A (PKA)- or protein kinase C (PKC)-dependent phosphorylation. To understand how activation of both kinases affects CFTR activity, transfected NIH/3T3 cells were stimulated with forskolin (FSK), phorbol myristate acetate (PMA), or prostaglandin F2alpha (PGF). PGF stimulates inositol trisphosphate and cAMP production in NIH/3T3 cells. As measured by I- efflux, maximal CFTR activity with PGF and FSK was equivalent and fivefold greater than that with PMA. Both PGF and PMA had additive effects on FSK-dependent CFTR activity. PMA did not increase cellular cAMP, and maximal PGF-dependent CFTR activity occurred with approximately 20% of the cellular cAMP observed with FSK-dependent activation. Staurosporine, but not H-89, inhibited CFTR activation and in vivo phosphorylation at low PGF concentrations. In contrast, at high PGF concentrations, CFTR activation and in vivo phosphorylation were inhibited by H-89. As judged by protease digestion, the sites of in vivo CFTR phosphorylation with FSK and PMA differed. For PGF, the data were most consistent with in vivo CFTR phosphorylation by PKA and PKC. Our data suggest that activation of PKC can enhance PKA-dependent CFTR activation.