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 bothkinases affects CFTR activity, transfected NIH/3T3 cells werestimulated with forskolin (FSK), phorbol myristate acetate (PMA), orprostaglandin F₂ (PGF). PGFstimulates inositol trisphosphate and cAMP production in NIH/3T3 cells.As measured by I efflux,maximal CFTR activity with PGF and FSK was equivalent and fivefoldgreater than that with PMA. Both PGF and PMA had additive effects onFSK-dependent CFTR activity. PMA did not increase cellular cAMP, andmaximal PGF-dependent CFTR activity occurred with ~20% of thecellular cAMP observed with FSK-dependent activation. Staurosporine,but not H-89, inhibited CFTR activation and in vivo phosphorylation atlow PGF concentrations. In contrast, at high PGF concentrations, CFTRactivation and in vivo phosphorylation were inhibited by H-89. Asjudged by protease digestion, the sites of in vivo CFTR phosphorylationwith FSK and PMA differed. For PGF, the data were most consistent within vivo CFTR phosphorylation by PKA and PKC. Our data suggest thatactivation of PKC can enhance PKA-dependent CFTR activation.