Prostaglandin F-2 alpha receptor-dependent regulation of prostaglandin transport

Prostaglandin (PG) F-2 alpha may act on its G protein-coupled receptor (FP) or be imported intracellularly via a transporter, which has high affinity for PGF(2 alpha) and PGE(2), but not prostacyclin (PGI(2)). In cells overex pressing the epitope-tagged FP together with the human prostaglandin transp orter (hPGT), stimulation of the FP with PGF(2 alpha) (1 nM-1 muM), or the less potent FP agonist, the isoprostane 8,12-iso-iPF(2 alpha)-III, inhibite d prostaglandin uptake via the hPGT. This effect was abolished by pretreatm ent of the cells with cholera toxin, but not with pertussis toxin. Furtherm ore, two dominant negative constructs directed against G alpha (s) partiall y blocked FP-mediated regulation of hPGT function, also suggesting G alpha (s) involvement in this phenomenon. Surprisingly, neither an activator (dib utyryl cyclic AMP) nor an inhibitor (H89) of cyclic AMP-dependent protein k inase had any effect on FP-mediated inhibition of hPGT activity. Furthermor e, although PGF(2 alpha) increases intracellular cyclic AMP via G alpha (s) activation, it does not induce phosphorylation of the transporter, excludi ng a role of cyclic AMP-dependent protein kinase in hPGT regulation. Activa tion of the PGI(2) receptor, which is also coupled to G alpha (s) does not regulate hPGT activity, despite markedly augmenting adenylate cyclase activ ation. In conclusion, activation of the FP reduces intracellular import of prostaglandins for metabolic inactivation, increasing prostanoid availabili ty for membrane receptor activation. This effect seems to be mediated via G alpha (s), independent of adenylate cyclase and cyclic AMP-dependent prote in kinase activation.