The delayed release of PGE₂ mediated by PAR1 involves slowly developing production of arachidonic acid in rat gastric mucosal epithelial cells

Abstract

We previously showed that activation of proteinase‐activated receptor‐1 (PAR1) caused delayed (18 h later) PGE2 release in rat gastric mucosal epithelial RGM1 cells, although the maximal up‐regulation of COX‐2 protein was observed much earlier (6 h later). In this study, we analyzed mechanisms for the delay of PGE2 release caused by PAR1 stimulation in RGM1 cells. Stimulation with a PAR1‐activating peptide, TFLLR‐NH2 (TF), in combination with arachidonic acid (AA) or linoleic acid (LA) induced rapid and synergistic increase in PGE2 release within 3 h. CP‐24879, a Δ5/Δ6‐desaturase inhibitor, suppressed the PGE2 release induced by TF plus LA, but not by TF plus AA or TF alone, at 18 h. The TF‐induced delayed PGE2 release was suppressed by combined application of inhibitors of cPLA2, iPLA2 and sPLA2, but not by each of them. Protein levels of microsomal PGE synthase (mPGES)‐1, mPGES‐2 and cytosolic PGES were unchanged by stimulation with TF. These data suggest that the delay of PAR1‐triggered PGE2 release is due to slowly developing AA production in RGM1 cells, and that three isozymes of PLA2 may complementarily contribute to the AA production.