Transforming growth factor-α stimulates prostaglandin generation through cytosolic phospholipase A2 under the control of p11 in rat gastric epithelial cells

摘要

The regulatory effects of transforming growth factor (TGF)-α on phospholipase A2 (PLA2) isozymes contributing to prostaglandin generation in rat gastric epithelial RGM1 cells were examined.Stimulation with TGF-α for 24 h time-dependently induced prostaglandin E2 generation with an increase in cyclo-oxygenase-2 protein. The TGF-α-induced prostaglandin E2 generation was suppressed by NS-398, a cyclo-oxygenase-2 inhibitor.TGF-α stimulated the activity and the protein synthesis of cytosolic PLA2 (cPLA2). A time-dependent increase in cPLA2 protein occurred in parallel with PGE2 generation, which was inhibited by methyl arachidonyl fluorophosphonate (MAFP), a cPLA2 inhibitor. However, no change in activity of secretory PLA2 or Ca+2-independent PLA2 was observed in the TGF-α-stimulated cells.Stimulation with the Ca2+ ionophore A23187 for 10 min induced MAFP-sensitive arachidonic acid liberation. Interestingly, preincubation with TGF-α for 24 h diminished A23187-stimulated arachidonic acid liberation despite the increase in cPLA2 protein.Under the conditions, TGF-α was found to increase p11, an endogenous cPLA2 suppressor, also known as annexin II light chain. The TGF-α-induced increase in p11 was suppressed by tyrphostin AG1478, an inhibitor of tyrosine kinase of epidermal growth factor receptor, which was also found to restore the inhibition by TGF-α of A23187-stimulated arachidonic acid liberation. However, TGF-α did not alter protein levels of annexin II heavy chain.These results suggest that TGF-α stimulates prostaglandin generation through an increase in cPLA2, the hydrolytic action of which may be under the control of p11.