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

1 The regulatory effects of transforming growth factor (TGF)-alpha on phospholipase A(2) (PLA(2)) isozymes contributing to prostaglandin generation in rat gastric epithelial RGM1 cells were examined. 2 Stimulation with TGF-alpha for 24 h time-dependently induced prostaglandin E-2 generation with an increase in cyclo-oxygenase-2 protein. The TGF-alpha -induced prostaglandin E-2 generation was suppressed by NS-398, a cyclo-oxygenase-2 inhibitor. 3 TGF-alpha stimulated the activity and the protein synthesis of cytosolic PLA(2) (cPLA(2)). A time-dependent increase in cPLA(2) protein occurred in parallel with PGE(2) generation, which was inhibited by methyl arachidonyl fluorophosphonate (MAFP), a cPLA(2) inhibitor. However, no change in activity of secretory PLA(2) or Ca+2-independent PLA(2) was observed in the TGF-alpha -stimulated cells. 4 Stimulation with the Ca2+ ionophore A23187 for 10 min induced MAFP-sensitive arachidonic acid liberation. Interestingly, preincubation with TGF-alpha for 24 h diminished A23187-stimulated arachidonic acid liberation despite the increase in cPLA(2) protein. 5 Under the conditions, TCF-alpha was found to increase pll, an endogenous cPLA(2) suppressor, also known as annexin II light chain. The TGF-alpha -induced increase in pll 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-alpha of A23187-stimulated arachidonic acid liberation However, TGF-alpha did not alter protein levels of annexin II heavy chain. 6 These results suggest that TGF-alpha stimulates prostaglandin generation through an increase in cPLA(2), the hydrolytic action of which may be under the control of pll.