Secretory phospholipase A(2) mediates cooperative prostaglandin generationby growth factor and cytokine independently of preceding cytosolic phospholipase A(2) expression in rat gastric epithelial cells

Transforming growth factor (TGF)-alpha and interleukin (IL)-1 beta are resp onsible for the healing of gastric lesions through, in part, prostaglandin (PG) generation. We examined the contribution of cytosolic and secretory ph ospholipase A(2)s (cPLA(2) and sPLA(2)) to the PC generation by rat gastric epithelial cells in response to both stimuli. Stimulation with TGF-alpha f or 24 h increased cPLA(2) and cyclooxygenase (COX)-2 markedly, PGE(2) sligh tly, and type IIA sPLA(2) and COX-1 not at all, whereas IL-1 beta increased sPLA(2) only. Both stimuli synergistically increased PGE(2), sPLA(2), and the two COXs but not cPLA(2). The onset of the PGE(2) generation paralleled the sPLA(2) release but was apparently preceded by increases in cPLA(2) an d the two COXs, The increase in PGE(2) was impaired by inhibitors for sPLA( 2) and COX-2 but not COX-1. cPLA(2) inhibitors suppressed PGE(2) generation by TGF-alpha alone but not augmentation of PGE(2) generation or sPLA(2) re lease by IL-1 beta in combination with TGF-alpha. Furthermore, despite an i ncrease in cPLA(2) including its phosphorylated form (phosphoserine), A2318 7-induced arachidonic acid liberation was impaired in the TGF-alpha/ IL-1 b eta -stimulated cells, in which p11, a putative cPLA(2) inhibitory molecule , was also increased and co-immunoprecipitated with cPLA(2). These results suggest that synergistic stimulation of sPLA(2) and COX-2 expression by TGF -alpha and IL-1 beta results in an increase in PGE(2).(.) Presumably, the p receding cPLA(2) expression is not involved in the PGE(2) generation, becau se of impairment of its hydrolytic activity in the stimulated cells.