Induction of cytosolic phospholipase A(2) by oncogenic Ras is mediated through the JNK and ERK pathways in rat epithelial cells

Mutations in ras genes have been detected with high frequency in nonsmall c ell lung cancer cells (NSCLC) and contribute to transformed growth of these cells. It has previously been shown that expression of oncogenic forms of Ras in these cells is associated with elevated expression of cytosolic phos pholipase A(2) (cPLA(2)) and cyclooxygenase-2 (COX-2), resulting in high co nstitutive levels of prostaglandin production. To determine whether express ion of constitutively active Res is sufficient to induce expression of thes e enzymes in nontransformed cells, normal lung epithelial cells were transf ected with H-Ras, Stable expression of H-Ras increased expression of cPLA(2 ) and COX-2 protein. Transient transfection with II-Pas increased promoter activity for both enzymes. H-Ras expression also activated all three famili es of MAP kinase: ERKs, JNKs, and p38 MAP kinase, Expression of constitutiv ely active Raf did not increase either cPLA(2) or COX-2 promoter activity, but inhibition of the ERK pathway with pharmacological agents or expression of dominant negative ERK partially blocked the H-Ras-mediated induction of cPLA(2) promoter activity. Expression of dominant negative JNK kinases dec reased cPLA(2) promoter activity in NSCLC cell lines and inhibited H-Ras-me diated induction in normal epithelial cells, whereas expression of construc ts encoding constitutively active JNKs increased promoter activity. Inhibit ion of p38 MAP kinase or NF-KB had no effect on cPLA(2) expression. Truncat ional analysis revealed that the region of the cPLA(2) promoter from -58 to +12 contained sufficient elements to mediate H-Ras induction. We conclude that expression of oncogenic forms of Res directly increases cPLA(2) expres sion in normal epithelial cells through activation of the JNK and ERR pathw ays.