12(S)-HYDROXYEICOSATETRAENOIC ACID REGULATES DNA-SYNTHESIS AND PROTOONCOGENE EXPRESSION INDUCED BY EPIDERMAL GROWTH-FACTOR AND INSULIN IN RAT LENS EPITHELIUM

Neonatal rat lens epithelium has a high 12(S)hydroxyeicosatetraenoic a cid [12(S)-HETE] synthetic capacity, which decreases as epithelial cel l proliferation decreases with age. To determine whether products of t he 12-lipoxygenase pathway are involved in lens cell proliferation, we measured the effect of 12-lipoxygenase inhibitors on endogenous 12-HE TE production, epidermal growth factor/insulin-stimulated DNA synthesi s and protooncogene expression in cultured neonatal rat lens epithelia l cells. Incubation of neonatal rat lenses in epidermal growth factor plus insulin, which stimulated endogenous 12-HETE production 8- to 10- fold, also produced a transient induction of c-fos and c-myc mRNAs aft er 2 to 3 h, followed by a round of DNA synthesis approximately 20 h l ater. The lipoxygenase inhibitor, cinnamyl-3,4-dihydroxy-alpha-cyanoci nnamate, strongly inhibited both the endogenous 12-HETE synthesis and growth factor-stimulated DNA synthesis with a half-maximal inhibition between 10 and 20 mu M Cinnamyl-3,4-dihydroxy-alpha-cyanocinnamate (10 mu M) also inhibited the expression of c-fos and c-myc mRNA and, to a lesser extent, c-jun mRNA. The inhibitory effects of cinnamyl-3,4-dih ydroxy-alpha-cyanocinnamate on protooncogene expression and DNA synthe sis were prevented by 0.3 mu M 12(S)-HETE but not by equivalent concen trations of either 5(S)-HETE or 15(S)-HETE. These findings suggest tha t endogenously synthesized 12(S)-HETE may mediate epidermal growth fac tor/insulin-stimulated DNA synthesis in neonatal rat lens epithelial c ells by regulating protooncogene expression.