Mitogenic signaling by epidermal growth factor (EGF), but not platelet-derived growth factor, requires arachidonic acid metabolism in BALB/c 3T3 cells. Modulation of EGF-dependent c-myc expression by prostaglandins.

Abstract

Previously, we have shown that prostaglandins are necessary, but not sufficient, for the stimulation of mitogenesis in BALB/c 3T3 fibroblasts by epidermal growth factor (EGF) (Nolan, R. D., Danilowicz, R. M., and Eling, T. E. (1988) Mol. Pharmacol. 33, 650-656). The purpose of this work was to extend these findings to another potent mitogen, platelet-derived growth factor (PDGF), and to determine if metabolism of arachidonic acid to prostaglandins is necessary for stimulation of expression of the protooncogene c-myc by EGF, which is an early event in the mitogenic cascade. In BALB/c 3T3 cells grown to about 70% confluence and deprived of serum for 16-24 h, PDGF stimulated [3H]thymidine uptake into DNA significantly in a concentration-dependent manner, but did not increase production of prostaglandin E2 (PGE2). The addition of indomethacin, a prostaglandin H synthase inhibitor, or nordihydroguaiaretic acid, a lipoxygenase inhibitor, did not affect PDGF-stimulated thymidine uptake into DNA. In addition, PGE2 enhanced EGF-dependent, but not PDGF-dependent, mitogenesis. Taken together, the data support the hypothesis that prostaglandins are not involved in PDGF-dependent mitogenesis. In contrast, indomethacin (10(-6) M) and nordihydroguaiaretic acid (10(-6) M) inhibited EGF-stimulated thymidine uptake and c-myc expression by approximately 50%. Addition of PGG2 (10(-7) to 10(-5) M) in the presence of indomethacin and EGF restored the ability of EGF to elevate c-myc RNA levels and DNA synthesis. When PGF2 alpha (10(-8) to 10(-5) M) was added in the presence of EGF, c-myc RNA levels and thymidine incorporation were elevated up to 5-6-fold above levels observed with EGF alone. These data support the hypothesis that metabolism of arachidonic acid to prostaglandins is necessary for stimulation of c-myc expression by EGF in BALB/c 3T3 cells.