3‐OH flavone inhibition of epidermal growth factor‐induced proliferaton through blocking prostaglandin E2 production

Abstract

Epidermal growth factor (EGF) has been shown to induce proliferation in cells, however, the role of prostaglandin E₂ (PGE₂) plays in EGF‐induced proliferation in still unclear. EGF and PGE₂ showed proliferation responses in epidermoid carcinoma cell A431 by MTT and [³H] thymidine incorporation assay. Activation of the EGF receptor and extracellular signal‐regulated protein kinases (ERK1/2), but not p38 and JNK, appeared 10 min after EGF treatment, whereas total amounts of ERK1/2, p38 and JNK remained unchanged in A431 cells, accompanied by induction of COX‐2 and PGE₂ production. PD98059, a specific ERK1/2 inhibitor, inhibited EGF‐induced proliferation with concomitant decreases in ERK1/2 phosphorylation and COX‐2/PGE₂ induction. Non‐steroid anti‐inflammatory drugs (NSAIDs) such as aspirin and diclofenac, a COX activity inhibitor, inhibited EGF‐induced proliferation by blocking PGE₂ production. The addition of PGE₂ reversed the inhibitory effects of PD98059, aspirin, and diclofenac on EGF‐induced proliferation. This suggests that COX‐2/PGE₂ activation involves in EGF‐induced proliferation and locates at the downstream of ERK1/2 activation. Furthermore, the natural product, 3‐OH flavone, showed the most‐potent inhibitory activity on EGF‐induced proliferation among 9 structurally‐related compounds, and suppression of EGF receptor phosphorylation, ERK1/2 phosphorylation, and COX‐2/PGE₂ production by 3‐OH flavone was identified. PGE₂ addition attenuates the inhibitory activity of 3‐OH flavone on EGF‐induced proliferation by MTT assay and colony formation by soft agar assay. Additionally, 3‐OH flavone also showed more‐specific inhibition on EGF‐ than on fetal bovine serum (FBS)‐induced proliferation in A431 cells. Results of our present study provide evidence to demonstrate that PGE₂ is an important downstream molecule in EGF‐induced proliferation, and 3‐OH flavone, which inhibits PGE₂ production by blocking MAPK cascade, might reserve potential for development as an anti‐cancer drug.