Enhancement of Prostaglandin E2 Production by Epidermal Growth Factor Requires the Coordinate Activation of Cytosolic Phospholipase A2 and Cyclooxygenase 2 in Human Squamous Carcinoma A431 Cells

We demonstrated the effect of epidermal growth factor (EGF) on the production of PGE₂ in human squamous carcinoma A431 cells. The production of PGE₂ was increased by stimulating the cells with EGF for 2 h and reached a maximum for 10 h. EGF was also found to augment the release of arachidonic acid (AA) following the increase in phospholipase A₂ (PLA₂) activity (1.7-fold). The induced PLA₂ activity was diminished by 4-bromophenacyl bromide, but not by dithiothreitol, indicating that the EGF-induced release of AA was due to the increase in the activity of cytosolic PLA₂ (cPLA₂). On the other hand, cyclooxygenase (COX) activity was increased (1.6-fold) within 2 h after the EGF-treatment and the induced activity was inhibited by cycloheximide. In addition, Northern blot analysis showed that the level of COX-2 mRNA was increased by the EGF-treatment, whereas no COX-2 mRNA was detected in the untreated cells, indicating that the EGF-induced COX activity was resulted from the increase in the production of COX-2. These results suggest that EGF augments the production of PGE₂ by increasing not only the activity of cPLA₂ but also the production of COX-2 in A431 cells.