Recovery of prostaglandin synthesis in rat glomerular mesangial cells after aspirin inhibition: Induction of cyclooxygenase activity by serum and epidermal growth factor

We assessed cyclooxygenase activity in cultured rat mesangial cells by measuring prostaglandin production with reverse phase HPLC upon addition of exogenous ¹⁴C arachidonic acid. The profile of prostaglandins produced was PGE₂>PGF₂α≫6-keto PGF₁α ≫ thromboxane and PGD₂. In quiescent mesangial cells, exposure to 300 μM aspirin for 30 minutes irreversibly inhibited cyclooxygenase activity: after 5 hours, cyclooxygenase activity was only 19±3% of control. Addition of 10% fetal bovine serum after aspirin inactivation stimulated time-dependent recovery of cyclooxygenase activity to 118±30% of control by 5 hours. Serum induced-recovery was significantly inhibited by the simultaneous administration of the protein kinase C inhibitor, staurosporine. Phorbol myristate acetate also induced recovery of cyclooxygenase activity, suggesting that protein kinase C may be involved in the signaling process. In addition to serum, epidermal growth factor was also found to lead to partial recovery of cyclooxygenase activity. The serum and EGF-induced recoveries were inhibitable by cycloheximide and actinomycin D. These results suggest that recovery of cyclooxygenase activity in mesangial cells is stimulated by EGF and other components of serum, is dependent upon new protein synthesis and appears to be transcriptionally regulated.