Coordinate up‐ and down‐regulation of glutathione‐dependent prostaglandin E synthase and cyclooxygenase‐2 in A549 cells: Inhibition by NS‐398 and leukotriene C4

Abstract

Recently, a microsomal protein with 38% sequence identity to microsomal glutathione S‐transferase 1 was shown to constitute an inducible, glutathione‐dependent prostaglandin E synthase (PGES). To investigate the relationship between cyclooxygenase and PGES, a time‐course study on protein expression was performed in A549 cells after treatment with interleukin‐1β. The result demonstrated a tandem expression of cyclooxygenase‐2 and PGES. The observed induction of PGES protein correlated with microsomal PGES activity. No comparable PGES activity was observed in the absence of glutathione or in the cytosolic fraction. In addition, tumour necrosis factor‐α was found to induce PGES in these cells. Dexamethasone was found to completely suppress the effect of both cytokines on PGES induction. We also describe a quantitative method, based on RP‐HPLC with UV detection for the measurements of PGES activity. This method was used to screen potential PGES inhibitors. Several nonsteroidal anti‐inflammatory drugs, stable prostaglandin H 2 analogues and cysteinyl leukotrienes were screened for inhibition of PGES activity. NS‐398, sulindac sulfide and leukotriene C 4 were all found to inhibit PGES activity with IC 50 values of 20 µ m, 80 µ m and 5 µ m, respectively. In conclusion, it appears that PGES and cyclooxygenase‐2 are functionally coupled in A549 cells and that a required coordinate expression of these enzymes allows for efficient biosynthesis of prostaglandin E 2.