Regulation of Cyclo-oxygenase Gene Expression in Rat Smooth Muscle Cells by Catalase

Abstract

We have studied, in detail, the effect of catalase, one of the naturally occurring antioxidant enzymes, on the expression of cyclo-oxygenase (COX) mRNA and protein in rat aortic smooth muscle cells (RASMC). The activity of COX enzyme within the cells was also determined. Catalase either alone or in combination with interleukin-1β (IL-1β) enhanced mRNA and protein expression for cyclo-oxygenase 2 (COX-2) in a concentration-dependent manner. However, it did not affect the expression of mRNA or protein for cyclo-oxygenase 1 (COX-1). The expression of mRNA for COX-2 induced by catalase was blocked completely by actinomycin D (ACT) or cycloheximide (CHX). In comparison, expression of mRNA for COX-2 stimulated by IL-1β was inhibited by actinomycin D, but not by cycloheximide. This suggests that induction of the synthesis of mRNA for COX-2 by catalase and IL-1β involves different mechanisms. In particular, the induction of mRNA for COX-2 by catalase requires on-going protein and RNA synthesis, but the induction following exposure to IL-1β does not. The increase in expression of mRNA for COX-2 induced by catalase may be related to the ability of catalase to stimulate cyclic AMP response element (CRE) and NF-IL6 transcription factors, but not nuclear factor kappa B (NF-κB), for electrophoretic mobility shift assays (EMSA) showed that catalase enhanced nuclear factor binding to cyclic AMP response element and NF-IL6 but not to NF-κB. Catalase exerted a biphasic effect on prostaglandin synthesis. At low concentrations it enhanced prostaglandin production, but at high concentrations it tended to inhibit it. These findings suggest that catalase has differential and multiple effects on COX expression and activity in rat aortic smooth muscle cells.