15-Deoxy-delta12,14-prostaglandin-J(2) (15d-PGJ(2)) has potent anti-inflammatory effects including the inhibition of interleukin-1beta (IL-1beta)-induced expression of cyclooxygenase-2 (COX-2) and prostaglandin E(2) (PGE(2)) production in several cell types. 15d-PGJ(2) contains an alpha,beta-unsaturated electrophilic ketone and several evidences suggest that thiol reducing agents prevent or revert the cellular effects of 15d-PGJ(2). The present study was devoted to analyze the effect of 15d-PGJ(2) on COX-2 expression in cultured human mesangial cells (HMC). 15d-PGJ(2) induced an increase in the reduced glutathione (GSH) content and up-regulated COX-2 protein expression, but not COX-1, in a manner which was unaffected by selective peroxisome proliferator-activated receptor gamma (PPARgamma) blockade nor mimicked by ciglitazone, a PPARgamma agonist. N-acetylcysteine (NAC), a thiol reducing agent, but not reactive oxygen species scavengers, prevented 15d-PGJ(2)-induced COX-2 up-regulation. Depletion of GSH by buthionine sulfoximine, which diminishes thiol antioxidant activity, cooperated with 15d-PGJ(2) to accumulate COX-2. Therefore, 15d-PGJ(2) up-regulated COX-2 through a thiol antioxidant-sensitive mechanism. Interestingly, NAC did not inhibit the COX-2 expression induced by the electrophilic alpha,beta-unsaturated compound PGA(2). Up-regulation of COX-2 by 15d-PGJ(2) did not result in increased PGE(2) production. Furthermore, preincubation with 15d-PGJ(2) inhibited IL-1beta-induced PGE(2) production although IL-1beta-induced COX-2 expression remained unaffected by the treatment with 15d-PGJ(2). On the contrary, PGA(2) elicited an increase in PGE(2) production and it acted synergistically with IL-1beta to enhance PGE(2) production. These results indicate for the first time that 15d-PGJ(2) inhibits PGE(2) production independently of its effect on COX-2 expression.