15-Deoxy-Δ12,14-prostaglandin J2 suppresses IL-6-induced STAT3 phosphorylation via electrophilic reactivity in endothelial cells

In this study, the effects of 15d-PGJ2 were investigated in IL-6-activated endothelial cells (ECs). 15d-PGJ2 was found to abrogate phosphorylation on tyr705 of STAT3 in IL-6-treated ECs, in a dose- and time-dependent manner, but did not inhibit serine phosphorylation of STAT3 and the upperstream JAK2 phosphorylation. Other PPAR activators, such as WY1643 or ciglitazone, had no effect upon IL-6-induced STAT3 phosphorylation. Additionally, neither orthovanadate nor l-NAME treatment reverses the inhibition of STAT3 phosphorylation by 15d-PGJ2. Otherwise, the effect of 15d-PGJ2 requires the α,β-unsaturated carbonyl group in the cyclopentane ring. A 15d-PGJ2 analog, 9,10-Dihydro-15d-PGJ2, which lack α,β-unsaturated carbonyl group showed no increase in ROS production and no effect in inhibition of IL-6-induced STAT3 phosphorylation. The electrophilic compound, acrolein, mimics the inhibition effect of 15d-PGJ2. Among the antioxidants, only NAC and glutathione reversed the effects of 15d-PGJ2. NAC, glutathione and DTT all reversed the inhibition of STAT3 phosphorylation when preincubated with 15d-PGJ2. The inhibition of ICAM-1 gene expression by 15d-PGJ2 was abrogated by NAC and glutathione in IL-6-treated ECs. Taken together, these results suggest that 15d-PGJ2 inhibits IL-6-stimulated phosphorylation on tyr705 of STAT3 dependent on its own electrophilic reactivity in ECs.