Stress protein activation by the cyclopentenone prostaglandin 15-deoxy-Δ12,14-prostaglandin J2 in human mesangial cells

Background. The cyclopentenone prostaglandin 15-deoxy-(12,14) -prostaglandin J(2) (15dPGJ(2)) affects mesangial proliferation, survival and production of proinflammatory proteins. During a survey of the mesangial cell proteome after treatment with 15dPGJ(2), heat shock protein 70 (HSP70) was found to be the most conspicuously up-regulated protein, suggesting that stress proteins are key mediators or modulators of the effects of 15dPGJ(2). Because cyclopentenone prostaglandins are highly reactive toward intracellular thiols, the role of intracellular thiol modification in the stress response to 15dPGJ(2) was examined. Methods. Human mesangial cells were treated with 15dPGJ(2) and intracellular thiol status was monitored by the fluorescent thiol probe monobromobimane (MBB). Specific intracellular thiol pools were manipulated by treating the cells with buthionine sulfoximine (BSO) to deplete glutathione (GSH), or phenylarsine oxide (PAO) to modify protein vicinal dithiols. Transcription pathways were examined with reporter gene or adenoviral constructs. Results. 15dPGJ(2) decreased mesangial GSH and other intracellular thiols, but depletion of GSH specifically with BSO did not induce HSP70. Thiol-replenishing reagents, which can restore modified protein thiols, attenuated 15dPGJ(2)-induced HSP70 levels. Furthermore, PAO mimicked the effects of 15dPGJ(2) on HSP70. 15dPGJ(2) also activated the stress-responsive transcription factor Nrf2, which requires thiol modification of its cytoplasmic inhibitor protein for transcriptional activity, and induced the Nrf2-dependent stress protein heme oxygenase-1 (HO-1). Conclusion. 15dPGJ(2) activates a stress response in human mesangial cells by covalent modification of protein thiols through its unique cyclopentenone ring structure. This stress response may be beneficial in preventing renal cell injury or death during kidney inflammation or ischemia.