Interleukin-1 stimulates Jun N-terminal/stress-activated protein kinase byan arachidonate-dependent mechanism in mesangial cells

Background. We have studied interleukin-l (IL-1)-stimulated signals and gen e expression in mesangial cells (MCs) to identify molecular mechanisms of M C activation, a process characteristic of glomerular inflammation. The JNK1 pathway has been implicated in cell fate decisions, and IL-1 stimulates th e Jun N-terminal/stress-activated protein kinases (JNK1/SAPK). However, ear ly postreceptor mechanisms by which IL-1 activates these enzymes remain unc lear. Free arachidonic acid (AA) activates several protein kinases, and bec ause IL-I rapidly stimulates phospholipase Az (PLA:) activity to release AA , IL-l-induced activation of JNK1/SAPK may be mediated by AA release. Methods. MCs were grown from collagenase-treated glomeruli, and JNK/SAPK ac tivity in MC lysates was determined using an immunocomplex kinase assay. Results. Treatment of MCs with IL-1 alpha induced a time-dependent increase in JNK1/SAPK kinase activity, assessed by phosphorylation of the activatin g transcription factor-2 (ATF-2). Using similar incubation conditions, IL-1 also increased [H-3]AA release from MCs. Pretreatment of MCs with aristolo chic acid, a PLA(2) inhibitor, concordantly reduced IL-I-regulated [H-3]AA release and JNK1/SAPK activity, suggesting that cytosolic AA in part mediat es IL-l-induced JNK1/SAPK activation. Addition of AA stimulated JNK1/SAPK a ctivity in a time- and concentration-dependent manner. This effect was AA s pecific, as only AA and its precursor linoleic acid stimulated JNK1/SAPK ac tivity. Other fatty acids failed to activate JNK1/SAPK. Pretreatment of MCs with specific inhibitors of AA oxidation by cyclooxygenase, lipoxygenase, and cytochrome P-450 epoxygenase had no effect on either IL-1- or AA-induce d JNK1/SAPK activation. Furthermore, stimulation of MCs with the exogenous cyclooxygenase-, lipoxygenase-, phosphodiesterase-, and epoxygenase-derived arachidonate metabolites, in contrast to AA itself, did not activate JNK1/ SAPK. Conclusion. We conclude that IL-1-stimulated AA release, in part, mediates stimulation of JNK1/SAPK activity and that AA activates JNK1/SAPK by a mech anism that does not require enzymatic oxygenation. JNK1 signaling pathway c omponents may provide molecular switches that mediate structural rearrangem ents and biochemical processes characteristic of MC activation and could pr ovide a novel target(s) for therapeutic intervention.