ARACHIDONIC-ACID MEDIATES INTERLEUKIN-1 AND TUMOR NECROSIS FACTOR-ALPHA-INDUCED ACTIVATION SF THE C-JUN AMINO-TERMINAL KINASES IN STROMAL CELLS

We have previously shown that arachidonic acid mediates interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha)-induced transcripti on of c-jun. The signaling pathway of arachidonic: acid-induced c-jun transcription was independent of protein kinase C activation and invol ved a tyrosine kinase-dependent process. The present study was underta ken to further elucidate the signal transduction pathway of arachidona te-induced c-jun transcription. We used a glutathione-S-transferase-c- jun fusion protein containing the amino-terminal domain of c-jun (resi dues 5 to 89) to explore the hypothesis that arachidonic acid stimulat es c-jun amino-terminal kinase (JNK) activity in the murine stromal ce ll line +/+.1 LDA 11. Extracts from arachidonic acid-treated cells cat alyzed phosphorylation of the c-jun fusion protein, indicating stimula tion of JNK activity. Similar results were obtained when cells were ch allenged with IL-1 and TNF-alpha. The effect of arachidonic acid was s pecific, because extracts from stimulated cells failed to phosphorylat e a mutated fusion protein in which serine 63 and 73 of c-jun were eac h substituted with leucine. Arachidonic acid induced JNK activation in a time- and dose-dependent manner that was not mimicked by saturated fatty acids such as palmitic acid or other unsaturated fatty acids fro m the n-3, n-6, or n-9 series. Furthermore, other lipids, such as diac ylglycerol, phosphatidic acid, and C-2-ceramide, failed to induce a si gnificant increase in JNK activity. Treatment of stromal cells with pr opyl gallate, a dual inhibitor of lipoxygenase and cyclooxygenase enzy mes, did not affect the ability of arachidonic acid to induce JNK acti vation. Moreover, ETYA (5,8,11,14-eicosatetraynoic acid), a nonmetabol izable arachidonate analogue, also induced JNK activation. These resul ts are consistent with the hypothesis that the signal transduction pat hway by which arachidonate stimulates c-jun transcription involves act ivation of the JNK cascade. Furthermore, arachidonic acid itself and n ot ifs cyclooxygenase or lipoxygenase metabolites is involved in stimu lating JNK activity. Thus, arachidonic acid may act as a second messen ger in mediating the effects of IL-1 and TNF-alpha in the activation o f c-jun. (C) 1996 by The American Society of Hematology.