Interleukin-4 enhances 15-lipoxygenase activity and incorporation of 15(S)-HETE into cellular phospholipids in cultured pulmonary epithelial cells

15(S)-Hydroxyeicosatetraenoic acid (15[S]-HETE) is a 15-lipoxygenase (15-LO ) metabolite that may play an important role in different pulmonary disease s. 15-HETE is synthesized by different epithelial cells and may be subseque ntly incorporated into cellular phospholipids. We studied the role of inter leukin-4 (IL-4) on 15-LO activity and on 15(S)-HETE incorporation into cell ular phospholipids by WI-26 pulmonary epithelial cells. 15-LO activity was evaluated by measuring 15(S)-HETE production, through combined reverse-phas e-high-pressure liquid chromatography (RP-HPLC) separation and specific rad ioimmunoassay (RIA), after incubation with arachidonic acid (AA). We also s tudied 15-LO messenger RNA (mRNA) expression, using primed in situ (PRINS) labeling. IL-4 (10 ng/ml) markedly increased the percentage of 15 LO mRNA-b earing cells as well as 15-LO activity after 24, 48, and 72 h, with a maxim al response at 48 h. Uptake and incorporation into cellular phospholipid wa s studied with [H-3]15(S)-HETE, which showed that IL-4 was able to increase significantly 15(S)-HETE incorporation into WI-26 cells, with a maximal ef fect observed at 72 h. Cellular-lipid-associated [H-3]15(S)-HETE, evaluated with RP-HPLC after base-catalyzed hydrolysis, increased concomitantly with disappearance of the radiolabel from the supernatant. Class separation of cellular lipids with normal-phase HPLC (NP-HPLC) showed that IL-4 increased [H-3]15(S)-HETE incorporation mainly in the phosphatidylinositol (PI) frac tion. The ability of IL-4 to promote 15-LO activity and incorporation into cellular phospholipids of human lung epithelial cells may be important in a irway inflammation and in modulation of the potential autocrine function of 15(S)-HETE.