New role for 15-hydroxyeicosatetraenoic acid. Activator of leukotriene biosynthesis in PT-18 mast/basophil cells

Abstract

Leukotrienes are vasoactive arachidonic acid metabolites which are released by mast cells during hypersensitivity reactions. The mechanisms for regulating leukotriene biosynthesis are not well understood. A murine mast/basophil cell line (PT-18) was used to investigate this problem. Exogenously supplied [14C]arachidonic acid is not appreciably converted to leukotrienes by untreated PT-18 cells. However, when the cells were preincubated with the lymphocyte product 15-hydroxyeicosatetraenoic acid (15-HETE), addition of [14C]arachidonic acid consistently resulted in a dose-dependent synthesis of large amounts of both [14C]leukotriene B4 and [14C]5-HETE. These metabolites were isolated by high pressure liquid chromatography, converted to the methyl ester trimethylsilyl ether derivatives, and the structures confirmed by gas chromatography-mass spectrometry. These findings indicate that 15-HETE induces a direct activation of a cryptic 5-lipoxygenase in these cells. The closely related 12-HETE was ineffective. The activation phenomenon occurs rapidly and is reversible. Furthermore, the activation appears to be highly cell- and enzyme-specific, since lipoxygenases in three primary cell types including one that contains a 5-lipoxygenase and six other cell lines did not show this specific induction of leukotriene biosynthesis by 15-HETE. This report is the first evidence that 15-HETE, a major arachidonate metabolite in lymphocytes, can act as a signal to activate leukotriene production by susceptible mast cells.