Decreased leukotriene C₄ synthesis accompanies adherence-dependent nuclear import of 5-lipoxygenasee in human blood eosinophils

The enzyme 5-lipoxygenase (5-LO) catalyzes the synthesis of leukotrienes (LTs) from arachidonic acid (AA). Adherence or recruitment of polymorphonuclear neutrophils (PMN) induces nuclear import of 5-LO from the cytosol, which is associated with enhanced LTB₄ synthesis upon subsequent cell stimulation. In this study, we asked whether adherence of human eosinophils (EOS) causes a similar redistribution of 5-LO and an increase in LTC₄ synthesis. Purified blood EOS examined either in suspension or after adherence to fibronectin for 5 min contained only cytosolic 5-LO. Cell stimulation resulted in activation of 5-LO, as evidenced by its translocation to membranes and LTC₄ synthesis. As with PMN, adherence of EOS to fibronectin for 120 min caused nuclear import of 5-LO. Unexpectedly, however, adherence also caused a time-dependent decrease in LTC₄ synthesis: EOS adhered for 120 min produced 90% less LTC₄ than did cells adhered for 5 min. Adherence did not diminish the release of [³H]AA from prelabeled EOS or reduce the synthesis of the prostanoids thromboxane and PGE₂. Also, inhibition of LTC₄ production caused by adherence could not be overcome by the addition of exogenous AA. Adherence increased, rather than decreased, LTC₄ synthase activity. However, the stimulation of adherent EOS failed to induce translocation of 5-LO from the nucleoplasm to the nuclear envelope. This resistance to activation of the nuclear pool of 5-LO with diminished LT production represents a novel mode of regulation of the enzyme, distinct from the paradigm of up-regulated LT synthesis associated with intranuclear localization of 5-LO observed in PMN and other cell types.