Cell biology of the 5-lipoxygenase pathway.

The initial enzymatic steps in leukotriene synthesis occur at the nuclear envelope. Cytosolic phospholipase A2 translocates from the cytoplasm to selectively hydrolyze nuclear envelope phospholipids, releasing free arachidonate. 5-Lipoxygenase-activating protein, an arachidonate transfer protein, then binds arachidonate and presents it to 5-lipoxygenase (5-LO), which catalyzes a two-step reaction to produce leukotriene A4. In resting human and rat peripheral blood neutrophils, 5-LO is localized to the cytoplasm; in rat basophilic leukemia cells and human alveolar macrophages, however, it is found predominantly in the nucleus. Immunofluorescence microscopy studies demonstrate that both cytoplasmic and nuclear 5-LO move to the nuclear envelope following cell activation. Many questions remain unanswered regarding the significance of nuclear 5-LO, potential autocrine actions of leukotrienes, and intracellular trafficking of these enzymes and their products.