Studies on the Regulation and Localization of 5‐Lipoxygenase in Human B‐Lymphocytes

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Abstract
Stimulated B-lymphocytes, isolated from patients with chronic lymphocytic leukemia of B-cell type (B-CLL cells) or from human tonsils, produced similar amounts of leukotriene (LT) B4 and 5-hydroxyeicosatetraenoic acid (5-HETE) as polymorphonuclear granulocytes. Unlike intact granulocytes or monocytes, human B-lymphocytes require calcium ionophore, exogenous arachidonic acid and an oxidative environment in order to produce 5-lipoxygenase products. Several thiol-reactive compounds such as N-ethylmaleimide, methyl methanethiosulfonate, azodicarboxylic acid bis[dimethylamide] (diamide) as well as hydrogen peroxide were all found to stimulate cellular leukotriene biosynthesis. Reverse transcriptase (RT)-PCR analysis demonstrated the expression of 5-lipoxygenase, 5-lipoxygenase-activating protein (FLAP) and LTA4 hydrolase mRNA in B-CLL cells. Western blot analysis demonstrated a band corresponding to the molecular size of FLAP in the B-CLL cell membrane. Furthermore, MK886, the FLAP-binding cellular leukotriene biosynthesis inhibitor, reduced both LTB4 and 5-HETE formation. Immunocytochemistry showed that 5-lipoxygenase was mainly localized in the nuclei of non-activated B-CLL cells, tonsillar B-lymphocytes and monoclonal B-cells. In contrast, neither human peripheral T-lymphocytes nor Jurkat cells were stained. These results suggest that 5-lipoxygenase and its products function in the nucleus of B-lymphocytes.