STUDIES ON THE REGULATION AND LOCALIZATION OF 5-LIPOXYGENASE IN HUMANB-LYMPHOCYTES

Stimulated B-lymphocytes, isolated from patients with chronic lymphocy tic leukemia of B-cell type (B-CLL cells) or from human tonsils, produ ced similar amounts of leukotriene (LT) B-4 and 5-hydroxyeicosatetraen oic acid (5-HETE) as polymorphonuclear granulocytes. Unlike intact gra nulocytes or monocytes, human B-lymphocytes require calcium ionophore, exogenous arachidonic acid and an oxidative environment in order to p roduce 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 fo und to stimulate cellular leukotriene biosynthesis. Reverse transcript ase (RT)-PCR analysis demonstrated the expression of 5-lipoxygenase, 5 -lipoxygenase-activating protein (FLAP) and LTA(4) 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, M K886, the FLAP-binding cellular leukotriene biosynthesis inhibitor, re duced both LTB(4) and 5-HETE formation. Immunocytochemistry showed tha t 5-lipoxygenase was mainly localized in the nuclei of non-activated B -CLL cells, tonsillar B-lymphocytes and monoclonal B-cells. In contras t, neither human peripheral T-lymphocytes nor Jurkat cells were staine d. These results suggest that 5-lipoxygenase and its products function in the nucleus of B-lymphocytes.