SELENIUM-DEPENDENT PEROXIDASES SUPPRESS 5-LIPOXYGENASE ACTIVITY IN B-LYMPHOCYTES AND IMMATURE MYELOID CELLS - THE PRESENCE OF PEROXIDASE-INSENSITIVE 5-LIPOXYGENASE ACTIVITY IN DIFFERENTIATED MYELOID CELLS

Differentiation of HL-60 cells by dimethylsulfoxide induces 5-lipoxyge nase protein expression, but only low cellular 5-lipoxygenase activity . Similarly, B-lymphocytes express 5-lipoxygenase protein and show act ivity in cell homogenates but not in intact cells. Hen, we demonstrate that suppression of cellular 5-lipoxygenase activity in these cell li nes is serum dependent and that the serum effect can be mimicked by se lenium. Selenium-dependent inhibition of 5-lipoxygenase activity was a lso observed in the corresponding cell homogenates or 100000 x g super natants when dithiothreitol or glutathione (GSH) was added. The proper ties of the endogenous selenium-dependent inhibitor, i.e. molecular ma ss, utilization of GSH and dithiothreitol as substrates, sensitivity t o iodacetate, inhibition of 5-lipoxygenase activity in the presence of the GPx-1 inhibitor mercaptosuccinate, suggest that a selenoenzyme wi th properties of the phospholipid hydroperoxide glutathione peroxidase (GPx-4) is responsible for the 5-lipoxygenase inhibition in BL41-E95- A and immature HL-60 cells. Differentiation of HL-60 cells in the pres ence of 1,25-dihydroxyvitamin D-3 and transforming growth factor-beta (TGF beta) upregulated cellular 5-lipoxygenase activity regardless of whether the cells were grown with or without serum or selenium. Also, 5-lipoxygenase activity in homogenates or 100000 x g supernatants of 1 ,25-dihydroxyvitamin D-3/TGF beta differentiated HL-60 cells and of hu man granulocytes was not inhibited by dithiothreitol or GSH. Thus, aft er 1,25-dihydroxyvitamin D-3/TGF beta differentiation HL-60 cells rese mble normal granulocytes with respect to the high 5-lipoxygenase activ ity in intact cells and to the dithiothreitol effects in broken cell p reparations. Combination experiments with 100000 x g supernatants of B L41-E95-A cells and neutrophils revealed that the high 5-lipoxygenase activity of granulocytes is due to stability of the 5-lipoxygenase cat alytic activity against selenium-dependent peroxidases, but not to low peroxidase activity. Our data suggest that the capability of mature m yeloid cells to release large amounts of leukotrienes after stimulatio n is due to a peroxidase-insensitive 5-lipoxygenase catalytic activity .