Activity and protein distribution of 12-lipoxygenase in HEL cells: Induction of membrane-association by phorbol ester TPA, modulation of activity by glutathione and 13-HPODE, and Ca 2+-dependent translocation to membranes

Abstract

The understanding of the intracellular regulation of 12-lipoxygenase requires a knowledge of the distribution of both enzyme protein and its activity. In human erythroleukemia cells, the membrane fraction contains about 90% of the total cellular 12-lipoxygenase activity, whereas only approximately 10% of 12-lipoxygenase activity resides in the cytosol. However, the majority of the cellular 12-lipoxygenase protein is found in the cytosol. Pretreatment of cells for 0–3 days with 160 nM TPA caused a marked, time-dependent increase in membrane-bound 12-lipoxygenase activity and protein, respectively. In contrast, the cytosolic amount of 12-lipoxygenase protein and activity, respectively, were minimally altered by this TPA treatment. Recombining the active membrane fraction with cytosol resulted in no significant inhibition of its 12-lipoxygenase activity, but the addition of GSH to the membrane fraction inhibited 12-lipoxygenase activity in a dose-dependent manner. On the other hand, the cytosolic enzyme can be rendered active in the presence of 1 μM 13-hydroperoxyoctadecadienoic acid. In HEL cell homogenates, a partial translocation of the cytosolic enzyme to the membrane takes place in a Ca 2+-dependent manner, resulting in an increase in membrane-associated 12-lipoxygenase activity and a concomitant decrease in cytosolic 12-lipoxygenase activity above 0.1 μM Ca 2+.