Influence of arachidonate metabolism on enhancement of intracellular transglutaminase activity in mouse peritoneal macrophages

We examined whether arachidonate metabolism exerted any influence on the enhancement of intracellular transglutaminase activity in mouse peritoneal macrophages. Enhancement of the intracellular transglutaminase activity was observed on stimulation of macrophages with normal sheep red blood cells (SRBC) or immunoglobulin G (IgG)-coated SRBC, and was inhibited by inhibitors of phospholipase A2 and cyclooxygenase. Moreover, prostaglandin E2 (PGE2), a main product of the cyclooxygenase pathway, leukotriene B4 (LTB4), a product of 5-lipoxygenase, and arachidonic acid also could directly induce high levels of intracellular transglutaminase activity without stimulation of macrophages by SRBC or IgG-coated SRBC, but leukotriene C4, prostaglandin D2, and prostacyclin were unable to induce high activity of the enzyme. Enhancement of transglutaminase activity induced by LTB4 was inhibited by cyclooxygenase inhibitor, but the enzyme activity induce by PGE2 was not inhibited. Furthermore, the quantity of PGE2 released into the culture medium of macrophages stimulated with SRBC or IgG-coated SRBC correlated well with the activity of intracellular transglutaminase in macrophages. Moreover, enhancement of transglutaminase activity by treatment of macrophages with SRBC or IgG-coated SRBC was partially suppressed by sodium benzoate, which is a scavenger of hydroxy radical. These findings suggest that arachidonate metabolism, in particular the cyclooxygenase pathway, plays an important role in the enhancement of intracellular transglutaminase activity.