Cytosolic Phospholipase A2 Activity Associated with Nuclei Is Not Inhibited by Arachidonyl Trifluoromethyl Ketone in Macrophages Stimulated with Receptor-Recognized Forms of α2-Macroglobulin

We have studied the translocation of cytosolic phospholipase A2 (cPLA2) to nuclei in macrophages stimulated with receptor-recognized forms of α2-macroglobulin (α2M*). Translocation of phosphorylated cPLA2 to nuclei was determined by immunoprecipitation of cPLA2 in 32Pi-labeled cells. The identity of cPLA2 was established by comparing its mobility on gels with an authentic cPLA2 standard. cPLA2 activity was quantified by measuring the release of [14C]arachidonic acid from the substrate 1-palmitoyl-2-[1-14C]arachidonyl-sn-glycerophosphatidylcholine. α2M* caused a two- to threefold increase in cPLA2 phosphorylation and its translocation to nuclei. The p38 MAPK inhibitor SB203580, PKC inhibitor chelerythrin, or depletion of intracellular Ca2+ profoundly decreased cPLA2 activity in nuclei isolated from agonist-stimulated cells. The requirement for Ca2+, PKC, and p38 MAPK activation appears to be of major importance for nuclear cPLA2 activity. In contrast to cellular cPLA2 activity, nuclear cPLA2 activity was not inhibited by arachidonyl trifluoromethyl ketone (AACOCF3) in agonist-stimulated cells. It is concluded that the association of cPLA2 with nuclear membranes in agonist-stimulated cells modifies the activity and the sensitivity of the enzyme to inhibition by AACOCF3 in this phospholipid environment.