Induction of cyclooxygenase-2 synthesis by ligation of the macrophage α 2-macroglobulin signalling receptor

Abstract

We have studied the induction of cyclooxygenase-2 (COX-2) in macrophages consequent to ligating the α 2-macroglobulin (α 2M) signalling receptor (α 2MSR) with receptor-recognized forms of α 2M (α 2M*). Macrophage stimulation with α 2M* increased total cellular and nuclear COX-2 two- to threefold. The maximal increase in COX-2 occurred at a ligand concentration of 50–100 pM and after 2 h. Modulation of intracellular Ca 2+ levels or incubation of [ 35S] methionine-labelled macrophages with actinomycin D, prior to treatment with α 2M*, markedly reduced the induction of total cellular and nuclear COX-2. Protein kinase C (PKC) or phospholipase A 2 (PLA 2) inhibition in α 2M*-stimulated macrophages or inhibition of the p21 ras -dependent mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI 3-kinase) signalling pathways also significantly reduced α 2M*-induced total cellular and nuclear COX-2 expression. Thus, COX-2 induction is dependent on cPLA 2 activity, Ca 2+ mobilization, and PKC activity and requires participation of both the p21 ras -dependent MAPK and PI 3-kinase signalling pathways. COX-2 activation may mediate α 2M*-induced mitogenesis, which we have previously observed in this and other cell types.