Macrophages play a key role in atherosclerosis involving an increased production of extracellular matrix metalloproteinase-9 (MMP-9). LRP1 is a LDL receptor gene family member constituted by a 515-kDa extracelullar á chain and 85-kDa transmembrane and intracelullar â chain. LRP1 á chain contains multiple ligand recognition sites and â chain harbors motifs for endocytosis and intracellular signalling events. a2-macroglobulin-protease complexes (a2M*) is recognized by LRP1 and its binding is inhibited by RAP. Previously, we have demonstrated that á2M*/LRP1 interaction promotes cell proliferation mediated by intracelullar Ca2+ mobilization, MAPK-ERK1/2 phosphorylation and PKC activation in J774 cells. In this work we investigated whether the á2M*/LRP1-activated intracellular signaling events modify the MMP-9 synthesis in J774 macrophage-derived cell line. By Western blot we observed that a2M* 20 nM promoted MAPK-ERK1/2 phosphorilation, which was inhibited by PD98059, RAP, BAPTA and Calphostin C. By RT-PCR we showed that a2M* induced MMP-9 mRNA expression. By zymography we demonstrated that a2M* increased activity of MMP-9 in conditioned medium of J774 cells incubated with a2M*. The a2M-induced MMP-9 synthesis was abolished by the presence of PD98059, RAP, BAPTA and Calphostin C. Thus, the á2M*/LRP1 interaction increases MMP-9 synthesis mediated by intracellular signaling activation.
