LDL receptor-related protein (LRP1) is a LDL receptor gene family member synthesized and processed into 515-kDa extracellular α chain and 85-kDa trans-membrane and intracellular β chain. LRP-1 α chain contains multiple ligand recognition sites and β chain harbor motifs for endocytosis and intracellular signaling events. α2-macroglobulin-protease complex (α2M*) is recognized by LRP1. Previously we demonstrated that α2M* induces cell proliferation and intracellular MAPK activation. However, the molecular mechanisms that promote this intracellular signaling activation are, at the present, unknown. Herein, we evaluate the putative participation of PKC enzymes and intracellular calcium rise on the α2M*-induced MAPK activation in two macrophage-derived cell lines, J774 and RAW 264.7. By Western blot we observed that calphostin-C blocks ERK1/2 phosphorylation in J774 and RAW 264.7 cells. To know the type of PKC involved, different inhibitors of PKC isoenzymes were used, such as RO-32-0432, GÖ-6976 and rottlerin. We demonstrated that the α2M*-induced ERK1/2 phosphorylation was inhibited by PKCα and PKC αβI inhibitors, respectively. When J774 and RAW 264.7 were incubated with BAPTA-AM, the α2M*-induced ERK1/2 phosphorilation was also fully blocked. Our data demonstrate that α2M*-induced MAPK phosphorylation is mediated by PKCα/αβI activation and intracellular calcium mobilization.
