ALPHA 2M-LRP-1 INDUCES ERK1/2 PHOSPHORYLATION BY INTRACELLULAR CALCIUM AND PKC ACTAVATION IN J774 CELLS

CÁCERES LC; SAHORES MM; BARCELONA PF; CHIABRANDO GA

Rosarior, Santa Fé, Republica Argentina.

Congreso; SAIB 2006 (XLII Reunión Anual de Sociedad Argentina en Bioquimica y Biologia Molecular).; 2006

Sociedad Argentina en Bioquimica y Biologia Molecular

LRP-1 is a LDL receptor gene family member synthesized and processed into 515-kDa extracelullar alpha chain and 85-kDa transmembrane and intracelullar alpha chain . LRP-1 alpha chain contains multiple ligand recognition sites and alpha chain harbors motifs for endocytosis and signaling. In addition to a₂-macroglobulin-protease complexes (a₂M*), LRP-1 also recognizes proteases and lactoferrin. The receptor-associated protein (RAP) inhibits the binding of LRP-1 ligands. Previously, we have demonstrated that a₂M* promotes cell proliferation and intracelullar calcium in J774 cells by LRP-1, but the signaling mechanisms are unknown yet. Herein we evaluate the signaling effects of a₂M* and other LRP-1 ligands. By Western blot we observed that a₂M* 60 nM promoted MAPK-ERK1/2 phosphorilation, whereas RAP and lactoferrin did not induce it. The a₂M*-induced ERK1-2-MAPK phosphorilation was inhibited by MEK-1 PD98059 inhibitor and RAP. When the J774 cells were cultured with Ca²⁺ antagonist BAPTA and the PKC Calphostin C inhibitor, the a₂M*-induced ERK1-2-MAPK phosphorilation was blocked. In conclusion, a₂M* induces ERK1-2-MAPK activation by intracellular calcium rises and PKC activation mediated by LRP-1 in J774 cells. Other LRP-1 ligands did not induce intracellular signal. Thus, the ligand recognition in the LRP-1 alpha chain might regulate and activate different downstream signaling pathways.