Ligation of Cell Surface-Associated Glucose-Regulated Protein 78 by Receptor-Recognized Forms of α2-Macroglobulin: Activation of p21-Activated Protein Kinase-2-Dependent Signaling in Murine Peritoneal Macrophages

Abstract

Previous studies of the plasma proteinase inhibitor α2-macroglobulin (α2M) demonstrated that α2M-proteinase complexes (α2M*) modulate immune responses and promotes macrophage locomotion and chemotaxis. α2M* binds to cell surface-associated glucose-regulated protein 78 (GRP78), which activates downstream signaling events. The role of p21-activated protein kinase-1 and -2 (PAK-1 and -2) in promoting cellular motility is well documented. In the current study, we examined the ability of α2M* to activate PAK-1 and PAK-2. Upon macrophage stimulation with α2M*, PAK-2 is autophosphorylated, resulting in increased kinase activity; however, PAK-1 is negligibly affected. α2M*-stimulated macrophages showed a marked elevation in the levels of Rac·GTP. Receptor tyrosine phosphorylation upon binding of α2M* to GRP78, recruits PAK-2 to the plasma membrane via the adaptor protein NCK. Consistent with this hypothesis, silencing of GRP78 gene expression greatly attenuated the levels of membrane-associated PAK-2 and NCK. PAK-2 activity was markedly decreased by inhibition of tyrosine kinases and PI3K before α2M* stimulation. We further demonstrate that phosphorylation of Lin-11, Isl-1, Mec-3 (LIM) kinase and cofilin is promoted by treating macrophages with α2M*. Thus, α2M* regulates activation of the PAK-2-dependent motility mechanism in these cells.

Visceral Adipose Tissue-derived Serine Proteinase Inhibitor Inhibits Apoptosis of Endothelial Cells as a Ligand for the Cell-Surface GRP78/Voltage-dependent Anion Channel Complex

“…In many tumor cells, α2M binds to cell-surface GRP78/ MTJ-1, activates phosphatidylinositol 3-kinase/Akt signal to suppress apoptotic pathways, concomitantly upregulates nuclear factor-κB, and induces unfolded protein response so that cell proliferation occurs. [24][25][26][27] In addition to α2M, teratocarcinoma-derived growth factor-1 (Cripto) and GRP78 form a complex at the cell surface and enhance the cell growth by inhibiting transforming growth factor-β signaling events. 21 Truncated cadherin and GRP78 exert the activation of Akt and promote the survival of vascular endothelial cells.…”

GRP78/BiP Is Required for Cell Proliferation and Protecting the Inner Cell Mass from Apoptosis during Early Mouse Embryonic Development

“…The recent discovery of GRP78 in the cell surface of stimulated endothelial cells and tumor cells and its require- on May 12, 2018 by guest http://mcb.asm.org/ ment for ligand activities further suggests a critical and novel role of GRP78 in cell surface receptor signaling pathways (1,4,7,36). Despite these advances, little is known about the physiological role that GRP78 plays in development.…”

Heme Degradation and Vascular Injury

“…Thus, haptoglobin and hemopexin have significant antioxidant properties by binding plasma hemoglobin and free heme and preventing heme release of redox-active iron. In addition, CD91-heme-hemopexin receptor complexes are able to induce intra-and extracellular antioxidant activities (99). HO-1, transferrin, transferrin receptor, and ferritin are all regulated to some degree by the binding of heme-hemopexin complexes to the CD91 receptor (144).…”