Investigation On Interaction Of Class A Scavenger Receptors And Glucose Regulated Protein 78

Class A scavenger receptors(SR-A)are typeⅡtrimeric transmembrane glycoproteins mainly expressed on macrophages.A diverse group of polyanionic compounds have been identified as the ligands for SR-A.The SR-A-mediated cellular internalization of chemically modified low density lipoprotein(LDL)contributes to intracellular lipid accumulation in macrophages.The cytoplasmic domain of the receptor is responsible for highly efficient internalization of the receptor-ligand complex,cells adhesion,and the receptor expression on cell surface.Our previous studies have demonstrated that Glucose regulated protein 78(GRP78)was capable of binding to CSR-A as shown by a glutathione S-transferase-CSR-A fusion protein-based pull-down assay.In this study,immunoprecipitation tests demonstrated the specific binding of GRP78 with SR-A in cell lysates.RNA interfere expression of GRP78 resulted in an up-regulation of acLDL uptake by SR-A without altering cellular SR-A expression and binding ability.The presence of acLDL reduced binding of GRP78 to SR-A in cells and hence prompted uptake of acLDL by SR-A stably expressed HEK 293 cells,which was generated in this study.Our results suggest that GRP78 may act as an adaptor of SR-A to regulate internalization of modified LDL into macrophages.Furthermore,we identified a few proteins to bind simultaneously with SR-A and GRP78 by immunoprecipitation,two-dimensional gel electrophoresis and peptide mass fingerprinting analysis.Overexpression of GRP78 prompted SR-A-mediated secretion of TNF-αThis effect might operate via the activation of MAPK/ERK kinsase (MEK)-Extracellular regulated protein kinases(ERK)signaling pathway. Our results demonstrated that GRP78 may act as an important regulator to modulate SR-A functions in macrophages.