title: Serum amyloid A binding to CLA-1 (CD36 and LIMPII analogous-1) mediates serum amyloid A protein-induced activation of ERK1/2 and p38 mitogen-activated protein kinases.
abstract: Serum amyloid A protein (SAA) is an acute-phase reactant, known to mediate pro-inflammatory cellular responses. This study reports that CLA-1 (CD36 and LIMPII Analogous-1; human orthologue of the Scavenger Receptor Class B Type I (SR-BI)) mediates SAA uptake and downstream SAA signaling. Flow cytometry experiments revealed more than a 5-fold increase of Alexa-488 SAA uptake in HeLa cells stably transfected with CLA-1. Alexa 488-HDL uptake directly correlated with SAA uptake when determined in several CLA-1 stably transfected HeLa cell clones expressing various levels of CLA-1. SAA directly binds to CLA-1 as determined by cross-linking and colocalization of anti-CLA-1 antibody with SAA. SAA was co-internalized with transferrin to the endocytic recycling compartment pointing to a potential site of SAA metabolism. Alexa-488 SAA uptake in the CLA-1-overexpressing HeLa cells, as well as in THP-1 monocyte cell line, can be efficiently blocked by unlabeled SAA, high density lipoprotein, and other CLA-1 ligands. At the same time, markedly enhanced levels of phosphorylation of the mitogen-activated protein kinases (MAPKs), ERK1/2, and p38, were observed in cells stably transfected with CLA-1 cells following SAA stimulation when compared with mock transfected cells. The levels of the SAA-induced interleukin-8 (IL-8) secretion by CLA-1-overexpressing cells also significantly exceeded (5- to 10-fold) those detected for control cells. Synthetic amphipathic peptides possessing a structural alpha-helical motif inhibited SAA-induced activation of both MAPKs and IL-8 secretion in THP-1 cells. The results of this study demonstrate for the first time that CLA-1 functions as an endocytic SAA receptor and is involved in SAA-mediated cell signaling events associated with the immune-related and inflammatory effects of SAA.
authors.affiliation: Department of Laboratory Medicine, W. G. Magnuson Clinical Center, NHLBI, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Irina N
authors.initials: IN
authors.lastname: Baranova
authors.forename: Tatyana G
authors.initials: TG
authors.lastname: Vishnyakova
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Bocharov
authors.forename: Roger
authors.initials: R
authors.lastname: Kurlander
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Chen
authors.forename: Michael L
authors.initials: ML
authors.lastname: Kimelman
authors.forename: Alan T
authors.initials: AT
authors.lastname: Remaley
authors.forename: Gyorgy
authors.initials: G
authors.lastname: Csako
authors.forename: Fairwell
authors.initials: F
authors.lastname: Thomas
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Eggerman
authors.forename: Amy P
authors.initials: AP
authors.lastname: Patterson
mesh_terms: D020816:Amino Acid Motifs; D001665:Binding Sites; D001667:Binding, Competitive; D015153:Blotting, Western; D018955:CD36 Antigens / Q000096:biosynthesis*; D004305:Dose-Response Relationship, Drug; D004705:Endocytosis; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005434:Flow Cytometry; D005456:Fluorescent Dyes / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D006834:Hydrazines / Q000494:pharmacology; D016209:Interleukin-8 / Q000378:metabolism; D008024:Ligands; D020935:MAP Kinase Signaling System; D018613:Microscopy, Confocal; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010455:Peptides / Q000737:chemistry; D010766:Phosphorylation; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011971:Receptors, Immunologic / Q000378:metabolism*; D051116:Receptors, Scavenger; D051122:Scavenger Receptors, Class B; D000685:Serum Amyloid A Protein / Q000096:biosynthesis*; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: C417561:Alexa 488 hydrazide; D018955:CD36 Antigens; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D006834:Hydrazines; D016209:Interleukin-8; D008024:Ligands; D010455:Peptides; D011971:Receptors, Immunologic; D051116:Receptors, Scavenger; C495124:SCARB1 protein, human; D051122:Scavenger Receptors, Class B; D000685:Serum Amyloid A Protein; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases