title: Scavenger receptor SREC-I mediated entry of TLR4 into lipid microdomains and triggered inflammatory cytokine release in RAW 264.7 cells upon LPS activation.
abstract: Scavenger receptor associated with endothelial cells I (SREC-I) was shown to be expressed in immune cells and to play a role in the endocytosis of peptides and antigen presentation. As our previous studies indicated that SREC-I required intact Toll-like receptor 4 (TLR4) expression for its functions in tumor immunity, we examined potential interactions between these two receptors. We have shown here that SREC-I became associated with TLR4 on binding bacterial lipopolysaccharides (LPS) in RAW 264.7 and HEK 293 cells overexpressing these two receptors. The receptors then became internalized together in intracellular endosomes. SREC-I promoted TLR4-induced signal transduction through the NF-kB and MAP kinase pathways, leading to enhanced inflammatory cytokine release. Activation of inflammatory signaling through SREC-I/TLR4 complexes appeared to involve recruitment of the receptors into detergent-insoluble, cholesterol-rich lipid microdomains that contained the small GTPase Cdc42 and the non-receptor tyrosine kinase c-src. Under conditions of SREC-I activation by LPS, TLR4 activity required Cdc42 as well as cholesterol and actin polymerization for signaling through NF-kB and MAP kinase pathways in RAW 264.7 cells. SREC-I appeared to respond differently to another ligand, the molecular chaperone Hsp90 that, while triggering SREC-I-TLR4 binding caused only faint activation of the NF-kB pathway. Our experiments therefore indicated that SREC-I could bind LPS and might be involved in innate inflammatory immune responses to extracellular danger signals in RAW 264.7 cells or bone marrow-derived macrophages.
authors.affiliation: Molecular and Cellular Radiation Oncology, Beth Israel Deaconess Medical Center, Harvard Medical School, Center for Life Sciences, 3 Blackfan Circle, Boston, Massachusetts, United States of America.
authors.forename: Ayesha
authors.initials: A
authors.lastname: Murshid
authors.affiliation: Stress Response Center, Boston University Medical Center, Boston, Massachusetts, United States of America.
authors.forename: Jianlin
authors.initials: J
authors.lastname: Gong
authors.affiliation: Molecular and Cellular Radiation Oncology, Beth Israel Deaconess Medical Center, Harvard Medical School, Center for Life Sciences, 3 Blackfan Circle, Boston, Massachusetts, United States of America.
authors.forename: Thomas
authors.initials: T
authors.lastname: Prince
authors.affiliation: Molecular and Cellular Radiation Oncology, Beth Israel Deaconess Medical Center, Harvard Medical School, Center for Life Sciences, 3 Blackfan Circle, Boston, Massachusetts, United States of America; School of Biosciences and Biomedical Research Institute, Pontifícia Universidade Católica do Rio Grande do Sul (PUCRS), Porto Alegre, RS, Brazil.
authors.forename: Thiago J
authors.initials: TJ
authors.lastname: Borges
authors.affiliation: Molecular and Cellular Radiation Oncology, Beth Israel Deaconess Medical Center, Harvard Medical School, Center for Life Sciences, 3 Blackfan Circle, Boston, Massachusetts, United States of America.
authors.forename: Stuart K
authors.initials: SK
authors.lastname: Calderwood
mesh_terms: D000818:Animals; D016207:Cytokines / Q000276:immunology; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D018836:Inflammation Mediators / Q000276:immunology; D008070:Lipopolysaccharides / Q000276:immunology*; D021962:Membrane Microdomains / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D020928:Mitogen-Activated Protein Kinases / Q000276:immunology; D016328:NF-kappa B / Q000276:immunology; D000067996:RAW 264.7 Cells / Q000276:immunology*; D051116:Receptors, Scavenger / Q000276:immunology*; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000276:immunology*
chemical_list: D016207:Cytokines; D018836:Inflammation Mediators; D008070:Lipopolysaccharides; D016328:NF-kappa B; D051116:Receptors, Scavenger; C000606500:SREC-I protein, mouse; D051197:Toll-Like Receptor 4; D020928:Mitogen-Activated Protein Kinases
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