title: Endotoxin Tolerance Inhibits Lyn and c-Src Phosphorylation and Association with Toll-Like Receptor 4 but Increases Expression and Activity of Protein Phosphatases.
abstract: Endotoxin tolerance protects the host by limiting excessive 'cytokine storm' during sepsis, but compromises the ability to counteract infections in septic shock survivors. It reprograms Toll-like receptor (TLR) 4 responses by attenuating the expression of proinflammatory cytokines without suppressing anti-inflammatory and antimicrobial mediators, but the mechanisms of reprogramming remain unclear. In this study, we demonstrate that the induction of endotoxin tolerance in human monocytes, THP-1 and MonoMac-6 cells inhibited lipopolysaccharide (LPS)-mediated phosphorylation of Lyn, c-Src and their recruitment to TLR4, but increased total protein phosphatase (PP) activity and the expression of protein tyrosine phosphatase (PTP) 1B, PP2A, PTP nonreceptor type (PTPN) 22 and mitogen-activated protein kinase phosphatase (MKP)-1. Chemical PP inhibitors, okadaic acid, dephostatin and cantharidic acid markedly decreased or completely abolished LPS tolerance, indicating the importance of phosphatases in endotoxin tolerization. Overexpression of PTPN22 decreased LPS-mediated nuclear factor (NF)-x03BA;B activation, p38 phosphorylation and CXCL8 gene expression, while PTPN22 ablation upregulated LPS-induced p65 NF-x03BA;B and p38 phosphorylation and the expression of TNF-α and pro-IL-1β mRNA, indicating PTPN22 as an inhibitor of TLR4 signaling. Thus, LPS tolerance interferes with TLR4 signaling by inhibiting Lyn and c-Src phosphorylation and their recruitment to TLR4, while increasing the phosphatase activity and expression of PP2A, PTPN22, PTP1B and MKP1.
authors.affiliation: Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Md., USA.
authors.forename: Yanbao
authors.initials: Y
authors.lastname: Xiong
authors.forename: Michael
authors.initials: M
authors.lastname: Murphy
authors.forename: Tissa T
authors.initials: TT
authors.lastname: Manavalan
authors.forename: Goutham
authors.initials: G
authors.lastname: Pattabiraman
authors.forename: Fu
authors.initials: F
authors.lastname: Qiu
authors.forename: Hui-Hsin
authors.initials: HH
authors.lastname: Chang
authors.forename: I-Cheng
authors.initials: IC
authors.lastname: Ho
authors.forename: Andrei E
authors.initials: AE
authors.lastname: Medvedev
mesh_terms: D000081247:CSK Tyrosine-Protein Kinase; D045744:Cell Line, Tumor; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects* / Q000276:immunology; D006801:Humans; D007108:Immune Tolerance / Q000187:drug effects* / Q000235:genetics; D008070:Lipopolysaccharides / Q000276:immunology / Q000494:pharmacology*; D009000:Monocytes / Q000276:immunology*; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000276:immunology*; D015398:Signal Transduction / Q000187:drug effects* / Q000235:genetics / Q000276:immunology; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000276:immunology*; D019061:src-Family Kinases / Q000235:genetics / Q000276:immunology*
chemical_list: D008070:Lipopolysaccharides; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D000081247:CSK Tyrosine-Protein Kinase; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; C000631346:CSK protein, human; D010749:Phosphoprotein Phosphatases