title: Phosphatase holoenzyme PP1/GADD34 negatively regulates TLR response by inhibiting TAK1 serine 412 phosphorylation.
abstract: The molecular mechanisms that fine tune TLRs responses need to be fully elucidated. Protein phosphatase-1 (PP1) has been shown to be important in cell death and differentiation. However, the roles of PP1 in TLR-triggered immune response remain unclear. In this study, we demonstrate that PP1 inhibits the activation of the MAPK and NF-κB pathway and the production of TNF-α, IL-6 in macrophages triggered by TLR3, TLR4, and TLR9 in a phosphatase-dependent manner. Conversely, PP1 knockdown increases TLRs-triggered signaling and proinflammatory cytokine production. Tautomycetin, a specific inhibitor of PP1, aggravates LPS-induced endotoxin shock in mice. We further demonstrate that PP1 negatively regulates TLR-triggered signaling by targeting TGF-β-activated kinase 1 (TAK1) serine 412 (Ser412) phosphorylation, which is required for activation of TAK1-mediated IL-1R and TLR signaling. Mutation of TAK1 Serine 412 to alanine (S412A) significantly inhibits TLR/IL-1R-triggered NF-κB and MAPK activation and induction of proinflammatory cytokines in macrophage and murine embryonic fibroblast cells. DNA damage-inducible protein 34 (GADD34) specifies PP1 to dephosphorylate TAK1 at Ser412. GADD34 depletion abolished the interaction between TAK1 and PP1, and it relieved PP1 overexpression-induced inhibition of TLRs signaling and proinflammatory cytokine production. In addition, knockdown of GADD34 significantly promotes TLR-induced TAK1 Ser412 phosphorylation, downstream NF-κB and MAPK activation, and proinflammatory cytokine production. Therefore, PP1, as a physiologic inhibitor, together with its regulatory subunit GADD34, tightly controls TLR-induced TAK1 Ser412 phosphorylation, preventing excessive activation of TLRs and protecting the host from overwhelmed inflammatory immune responses.
authors.affiliation: Institute of Immunology, School of Medicine, Zhejiang University, Hangzhou 310058, China.
authors.forename: Meidi
authors.initials: M
authors.lastname: Gu
authors.forename: Chuan
authors.initials: C
authors.lastname: Ouyang
authors.forename: Wenlong
authors.initials: W
authors.lastname: Lin
authors.forename: Ting
authors.initials: T
authors.lastname: Zhang
authors.forename: Xuetao
authors.initials: X
authors.lastname: Cao
authors.forename: Zongping
authors.initials: Z
authors.lastname: Xia
authors.forename: Xiaojian
authors.initials: X
authors.lastname: Wang
mesh_terms: D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D005663:Furans / Q000494:pharmacology; D057809:HEK293 Cells; D006367:HeLa Cells; D020035:Holoenzymes / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D006801:Humans; D015850:Interleukin-6 / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D008055:Lipids / Q000494:pharmacology; D020930:MAP Kinase Kinase Kinases / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D008264:Macrophages / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D020928:Mitogen-Activated Protein Kinases / Q000276:immunology / Q000378:metabolism; D018448:Models, Immunological; D009154:Mutation / Q000276:immunology; D016328:NF-kappa B / Q000276:immunology / Q000378:metabolism; D010766:Phosphorylation / Q000276:immunology; D054645:Protein Phosphatase 1 / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D034622:RNA Interference; D012694:Serine / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D015398:Signal Transduction / Q000276:immunology*; D051193:Toll-Like Receptors / Q000276:immunology* / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D000099151:MAP Kinase Kinase Kinase 7
chemical_list: D005663:Furans; D020035:Holoenzymes; D015850:Interleukin-6; D008055:Lipids; D020930:MAP Kinase Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D016328:NF-kappa B; D054645:Protein Phosphatase 1; D012694:Serine; D051193:Toll-Like Receptors; D014409:Tumor Necrosis Factor-alpha; D000099151:MAP Kinase Kinase Kinase 7; C058744:tautomycetin; C513256:Ppp1r15a protein, mouse