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: Meidi Gu, Chuan Ouyang, Wenlong Lin, Ting Zhang, Xuetao Cao, Zongping Xia, Xiaojian Wang
• Journal: Journal of immunology (Baltimore, Md. : 1950) (J Immunol) Vol. 192 Issue 6 Pg. 2846-56 (Mar 15 2014) ISSN: 1550-6606 [Electronic] United States
• PMID: 24534530 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Furans
• Holoenzymes
• Interleukin-6
• Lipids
• NF-kappa B
• Toll-Like Receptors
• Tumor Necrosis Factor-alpha
• tautomycetin
• Serine
• Mitogen-Activated Protein Kinases
• MAP Kinase Kinase Kinases
• MAP kinase kinase kinase 7
• Ppp1r15a protein, mouse
• Protein Phosphatase 1

Topics

• Animals
• Cell Line
• Cells, Cultured
• Furans (pharmacology)
• HEK293 Cells
• HeLa Cells
• Holoenzymes (genetics, immunology, metabolism)
• Humans
• Interleukin-6 (genetics, immunology, metabolism)
• Lipids (pharmacology)
• MAP Kinase Kinase Kinases (genetics, immunology, metabolism)
• Macrophages (drug effects, immunology, metabolism)
• Mice
• Mice, Inbred C57BL
• Mice, Knockout
• Mitogen-Activated Protein Kinases (immunology, metabolism)
• Models, Immunological
• Mutation (immunology)
• NF-kappa B (immunology, metabolism)
• Phosphorylation (immunology)
• Protein Phosphatase 1 (genetics, immunology, metabolism)
• RNA Interference
• Serine (genetics, immunology, metabolism)
• Signal Transduction (immunology)
• Toll-Like Receptors (immunology, metabolism)
• Tumor Necrosis Factor-alpha (genetics, immunology, metabolism)