title: Phosphoinositide-dependent kinase-1 inhibits TRAF6 ubiquitination by interrupting the formation of TAK1-TAB2 complex in TLR4 signaling.
abstract: Phosphoinositide-dependent protein kinase 1 (PDK1) plays a key role in the phosphoinositide 3-kinase (PI3K)-PDK1-Akt pathway that induces cell survival and cardiovascular protections through anti-apoptosis, vasodilation, anti-inflammation, and anti-oxidative stress activities. Although several reports have proposed the negative role of PDK1 in Toll-like receptor 4 (TLR4) signaling, the molecular mechanism is still unknown. Here we show that PDK1 inhibits tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6) ubiquitination by interrupting the complex between transforming growth factor beta-activated kinase 1 (TAK1) and TAK1 binding protein 2 (TAB2), which negatively regulates TAK1 activity. The overexpression of PDK1 in 293/TLR4 cells resulted in suppressions of nuclear factor kappa B (NF-κB) activation and production of proinflammatory cytokines including interleukin (IL)-6 and TNF-α in response to lipopolysaccharide stimulation. Conversely, THP-1 human monocytes transiently cultured in low glucose medium displayed down-regulated PDK1 expression, and significantly enhanced TLR4-mediated signaling for the activation of NF-κB, demonstrating a negative role of PDK1. Biochemical studies revealed that PDK1 significantly interacted with TAK1, resulting in the inhibition of the association of TAB2 with TAK1, which led to the attenuation of TRAF6 ubiquitination. Moreover, PDK1-knockdown THP-1 cells displayed enhancement of downstream signals, activation of NF-κB, and increased production of pro-inflammatory cytokines IL-6, IL-1β, and TNF-α, which potentially led to the up-regulation of NF-κB-dependent genes in response to TLR4 stimulation. Collectively, the results demonstrate that PDK1 inhibits the formation of the TAK1-TAB2-TRAF6 complex and leads to the inhibition of TRAF6 ubiquitination, which negatively regulates the TLR4-mediated signaling for NF-κB activation.
authors.affiliation: Department of Molecular Cell Biology and Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea.
authors.forename: Gyuyoung
authors.initials: G
authors.lastname: Moon
authors.affiliation: Department of Molecular Cell Biology and Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea.
authors.forename: Juhong
authors.initials: J
authors.lastname: Kim
authors.affiliation: Department of Molecular Cell Biology and Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea.
authors.forename: Yoon
authors.initials: Y
authors.lastname: Min
authors.affiliation: Department of Molecular Cell Biology and Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea.
authors.forename: Sae Mi
authors.initials: SM
authors.lastname: Wi
authors.affiliation: Department of Pathology and Laboratory Medicine, Weill Cornell Medical College, New York, NY 10065, USA.
authors.forename: Jae-Hyuck
authors.initials: JH
authors.lastname: Shim
authors.affiliation: Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, MA 02115, USA; Department of Medicine, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Eunyoung
authors.initials: E
authors.lastname: Chun
authors.affiliation: Department of Molecular Cell Biology and Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea. Electronic address: thylee@skku.edu.
authors.forename: Ki-Young
authors.initials: KY
authors.lastname: Lee
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D004789:Enzyme Activation; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D006801:Humans; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D011485:Protein Binding; D060066:Protein Interaction Maps; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D015398:Signal Transduction; D048029:TNF Receptor-Associated Factor 6 / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D054875:Ubiquitination; D000099151:MAP Kinase Kinase Kinase 7
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D020930:MAP Kinase Kinase Kinases; D016328:NF-kappa B; D017346:Protein Serine-Threonine Kinases; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D048029:TNF Receptor-Associated Factor 6; D051197:Toll-Like Receptor 4; D000099151:MAP Kinase Kinase Kinase 7; C000631429:PDK1 protein, human; C410585:TAB2 protein, human; C495345:TLR4 protein, human
keywords: PDK1; TAB2; TAK1; TLR4; TRAF6; Ubiquitination