title: Toll-like receptor 4/spleen tyrosine kinase complex in high glucose signal transduction of proximal tubular epithelial cells.
abstract: OBJECTIVE
  High glucose activates spleen tyrosine kinase (Syk) in human proximal tubular epithelial cells (HK-2 cells), which leads to NF-κB activation and transforming growth factor-β1 (TGF-β1) production. We explored the signal transduction pathway from high glucose to Syk activation.
  
  
  METHODS
  The pathway was evaluated by siRNA transfection, immunoprecipitation and Western blot.
  
  
  RESULTS
  High glucose stimulated Syk activation within 10 min. Depletion of toll-like receptor 4 (TLR4) attenuated high glucose-induced Syk activation, NF-κB p65 nuclear translocation, and TGF-β1 production. In addition, TLR4 inhibitor (CLI-095), TLR4-neutralizing antibody, and depletion of myeloid differentiation factor 88 (MyD88) all attenuated high glucose-induced Syk activation. As an evidence of TLR4 activation, interleukin-1 receptor-associated kinase 1 was recruited to MyD88 and TLR4 upon exposure to high glucose. Syk was co-immunoprecipitated with TLR4, and Syk bound to TLR4 was activated by high glucose. High-mobility group box-1 (HMGB-1), an endogenous activator of TLR4, rapidly increased in TLR4 immunoprecipitates upon high glucose stimulation, and this association was reduced by N-acetylcysteine, an antioxidant. An HMGB-1 inhibitor glycyrrhizin suppressed high glucose-induced Syk activation.
  
  
  CONCLUSIONS
  Syk is constitutively associated with TLR4. High glucose induces an immediate, reactive oxygen species-dependent, extracellular release of HMGB-1 which binds to TLR4 and activates it, leading to Syk activation.
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Asan Medical Center, College of Medicine, University of Ulsan, Seoul, Korea.
authors.forename: Won Seok
authors.initials: WS
authors.lastname: Yang
authors.forename: Joon-Seok
authors.initials: JS
authors.lastname: Kim
authors.forename: Nam Jeong
authors.initials: NJ
authors.lastname: Han
authors.forename: Mee Jeong
authors.initials: MJ
authors.lastname: Lee
authors.forename: Su-Kil
authors.initials: SK
authors.lastname: Park
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D019695:Glycyrrhizic Acid / Q000494:pharmacology; D006801:Humans; D053592:Interleukin-1 Receptor-Associated Kinases / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D053594:Myeloid Differentiation Factor 88 / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D000072377:Syk Kinase; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D051996:Transcription Factor RelA / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000378:metabolism
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D053594:Myeloid Differentiation Factor 88; D017382:Reactive Oxygen Species; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D051996:Transcription Factor RelA; D053773:Transforming Growth Factor beta1; D019695:Glycyrrhizic Acid; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D053592:Interleukin-1 Receptor-Associated Kinases; D005947:Glucose; D000111:Acetylcysteine