TNF-alpha-induced NF-kappaB/RelA Ser(276) phosphorylation and enhanceosome formation is mediated by an ROS-dependent PKAc pathway

Cell Signal. 2007 Jul;19(7):1419-33. doi: 10.1016/j.cellsig.2007.01.020. Epub 2007 Jan 25.

Abstract

Tumor necrosis factor-alpha (TNF-alpha) is a potent mediator of inflammation, inducing expression of a gene network mediated by NF-kappaB. Previously we found that TNF-alpha-induced reactive oxygen species (ROS) production is required for NF-kappaB action because antioxidants inhibited TNF-alpha-inducible IL-8 expression without affecting its nuclear translocation. Here, we further investigated this ROS pathway controlling NF-kappaB/RelA dependent gene expression. We observed that TNF-alpha enhanced ROS production approximately 2-fold 20 min after stimulation and significantly increased oxidative DNA damage (8-oxoguanine lesions) over controls. Treatment with chemically unrelated antioxidants specifically inhibited expression of TNF-inducible NF-kappaB-dependent genes without producing detectable cytotoxicity or affecting GAPDH expression. We found that TNF-alpha-induced NF-kappaB/RelA Ser(276) phosphorylation, a modification critical for its transcriptional activity, was inhibited by abrogation of the ROS signaling pathway, whereas NF-kappaB/RelA Ser(536) phosphorylation was not. Interestingly, antioxidant treatment selectively inhibited TNF-alpha-induced catalytic activity of cAMP dependent protein kinase A (PKAc) but not mitogen-stress related kinase-1 (MSK1), kinases known to phosphorylate RelA at Ser(276). Using PKAc inhibitors and siRNA mediated PKAc knockdown, TNF-alpha-induced Ser(276) phosphorylation and IL-8 expression were both significantly reduced, indicating PKAc is required for RelA Ser(276) phosphorylation. Consistently, a site mutation of Rel A (Ser(276) to Ala) in RelA-deficient embryonic fibroblasts failed to activate IL-8 Luciferase activity in response to TNF-alpha. Furthermore, TNF-alpha-inducible NF-kappaB/RelA interaction with the co-activator CBP/p300, essential for enhanceosome formation, was attenuated by antioxidant treatment. Using chromatin immunoprecipitation assay (ChIP), we observed that recruitment of p300 and RNA polymerase II (Pol II) to the IL-8 promoter was also abrogated by antioxidant. These results indicate that the ROS-mediated TNF-alpha-induced IL-8 transcription is regulated by NF-kappaB/RelA phosphorylation at the critical Ser(276) residue by PKAc, resulting in stable enhanceosome formation on target genes. These studies provide insight into a novel antioxidant-sensitive pathway that can be targeted to inhibit NF-kappaB-mediated inflammation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antioxidants / metabolism
  • Cell Nucleus / drug effects
  • Cell Nucleus / metabolism
  • Cyclic AMP-Dependent Protein Kinases / metabolism*
  • Dimethyl Sulfoxide / pharmacology
  • Enzyme Activation / drug effects
  • Humans
  • Interleukin-8 / metabolism
  • Mice
  • Mitogen-Activated Protein Kinases / metabolism
  • Phosphoserine / metabolism*
  • Protein Binding / drug effects
  • Protein Transport / drug effects
  • Reactive Oxygen Species / metabolism*
  • Signal Transduction / drug effects
  • Transcription Factor RelA / metabolism*
  • Transcription, Genetic / drug effects
  • Tumor Necrosis Factor-alpha / pharmacology*
  • U937 Cells
  • p300-CBP Transcription Factors / metabolism

Substances

  • Antioxidants
  • Interleukin-8
  • Reactive Oxygen Species
  • Transcription Factor RelA
  • Tumor Necrosis Factor-alpha
  • Phosphoserine
  • p300-CBP Transcription Factors
  • Cyclic AMP-Dependent Protein Kinases
  • Mitogen-Activated Protein Kinases
  • Dimethyl Sulfoxide