title: Regulation of signal transducer and activator of transcription 3 enhanceosome formation by apurinic/apyrimidinic endonuclease 1 in hepatic acute phase response.
abstract: The signal transducer and activator of transcription-3 (STAT3) is a latent IL-6 inducible transcription factor that mediates hepatic and vascular inflammation. In this study, we make the novel observation that STAT3 forms an inducible complex with the apurinic/apyrimidinic endonuclease 1 (APE1)/redox effector factor-1 (APE1/Ref-1), an essential multifunctional protein in DNA base excision repair, and studied the role of APE1/Ref-1 in STAT3 function. Using a transfection-coimmunoprecipitation assay, we observed that APE1 selectively binds the NH(2)-terminal acetylation domain of STAT3. Ectopic expression of APE1 potentiated inducible STAT3 reporter activity, whereas knockdown of APE1 resulted in reduced IL-6-inducible acute-phase reactant protein expression (C-reactive protein and serum amyloid P) and monocyte chemotactic protein-1 expression. The mechanism for APE1 requirement in IL-6 signaling was indicated by reduced STAT3 DNA binding activity observed in response to small interfering RNA-mediated APE1 silencing. Consistent with these in vitro studies, we also observed that lipopolysaccharide-induced activation of acute-phase reactant protein expression is significantly abrogated in APE1 heterozygous mice compared with wild-type mice. IL-6 induces both STAT3 and APE1 to bind the suppressor of cytokine signaling-3 and gamma-fibrionogen promoters in their native chromatin environment. Moreover, we observed that APE1 knockdown destabilized formation of the STAT3-inducible enhanceosome on the endogenous gamma-fibrionogen promoter. Taken together, our study indicates that IL-6 induces a novel STAT3-APE1 complex, whose interaction is required for stable chromatin association in the IL-6-induced hepatic acute phase response.
authors.affiliation: Department of Internal Medicine and the Sealy Center for Molecular Medicine, University of Texas Medical Branch, Galveston, Texas 77555-1060, USA. suray@utmb.edu
authors.forename: Sutapa
authors.initials: S
authors.lastname: Ray
authors.forename: Chang
authors.initials: C
authors.lastname: Lee
authors.forename: Tieying
authors.initials: T
authors.lastname: Hou
authors.forename: Kishor K
authors.initials: KK
authors.lastname: Bhakat
authors.forename: Allan R
authors.initials: AR
authors.lastname: Brasier
mesh_terms: D000209:Acute-Phase Proteins / Q000235:genetics / Q000378:metabolism; D000210:Acute-Phase Reaction / Q000139:chemically induced / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D018932:Chemokine CCL2 / Q000235:genetics / Q000378:metabolism; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D004742:Enhancer Elements, Genetic / Q000187:drug effects; D005340:Fibrinogen / Q000235:genetics; D055785:Gene Knockdown Techniques / Q000379:methods; D016762:Genes, fos / Q000187:drug effects; D056945:Hep G2 Cells; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D011401:Promoter Regions, Genetic / Q000187:drug effects; D054730:Protein Interaction Domains and Motifs; D012319:RNA Polymerase II / Q000378:metabolism; D034741:RNA, Small Interfering; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000235:genetics; D050880:p300-CBP Transcription Factors / Q000378:metabolism
chemical_list: D000209:Acute-Phase Proteins; D018932:Chemokine CCL2; D004268:DNA-Binding Proteins; D015850:Interleukin-6; D034741:RNA, Small Interfering; D050796:STAT3 Transcription Factor; C491411:Socs3 protein, mouse; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D005340:Fibrinogen; D050880:p300-CBP Transcription Factors; D012319:RNA Polymerase II; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase