title: NF-κB suppresses HIF-1α response by competing for P300 binding.
abstract: Hypoxia has emerged as a key determinant of osteogenesis. HIF-1α is the transcription factor mediating hypoxia responses that include induction of VEGF and related bone induction. Inflammatory signals antagonize bone repair via the NF-κB pathway. The present investigation explored the functional relationship of hypoxia (HIF-1α function) and inflammatory signaling (NF-κB) in stem like and osteoprogenitor cell lines. The potential interaction between HIF-1α and NF-κB signaling was explored by co-transfection studies in hFOB with p65, HIF-1α and 9x-HRE-luc or HIF-1α target genes reporter plasmids. Nuclear cross-talk was directly tested using the mammalian Gal4/VP16 two-hybrid, and confirmed by co-immunoprecipitation/western blotting assays. The results show that inflammatory stimulation (TNF-α treatment) causes a marked inhibition of HIF-1α function at the HRE in all cell lines studied. Also, co-transfection with p65 expression vector leads to reduced hVEGFp transcription after DFO-induced hypoxia. However, TNF-α treatment had little effect on HIF-1α mRNA levels. The functional interaction of Gal4-HIF-1α and VP16-p300 fusion proteins is effectively blocked by expression of p65 in a dose dependent manner. It was concluded that NF-κB-mediated inflammatory signaling is able to block HIF-1α transactivation at HRE-encoding genes by direct competition for p300 binding at the promoter. Inflammation may influence the stem cell niche and tissue regeneration by influencing cellular responses to hypoxia.
authors.affiliation: Universidade Católica de Brasília, Pós-Graduação em Ciências Genômicas e Biotecnologia, SGAN Quadra 916, Av. W5 Norte, 70790-160 Brasília, DF, Brazil.
authors.forename: Daniela B S
authors.initials: DB
authors.lastname: Mendonça
authors.forename: Gustavo
authors.initials: G
authors.lastname: Mendonça
authors.forename: Francisco J L
authors.initials: FJ
authors.lastname: Aragão
authors.forename: Lyndon F
authors.initials: LF
authors.lastname: Cooper
mesh_terms: D015687:Cell Hypoxia / Q000235:genetics; D002460:Cell Line; D050881:E1A-Associated p300 Protein / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D007249:Inflammation / Q000235:genetics; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D010012:Osteogenesis / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D051996:Transcription Factor RelA / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics*
chemical_list: D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D016328:NF-kappa B; D012333:RNA, Messenger; D051996:Transcription Factor RelA; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; C496319:NOS2 protein, human; D052247:Nitric Oxide Synthase Type II; D050881:E1A-Associated p300 Protein; C494360:EP300 protein, human