title: BAG-1 interacts with the p50-p50 homodimeric NF-κB complex: implications for colorectal carcinogenesis.
abstract: Understanding the mechanisms that promote aberrant tumour cell survival is critical for the determination of novel strategies to combat colorectal cancer (CRC). We have recently shown that the anti-apoptotic protein BAG-1, highly expressed in pre-malignant and CRC tissue, can potentiate cell survival through regulating NF-κB transcriptional activity. In this study, we identify a novel complex between BAG-1 and the p50-p50 NF-κB homodimers, implicating BAG-1 as a co-regulator of an atypical NF-κB pathway. Importantly, the BAG-1-p50 complex was detected at gene regulatory sequences including the epidermal growth factor receptor (EGFR) and COX-2 (PTGS2) genes. Suppression of BAG-1 expression using small interfering RNA was shown to increase EGFR and suppress COX-2 expression in CRC cells. Furthermore, mouse embryonic fibroblasts derived from the NF-κB1 (p105/p50) knock-out mouse were used to demonstrate that p50 expression was required for BAG-1 to suppress EGFR expression. This was shown to be functionally relevant as attenuation of BAG-1 expression increased ligand activated phosphorylation of EGFR in CRC cells. In summary, this paper identifies a novel role for BAG-1 in modulating gene expression through interaction with the p50-p50 NF-κB complexes. Data presented led us to propose that BAG-1 can act as a selective regulator of p50-p50 NF-κB responsive genes in colorectal tumour cells, potentially important for the promotion of cell survival in the context of the fluctuating tumour microenvironment. As BAG-1 expression is increased in the developing adenoma through to metastatic lesions, understanding the function of the BAG-1-p50 NF-κB complexes may aid in identifying strategies for both the prevention and treatment of CRC.
authors.affiliation: School of Cellular & Molecular Medicine, University of Bristol, Bristol, UK.
authors.forename: S L
authors.initials: SL
authors.lastname: Southern
authors.forename: T J
authors.initials: TJ
authors.lastname: Collard
authors.forename: B C
authors.initials: BC
authors.lastname: Urban
authors.forename: V R
authors.initials: VR
authors.lastname: Skeen
authors.forename: H J
authors.initials: HJ
authors.lastname: Smartt
authors.forename: A
authors.initials: A
authors.lastname: Hague
authors.forename: F
authors.initials: F
authors.lastname: Oakley
authors.forename: P A
authors.initials: PA
authors.lastname: Townsend
authors.forename: N D
authors.initials: ND
authors.lastname: Perkins
authors.forename: C
authors.initials: C
authors.lastname: Paraskeva
authors.forename: A C
authors.initials: AC
authors.lastname: Williams
mesh_terms: D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic / Q000473:pathology*; D002478:Cells, Cultured; D047369:Chromatin Immunoprecipitation; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D051546:Cyclooxygenase 2 / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D024202:Electrophoretic Mobility Shift Assay; D004622:Embryo, Mammalian; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism*; D005347:Fibroblasts; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007124:Immunoenzyme Techniques; D047468:Immunoprecipitation; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000502:physiology*; D052002:NF-kappa B p50 Subunit / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D055503:Protein Multimerization; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: C091732:BCL2-associated athanogene 1 protein; D004268:DNA-Binding Proteins; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D014157:Transcription Factors; D008156:Luciferases; D051546:Cyclooxygenase 2; D066246:ErbB Receptors