title: BAG-1 suppresses expression of the key regulatory cytokine transforming growth factor β (TGF-β1) in colorectal tumour cells.
abstract: As colorectal cancer remains the second highest cause of cancer-related deaths in much of the industrialised world, identifying novel strategies to prevent colorectal tumour development remains an important challenge. BAG-1 is a multi-functional protein, the expression of which is up-regulated at relatively early stages in colorectal tumorigenesis. Importantly, BAG-1 is thought to enhance colorectal tumour progression through promoting tumour cell survival. Here, we report for the first time a novel role for BAG-1, establishing it as a suppressor of transforming growth factor β (TGF-β1) expression in colorectal tumour cells. Microarray analysis first highlighted the possibility that BAG-1 may regulate TGF-β1 expression, a key cytokine in normal colonic tissue homoeostasis. Q-RT-PCR and ELISA demonstrated TGFB1 mRNA and protein expression to be significantly increased when BAG1 levels were reduced by small interfering RNA; additionally, induction of BAG-1L caused suppression of TGFB1 mRNA in colorectal tumour cells. Using reporter and chromatin immunoprecipitation assays, a direct association of BAG-1 with the TGFB1 gene regulatory region was identified. Immunohistochemistry and Weiser fraction data indicated that the levels of BAG-1 and TGF-β1 are inversely correlated in the normal colonic epithelium in vivo, consistent with a role for BAG-1-mediated repression of TGF-β1 production. In vitro studies showed that the change in TGF-β1 production following manipulation of BAG-1 is functionally relevant; through induction of anchorage-independent growth in TGF-β1-dependent normal rat kidney fibroblasts and regulation of SMAD2 phosphorylation in TGF-β1-sensitive adenoma cells. Taken together, this study identifies the anti-apoptotic protein BAG-1 as a suppressor of the inhibitory growth factor TGF-β1, suggesting that high expression of BAG-1 can impact on a number of the hallmarks of cancer, of potential importance in promoting the early stages of colorectal tumorigenesis. Establishing BAG-1 as a repressor of TGF-β1 has important biological implications, and highlights a new role for BAG-1 in colorectal tumorigenesis.
authors.affiliation: School of Cellular and Molecular Medicine, University of Bristol, Bristol, UK.
authors.forename: V R
authors.initials: VR
authors.lastname: Skeen
authors.forename: T J
authors.initials: TJ
authors.lastname: Collard
authors.forename: S L
authors.initials: SL
authors.lastname: Southern
authors.forename: A
authors.initials: A
authors.lastname: Greenhough
authors.forename: A
authors.initials: A
authors.lastname: Hague
authors.forename: P A
authors.initials: PA
authors.lastname: Townsend
authors.forename: C
authors.initials: C
authors.lastname: Paraskeva
authors.forename: A C
authors.initials: AC
authors.lastname: Williams
mesh_terms: D002277:Carcinoma / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008954:Models, Biological; D011485:Protein Binding; D012045:Regulatory Sequences, Nucleic Acid; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D053773:Transforming Growth Factor beta1 / Q000235:genetics* / Q000378:metabolism
chemical_list: C091732:BCL2-associated athanogene 1 protein; D004268:DNA-Binding Proteins; D014157:Transcription Factors; D053773:Transforming Growth Factor beta1