Roles of Brahma and Brahma/SWI2-related gene 1 in hypoxic induction of the erythropoietin gene.
Upon hypoxia, the human erythropoietin (EPO) gene is transactivated by the heterodimeric hypoxia-inducible factor 1 (HIF-1). Mammalian SWI/SNF is a chromatin-remodeling complex involved in the modulation of gene expression. We demonstrate that Brahma (Brm) and Brahma/SWI2-related gene 1 (Brg-1), alternative ATPase subunits of SWI/SNF, potentiate reporter gene activation mediated by HIF-1 in an ATPase-dependent manner. Brm was more potent than Brg-1 in the reporter gene assays. Simultaneous depletion of both Brm and Brg-1 by small interfering RNAs significantly compromised the transcription of the endogenous EPO gene triggered by hypoxia. Whereas knocking down Brm alone resulted in a moderate reduction in transcription of the EPO gene, depletion of Brg-1 resulted in an augmentation of transcription of both the EPO gene and the Brm gene, indicating that Brm can compensate for loss of Brg-1. Chromatin immunoprecipitation (ChIP) and sequential ChIP (re-ChIP) analysis showed that both Brm and Brg-1 associate with the enhancer region of the EPO gene in vivo in a hypoxia-dependent fashion and that each is present in a complex with HIF-1. Brm and Brg-1 were also recruited to the promoter of the vascular endothelial growth factor (VEGF) gene in a hypoxia-dependent fashion, although hypoxic induction of VEGF transcription was not affected by depletions of either or both Brm and Brg-1. Together these studies reveal a novel role for SWI/SNF in the activation of transcription of the EPO gene, indicate an important communication and compensation between Brm and Brg-1, and suggest that the requirement for SWI/SNF during hypoxic induction is gene-specific.
Wang
Feng
F
Department of Pathology and Laboratory Medicine, Jonsson Comprehensive Cancer Center, Molecular Biology Institute, UCLA, Los Angeles, California 90095, USA.
Zhang
Ruixue
R
Beischlag
Timothy V
TV
Muchardt
Christian
C
Yaniv
Moshe
M
Hankinson
Oliver
O
D020413:3' Untranslated Regions; D018797:Cell Cycle Proteins / Q000378:metabolism / Q000502:physiology*; D002460:Cell Line; D045744:Cell Line, Tumor; D002843:Chromatin / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004265:DNA Helicases; D019281:Dimerization; D029721:Drosophila Proteins; D004742:Enhancer Elements, Genetic; D004921:Erythropoietin / Q000096:biosynthesis* / Q000235:genetics; D017930:Genes, Reporter; D005822:Genetic Vectors; D006657:Histones / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D000860:Hypoxia; D047468:Immunoprecipitation; D008156:Luciferases / Q000378:metabolism; D008957:Models, Genetic; D009687:Nuclear Proteins / Q000378:metabolism / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015534:Trans-Activators / Q000378:metabolism / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
D020413:3' Untranslated Regions; D018797:Cell Cycle Proteins; D002843:Chromatin; D003432:Cross-Linking Reagents; D029721:Drosophila Proteins; D006657:Histones; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D015534:Trans-Activators; D014157:Transcription Factors; D042461:Vascular Endothelial Growth Factor A; C086469:brm protein, Drosophila; D004921:Erythropoietin; D008156:Luciferases; C084108:SMARCA4 protein, human; D004265:DNA Helicases; D010100:Oxygen