title: Cell signaling switches HOX-PBX complexes from repressors to activators of transcription mediated by histone deacetylases and histone acetyltransferases.
abstract: The Hoxb1 autoregulatory element comprises three HOX-PBX binding sites. Despite the presence of HOXB1 and PBX1, this enhancer fails to activate reporter gene expression in retinoic acid-treated P19 cell monolayers. Activation requires cell aggregation in addition to RA. This suggests that HOX-PBX complexes may repress transcription under some conditions. Consistent with this, multimerized HOX-PBX binding sites repress reporter gene expression in HEK293 cells. We provide a mechanistic basis for repressor function by demonstrating that a corepressor complex, including histone deacetylases (HDACs) 1 and 3, mSIN3B, and N-CoR/SMRT, interacts with PBX1A. We map a site of interaction with HDAC1 to the PBX1 N terminus and show that the PBX partner is required for repression by the HOX-PBX complex. Treatment with the deacetylase inhibitor trichostatin A not only relieves repression but also converts the HOX-PBX complex to a net activator of transcription. We show that this activation function is mediated by the recruitment of the coactivator CREB-binding protein by the HOX partner. Interestingly, HOX-PBX complexes are switched from transcriptional repressors to activators in response to protein kinase A signaling or cell aggregation. Together, our results suggest a model whereby the HOX-PBX complex can act as a repressor or activator of transcription via association with corepressors and coactivators. The model implies that cell signaling is a direct determinant of HOX-PBX function in the patterning of the animal embryo.
authors.affiliation: McGill Cancer Centre, McGill University, Montréal, Québec, Canada H3G 1Y6.
authors.forename: M
authors.initials: M
authors.lastname: Saleh
authors.forename: I
authors.initials: I
authors.lastname: Rambaldi
authors.forename: X J
authors.initials: XJ
authors.lastname: Yang
authors.forename: M S
authors.initials: MS
authors.lastname: Featherstone
mesh_terms: D000123:Acetyltransferases / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D050882:CREB-Binding Protein; D002460:Cell Line; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051548:Histone Acetyltransferases; D056572:Histone Deacetylase Inhibitors; D006655:Histone Deacetylases / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D015398:Signal Transduction; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; C101121:HOXB1 homeodomain protein; D056572:Histone Deacetylase Inhibitors; D018398:Homeodomain Proteins; C489520:Hoxd4 protein, mouse; D006877:Hydroxamic Acids; D009687:Nuclear Proteins; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C083400:PBX1 protein, human; C072064:HOXD10 protein, human; C012589:trichostatin A; D000123:Acetyltransferases; D050882:CREB-Binding Protein; C494363:CREBBP protein, human; C494364:Crebbp protein, mouse; D051548:Histone Acetyltransferases; D017868:Cyclic AMP-Dependent Protein Kinases; D006655:Histone Deacetylases