title: Histone deacetylation of RB-responsive promoters: requisite for specific gene repression but dispensable for cell cycle inhibition.
abstract: The retinoblastoma tumor suppressor protein (RB) is targeted for inactivation in the majority of human tumors, underscoring its critical role in attenuating cellular proliferation. RB inhibits proliferation by repressing the transcription of genes that are essential for cell cycle progression. To repress transcription, RB assembles multiprotein complexes containing chromatin-modifying enzymes, including histone deacetylases (HDACs). However, the extent to which HDACs participate in transcriptional repression and are required for RB-mediated repression has not been established. Here, we investigated the role of HDACs in RB-dependent cell cycle inhibition and transcriptional repression. We find that active RB mediates histone deacetylation on cyclin A, Cdc2, topoisomerase IIalpha, and thymidylate synthase promoters. We also demonstrate that this deacetylation is HDAC dependent, since the HDAC inhibitor trichostatin A (TSA) prevented histone deacetylation at each promoter. However, TSA treatment blocked RB repression of only a specific subset of genes, thereby demonstrating that the requirement of HDACs for RB-mediated transcriptional repression is promoter specific. The HDAC-independent repression was not associated with DNA methylation or gene silencing but was readily reversible. We show that this form of repression resulted in altered chromatin structure and was dependent on SWI/SNF chromatin remodeling activity. Importantly, we find that cell cycle inhibitory action of RB is not intrinsically dependent on the ability to recruit HDAC activity. Thus, while HDACs do play a major role in RB-mediated repression, they are dispensable for the repression of critical targets leading to cell cycle arrest.
authors.affiliation: Department of Cell Biology, Vontz Center for Molecular Studies, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0521, USA.
authors.forename: Hasan
authors.initials: H
authors.lastname: Siddiqui
authors.forename: David A
authors.initials: DA
authors.lastname: Solomon
authors.forename: Ranjaka W
authors.initials: RW
authors.lastname: Gunawardena
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.forename: Erik S
authors.initials: ES
authors.lastname: Knudsen
mesh_terms: D000107:Acetylation; D000818:Animals; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D004318:Doxycycline / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism; D005786:Gene Expression Regulation; D006655:Histone Deacetylases / Q000378:metabolism*; D006657:Histones / Q000378:metabolism*; D006801:Humans; D006877:Hydroxamic Acids / Q000378:metabolism; D009097:Multienzyme Complexes; D011401:Promoter Regions, Genetic; D051381:Rats; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D006657:Histones; D006877:Hydroxamic Acids; D009097:Multienzyme Complexes; D012097:Repressor Proteins; D016160:Retinoblastoma Protein; C012589:trichostatin A; D006655:Histone Deacetylases; D004318:Doxycycline