title: Ezh2 reduces the ability of HDAC1-dependent pRb2/p130 transcriptional repression of cyclin A.
abstract: The polycomb group (PcG) proteins are known to be involved in maintaining the silenced state of several developmentally regulated genes. Enhancer of zeste homolog 2 (Ezh2), a member of this large protein family, has also been shown to be deregulated in different tumor types and its role, both as a potential primary effector and as a mediator of tumorigenesis, has become a subject of increased interest. We observed that Ezh2 binds to pRb2/p130, a member of the retinoblastoma family; as such, we were led to consider the possible ability of Ezh2 to modulate cell cycle progression. Both Ezh2 and pRb2/p130 repress gene expression by recruiting histone deacetylase (HDAC1), which decreases DNA accessibility for activating transcription factors. Additionally, we observed that Ezh2 interacts with the C-terminal region of pRb2/p130, essential for interaction with HDAC1. We show that Ezh2 is able to reverse pRb2/p130-HDAC1-mediated repression of the cyclin A promoter. This indicates a functional role of this complex in regulating cyclin A expression, known to be crucial in mediating cell cycle advancement. We also detected a significant decrease in the retention of HDAC1 activity associated with pRb2/p130 when Ezh2 was overexpressed. Finally, electromobility shift assays (EMSA) demonstrated that overexpression of Ezh2 caused the abrogation of the pRb2/p130-HDAC1 complex on the cyclin A promoter. These data, taken together, suggest that Ezh2 competes with HDAC1 in binding to pRb2/p130, disrupting their occupancy on the cyclin A promoter. In this study, we propose a new mechanism for the functional inactivation of pRb2/p130 that ultimately contributes to cell cycle progression and malignant transformation.
authors.affiliation: Sbarro Institute for Cancer Research and Molecular Medicine, Center for Biotechnology, Temple University, Philadelphia, PA 19122, USA.
authors.forename: Tiziana
authors.initials: T
authors.lastname: Tonini
authors.forename: Luigi
authors.initials: L
authors.lastname: Bagella
authors.forename: Giuseppina
authors.initials: G
authors.lastname: D'Andrilli
authors.forename: Pier Paolo
authors.initials: PP
authors.lastname: Claudio
authors.forename: Antonio
authors.initials: A
authors.lastname: Giordano
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001943:Breast Neoplasms; D002460:Cell Line; D045744:Cell Line, Tumor; D019925:Cyclin A / Q000235:genetics*; D004268:DNA-Binding Proteins; D000071221:Enhancer of Zeste Homolog 2 Protein; D005260:Female; D056284:Histone Deacetylase 1; D006655:Histone Deacetylases / Q000378:metabolism*; D011495:Histone-Lysine N-Methyltransferase; D006801:Humans; D008297:Male; D051379:Mice; D010957:Plasmids; D063151:Polycomb Repressive Complex 2; D011467:Prostate; D011471:Prostatic Neoplasms; D011506:Proteins / Q000235:genetics* / Q000378:metabolism*; D050717:Retinoblastoma-Like Protein p130; D014157:Transcription Factors; D014158:Transcription, Genetic
chemical_list: D019925:Cyclin A; D004268:DNA-Binding Proteins; D011506:Proteins; C493837:RBL2 protein, human; C493838:Rbl2 protein, mouse; D050717:Retinoblastoma-Like Protein p130; D014157:Transcription Factors; C498409:EZH2 protein, human; D000071221:Enhancer of Zeste Homolog 2 Protein; C498410:Ezh2 protein, mouse; D011495:Histone-Lysine N-Methyltransferase; D063151:Polycomb Repressive Complex 2; C110550:HDAC1 protein, human; D056284:Histone Deacetylase 1; D006655:Histone Deacetylases