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Transcriptional coactivator p300 stimulates cell type-specific gene expression in cardiac myocytes
K Hasegawa1, M B Meyers, R N Kitsis
1Department of Medicine (Cardiology), Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Abstract:
Terminal differentiation is characterized by cell cycle arrest and the expression of cell type-specific genes. Previous work has suggested that the p300 family of transcriptional coactivators plays an important role in preventing the re-initiation of DNA synthesis in terminally differentiated cardiac myocytes. In this study, we investigated whether p300 proteins are also involved in the transcriptional activation of cell type-specific genes in these cells. Since p300 function can be abrogated through direct binding by the adenovirus E1A protein, we overexpressed E1A in cardiac myocytes using recombinant adenoviral vectors. The expression of transfected reporter genes driven by alpha- or beta-myosin heavy chain promoters was markedly diminished by expression of the 12 S E1A protein. In contrast, the activity of a promoter derived from the ubiquitously expressed beta-actin gene was affected only modestly. While an E1A mutant unable to bind members of the retinoblastoma family of pocket proteins decreased the activity of alpha- and beta-myosin heavy chain promoters to nearly the same extent as wild type 12 S E1A, transcriptional repression by a mutant defective for p300 binding was severely impaired. Furthermore, overexpression of p300 and, to an even greater extent, p300del33, a mutant lacking residues required for binding by E1A, relieved E1A's repression of beta-myosin heavy chain promoter activity while having no effect on the activity of the beta-actin promoter. Thus, E1A's transcriptional repression of cell type-specific genes in cardiac myocytes is mediated through its binding of p300 proteins, and these proteins appear to be involved in maintaining both cell type-specific gene expression and cell cycle arrest in cardiac myocytes.
Insights
Adenovirus E1A protein represses cardiac myocyte gene expression by binding p300 proteins. These p300 proteins are crucial for maintaining cell-specific genes and cell cycle arrest in these differentiated cells.
Area of Science:
- Molecular Biology
- Cell Biology
- Cardiology
Background:
- Terminal differentiation involves cell cycle arrest and specific gene expression.
- p300 transcriptional coactivators are implicated in preventing DNA re-initiation in cardiac myocytes.
- The adenovirus E1A protein can inhibit p300 function.
Purpose of the Study:
- To investigate the role of p300 proteins in transcriptional activation of cell type-specific genes in cardiac myocytes.
- To determine if adenovirus E1A-mediated repression of cardiac myocyte genes involves p300 proteins.
Main Methods:
- Overexpression of adenovirus E1A in cardiac myocytes using recombinant adenoviral vectors.
- Assessed reporter gene expression driven by alpha-myosin heavy chain, beta-myosin heavy chain, and beta-actin promoters.
- Utilized E1A and p300 mutants to dissect protein-protein interactions and functional consequences.
Main Results:
- E1A significantly diminished alpha- and beta-myosin heavy chain promoter activity, with minimal effect on the beta-actin promoter.
- E1A's repression of cardiac-specific promoters was impaired in a mutant defective for p300 binding.
- Overexpression of p300 or a p300 mutant resistant to E1A binding relieved E1A-mediated repression of the beta-myosin heavy chain promoter.
Conclusions:
- Adenovirus E1A represses cell type-specific gene expression in cardiac myocytes via binding to p300 proteins.
- p300 proteins are essential for maintaining both cell type-specific gene expression and cell cycle arrest in cardiac myocytes.
- This study elucidates a mechanism by which viral proteins can interfere with cardiomyocyte differentiation and function.