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J. Biol. Chem., Vol. 282, Issue 10, 7001-7010, March 9, 2007

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Repression of p53-mediated Transcription by Adenovirus E1B 55-kDa Does Not Require Corepressor mSin3A and Histone Deacetylases^*

From the Department of Anatomy and Cell Biology, and Shands Cancer Center Programs in Cancer Genetics, Epigenetics and Tumor Virology, and Cell Signaling, Apoptosis and Cancer, University of Florida College of Medicine, Gainesville, Florida 32611-3633

The Ad E1B 55-kDa protein (E1B) is a potent transcriptional repressor. In vitro biochemical studies revealed that direct p53-E1B interaction is essential for E1B to block p53-activated transcription and a corepressor may be involved. To understand how E1B represses p53-mediated transcription in vivo, we expressed E1B in several tumor cell lines that express wild type p53. Here we show that E1B strongly suppresses the expression of p53 target genes such as p21 and Puma- in normal growth conditions or after cells were treated with p53-activating chemotherapeutic agents, suggesting that E1B-mediated gene repression is dominant and cannot be reversed via p53 activation. Interestingly, we found that E1B binds to corepressor mSin3A. Mutagenesis analysis indicated that the sequence motif "LHLLA" near the NH₂ terminus of E1B is responsible for mSin3A binding, and this motif is conserved among E1B proteins from different Ad serotypes. The conserved paired amphipathic helix domain 1 of mSin3A is critical for mSin3A-E1B interaction. Surprisingly, E1B mutants that cannot bind to mSin3A can still repress p53 target genes, indicating that it is not the corepressor required for E1B-mediated gene repression. In support of this notion, repression of p53 target genes by E1B is insensitive to HDAC inhibitor trichostatin A. We further show that both the NH₂- and COOH-terminal domains of E1B are required for the repression function. Therefore, E1B employs a unique repression mechanism to block p53-mediated transcription.

Received for publication, November 20, 2006

^* This work was supported by National Institutes of Health Grant (RO1 CA92236) (to D. L.), a Career Investigator Award from the American Lung Association Florida Inc. (to D. L.), and the Howard Hughes Medical Institute Biomedical Research Support Program for Medical Schools to the University of Florida College of Medicine. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1–S6.

¹ Current address: Applied Genetic Technologies Corp., 11801 Research Dr., Suite D, Alachua, FL 32615.

² To whom correspondence should be addressed: 1376 Mowry Rd., Gainesville, FL 32611-3633. Tel.: 352-273-8188; Fax: 352-273-8285; E-mail: dliao{at}ufl.edu.

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