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J. Biol. Chem., Vol. 282, Issue 40, 29284-29295, October 5, 2007

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Stabilization of p53 in Human Cytomegalovirus-initiated Cells Is Associated with Sequestration of HDM2 and Decreased p53 Ubiquitination^*

Zhenping Chen, Eugene Knutson, Shuo Wang, Luis A. Martinez, and Thomas Albrecht¹

From the Departments of Microbiology and Immunology and Otolaryngology, University of Texas Medical Branch, Galveston, Texas 77555-1019

Human cytomegalovirus (HCMV) induces serum- or density-arrested human lung (LU) cells to traverse the cell cycle, providing it with a strategy to replicate in post-mitotic cells that are its cellular substrate in vivo. HCMV infection also induces high cellular levels of p53, seemingly in contradiction to the observed cell cycle progression. This study was undertaken to examine the mechanism(s) of the increased p53 abundance. HCMV infection caused a 4-fold increase in p53 that preceded a substantial increase in p53 transcripts by more than 24 h. p53 was stabilized in HCMV-infected cells (from a half-life of less than 30 min to about 8 h) and was less sensitive to proteasome-mediated degradation. Ubiquitination of p53 in mock-infected LU cells was sensitive to inhibition by trans-4-iodo, 4'-boranyl-chalcone, consistent with HDM2-catalyzing ubiquitination of p53. In HCMV-infected cells, ubiquitination of p53 was essentially undetectable. Although HDM2 had a nuclear distribution in mock-infected LU cells, in HCMV-infected cells HDM2 was translocated to the cytoplasm beginning at 12 h and demonstrated decreased cellular abundance thereafter. HDM2 was stabilized in the HCMV-infected cells by MG132, indicating a shift from p53 to HDM2 ubiquitination. p53 demonstrated a predominantly nuclear distribution in HCMV-infected cells through 48 h, resulting in p53 and HDM2 in distinct subcellular compartments. The principal mechanism responsible for increased p53 stabilization was nuclear export and degradation of HDM2. Thus, HCMV uses a shift from p53 to HDM2 ubiquitination and destabilization to obtain protracted high levels of p53, while promoting cell cycle traverse.

Received for publication, June 29, 2007 , and in revised form, August 3, 2007.

^* This work was supported by National Center for Research Resources Grant RR14712 (to T. A.), NICR Grant DE11389 (to T. A.), NIEHS Grants ES10018 (to P. Muganda) and ES06676 (to R. S. Lloyd) from the National Institutes of Health. 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.

¹ To whom correspondence should be addressed: Infectious Disease and Toxicology Optical Imaging Center, Dept. of Microbiology and Immunology, University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-1019. Tel.: 409-772-0063; Fax: 409-772-5065; E-mail: talbrech{at}utmb.edu.

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