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Molecular and Cellular Biology, December 2004, p. 10366-10380, Vol. 24, No. 23
0270-7306/04/$08.00+0     DOI: 10.1128/MCB.24.23.10366-10380.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

p53 Stabilization and Accumulation Induced by Human Vaccinia-Related Kinase 1

Francisco M. Vega, Ana Sevilla, and Pedro A. Lazo*

Instituto de Biología Molecular y Celular del Cáncer, Consejo Superior de Investigaciones Científicas-Universidad de Salamanca, Campus Miguel de Unamuno, Salamanca, Spain

Received 21 December 2003/ Returned for modification 11 February 2004/ Accepted 16 August 2004

Variations in intracellular levels of p53 regulate many cellular functions and determine tumor susceptibility. Major mechanisms modulating p53 levels include phosphorylation and interaction of p53 with specific ubiquitin ligases that promote its degradation. N-terminal phosphorylation regulates the interaction of p53 with several regulatory molecules. Vaccinia-related kinase 1 (VRK1) is the prototype of a new Ser-Thr kinase family in the human kinome. VRK1 is located in the nucleus outside the nucleolus. Overexpression of VRK1 increases the stability of p53 by a posttranslational mechanism leading to its accumulation by a mechanism independent of the Chk2 kinase. Catalytically inactive VRK1 protein (a K179E mutant) does not induce p53 accumulation. VRK1 phosphorylates human p53 in Thr18 and disrupts p53-Mdm2 interaction in vitro, although a significant decrease in p53 ubiquitination by Mdm2 in vivo was not detected. VRK1 kinase does not phosphorylate Mdm2. VRK1-mediated p53 stabilization was also detected in Mdm2–/– cells. VRK1 also has an additive effect with MdmX or p300 to stabilize p53, and p300 coactivation and acetylation of p53 is enhanced by VRK1. The p53 stabilized by VRK1 is transcriptionally active. Suppression of VRK1 expression by specific small interfering RNA provokes several defects in proliferation, situating the protein in the regulation of this process. VRK1 might function as a switch controlling the proteins that interact with p53 and thus modifying its stability and activity. We propose VRK1 as the first step in a new pathway regulating p53 activity during cell proliferation.

* Corresponding author. Mailing address: Centro de Investigación del Cáncer, C.S.I.C.-Universidad de Salamanca, Campus Miguel de Unamuno, E-37007 Salamanca, Spain. Phone: 34 923 294 804. Fax: 34 923 294 795. E-mail: plazozbi{at}usal.es.

Molecular and Cellular Biology, December 2004, p. 10366-10380, Vol. 24, No. 23
0022-538X/04/$08.00+0     DOI: 10.1128/MCB.24.23.10366-10380.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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Copyright © 2004 by the American Society for Microbiology. All rights reserved.