¹Department of Pathology and Cell Biology, College of Physicians and Surgeons, Institute for Cancer Genetics, Columbia University, 1130 St. Nicholas Ave, New York, NY 10032, USA

Correspondence: W Gu, Department of Pathology and Cell Biology, Institute for Cancer Genetics, Columbia University, 1130 St. Nicholas Ave, #609A, New York, NY 10032, USA. Tel: 212 851 5282; Fax: 212 851 5284; E-mail: wg8@columbia.edu

Received 9 March 2009; Revised 7 May 2009; Accepted 7 May 2009; Published online 19 June 2009.

Abstract

p53 is a central integrator of a plethora of signals and outputs these signals in the form of tumor suppression. It is well accepted that ubiquitination plays a major part in p53 regulation. Nonetheless, the molecular mechanisms by which p53 activity is controlled by ubiquitination are complex. Mdm2, a RING oncoprotein, was once thought to be the sole E3 ubiquitin ligase for p53, however recent studies have shown that p53 is stabilized but still degraded in the cells of Mdm2-null mice. Although the essential role of Mdm2 in p53 regulation is well established, there are an increasing number of other E3 ligases implicated in Mdm2-independent regulation of p53 by ubiquitination. The different types of ubiquitination on p53 by various E3 ligases have been linked to its differential effects on p53-mediated stress responses. In addition to proteasome-mediated degradation, ubiquitination of p53 acts as signals for degradation-independent functions, such as nuclear export. The function of ubiquitinated p53 varies in the nucleus and cytosol underlying the many potential contributions ubiquitinated p53 may have in promoting cell proliferation or death. Thus, p53 requires multiple layers of regulatory control to ensure correct temporal and spatial functions.