Article

p53--a Jack of all trades but master of none.

Department of Pathology and Helen Diller Family Comprehensive Cancer Centre, University of California San Francisco, 513 Parnassus Avenue, Room HSW-450A, UCSF Box 0502, San Francisco, California 94143-0502, USA.
Nature Reviews Cancer (Impact Factor: 29.54). 09/2009; 9(11):821-9. DOI: 10.1038/nrc2728
Source: PubMed

ABSTRACT Cancers are rare because their evolution is actively restrained by a range of tumour suppressors. Of these p53 seems unusually crucial as either it or its attendant upstream or downstream pathways are inactivated in virtually all cancers. p53 is an evolutionarily ancient coordinator of metazoan stress responses. Its role in tumour suppression is likely to be a relatively recent adaptation, which is only necessary when large, long-lived organisms acquired the sufficient size and somatic regenerative capacity to necessitate specific mechanisms to reign in rogue proliferating cells. However, such evolutionary reappropriation of this venerable transcription factor entails compromises that restrict its efficacy as a tumour suppressor.

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    ABSTRACT: About 50% of human cancers harbor somatic mutations of the tumor suppressor p53 (p53 or Trp53) gene. Many of those mutations result in the inactivation of the p53 pathway and are often associated with the stabilization and accumulation of mutant p53 proteins. Therefore, increased p53 expression in tumors is frequently used as a surrogate marker for p53 mutation and inactivation. Moreover, this elevated p53 expression also makes it an ideal tumor associated antigen (TAA) for cancer vaccines. Recent advances in our understanding of p53 as a crucial transcription factor reveal that p53 is an important sensor of cellular stress under genotoxic, chemotoxic, pathological, and even normal physiological conditions. Experimental and clinical observations by our laboratory and others have demonstrated that p53 also participates in immune regulation as p53 dysfunction skews host immune responses towards pro-inflammation, which further promotes tumor progression. Furthermore, recent studies using a genetic approach revealed that p53-restoration or re-activation led to tumor regression and clearance, which were at least partially caused by the activation of innate antitumor immunity. Since many of the currently used cancer therapeutics, including radiotherapy and chemotherapy, disrupt tumor growth by inducing DNA damage via genotoxic or chemotoxic stress, which activates the p53 pathway in the tumor microenvironment, we postulate that some of those observed therapeutic benefits might also be partially mediated through their immune stimulatory effects. Here, we briefly review our current understanding of the potential cellular and molecular mechanisms by which p53 participates in immune regulation and, subsequently, extend our discussion to the immunostimulatory potential of existing and new approaches of targeting the p53-pathway to alter the immunological landscape of tumors for maximizing immunotherapy outcome.
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    ABSTRACT: The tumor suppressor p53 plays a central role in cell fate decisions after DNA damage. Programmed Cell Death 5 (PDCD5) is known to interact with the p53 pathway to promote cell apoptosis. Recombinant human PDCD5 can significantly sensitize different cancers to chemotherapies. In the present paper, we construct a computational model that includes PDCD5 interactions in the p53 signaling network and study the effects of PDCD5 on p53-mediated cell fate decisions during the DNA damage response. Our results revealed that PDCD5 functions as a co-activator of p53 that regulates p53-dependent cell fate decisions via the mediation of p53 dynamics. The effects of PDCD5 are dose-dependent such that p53 can display either sustained or pulsed dynamics at different PDCD5 levels. Moreover, PDCD5 regulates caspase-3 activation via two mechanisms during the two phases of sustained and pulsed p53 dynamics. This study provides insights regarding how PDCD5 functions as a regulator of the p53 pathway and might be helpful for increasing our understanding of the molecular mechanisms by which PDCD5 can be used to treat cancers.
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