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Trends Mol Med. 2017 Apr;23(4):310-319. doi: 10.1016/j.molmed.2017.02.001. Epub 2017 Mar 7.

p21: A Two-Faced Genome Guardian.

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DNA Damage Laboratory, Physics Department, School of Applied Mathematical and Physical Sciences, National Technical University of Athens (NTUA), Iroon Polytechniou 9, Zografou 15780, Athens, Greece. Electronic address:
Division of Radiation Oncology and Cancer Imaging, Peter MacCallum Cancer Centre and The Sir Peter MacCallum Department of Oncology, University of Melbourne, 305 Grattan street, Melbourne VIC 3000, Australia.
Developmental Therapeutics Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.


Upon DNA damage or other stressors, the tumor suppressor p53 is activated, leading to transient expression of the cyclin-dependent kinase inhibitor (CKI) p21. This either triggers momentary G1 cell cycle arrest or leads to a chronic state of senescence or apoptosis, a form of genome guardianship. In the clinic, the presence of p21 has been considered an indicator of wildtype p53 activity. However, recent evidence suggests that p21 also acts as an oncogenic factor in a p53-deficient environment. Here, we discuss the controversial aspects of the two-faced involvement of p21 in cancer and speculate on how this new information may increase our understanding of its role in cancer pathogenesis. Prevailing notions indicate that p21 might also act as antiapoptotic agent, which may have relevant implications for future therapeutic strategies.


cancer; error-prone repair; genomic instability; p21 overexpression; p53 deficiency

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