Review
Multiple roles of the cell cycle inhibitor p21CDKN1A in the DNA damage response

https://doi.org/10.1016/j.mrrev.2010.01.009Get rights and content

Abstract

Among cell cycle regulatory proteins that are activated following DNA damage, the cyclin-dependent kinase inhibitor p21CDKN1A plays essential roles in the DNA damage response, by inducing cell cycle arrest, direct inhibition of DNA replication, as well as by regulating fundamental processes, like apoptosis and transcription. These functions are performed through the ability of p21 to interact with a number of proteins involved in these processes. Despite an initial controversy, during the last years several lines of evidence have also indicated that p21 may be directly involved in DNA repair. In particular, the participation of p21 in nucleotide excision repair (NER), base excision repair (BER), and DNA translesion synthesis (TLS), has been suggested to occur thanks to its interaction with proliferating cell nuclear antigen (PCNA), a crucial protein involved in several aspects of DNA metabolism, and cell-cycle regulation.

In this review, the multiple roles of p21 in the DNA damage response, including regulation of cell cycle, apoptosis and gene transcription, are discussed together with the most recent findings supporting the direct participation of p21 protein in DNA repair processes. In particular, spatio-temporal dynamics of p21 recruitment to sites of DNA damage will be considered together with several lines of evidence indicating a regulatory role for p21. In addition, the relevance of post-translational regulation in the fate (e.g. degradation) of p21 protein after cell exposure to DNA damaging agents will be analyzed. Both sets of evidence will be discussed in terms of the overall DNA damage response.

Introduction

Exposure to different environmental stress conditions, including radiation (like ionizing and UV radiation), may induce the formation of a variety of DNA genotoxic lesions that cells must remove in order to avoid genomic instability, and to prevent cancer formation. To this end, virtually every organism has developed highly conserved genome surveillance and signaling mechanisms, collectively known as the DNA damage response (DDR). This pathway consists of DNA damage signaling cascade (cell cycle checkpoints), and of DNA repair processes able to recognize and remove a great number of DNA lesions [1].

Among the factors involved in this pathway, p21CDKN1A protein contributes to the cell response to DNA damage, by regulating fundamental processes, like cell cycle progression, apoptosis, and transcription [2], [3]. However, participation of p21 in all these pathways may occur not only after DNA damage, but also in physiological conditions (e.g. differentiation) [4], [5]. p21CDKN1A (also known as p21Cip1/Waf11/Sdi1), the first identified inhibitor of cyclin/cyclin-dependent kinase (CDK) complexes, was independently isolated as a CDK-binding protein [6], as a growth-inhibitory gene upregulated by p53 [7], or overexpressed in senescent fibroblasts [8]. The main role of p21 in cell-cycle regulation is performed by inhibiting the activity of cyclin-CDK complexes, thanks to direct interaction through specific sequences (termed CDK and Cy motifs) in the N-terminal domain of the protein [9], [10], [11], [12]. Cell cycle progression may be also regulated by p21 independently of cyclins and CDKs, thanks to the strong affinity binding to proliferating cell nuclear antigen (PCNA) [13], [14], [15], [16], a protein playing a central role in DNA replication and repair, as well as in other processes of DNA metabolism [17], [18]. This association may interfere with PCNA-dependent enzyme activities involved in DNA synthesis [18].

In contrast with the negative cell-cycle regulation, p21 may also serve as an assembly factor for cyclin D-CDK4/6, thus promoting (only at low concentrations) cyclin D-dependent events, and downstream activation of cyclin E-CDK2 [4], [5].

Being intrinsically unstructured in solution, p21 protein may adopt an extended conformation [19], which may facilitate and explain its ability to interact with a number of different proteins involved in the above processes (Fig. 1). Intriguingly, several reports have also suggested a direct participation of p21 in DNA repair, although this aspect has remained for long time controversial, not only because of different model systems investigated, but also because multiple mechanisms involved in the post-translational regulation of p21 protein, influence its functions [20].

This review will focus on the main functions of p21 in DDR, i.e. the regulation of cell cycle progression, transcription, and apoptosis, and will emphasize on the more recent findings supporting a direct participation of p21 in the DNA repair process, also in light of the relevance of post-translational regulation of p21 protein in the overall DDR.

Section snippets

Cell-cycle regulation

p21 is the principal mediator of cell cycle arrest in response to DNA damage, not only by inactivating G1-phase cyclins/CDKs complexes, but also through other processes, which possibly include direct interaction with PCNA to inhibit DNA replication, and indirect effects mediated by interaction with other cell cycle regulators. In addition, p21 has been shown to play a role in the maintenance of G2-phase arrest, through multiple mechanisms.

The demonstration that p21 is involved in cell response

Post-translational regulation of p21 in the DNA damage response

Most of the mechanisms regulating p21 expression at the transcriptional level, have been extensively described elsewhere [2], [5], [53], and they will be not further discussed. Instead, the relevance of post-translational modifications of p21 (i.e. phosphorylation and ubiquitination) in the regulation of protein stability will be approached here, in light of the outcome of DDR. Several studies have been devoted to explaining mechanisms, both at basal level and after DNA damage, regulating p21

Conclusions and perspectives

The protective effects of p21 against DNA damage and genome instability are supported not only by the role played by p21 in multiple processes evoked by DNA damage, but also by the evidence that lack of p21 may induce tumorigenesis [160]. Direct inhibition of cell cycle progression, together with indirect effects on cell-cycle related genes, are important but not unique functions of p21 helping cells to deal with DNA damage, as well as other types of stress (e.g. oncogene activation). The

Conflict of interest statement

The authors declare that they do not have any conflict of interest in this manuscript and in the work described therein.

Acknowledgements

We apologize to those colleagues whose work could not be cited owing to space limitation. Research in the author laboratories is supported in part by MIUR grants, and by the AIRC IG grant no. 5126.

References (161)

  • H. Mattock et al.

    Inhibition of cell proliferation by the PCNA-binding protein region of p21 expressed as a GFP miniprotein

    Exp. Cell Res.

    (2001)
  • G. Bornstein et al.

    Role of the SCFSkp2 ubiquitin ligase in the degradation of p21Cip1 in S phase

    J. Biol. Chem.

    (2003)
  • V. Gottifredi et al.

    Decreased p21 levels are required for efficient restart of DNA synthesis after S phase block

    J. Biol. Chem.

    (2004)
  • V.A. Smits et al.

    p21 inhibits Thr161 phosphorylation of Cdc2 to enforce the G2 DNA damage checkpoint

    J. Biol. Chem.

    (2000)
  • S. Liu et al.

    Differential effects of cell cycle regulatory protein p21(WAF1/Cip1) on apoptosis and sensitivity to cancer chemotherapy

    Drug Resist. Update

    (2003)
  • J.L. Gervais et al.

    Cleavage of CDK inhibitor p21(Cip1/Waf1) by caspases is an early event during DNA damage-induced apoptosis

    J. Biol. Chem.

    (1998)
  • B. Levkau et al.

    Cleavage of p21Cip1/Waf1 and p27Kip1 mediates apoptosis in endothelial cells through activation of Cdk2: role of a caspase cascade

    Mol. Cell

    (1998)
  • Y.H. Jin et al.

    Caspase 3-mediated cleavage of p21WAF1/CIP1 associated with the cyclin A-cyclin-dependent kinase 2 complex is a prerequisite for apoptosis in SK-HEP-1 cells

    J. Biol. Chem.

    (2000)
  • S. Huang et al.

    Sustained activation of the JNK cascade and rapamycin-induced apoptosis are suppressed by p53/p21(Cip1)

    Mol. Cell

    (2003)
  • H.V. Le et al.

    Cyclin-dependent kinase inhibitors uncouple cell cycle progression from mitochondrial apoptotic functions in DNA-damaged cancer cells

    J. Biol. Chem.

    (2005)
  • R.H. Weiss

    p21Waf1/Cip1 as a therapeutic target in breast and other cancers

    Cancer Cell

    (2003)
  • R.H. Weiss et al.

    Suppression of breast cancer growth and angiogenesis by an antisense oligodeoxynucleotide to p21(Waf1/Cip1)

    Cancer Lett.

    (2003)
  • S.H. Park et al.

    Antisense attenuation of p21 sensitizes kidney cancer to apoptosis in response to conventional DNA damaging chemotherapy associated with enhancement of phospho-p53

    J. Urol.

    (2008)
  • A.L. Gartel

    The conflicting roles of the cdk inhibitor p21CIP1/WAF1 in apoptosis

    Leuk. Res.

    (2005)
  • M. Savio et al.

    Degradation of p21CDKN1A after DNA damage is independent of type of lesion, and is not required for DNA repair

    DNA Repair

    (2009)
  • K Fujiwara et al.

    Pivotal role of the cyclin-dependent kinase inhibitor p21WAF1/CIP1 in apoptosis and autophagy

    J. Biol. Chem.

    (2008)
  • G. Zhang et al.

    Multiple cyclin kinase inhibitors promote bile acid-induced apoptosis and autophagy in primary hepatocytes via p53-CD95-dependent signaling

    J. Biol. Chem.

    (2008)
  • O. Coqueret et al.

    Functional interaction of STAT3 transcription factor with the cell inhibitor p21WAF1/CIP1/SDI1

    J. Biol. Chem.

    (2000)
  • H. Kitaura et al.

    Reciprocal regulation via protein–protein interaction between c-Myc and p21(cip1/waf1/sdi1) in DNA replication and transcription

    J. Biol. Chem.

    (2000)
  • J. Wang et al.

    Glucocorticoid-induced tumor necrosis factor receptor is a p21Cip1/WAF1 transcriptional target conferring resistance of keratinocytes to UV light-induced apoptosis

    J. Biol. Chem.

    (2005)
  • A. Vigneron et al.

    The cell cycle inhibitor p21waf1 binds to the myc and cdc25A promoters upon DNA damage and induces transcriptional repression

    J. Biol. Chem.

    (2006)
  • F. Brouillard et al.

    Concomitant increase of histone acetyltransferase activity and degradation of p300 during retinoic acid-induced differentiation of F9 cells

    J. Biol. Chem.

    (2003)
  • G.P. Dotto

    p21(WAF1/Cip1): more than a break to the cell cycle?

    Biochim. Biophys. Acta

    (2000)
  • C.J. Sherr et al.

    CDK inhibitors: positive and negative regulators of G1 phase progression

    Genes Dev.

    (1999)
  • J.W. Harper et al.

    The p21 cdk-interacting protein Cip1 is a potent inhibitor of G1 cyclin-dependent kinases

    Cell

    (1993)
  • J. Chen et al.

    Separate domains of p21 involved in the inhibition of Cdk kinase and PCNA

    Nature

    (1995)
  • F. Goubin et al.

    Identification of binding domains on the p21Cip1 cyclin-dependent kinase inhibitor

    Oncogene

    (1995)
  • J. Chen et al.

    Cyclin-binding motifs are essential for the function of p21Cip1

    Mol. Cell. Biol.

    (1996)
  • R. Fotedar et al.

    p21 contains independent binding sites for cyclin and cdk2: both sites are required to inhibit cdk2 kinase activity

    Oncogene

    (1996)
  • H. Flores-Rozas et al.

    Cdk-interacting protein 1 directly binds with proliferating cell nuclear antigen and inhibits DNA replication catalyzed by the DNA polymerase delta holoenzyme

    Proc. Natl. Acad. Sci. U.S.A.

    (1994)
  • S. Waga et al.

    The p21 inhibitor of cyclin-dependent kinases controls DNA replication by interaction with PCNA

    Nature

    (1994)
  • Y. Luo et al.

    Cell-cycle inhibition by independent CDK and PCNA binding domains in p21

    Nature

    (1995)
  • L.T. Chen et al.

    Characterization of p21Cip1/Waf1 peptide domains required for cyclin E/cdk2 and PCNA interactions

    Oncogene

    (1996)
  • E. Prosperi

    The fellowship of the rings: distinct pools of proliferating cell nuclear antigen (PCNA) trimer at work

    FASEB J.

    (2006)
  • V Esteve et al.

    The structural plasticity of the C terminus of p21Cip1 is a determinant for target protein recognition

    ChemBioChem.

    (2003)
  • E.S. Child et al.

    The intricacies of p21 phosphorylation: protein/protein interactions, subcellular localization and stability

    Cell Cycle

    (2006)
  • T Waldman et al.

    p21 is necessary for the p53-mediated G1 arrest in human cancer cells

    Cancer Res.

    (1995)
  • J. Brugarolas et al.

    Inhibition of cyclin-dependent kinase 2 by p21 is necessary for retinoblastoma protein-mediated G1 arrest after gamma-irradiation

    Proc. Natl. Acad. Sci. U.S.A.

    (1999)
  • W.S. el-Deiry et al.

    WAF1/CIP1 is induced in p53-mediated G1 arrest and apoptosis

    Cancer Res.

    (1994)
  • J Brugarolas et al.

    Radiation-induced cell cycle arrest compromised by p21 deficiency

    Nature

    (1995)
  • Cited by (0)

    View full text