Upstream eventp21 (CDKN1A) expression, increase
cell cycle, disrupted
Key Event Relationship Overview
AOPs Referencing Relationship
|AOP Name||Adjacency||Weight of Evidence||Quantitative Understanding|
|Histone deacetylase inhibition leading to testicular toxicity||adjacent||High||Moderate|
|Homo sapiens||Homo sapiens||High||NCBI|
|Rattus norvegicus||Rattus norvegicus||High||NCBI|
|Mus musculus||Mus musculus||High||NCBI|
Life Stage Applicability
|Not Otherwise Specified||High|
Key Event Relationship Description
Cell cycle regulation through p21 (cyclin dependent kinase inhibitor 1A; CDKN1A) activation is demonstrated by the interactions of p21 with cyclins [Dotto, 2000]. p21 interacts directly with cyclins through a conserved region in close to its N-terminus (amino acids 17-24; Cy1) [Dotto, 2000]. The cyclin dependent kinase inhibitor, p21 has the secondary weak cyclin binding domain near its C-terminus region (amino acids 153-159), which overlaps with its proliferating cell nuclear antigen (PCNA) binding domain [Dotto, 2000]. Kinase activity of cyclin-dependent kinase (Cdk) was inhibited by Cy1 site of p21 that is important for the interaction of p21 with cyclin-Cdk complexes [Chen, 1996]. The p21 inhibits Cdk complexes such as cyclin A/E-Cdk2 or cyclin D-Cdk4 complexes, leading to the cell cycle disruption as G1/S arrest [Chen, 1996].
Evidence Supporting this KER
p21 has a separate cyclin-dependent kinase 2 (CDK2) binding site in its N-terminus region (amino acids 53-58) and optimal cyclin/CDK inhibition requires binding by this site as well as one of the cyclin binding sites [Dotto, 2000]. The peptide containing Cy1 site inhibited the kinase activity of cyclin E-Cdk2 and cyclin A-Cdk2 [Chen, 1996]. The p21WAF1/CIP1/sdi1 gene product inhibits the cyclin D/cdk4/6 and the cyclin E/cdk2 complexes in response to DNA-damage, resulting in G1/S arrest [Moussa, 2015, Ogryzko, 1997]. p21 inhibits cyclin-dependent kinases and regulates cell cycle to promote cell cycle arrest. Deletion of either cyclin binding site in N-terminus or C-terminus of p21, or CDK binding domain was sufficient for the kinase activity inhibition [Chen, 1996].
- TSA induces p21 expression leading to cell cycle arrest [Gartel, 2002].
- The up-regulation of p21 signaling and in testicular germ cells was observed in diabetes [Kilarkaje, 2015].
- A study investing the effects of miR-6734 that has a sequence homology with a specific region of p21WAF1/CIP1 promoter on HCT-116 colon cancer cell growth indicated that miR-6734 up-regulated p21 gene expression and induced cell cycle arrest [Kang, 2016]. This result suggests that the direct enhancement of p21 gene expression is related to the alteration of the cell cycle distribution [Kang, 2016].
- The study of postnatal telomere indicated that dysfunction of premature telomere induces cell-cycle arrest through p21 activation in mammalian cardiomyocytes [Aix, 2016].
- The p21WAF1/CIP1/sdi1 gene product inhibits the cyclin D/cdk4/6 and the cyclin E/cdk2 complexes in response to DNA-damage, resulting in G1/S arrest [Moussa, 2015, Ogryzko, 1997].
Uncertainties and Inconsistencies
TSA promotes apoptosis via HDAC inhibition and p53 signaling pathway activation [Deng, 2016a]. It is suggested that furazolidone induces reactive oxygen species leading to suppression of p-AKT and p21, and induction of apoptosis [Deng, 2016b]. The dual roles of p21 in cell cycle arrest and anti-apoptotic effect in the testicular germ cells of diabetic rats are suggested [Kilarkaje, 2015]. The anti-apoptotic effect of p21 is mediated by caspase-3 inhibition, which demonstrates the possibility of cell-cycle independent effect on apoptosis [Deng, 2016b]. It has been demonstrated that p21 induces apoptosis in human cervical cancer cell lines [Tsao, 1999], whereas p21 is implicated in apoptosis inhibition by blocking activation of caspase-3 or interacting with ASK1 [Gartel, 2002, Zhan, 2007]. Up-regulation of p21 is implicated in the activation of DNA damage pathways, and deletion of p21 improved stem cell function and lifespan without accelerating chromosomal instability, which indicates that p21-dependent checkpoint induction affects the longevity limit [Choudhury, 2007].
Quantitative Understanding of the Linkage
The peptide containing cyclin-binding domain of p21 in N-terminus inhibited the kinase activity of cyclin E-Cdk2 with 296 nM of the concentration in which kinase activity is inhibited in 50% (Ki) [Chen, 1996].
The peptide containing cyclin-binding domain of p21 in C-terminus showed 32,000, 800, or >300,000 nM of Ki for inhibition of the kinase activity of cyclin E-Cdk2, cyclin A-Cdk2 or cyclin D1-Cdk4, respectively [Chen, 1996].
Known modulating factors
Known Feedforward/Feedback loops influencing this KER
Domain of Applicability
DNA replication in Xenopus was suppressed by the GST fusion protein of p21 without amino acids 17-24 or the peptide containing cyclin binding site in N-terminus of p21 protein [Chen, 1996]. P21 regulates the E2F transcriptional activity to control cell cycle in human U2OS osteosarcoma cells (Homo sapiens) [Delavaine, 1999]. Cell cycle is regulated by p21 through cyclins and CDKs in mice (Mus musculus) [Sherr CJ, 2004].
Dotto GP (2000) p21WAF1/Cip1: more than a break to the cell cycle? Biochim Biophys Acta 1471: M43-M56
Chen J et al (1996) Cyclin-binding motifs are essential for the function of p21CIP1. Mol Cell Biol 16: 4673-4682
Moussa RS et al. (2015) Differential targeting of the cyclin-dependent kinase inhibitor, p21CIP/WAF1, by chelators with anti-proliferative activity in a range of tumor cell-types. Oncotarget 6:29694-29711
Ogryzko VV et al. (1997) WAF1 retards S-phase progression primarily by inhibition of cyclin-dependent kinases. Mol Cell Biol 17:4877-4882
Gartel AL and Tyner AL (2002) The role of the cyclin-dependent kinase inhibitor p21 in apoptosis. Mol Cancer Ther 1: 639-649
Kilarkaje N and Al-Bader MM. (2015) Diabetes-Induced Oxidative DNA Damage Alters p53-p21CIP1/Waf1 Signaling in the Rat Testis. Reproductive Sciences 22: 102–112
Kang MR et al (2016) miR-6734 up-regulates p21 gene expression and induces cell cycle arrest and apoptosis in colon cancer cells. PLoS One 11: e0160961
Aix E et al (2016) Postnatal telomere dysfunction induces cardiomyocyte cell-cycle arrest through p21 activation. J Cell Biol 213: 571-583
Deng Z et al. (2016a) Histone deacetylase inhibitor trichostatin A promotes the apoptosis of osteosarcoma cells through p53 signaling pathway activation. Int J Biol Sci 12:1298-1308
Deng S et al (2016b) P21Waf1/Cip1 plays a critical role in furazolidone-induced apoptosis in HepG2 cells through influencing the caspase-3 activation and ROS generation. Food Chem Toxicol 88: 1-12
Tsao YP et al (1999) Adenovirus-mediated p21WAF1/SDII/CIP1 gene transfer induces apoptosis of human cervical cancer cell lines. J Virology 73: 4983-4990
Zhan J et al (2007) Negative regulation of ASK1 by p21Cip1 involves a small domain that includes serine 98 that is phosphorylated by ASK1 in vivo. Mol Cell Biol 27: 3530-3541
Choudhury AR et al (2007) Cdkn1a deletion improves stem cell function and lifespan of mice with dysfunctional telomeres without accelerating cancer formation. Nat Genet 39: 99-105
Delavaine L and La Thangue NB (1999) Control of E2F activity by p21Waf1/Cip1. Oncogene 18: 5381-5392
Sherr CJ and Roberts JM (2004) Living with or without cyclins and cyclin-dependent kinases. Gene Dev 18: 2699-2711