Relationship: 1710



Histone acetylation, increase leads to p21 (CDKN1A) expression, increase

Upstream event


Histone acetylation, increase

Downstream event


p21 (CDKN1A) expression, increase

Key Event Relationship Overview


AOPs Referencing Relationship


AOP Name Adjacency Weight of Evidence Quantitative Understanding
Histone deacetylase inhibition leading to testicular toxicity adjacent Moderate Moderate

Taxonomic Applicability


Term Scientific Term Evidence Link
Homo sapiens Homo sapiens High NCBI
Rattus norvegicus Rattus norvegicus High NCBI
Mus musculus Mus musculus High NCBI

Sex Applicability


Sex Evidence
Unspecific High

Life Stage Applicability


Term Evidence
Not Otherwise Specified High

Key Event Relationship Description


Upon histone acetylation increase, p21 transcription and protein level are increased. Acetylation of p21 promoter and p21 mRNA level have a close correlation [Gurvich, 2004]. Transient histone hyperacetylation was sufficient for the activation of p21 [Wu, 2001]. Histone hyperacetylating agents butyrate and TSA induced p21 mRNA expression [Archer, 1998]. SAHA induced the accumulation of acetylated histones in the chromatin of the p21WAF1 gene and this increase was associated with an increase in p21WAF1 expression [Richon, 2000].


Evidence Supporting this KER


Biological Plausibility


HDIs induce histone hyperacetylation and p21 activation leading to the cell cycle arrest, which suggests the close correlation between histone hyperacetylation and p21. In the models proposed for the relationship between histone acetylation and transcription, histone acetylation can be untargeted and occur at both promoter and nonpromoter regions, targeted generally to promoter regions, or targeted to specific promoters by gene-specific activator proteins [Richon, 2000, Struhl, 1998]. Since several results supported a model in which increased histone acetylation is targeted to specific genes and occurs throughout the entire gene, not just the promoter regions, histone acetylation may leads to gene transcription of p21 [Richon, 2000].

Empirical Evidence


  • MAA induced histone acetylation of H4 in prostate cancer cells including LNCaP, C4-2B, PC-3 and DU-145 parallel with p21 mRNA level increase [Parajuli, 2014].
  • HDIs accumulated acetylation of histones and induced p21 protein and mRNA expression [Richon, 2000, Wu, 2001].

Uncertainties and Inconsistencies


There are several pathways to activate p21 promoter by HDI. A HDI, apicidin, induced p21WAF1/Cip1 mRNA independent of the de novo protein synthesis and activated the p21WAF1/Cip1 promoter through Sp1 sites [Han, 2001]. Pretreatment with selective PKC inhibitors calphostin A and rottlerin suppressed the promoter activity of p21WAF1/Cip1 activated by apicidin [Han, 2001]. Furthermore, apicidin-induced translocation of PKCe from cytosolic to particulate fraction was reversed by pretreatment with calphostin C, which suggests the PKCe involvement in apicidin-induced p21WAF1/Cip1 transcription [Han, 2001]. The p21 promoter activation through Sp1 sites induced by apicidin is thought to be independent of histone hyperacetylation [Han, 2001]. The apicidin is suggested to histone hyperacetylation leading to the antiproliferative activity [Han, 2000]. These results indicate the inconclusive discussion in the linkage between histone acetylation and p21 activation.

Quantitative Understanding of the Linkage


Histone H4 acetylation is induced with in 4 hrs and returned to basal level after 0.3 uM of trichostatin A (TSA) treatment [Wu JT].

Response-response Relationship


Dose-response of valproic acid (VPA) showed that 5, 10, and 20 mM of VPA inhibited HDAC6 and HDAC7 activity in 293T cells, and 0.1-2 mM of VPA induced acetylation of lysine in H3 in U937 cells [Gurvich 2004]. The p21 protein level was induced with the treatment of 0.25-2 mM of VPA in U937 cells [Gurvich 2004].



Time course for histone H4 hyperacetylation in response to in repeated doses of TSA every 8 hrs showed that histone hyperacetylation was peaked in 12 hrs in 8-fold increase and showed 5-fold increase in 24 hrs compared to control [Wu JT]. TSA (0.3 uM) induced p21 mRNA expression in 1 hr after stimulation and the induction is returned to the basal level in 24 hrs [Wu JT]. Sodium butyrate (5 mM) and repetitive doses of TSA (0.3 uM, every 8 hrs) induced the p21 mRNA level in 24 hrs in HT-29 cells [Wu JT]. Acetylation of p21 promoter and p21 mRNA induction were correlated in treatment of valproic acid and analogs [Gurvich 2004]. MAA-induced acetylation increase in histones H3 and H4 was occurred in 4, 8, 12 hrs and returned to basal level in 24 hrs after the treatment in rat testis [Wade 2008].

Known modulating factors


Known Feedforward/Feedback loops influencing this KER


Domain of Applicability


The relationship between increased histone acetylation and p21 expression increase is likely well conserved between species.

  • TSA and sodium butyrate induced p21 mRNA expression in HT-29 human colon carcinoma cells (Homo sapiens) [Wu, 2001].
  • VPA increased acetylation of histone H3 from 3 hrs to 72 hrs after the treatment, and increased p21 expression in 24 hrs after the treatment in K562 cells (Homo sapiens) [Gurvich, 2004].
  • Scriptaid, a HDI, up-regulated p21 mRNA expression in mouse embryonic kidney cells (Mus musculus) [Chen, 2011].



Gurvich N et al. (2004) Histone deacetylase is a target of valproic acid-mediated cellular differentiation. Cancer Res 64:1079-1086

Wu JT et al. (2001) Transient vs prolonged histone hyper acetylation: effects on colon cancer cell growth, differentiation, and apoptosis. Am J Physiol Gastrointest Liver Physiol 280:G482-G490

Archer SY et al. (1998) p21WAF1 is required for butyrate-mediated growth inhibition of human colon cancer cells. Proc Natl Acad Sci USA 95:6791-6796

Richon VM et al. (2000) Histone deacetylase inhibitor selectively induces p21WAF1 expression and gene-associated histone acetylation. Proc Natl Acad Sci 97:10014-10019

Struhl K. (1998) Histone acetylation and transcriptional regulatory mechanisms. Gene Dev 12:599-606

Parajuli KR et al. (2014) Methoxyacetic acid suppresses prostate cancer cell growth by inducing growth arrest and apoptosis. Am J Clin Exp Urol 2:300-313

Han JW et al. (2001) Activation of p21WAF1/Cip1 transcription through Sp1 sites by histone deacetylase inhibitor apicidin: involvement of protein kinase C. J Biol Chem 276:42084-42090

Han JW et al. (2000) Apidin, a histone deacetylase inhibitor, inhibits proliferation of tumor cells via induction of p21WAF1/Cip1 and gelsolin. Cancer Res 60:6068-6074

Wade MG et al. (2008) Methoxyacetic acid-induced spermatocyte death is associated with histone hyperacetylation in rats. Biol Reprod 78:822-831

Chen S et al (2011) Histone deacetylase (HDAC) activity for embryonic kidney gene expression, growth, and differentiation. J Biol Chem 286: 32775-32789