p21 in apoptosis: tools and targets

Choose the right tools for identifying roles of procaspase 3, caspase 8, ASK1 and galectin 8 in p21-mediated apoptosis.

p21 induction primarily inhibits apoptosis by causing cell cycle arrest and DNA repair. However, p21-arrested cells may be triggered to undergo apoptosis following activation of pro-apoptotic genes in a p53-dependent or -independent manner1. Studying p21 expression levels and its association of with pro-apoptotic proteins may yield better insights into the duality of p21 function.

Procaspase 3

Fas-mediated caspase 3 apoptosis is inhibited by the p21-procaspase 3 complex. Mitochondrial adaptor protein regulates p21-procaspase 3 complex and ensures cell survival2.

TypeReagent nameDescriptionAbID
AntibodyAnti-active Caspase-3 antibody
Validated using a knockout cell line
Type: Rabbit monoclonal antibody
Reactivity: Hu
Applications: IHC-Fr, IHC-P, WB, ICC/IF, WB
molecule compound
Actinomycin D (apoptotic activator)Activates Fas-mediated caspase 3 apoptosis. Causes downregulation of p21 and facilitates cell death3.ab141058
PAC-1 (caspase 3 activator)Potent caspase-3 activator (IC50 = 220 nM) with in vitro and in vivo activity4.ab142074
CytoPainter dyesVisualise mitochondrial staining of suspension or adherent cells.Click here



Cdk4 interacting protein that relives p21 from the p21-Cdk4 complex. Survivin facilitates p21-procaspase 3 interaction hence promoting suppression of Fas-mediated cell death5.

TypeReagent nameDescriptionAbID
AntibodyAnti-Survivin antibodyType: Rabbit monoclonal antibody
Reactivity: Hu
Applications: IHC-P, WB, IP, Flow Cyt, ICC/IF, ELISA
KitSurvivin SimpleStep ELISA® kit

Quantitatively measure surviving levels in various sample types6.

Reactivity: Hu
Range: 94 pg/ml - 6000 pg/ml
Method: Colorimetric



DR4 TRAIL receptor-dependent cleavage of initiator caspase 8 is blocked by p21 overexpression implicating p21 in cell survival via caspase 8 apoptosis7.

TypeReagent nameDescriptionAbID
AntibodyAnti-Caspase-8 antibodyValidated using a knockout cell lineType: Rabbit monoclonal antibody
Reactivity: Hu
Applications: ICC/IF, IHC-P, WB
Anti-DR4 antibodyType: Rabbit polyclonal
Reactivity: Hu
Applications: ICC/IF, IHC-P, WB


Apoptosis signal-regulating kinase 1 (ASK1) and p21 forms a complex implying the function of p21 as an antiapoptotic protein8. Phosphorylation of p21 at S98 by ASK1 is thought to regulate ASK1-p21 binding and ASK1 inactivation9.

TypeReagent nameDescriptionAbID
AntibodyAnti-ASK1 antibodyValidated using a knockout cell lineType: Rabbit monoclonal antibody
Reactivity: Hu, Mo
Applications: WB, IHC-P, ICC/IF, Flow Cyt

Galectin 8

Galectin 8 through the activation of JNK and PKB(Akt) promotes the accumulation of p21 and reduces the rate of DNA synthesis thereby inducing cell cycle arrest10.

TypeReagent nameDescriptionAbID
AntibodyAnti-Galectin 8 antibodyType: Rabbit monoclonal antibody
Reactivity: Hu
Applications: WB, IP, IHC-P, Flow Cyt, ICC/IF
Anti-pan-AKT antibody

Type: Rabbit polyclonal
Reactivity: Hu, Mo, Rt
Applications: ICC, IHC, WB, Flow Cyt, ELISA

Anti-JNK1/2/3 antibodyType: Rabbit monoclonal antibody
Reactivity: Hu, Mo, Rt, others
Applications: Flow Cyt, WB, IP, ICC/IF
molecule compound
WortmanninJNK and PI3K inhibitors that inhibit the cellular increase of p21. Wortmannin (1 μM), SP600125 (10 μM)10.ab120148
Cycloheximide (CHX)Galectin 8 causes cells to undergo apoptosis following p21 inhibition by CHX10.ab120093


  1. Abbas, T. & Dutta, A. p21 in cancer: intricate networks and multiple activities. Nat. Rev. Cancer 9, 400–414 (2009). Read more
  2. Suzuki, A., Tsutomi, Y., Yamamoto, N., Shibutani, T. & Akahane, K. Mitochondrial regulation of cell death: mitochondria are essential for procaspase 3-p21 complex formation to resist Fas-mediated cell death. Mol. Cell. Biol. 19, 3842–7 (1999). Read more
  3. Suzuki, A., Tsutomi, Y., Akahane, K., Araki, T. & Miura, M. Resistance to Fas-mediated apoptosis: activation of Caspase 3 is regulated by cell cycle regulator p21WAF1 and IAP gene family ILP. Oncogene 17, 931–939 (1998). Read more
  4. Peterson, Q. P. et al. PAC-1 activates procaspase-3 in vitro through relief of zinc-mediated inhibition. J. Mol. Biol. 388, 144–58 (2009). Read more
  5. Suzuki, A. et al. Survivin initiates procaspase 3/p21 complex formation as a result of interaction with Cdk4 to resist Fas-mediated cell death. Oncogene 19, 1346–1353 (2000). Read more
  6. Liu, Y. et al. Identification of bile survivin and carbohydrate antigen 199 in distinguishing cholangiocarcinoma from benign obstructive jaundice. Biomark. Med. 11, 11–18 (2017). Read more
  7. Xu, S.-Q. & El-Deiry, W. S. p21WAF1/CIP1 Inhibits Initiator Caspase Cleavage by TRAIL Death Receptor DR4. Biochem. Biophys. Res. Commun. 269, 179–190 (2000). Read more
  8. Schepers, H., Geugien, M., Eggen, B. J. L. & Vellenga, E. Constitutive cytoplasmic localization of p21Waf1/Cip1 affects the apoptotic process in monocytic leukaemia. Leukemia 17, 2113–2121 (2003). Read more
  9. Zhan, J. et al. 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, 3530–41 (2007). Read more
  10. Arbel-Goren, R., Levy, Y., Ronen, D. & Zick, Y. Cyclin-dependent kinase inhibitors and JNK act as molecular switches, regulating the choice between growth arrest and apoptosis induced by galectin-8. J. Biol. Chem. 280, 19105–19114 (2005). Read more