Cellular tumor antigen p53 (p53) - Cyclin-dependent kinase inhibitor 1A (p21) signaling axis (p53-p21 axis)

The p53-p21 G1 cell cycle checkpoint machinery is a critical regulatory axis that maintains genomic stability by controlling the transition from the G1 to the S phase in response to cellular stress [UniProt P04637, P38936]. The pathway is centered on the tumor suppressor p53, a transcription factor that is stabilized upon DNA damage or oncogenic signaling [PubMed PMID: 25207159]. Once activated, p53 binds to the promoter of the CDKN1A gene, leading to the production of the p21 protein, a potent inhibitor of cyclin-dependent kinases (CDKs) [StatPearls, Cell Cycle Checkpoints]. p21 specifically inhibits CDK2, CDK4, and CDK6, which prevents the phosphorylation of the retinoblastoma protein (Rb) and sequesters E2F transcription factors, effectively halting cell cycle progression [PubMed PMID: 11412634]. In many cancers, this machinery is disrupted by TP53 mutations or the overexpression of MDM2, which targets p53 for proteasomal degradation [NIH, NCI Dictionary]. Therapeutic strategies aim to restore this checkpoint by using MDM2 inhibitors to stabilize wild-type p53 or small molecules to reactivate mutant p53, thereby inducing p21-mediated growth arrest or apoptosis in tumor cells [PubMed PMID: 33035186].

Other names

p53-p21 G1 cell cycle checkpoint machineryTP53-CDKN1A pathwayp53-p21-DREAM pathwayG1/S checkpoint machinery

Stabilization or reactivation of p53 induces the transcription of p21, which inhibits CDK2/4/6-cyclin complexes, preventing Rb phosphorylation and arresting the cell cycle in the G1 phase.