Chronic p53-independent p21 expression causes genomic instability by deregulating replication licensing

Area of Science:

• Molecular Biology
• Cancer Biology
• Cell Cycle Regulation

Background:

• The cyclin-dependent kinase inhibitor p21(WAF1/CIP1) (p21) is a known cell-cycle regulator and senescence inducer, typically controlled by p53.
• Emerging evidence suggests p21 may possess oncogenic functions, a role that has remained poorly understood.
• This study investigates the potential tumor-promoting activities of p21.

Purpose of the Study:

• To elucidate the mechanism by which p21 contributes to cancer progression.
• To investigate the role of p21 in p53-mutant cancers and aggressive tumor cells.
• To analyze the phenotypic and genomic consequences of sustained p21 expression.

Main Methods:

• Utilized p21-inducible, p53-null cellular models, including cancerous and near-normal cells.
• Performed multifaceted phenotypic and genomic analyses.
• Investigated the effect of sustained p21 accumulation on cellular processes and molecular pathways.

Main Results:

• A subset of atypical cancer cells with high p21 expression exhibited proliferation, particularly in p53-mutant cancers.
• Emergence of a p21-expressing proliferating subpopulation after an initial senescence phase was observed.
• These proliferating cells displayed increased genomic instability, aggressiveness, and chemoresistance.
• Sustained p21 accumulation inhibited the CRL4-CDT2 ubiquitin ligase, leading to deregulated origin licensing and replication stress.

Conclusions:

• p21 can promote tumor growth by deregulating the DNA replication licensing machinery.
• This oncogenic role of p21 is p53-independent and associated with aggressive cancer phenotypes.
• The findings reveal an unconventional tumor-promoting function of p21, relevant for cancer treatment strategies.