p53 isoforms differentially impact on the POLι dependent DNA damage tolerance pathway.

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• The canonical p53 protein (p53α) regulates DNA damage tolerance (DDT) via complexes with translesion synthesis polymerase iota (POLι).
• This pathway involves p53's DNA-binding, oligomerization, and complex formation with POLι to slow DNA synthesis for replication barrier bypass.
• Alternative p53 isoforms, arising from different splicing or translation initiation, may modulate this canonical function.

Purpose of the Study:

• To investigate how alternative p53 isoforms (p53β, p53γ, Δ40p53α, Δ133p53α, Δ160p53α) affect the p53-POLι-dependent DDT pathway.
• To determine the impact of these isoforms on POLι recruitment, DNA replication dynamics, and recombination.
• To assess the consequences of co-expressing alternative isoforms with p53α, especially in cancer and stem cell contexts.

Main Methods:

• Assessing p53 isoform interactions with PCNA (proliferating cell nuclear antigen).
• Evaluating POLι recruitment to PCNA under replication stress (Mitomycin C treatment).
• Monitoring nascent DNA synthesis deceleration and recombination rates.
• Analyzing effects of co-expression of p53α with alternative isoforms on DNA replication.

Main Results:

• C-terminal p53 isoforms (p53β, p53γ) bind PCNA, while N-terminal truncated isoforms show reduced binding.
• All alternative isoforms impaired POLι recruitment and replication deceleration under stress, and failed to stimulate recombination.
• Δ133p53α and Δ160p53α caused replication fork stalling even without stress.
• Co-expression with p53α exacerbated DDT defects, with Δ133p53α and Δ160p53α showing the strongest inhibitory effect on p53α.

Conclusions:

• Alternative p53 isoforms interfere with the p53-POLι-dependent DDT pathway, compromising DNA repair and replication fidelity.
• The co-expression of alternative p53 isoforms with p53α, common in tumors and stem cells, impairs p53α's protective functions.
• These findings highlight the critical role of p53 isoform balance in maintaining genomic stability and suggest potential therapeutic targets in cancer.