Telomerase expression is sufficient for chromosomal integrity in cells lacking p53 dependent G1 checkpoint function

Area of Science:

• Cellular senescence and cancer research
• Genetics and molecular biology
• DNA damage response

Background:

• Human fibroblasts have a limited lifespan, ending in senescence.
• Loss of p53 function bypasses senescence, leading to increased chromosomal aberrations and decreased checkpoint functions.
• This study investigates the relationship between chromosomal instability and checkpoint dysfunction.

Purpose of the Study:

• To explore the interplay between chromosomal instability and checkpoint dysfunction in human fibroblasts.
• To determine the role of p53 status and telomerase expression in these processes.
• To understand the mechanisms driving chromosomal instability in cells with defective p53.

Main Methods:

• Derived human fibroblast lines expressing HPV16E6 oncoprotein or dominant-negative p53 alleles (A143V, H179Q).
• Investigated checkpoint functions (G1 and G2) after ionizing radiation exposure.
• Assessed chromosomal aberrations and cell proliferation with or without telomerase expression.

Main Results:

• Cells with normal p53 showed robust G1 arrest after radiation; p53-deficient cells showed attenuated G1 arrest.
• All cell lines maintained a normal G2 checkpoint response to DNA damage.
• Telomerase-negative cells exhibited increased chromosomal aberrations as they bypassed senescence.
• Telomerase expression in p53-defective cells prevented chromosomal aberrations and G2 checkpoint attenuation, allowing extensive proliferation.

Conclusions:

• Chromosomal instability in p53-defective cells is primarily driven by telomere erosion.
• Loss of the G1 DNA damage checkpoint is not the main cause of instability in this context.
• Telomere maintenance is crucial for preventing genomic instability in cells with compromised p53 function.