Aberrant cell cycle checkpoint function in transformed hepatocytes and WB-F344 hepatic epithelial stem-like cells

Area of Science:

• Molecular Biology
• Cell Biology
• Cancer Research

Background:

• Cell cycle checkpoints are crucial for maintaining genomic integrity and preventing cancer.
• Checkpoint dysfunction allows cells with damaged DNA to proliferate, potentially leading to tumor formation.
• Understanding checkpoint roles in hepatocarcinogenesis is vital for cancer prevention and treatment strategies.

Purpose of the Study:

• To investigate the function of G1, G2, and spindle assembly checkpoints in rat hepatocarcinogenesis.
• To analyze checkpoint responses in normal hepatocytes, hepatic stem-like cells (WB-F344), and their transformed derivatives.
• To determine if checkpoint abnormalities precede tumorigenicity in liver cancer development.

Main Methods:

• Assessed G1 checkpoint function by measuring S-phase reduction after ionizing radiation (IR).
• Quantified G2 checkpoint function by evaluating mitotic inhibition post-IR.
• Analyzed checkpoint function in normal hepatocytes, WB-F344 cells, and transformed cell lines.
• Examined alterations in p53 and p21(Waf1) expression and spindle assembly checkpoint activity.

Main Results:

• Transformed hepatocytes showed significant attenuation or ablation of G1 checkpoint function.
• WB-F344 cells exhibited G1 checkpoint function comparable to normal cells, except for one malignant line.
• All transformed hepatocyte and WB-F344 cell lines displayed attenuated G2 checkpoints.
• Checkpoint dysfunction, including altered p53/p21(Waf1) and spindle assembly defects, was observed before tumorigenicity.

Conclusions:

• Attenuation of G1 and G2 checkpoints is a common feature in transformed hepatocytes and WB-F344 cells.
• Aberrant cell cycle checkpoint function is detected early in hepatocarcinogenesis, preceding overt tumor formation.
• Checkpoint abnormalities contribute to the development of liver cancer by compromising genomic stability.