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Decrease in the frequency of X-ray-induced mutation by wild-type p53 protein in human osteosarcoma cells
N Yamagishi1, J Miyakoshi, H Takebe
1Department of Radiation Genetics, Faculty of Medicine, Kyoto University, Sakyo-ku, Japan.
Abstract:
Tumor suppressor p53 protein acts as a checkpoint factor following DNA damage. Inactivation of checkpoint control may increase the frequency of mutation following DNA damage, resulting in tumor progression. Here we examine whether wild-type (wt) p53 protein suppresses X-ray-induced mutations using an isopropyl-beta-D-thiogalactopyranoside (IPTG)-regulated p53 expression system in human osteosarcoma Saos-2 cells. Frequency of X-ray-induced mutations in the hypoxanthine-guanine phosphoribosyl transferase gene was enhanced about 10 and 20 times by 1 and 2 Gy respectively in cells without expression of wt p53 protein, while enhancement of mutations by X-rays was slight in cells with expression of wt p53 protein. Furthermore, arrest at the G/S boundary was induced by X-ray irradiation when p53 protein was expressed by treatment with IPTG. These findings suggest that wt p53 protein has a function in maintaining genomic stability after X-ray irradiation through the G1 checkpoint and loss of p53 function(s) may lead to tumor progression in multi-step tumorigenesis.
Insights
Wild-type p53 protein maintains genomic stability by suppressing X-ray-induced mutations. Loss of p53 function may lead to tumor progression, highlighting its role in cancer development.
Area of Science:
- Molecular Biology
- Cancer Research
- Genetics
Background:
- The p53 protein is a critical tumor suppressor involved in DNA damage response.
- Inactivation of DNA damage checkpoints can increase mutation frequency, potentially driving tumor progression.
Purpose of the Study:
- To investigate the role of wild-type (wt) p53 in suppressing X-ray-induced mutations.
- To determine if p53 expression influences genomic stability after DNA damage.
Main Methods:
- Utilized an isopropyl-beta-D-thiogalactopyranoside (IPTG)-regulated p53 expression system in human osteosarcoma Saos-2 cells.
- Assessed mutation frequency in the hypoxanthine-guanine phosphoribosyl transferase gene after X-ray irradiation.
- Monitored cell cycle progression, specifically G1/S checkpoint arrest.
Main Results:
- X-ray-induced mutations increased significantly (10-20 fold) in cells lacking wt p53 expression.
- Cells expressing wt p53 showed only a slight increase in mutations after X-ray exposure.
- X-ray irradiation induced G1/S cell cycle arrest in cells with IPTG-induced p53 expression.
Conclusions:
- Wild-type p53 protein actively maintains genomic stability following X-ray irradiation via the G1 checkpoint.
- Loss of p53 function is implicated in promoting tumor progression during multi-step carcinogenesis.