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J Korean Soc Ther Radiol Oncol > Volume 17(1); 1999 > Article
The Journal of the Korean Society for Therapeutic Radiology and Oncology 1999;17(1): 70-77.
The Expression of Oncogenes on the Radiation-induced Apoptosis in SCK Mammary Adenocarcinoma Cell Line
Hyung Sik Lee, Hong Kyu Park, Chang Won Song, Seon Min Yoon, Won Joo Hur, Su Jin Jeong, Sang Hwa Lee, Min Ho Jung, Heon Joo Park
1Department of Radiation Oncology and Dong A Cancer Care, Pusan, Korea.
2Department of Microbiology, College of Medicine, Dong A University, Pusan, Korea.
3Department of Microbiology, College of Medicine, Inha University, Incheon, Korea.
The expression of p53, p21/WAF/CIP, Bcl-2, and Bax underlying the radiation-induced apoptosis in different pH environments using SCK mammary adenocarcinoma cell line was investigated.
Mammary adenocarcinoma cells of A/J mice (SCK cells) in exponential growth phase were irradiated with a linear accelerator at room temperature. The cells were irradiated with 12 Gy and one hour later, the media was replaced with fresh media at a different pHs. After incubation at 37 degrees C for 0-48 h, the extent of apoptosis was determined using agarose gel electrophoresis and flow cytometry. The progression of cells through the cell cycle after irradiation in different pHs was also determined with flow cytometry. Western blot analysis was used to monitor p53, p21/WAF/CIP, Bcl-2, and Bax protein levels.
The induction of apoptosis by irradiation in pH 6.6 medium was markedly less than that in pH 7.5 medium. The radiation-induced G2/M arrest in pH 6.6 medium lasted markedly longer than that in pH 7.5 medium. Considerable amounts of p53 and p21 proteins already existed at pH 7.5 and increased the level of p53 and p21 significantly after 12 Gy X-irradiation. An incubation at pH 6.6 after 12 Gy X-irradiation did not change the level of p53 and p21 protein levels significantly. Bcl-2 proteins were not significantly affected by radiation and showed no correlation with cell susceptibility to radiation-induced apoptosis in different pHs. An exposure to 12 Gy of X-rays increased the level of Bax protein at pH 7.5 but at pH 6.6, it was slight.
The molecular mechanism underlying radiation-induced apoptosis in different pH environments using SCK mammary adenocarcinoma cell line was dependent of the expression p53 and p21/WAF/CIP proteins. We may propose following hypothesis that an acidic stress augments the radiation-induced G2/M arrest, which inhibiting the irradiated cells undergo post-mitotic apoptosis. The effects of environmental acidity on anti-apoptotic and pro-apoptotic function of Bcl-2 family was unclear in SCK mammary adenocarcinoma cell line.
Key Words: Radiation-induced apoptosis, Oncogene, Cell cycle
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