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J Korean Soc Ther Radiol > Volume 15(3); 1997 > Article
Journal of the Korean Society for Therapeutic Radiology 1997;15(3): 187-196.
Induction of Apoptosis and Expression of Apoptosis-related Gene Products in Response to Radiation in Murine Tumors
Jinsil Seong, Nancy R Hunter, Luka Milas
1Department of Radiation Oncology, Yonsei University Medical College, Seoul, Korea.
2Department of Experimental Radiation Oncology, The University of Texas M.D. Anderson Cancer Center, Houston TX 77030, USA.
To analyze the involvement of apoptosis regulatory genes p53, p21waf1/cip1, bax and bcl-2 in induction of apoptosis by radiation in murine tumors.
The radiation-sensitive ovarian carcinoma OCa-I, and the radiation-resistant hepatocarcinoma HCa-I were used. Tumors, 8 mm in diameter, were irradiated with 25 Gy and at various times after irradiation, ranging from 1 to 48 h, were analyzed histologically for apoptosis and by western blot for alterations in the expression of these genes. The p53 status of the tumors were determined by the polymerase chain reaction-single strand conformation polymorphism assay.
Both tumors were positive for wild-type p53. Radiation induced apoptosis in OCa-I but not in HCa-I. Apoptosis developed rapidly, peaked at 2 h after irradiation and returned to almost the background level at 48 h. In OCa-I radiation upregulated the expression of p53, p21waf1/cip1, and the bcl-2/bax ratio was decreased. In HCa-I radiation increased the expression of both p53 and p21waf1/cip1, although the increase of the latter was small. The bcl-2/bax ratio was greatly increased. In general the observed changes occurred within a few hours after irradiation, and either preceded or coincided with development of apoptosis.
The development of apoptosis required upregulation of both p53 and p21waf1/cip1 as well as a decrease in bcl-2/bax ratio. In contrast, an increase in bcl-2/bax ratio prevented apoptosis in the presence of upregulated p53 and p21waf1/cip1. These findings indentified the involvement of multiple oncogenes in apoptosis regulation in vivo and demonstrate the complexity that may be associated with the use of a single oncogene assessment for predicting the outcome of cancer therapy with cytotoxic agents.
Key Words: Apoptosis, Murine tumors, Radiation, p53, p21waf1/cip1, Bax and bcl-2
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