Enhanced expression of thymidine kinase in human cells following ionizing radiation.
OBJECTIVE
We investigated the induction of thymidine kinase transcription and enzymatic activity, and the activation of transcription factors binding to the thymidine kinase promoter, in human normal compared to tumor cells in culture before and after ionizing radiation.


METHODS
Northern blot, dot-blot, and thymidine kinase enzyme assays were used to observe thymidine kinase transcript and enzymatic changes before and after radiation. Temporal expression of thymidine kinase transcripts following an optimal induction dose of radiation was also studied. Gel mobility shift assays were performed using a 95-base pair fragment of the thymidine kinase promoter (containing the CCAAT box) to analyze transcription factor binding.


RESULTS
Thymidine kinase transcript and enzymatic levels were higher in human tumor compared to normal cells. In contrast, levels of x-ray-activated thymidine kinase transcription factors were not significantly different in human neoplastic compared to normal cells.


CONCLUSIONS
Elevated x-ray-induced thymidine kinase transcripts, enzymatic levels, and transcription factors are consistent with the loss of stringent cell growth regulation associated with neoplastic cells. The induction of thymidine kinase following ionizing radiation may be exploited in chemotherapeutic strategies which use halogenated pyrimidines and/or in various gene therapy strategies.
Boothman
D A
DA
University of Wisconsin, Department of Human Oncology, Madison 53792.
Davis
T W
TW
Sahijdak
W M
WM
D000818:Animals; D002478:Cells, Cultured; D004790:Enzyme Induction / Q000528:radiation effects; D015971:Gene Expression Regulation, Enzymologic / Q000528:radiation effects*; D006801:Humans; D009369:Neoplasms / Q000201:enzymology*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis; D013937:Thymidine Kinase / Q000096:biosynthesis* / Q000235:genetics; D014157:Transcription Factors / Q000378:metabolism; D014965:X-Rays
D012333:RNA, Messenger; D014157:Transcription Factors; D013937:Thymidine Kinase