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Thermal Response of Oncogene-transfected Rat Cells¹

Radiation Oncology Research Laboratory, Department of Radiation Oncology, University of California, San Francisco, California 94143

Rat embryo cells or Rat-1 fibroblasts were transfected with either an activated c-myc or a c-Ha-ras from the T24/EJ bladder carcinoma, or they were cotransfected with both. A gene conferring neomycin or hygromycin resistance was also cotransfected so that independent cell lines could be selected by growth in medium containing the antibiotic. Certain isolates from cells transfected with only one type of oncogene were further transformed by exposure to 600 cGy of 250-kVp X-rays. Successful transfection and transformation were characterized by altered morphology, increased plating efficiency, shorter doubling time, longer life span, foci formation, anchorage-independent growth, and Southern and Northern hybridization analysis.

The thermal response of these cells at different stages of oncogenic transformation was examined by exposing exponentially growing cells to 45°C for 0 to 45 min and measuring cellular survivals using colony formation assay. We found that cells transfected with myc oncogene, singly or in combination with ras, were more sensitive to thermal stress. Aside from that, the cells' thermal sensitivity was not affected by the degree or the nature of transformation.

¹ This work is supported in part by grants CA31397 (G. C. L., J. Y. M.) and CA42044 (C. C. L., B. E.) from the National Cancer Institute, NIH, Department of Health and Human Services, and by Grant DE-FG03-88ER60695 (C. C. L., and B. E.) from the Department of Energy.

² To whom requests for reprints should be addressed, at University of California, San Francisco, Department of Radiation Oncology, Radiation Oncology Research Laboratory, Mission Center 200, Box 0806, San Francisco, CA 94143-0806.

Received 9/14/89. Revised 1/ 8/90.

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