EXPRESSION OF TRANSFECTED RECOMBINANT ONCOGENES INCREASES RADIATION-RESISTANCE OF CLONAL HEMATOPOIETIC AND FIBROBLAST CELL-LINES SELECTIVELY AT CLINICAL LOW-DOSE RATE

To determine the effect of oncogene expression on γ radiation sensitivity of hematopoietic compared to fibroblastic cells, we selected clonal sublines of an interleukin-3 (IL-3)-dependent hematopoietic progenitor cell line 32D cl 3 and NIH/3T3 embryo fibroblastic cells following transfection with each oncogene linked to the mycophenolic acid resistance gene. Each mycophenolic acid-resistant subclone demonstrated high levels of specific poly(A)+ mRNA for each oncogene. The parent line 32D cl 3 demonstrated similar radiosensitivity at 116 cGy/min (D0 126, n̄ 1.17) compared to 5 cGy/min (D0 123, n̄ 1.65). This pattern was not altered in subclones of 32D cl 3 cells transfected with the epidermal growth factor (EGF) receptor gene and grown in EGF (at 116 cGy/min D0 104, n̄ 0.998, at 5 cGy/min D0 115, n̄ 1.09), or in 32D cl 3 cells expressing the v-sis oncogene (at 116 cGy/min D0 122.4, n̄ 1.79, at 5 cGy/min D0 135, n̄ 1.43). In contrast, expression of the transfected oncogenes v-erb-B, v-abl, or v-src conferred significant radioresistance at 5 cGy/min dose rate (D0 194, n̄ 1.77; D0 165.5, n̄ 1.56; D0 171, n̄ 1.28, respectively). With the exception of v-sis, oncogene expression resulted in nonautocrine factor independence of 32D cl 3 subclones, and production of donor origin tumors in syngeneic newborn or adult mice. Two rare spontaneous factor-independent subclones of 32D cl 3 were also tested. Nonautocrine clone 32D cl 2 demonstrated significantly increased radioresistance at low dose rate (D0 186, n̄ 1.63), while autocrine (IL-3 producing) subclone 32D cl 4 revealed no significant increase in radioresistance at 5 cGy/min. The parent fibroblast cell line NIH/3T3 showed an intrinsic relative radioresistance at low dose rate (at 5 cGy/min D0 157.3, n̄ 1.81, compared to 116 cGy/min D0 134.3, n̄ 1.57). Expression in NIH/3t3 of transfected oncogenes v-abl, v-fms, v-fos, or H-ras increased radioresistance at low dose rate (D0 208.6, n̄ 1.61; D0 206.6, n̄ 1.51; D0 167.5, n̄ 1.85; and D0 206.8, n̄ 1.08, respectively). Thus expression of each of several oncogenes induces resistance to γ irradiation at 5 cGy/min in hematopoietic and fibroblast cell lines. These data may help explain the clinical recurrence of oncogene-expressing leukemia and lymphoma cells after marrow stem cell ablative doses of low-dose-rate total-body irradiation.