| Abstract: |
Cesium-137 γ rays were used to transform rat embryo cells (REC) which were first transfected with activated c-myc or c-Ha-ras oncogenes to produce immortal cell lines (REC:myc and REC:ras). When exposed to 6 Gy of 137Cs γ rays, some cells became morphologically transformed with focus formation frequencies of ~3 x 10-4 for REC:myc and ~1 x 10-4 for REC:ras, respectively. Cells isolated from foci of γ-ray-transformed REC:myc (REC:myc:γ) formed anchorage-independent colonies and were tumorigenic in nude mice, but foci from γ-ray-transformed REC:ras (REC:ras:γ) did not exhibit either of these criteria of transformation. Similar to the results with γ irradiation, we observed a sequence-dependent phenomenon when myc and ras were transfected into REC, one at a time. REC immortalized by ras transfection were not converted to a tumorigenic phenotype by secondary transfection with myc, but REC transfected with myc were very susceptible to transformation by subsequent ras transfection. This suggests that myc- immortalized cells are more permissive to transformation via secondary treatments. In sequentially transfected REC, myc expression was high whether it was transfected first or second, whereas ras expression was highest when the ras gene was transfected secondarily into myc-containing REC. Molecular analysis of REC:ras:γ transformants showed no alterations in structure of the transfected ras or of the endogenous ras, myc, p53, or fos genes. The expression of ras and p53 was increased in some isolates of REC:ras:γ, but myc and fos expression were not affected. Similarly, REC:myc:γ transformants did not demonstrate rearrangement or amplification of the transfected or the endogenous myc genes, or of the potentially cooperating Ha-, Ki-, or N-ras genes. Northern hybridization analysis revealed increased expression of N- ras in two isolates, REC:myc:γ33 and γ41, but no alterations in the expression of myc, raf, Ha-ras, or Ki-ras genes in any REC:myc transformant. DNA from several transformed REC:myc:γ cell lines induced focus formation in recipient C3H 10T1/2 and NIH 3T3 cells. The NIH 3T3 foci tested positive when hybridized to a probe for rat repetitive DNA. A detailed analysis of the NIH 3T3 transformants generated from REC:myc:γ33 and γ41 DNA failed to detect Ha-ras, Ki-ras, raf, neu, trk, abl, fms, or src oncogenes of rat origin. Our results suggest that the p53 gene may be involved in the γ-ray-induced transformation of ras-immortalized REC and, similarly, the N-ras gene may be involved in the transformation of some isolates of myc-immortalized REC. In the remaining REC:myc:γ transformants other dominant-acting oncogenes may play a role in the transformation process. |
| Keywords: |
nonhuman; radiation dose; neoplasm; animal cell; animal; cell structure; embryo; transfection; radiation injury; carcinogenesis; cell transformation, neoplastic; oncogenes; rna; dna; cell transformation; rat; gamma irradiation; rats; oncogene ras; oncogene myc; in vitro; embryo cell; rats, inbred f344; gamma rays; cesium radioisotopes; dna transfection; priority journal; article; support, u.s. gov't, p.h.s.; support, u.s. gov't, non-p.h.s.; radiation genetics
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