👤 N Kyprianou

When nonmetastatic dimethylbenzanthracene-induced rat mammary cancer cells (RMC1) were transfected with a control plasmid containing the neomycin resistance gene (i.e., Neo/Only), none of the five clonal Neo/Only transfectants isolated and characterized was metastatic, only one of five had a single structural chromosomal abnormality, and only one of five had a single numerical chromosomal change not present in the untransfected parental RMC1 cells. In contrast, when RMC1 cells were transfected with a plasmid containing both the neo resistance and mutated v-H-ras oncogene (i.e., Neo/Ras), four of nine clonal Neo/Ras transfectants isolated and characterized were highly metastatic, and all nine had multiple structural and/or additional numerical chromosomal abnormalities. The frequency of transfectants which had structural and/or additional numerical chromosomal changes in Neo/Ras transfectants was significantly higher than that in Neo/Only transfectants (P less than 0.05). In addition, seven of nine Neo/Ras transfectants had structural abnormalities in chromosome 1, whereas none of five Neo/Only transfectants had such abnormalities (P less than 0.05). All four Neo/Ras transfectants that were highly metastatic had structural aberrations involving a gain in chromosome 4. In contrast, none of the three Neo/Ras transfectants which were of low metastatic ability had a similar aberration involving chromosome 4. Correlation between a gain in chromosome 4 and a gain of high metastatic ability was significantly (P less than 0.05). These results demonstrate that, when RMC1 cells are transfected with v-H-ras, transfectants expressing the mutated v-H-ras p21 become genetically unstable and undergo chromosomal changes. These studies suggest that, if the appropriate chromosomal changes occur, these v-H-ras transfectants acquire high metastatic ability. Show less

To study the relationship between metastatic ability and activated ras expression, a cloned, low metastatic, dimethylbenz(a)anthracene-induced rat mammary cancer cell line (RMC1) was transfected with the v-H-ras oncogene. Cloned transfectants were characterized as high, medium, or low expressors of the v-H-ras gene, on the basis of Southern, Northern, and Western blot analysis. Following s.c. inoculation in syngeneic rats, all transfectants produced tumors; however, the in vivo growth rate of cloned transfectants which expressed any level of v-H-ras oncogene was significantly higher (approximately 5-fold) than that observed in the untransfected RMC1 cells. Control (neo only) transfectants exhibited no change in growth rate and had a low metastatic ability comparable to that of the parental untransfected cells. Certain cloned v-H-ras expressing transfectants were highly metastatic to the lungs and lymph nodes. These highly metastatic H-ras transfectants differed widely however, in their level of H-ras expression. The lung colonization potential following i.v. inoculation was increased in all transfectants which expressed any level of v-H-ras gene. These studies suggest that while v-H-ras transfection can result in the development of metastatic ability in rat mammary cancer cells, there is no simple dose-response relationship between the level of v-H-ras expression in cloned rat mammary cancer cell transfectants and the development of experimental or spontaneous metastases. Show less