METABOLISM OF N-6 FATTY-ACIDS BY NIH-3T3 CELLS TRANSFECTED WITH THE RAS ONCOGENE

N-6 fatty acid metabolism was compared in NIH-3T3 cells and DT cells, which differ only in the presence of the v-Ki-ras oncogene. Non-dividi ng cells were incubated with [1-C-14]-labelled fatty acids (18:2n-6, 1 8:3n-6, 20:3n-6 and 20:4n-6) at different time intervals (2-24 h) and concentration (0-120 mu M). In both cells lines, the uptake of differe nt fatty acids from the medium was similar and reached a maximum at 6- 8 h. All fatty acids reached the same maximum level in DT cells, where as, the relative uptake of added fatty acids by NIH-3T3 cells was diff erent: 20:4n-6 > 20:3n-6 > 18:2n-6 = 18:3n-6. Throughout the incubatio n (2-24 h), desaturation and elongation of n-6 fatty acids was more ac tive in DT cells than in NIH-3T3 cells. However, in both cell lines, i ncubated with different n-6 fatty acid precursors, the levels of radio labelled 20:4n-6 were relatively constant. In DT cells, phosphatidylch oline was found to be the major fraction labelled with n-6 fatty acids precursors and those of endogenous synthesis, whereas, in NIH-3T3 cel ls the neutral lipid fraction, particularly triglycerides, was also st rongly labelled. In concentration dependent studies, phospholipid labe lling by fatty acids was saturable. At lower concentrations, especiall y in DT cells, phospholipids were labelled predominantly. As the conce ntration increased there was an overflow into the triglyceride fractio n. Since the differences in fatty acid metabolism between the two cell lines cannot be related to the growth rate, it is suggested that they were a consequence of the expression of the v-Ki-ras oncogene.