PROTEIN SYNTHESIS DURING ONCOGENIC TRANSFORMATION

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We compared 2-dimensional electropherograms of newly synthesized proteins from lines of NIH/3T3 cells transformed by a variety of retroviral oncogenes, from cellular revertant lines, and from a line (433.3) which expresses the v-ras oncogene in response to corticosteroids. We detected 7 proteins whose synthesis was strongly suppressed in cell lines tranformed by each of the six retroviral oncogenes we studied, and whose production was fully orpartially restored in two cellular revertant lines. Suppression of two of these proteins was also correlated with the initial appearance of morphological alteration during steroid-induced oncogene expression in 433.3 cells. These proteins (p37/4.78 and p41/4.75) were identified as tropomyosins, a group of at least 5 cytoskeletal proteins. Transformation by the papova viruses, SV-40 and polyoma, caused no suppression of synthesis of these tropomyosins. This indicated that suppression of tropomyosin synthesis is not a nonspecific response by cells to being forced to grow with the transformed phenotype, but is specifically associated with oncogenesis by diverse retroviral oncogenes. The results are consistent with the hypothesis that the different biochemical processes initiated by expression of structurally diverse retroviral oncogenes may converge on a limited number of common targets, one of which is the mechanism which regulates the synthesis of tropomyosins.