Differential expression of preproenkephalin and transin mRNAs following oncogenic transformation: evidence for two classes of oncogene induced genes.

FR3T3 rat embryo fibroblast cells express preproenkephalin mRNA after transformation by polyoma virus middle T or Ha-ras oncogenes. This effect was not seen in another rat embryo fibroblast cell line (Rat-1) or in FR3T3 cells transformed by Rous sarcoma virus, bovine papilloma virus type I or SV40. The elevation in preproenkephalin mRNA levels is thus cell specific and oncogene specific. These results contrast with those obtained for transin mRNA, which was observed in both Rat-1 and FR3T3 cells transformed by a number of different oncogenes. The expression of transin RNA correlated with the expression of the transformed phenotype. We suggest that genes induced by oncogenes in a given cell will fall into two classes: those linked to the expression of the transformed phenotype (expression induced by all oncogenes conferring this phenotype) and those induced as a consequence of activation of a specific cellular signaling system (expression induced by a subset of oncogenes linked to the signaling system in question). This system may prove useful in distinguishing oncogene-induced events that are related to cellular transformation from those that are secondary to eliciting the transformed phenotype.