Changes in cellular gene expression in rat thyroid epithelial cells transformed by the Kirsten murine sarcoma virus

We have exploited a recently characterized system of rat thyroid epithelial cells transformed by the wild-type ( wt) and a temperature-sensitive ( ts) mutant strain of the Kirsten murine sarcoma virus (Ki-MSV) in order to study the effects of the K- ras oncogene on the gene expression of differentiated thyroid epithelial cells. By using cDNAs isolated from normal thyroid glands as probes, we were able to identify three sets of cellular sequences whose expression is influenced by the v-K- ras oncogene. The first set of genes is irreversibly repressed by transformation with both the wt and the ts viruses. The second set of genes is repressed in the ts-Ki-MSV-transformed cells but not in the same cells grown at the nonpermissive temperature. A third set of genes is present at higher levels at the nonpermissive temperature than at the permissive temperature. This system has allowed us to isolate and characterize a number of cDNA clones belonging to each of these three sets of genes. These specific cDNAs are suitable probes to study phenotypical changes during transformation of epithelial cells.