Morphologic transformation and tumorigenicity are separate cellular phenotypes in transformed 10T1/2 cells. We have investigated the levels of expression of genes for c-myc, c-H-ras, c-K-ras, c-N-ras, TGF beta and Rb in 42 morphologically transformed 10T1/2 cell lines, in an attempt to define the molecular mechanisms governing morphologic transformation and tumorigenicity in the 10T1/2 cell system. The 10T1/2 cell lines investigated generally overexpressed mRNAs for c-myc, c-H-ras, and TGF beta relative to the levels expressed by wildtype 10T1/2 cells (levels of expression > 1.5-fold that of wildtype 10T1/2 cells). In contrast, only half of these cell lines overexpressed mRNAs for c-N-ras and/or Rb relative to wildtype 10T1/2 cells, and only 25% overexpressed c-K-ras mRNA. The mean levels of mRNA expression for each of c-K-ras, c-N-ras and TGF beta genes in tumorigenic cell lines were significantly greater than the mean levels of expression in non-tumorigenic cell lines, suggesting an association between tumorigenicity and the levels of expression of these specific genes. In contrast, levels of expression for c-myc, c-H-ras and Rb genes were not correlated with tumorigenicity. Cell lines that coexpressed high levels of c-K-ras, c-N-ras and TGF beta genes were likely to be tumorigenic (11/12 cell lines were tumorigenic), whereas cell lines that coexpressed low levels of these genes were unlikely to be tumorigenic (1/10 cell lines were tumorigenic). High expression of TGF beta was sufficient for tumorigenicity in the absence of high levels of expression of c-K-ras and c-N-ras (5/5 cell lines were tumorigenic). Elevated expression of either c-K-ras or c-N-ras alone was insufficient for tumorigenicity, however, coordinate overexpression of both c-K-ras and c-N-ras was associated with tumorigenicity irrespective of the expression status for TGF beta (13/15 cell lines were tumorigenic). These results suggest that overexpression of c-myc, c-H-ras and TGF beta are commonly associated with, and possibly mechanistically related to, the process of morphologic transformation in 10T1/2 cells. In addition, these results suggest that progression from morphologic transformation to tumorigenicity in 10T1/2 cell lines is frequently accompanied by overexpression of c-K-ras and c-N-ras, and by enhancement of the level of overexpression of TGF beta.
