© 1994 Oxford University Press
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Overexpression of c-K-ras, c-N-ras and transforming growth factor ß co-segregate with tumorigenicity in morphologically transformed C3H 10T1/2 cell lines
Department of Pathology, The University of North Carolina Chapel Hill, NC 27599-7525, USA
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Morphologic transformation and tumorigenicity are separate cellular phenotypes in transformed 1OT1/2 cells. We have investigated the levels of expression of genes for c-myc, c-H-ras, c-K-ras, c-N-ras, TGFß and Rb in 42 morphologically transformed 1OT1/2 cell lines, in an attempt to define the molecular mechanisnts governing morphologic transformation and tumorigenicity in the 1OT1/2 cell system. The 101 1/2 cell lines investigated generally overexpressed mRNAs for c-myc, c-H-ras, and TGFß relative to the levels expressed by wild- type 10T1 cells (levels of expression >1.5-fold that of wild- type 1011/2 cells). In contrast, only half of these cell lines overexpressed mRNAs for c-N-ras and/or Rb relative to wild- type 1OT1/2 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 TGFß genes in tumorigenic cell lines were significantly greater than the mean levels of expression in non-tumorigenic cell lines, suggesting an association between twnorigenicity 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 TGFß 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 tumorigenlc (1/10 cell lines were tumorigenic). High expression of TGFß 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 tumorlgenlclty, however, coordinate overexpresslon of both c-K-ras and c-ras was associated with tumorigenicity irrespective of the expression status for TGFß (13/15 cell lines were tuinorigenic). These results suggest that overexpresslon of c-ras, c-H-ras and TGFß are conunonly associated with, and possibly mechanistically related to, the process of morphologic transformation in 1OTI/2 cells. In addition, these results suggest that progression from morphologic transformation to tumorigenicity in 1011/2 cell lines is frequently accompanied by overexpression of c-K-ras and c-N-ras, and by enhancement of the level of overexpresslon of TGFß