R-Ras induces malignant, but not morphologic, transformation of NIH3T3 cells.
Although previous studies have not identified transforming properties of the Ras-related protein R-Ras, two recent observations have prompted our further evaluation of R-Ras function. First, we observed that mutant forms of the closely related R-Ras2/TC21 protein (approximately 70% identity) exhibited the same potent transforming activity as oncogenic Ras proteins. Second, R-Ras association with Bcl-2 suggested a possible role for R-Ras in apoptotic growth control. Therefore, we have performed a detailed analysis of R-Ras transforming potential in NIH3T3 cells. Whereas expression of a mutant R-Ras protein (38V; analogous to the 12V activating Ras mutation) did not induce morphologic transformation of NIH3T3 cells, R-Ras(38V)-expressing cells proliferated in low serum, formed colonies in soft agar, and formed progressive tumors in nude mice. Like Ras-transformed cells, R-Ras(38V)-transformed cells exhibited constitutively activated mitogen activated protein kinases. Furthermore, R-Ras(38V) stimulated transcriptional activation of Ras-responsive promoter elements, and this activity (and transformation) was blocked by Raf dominant negative proteins. Finally, whereas co-expression of Bcl-2 did not cause significant alteration in wild type or mutant R-Ras transforming activity, coexpression of v-Myc and R-Ras(38V) induced a striking morphologic transformation of NIH3T3 cells. Taken together, these observations suggest that aberrant R-Ras function may stimulate malignant transformation, in the absence of morphologic transformation, via up-regulation of part of the Ras signal transduction pathway.
Cox
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Department of Pharmacology, School of Medicine, University of North Carolina at Chapel Hill 27599-7365.
Brtva
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Lowe
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D016475:3T3 Cells; D000818:Animals; D002455:Cell Division; D002471:Cell Transformation, Neoplastic; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000502:physiology*; D016259:Genes, myc; D051379:Mice; D011505:Protein-Tyrosine Kinases / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000235:genetics; D019253:Proto-Oncogene Proteins c-bcl-2; D015398:Signal Transduction; D018631:ras Proteins / Q000235:genetics / Q000502:physiology*
D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011505:Protein-Tyrosine Kinases; D020558:GTP Phosphohydrolases; C513254:Rras protein, mouse; D018631:ras Proteins