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Ras, but not Src, transformation of RIE-1 epithelial cells is dependent on activation of the mitogen-activated
S M Oldham1, A D Cox, E R Reynolds
1Department of Pharmacology, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill 27599, USA.
Abstract:
Src transformation of NIH3T3 mouse fibroblasts has been shown to be dependent on Ras function. Since we recently showed that the signaling pathways that mediate Ras transformation of RIE-1 rat intestinal epithelial cells are distinct from those that cause Ras transformation of fibroblasts, we utilized three approaches to determine if Src transformation of RIE-1 cells is dependent on Ras. First, although both Ras and Src cause upregulation of an epidermal growth factor (EGF) receptor-dependent autocrine growth loop, only Ras transformation required this activity. Second, whereas both Src and Ras caused upregulation of the p42 and p44 mitogen-activated protein kinases (MAPKs), only Ras transformation was blocked by the inhibition of MAPK activation by treatment with the PD 98059 MEK inhibitor. Third, treatment with the farnesyltransferase inhibitor FTI-277 blocked Ras, but not Src, transformation. Taken together, these observations suggest that Src transformation of RIE-1 cells is not dependent on Ras. Finally, we determined that Ras activation of Raf-independent pathways alone is sufficient to cause growth transformation of RIE-1 cells. Thus, both Ras and Src cause transformation of RIE-1 cells via pathways distinct from those required to cause transformation of NIH3T3 cells.
Insights
Src transformation of rat intestinal cells is independent of Ras signaling. Unlike Ras, Src-induced cell transformation does not rely on epidermal growth factor receptor, mitogen-activated protein kinases, or farnesyltransferase activity.
Area of Science:
- Cell biology
- Molecular oncology
- Signal transduction
Background:
- Ras and Src are key oncogenes driving cell transformation.
- Ras transformation pathways differ between fibroblasts and epithelial cells.
- The role of Ras in Src-mediated transformation of epithelial cells is unclear.
Purpose of the Study:
- To investigate whether Src-mediated cell transformation in RIE-1 rat intestinal epithelial cells is dependent on Ras function.
- To elucidate the distinct signaling pathways utilized by Ras and Src in RIE-1 cell transformation.
Main Methods:
- Comparative analysis of Ras and Src transformation in RIE-1 cells.
- Assessment of epidermal growth factor (EGF) receptor-dependent autocrine growth loops.
- Evaluation of mitogen-activated protein kinase (MAPK) pathway activation using PD 98059.
- Inhibition of Ras and Src transformation using farnesyltransferase inhibitor (FTI-277).
Main Results:
- Src transformation of RIE-1 cells does not require the EGF receptor-dependent autocrine growth loop, unlike Ras transformation.
- MAPK pathway activation is essential for Ras transformation but not Src transformation in RIE-1 cells.
- FTI-277 inhibits Ras transformation but does not affect Src transformation in RIE-1 cells.
Conclusions:
- Src-mediated transformation of RIE-1 cells is independent of Ras.
- Ras and Src utilize distinct signaling mechanisms to transform RIE-1 cells.
- Ras can induce RIE-1 cell transformation through Raf-independent pathways.