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Raf-1 protein kinase is an integral component of the oncogenic signal cascade shared by epidermal growth factor and
S Kizaka-Kondoh1, K Sato, K Tamura
1Department of Molecular Genetics, Osaka University, Japan.
Abstract:
Our recent studies with cell mutants indicate that a cascade shared by the epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) signals exists in NRK cells and mediates oncogenic signals induced by many oncogenes (A. Masuda, S. Kizaka-Kondoh, H. Miwatani, Y. Terada, H. Nojima, and H. Okayama, New Biol. 4:489-503, 1992). We have employed the antisense RNA technique to investigate possible involvement of Raf-1 kinase in this signal transduction cascade. NRK cell clones highly reduced in the Raf-1 production are generated by the expression of a c-raf-1 antisense RNA. They have no apparent growth defects and retain proper mitotic responses to growth factors but are refractory to transformation by EGF or PDGF plus transforming growth factor beta, v-erbB, v-fms, v-K-ras, v-mos, v-fos, v-src, simian virus 40 large T, and polyomavirus middle T but not by v-raf or adenovirus E1A. These results not only support our model for the oncogenic signal cascade but also lead to the conclusion that Raf-1 protein kinase is a downstream component of this oncogenic signal cascade shared by EGF and PDGF.
Insights
This study reveals Raf-1 kinase is crucial for oncogenic signaling pathways shared by epidermal growth factor (EGF) and platelet-derived growth factor (PDGF). Reducing Raf-1 production blocks transformation by many oncogenes, confirming its role in this shared cascade.
Area of Science:
- Cell biology
- Molecular oncology
- Signal transduction
Background:
- Epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) signaling pathways share a common cascade in NRK cells.
- This shared cascade mediates oncogenic signals induced by various oncogenes.
- The precise role of Raf-1 kinase in this pathway remained to be elucidated.
Purpose of the Study:
- To investigate the involvement of Raf-1 kinase in the shared EGF and PDGF signal transduction cascade.
- To determine if Raf-1 kinase is a critical component of the oncogenic signaling pathway.
Main Methods:
- Utilized the antisense RNA technique to generate NRK cell clones with significantly reduced Raf-1 production.
- Expressed c-raf-1 antisense RNA in NRK cells to achieve targeted gene silencing.
- Assessed the transformation susceptibility of these modified NRK cells to various oncogenes and growth factors.
Main Results:
- NRK cell clones with reduced Raf-1 production exhibited no apparent growth defects or altered mitotic responses to growth factors.
- These Raf-1 deficient cells were refractory to transformation induced by EGF or PDGF in combination with TGF-beta, v-erbB, v-fms, v-K-ras, v-mos, v-fos, v-src, SV40 large T, and Py middle T.
- Transformation was still observed with v-raf and adenovirus E1A, suggesting pathway specificity.
Conclusions:
- Raf-1 protein kinase is a downstream component of the oncogenic signal cascade shared by EGF and PDGF.
- The findings support the proposed model for the oncogenic signal cascade involving Raf-1.
- This study highlights Raf-1 kinase as a key mediator in EGF/PDGF-driven oncogenesis.