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Full oncogenic activities of v-Src are mediated by multiple signaling pathways. Ras as an essential mediator for cell
J Odajima1, I Matsumura, J Sonoyama
1Department of Hematology/Oncology and Molecular Oncology, Biomedical Research Center, Osaka University Medical School, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan.
Abstract:
Tyrosine kinase oncoproteins cause simultaneous activation of multiple intracellular signaling pathways. However, the precise mechanisms by which individual pathways induce oncogenesis are not well understood. We have investigated the roles of individual signaling pathways in v-Src-dependent cell growth and survival by inhibiting one particular pathway. v-Src induced constitutive activation of signal transducers and activators of transcription 3 (STAT3), phosphatidylinositol 3-kinase, and Ras in murine Ba/F3 cells and led to factor-independent proliferation. Dominant-negative mutants of STAT3 (STAT3D) and phosphatidylinositol 3-kinase (Deltap85) inhibited v-Src-dependent growth by approximately 60 and approximately 40%, respectively. Moreover, dominant-negative Ras (N17) induced severe apoptosis, which was accompanied by down-regulation of Bcl-2 and activation of caspase-3. Although cells overexpressing Bcl-2 or caspase-3 inhibitors remained viable even when N17 was expressed, the growth was reduced by approximately 85%. During N17- and STAT3D-induced growth suppression, expression of cyclin D2, cyclin D3, c-myc, and c-fos was suppressed by N17, whereas that of cyclin D2, cyclin E, and c-myc was suppressed by STAT3D. Thus, v-Src-activated Ras and STAT3 are involved in distinct but partly overlapping transcriptional regulation of cell cycle regulatory molecules. These results suggest that the full oncogenic activity of v-Src requires simultaneous activation of multiple signalings, in which Ras is particularly required for survival.
Insights
v-Src oncoprotein activates multiple pathways, including STAT3 and Ras, driving cancer cell growth. Inhibiting Ras significantly impairs survival, while both Ras and STAT3 regulate cell cycle genes, highlighting the need for multiple pathways in oncogenesis.
Area of Science:
- Molecular Biology
- Oncology
- Cell Signaling
Background:
- Tyrosine kinase oncoproteins activate multiple intracellular pathways.
- The specific roles of individual pathways in oncogenesis are not fully understood.
Purpose of the Study:
- Investigate the roles of individual signaling pathways in v-Src-dependent cell growth and survival.
- Determine the contribution of STAT3, phosphatidylinositol 3-kinase, and Ras pathways to oncogenesis.
Main Methods:
- Utilized dominant-negative mutants to inhibit specific signaling pathways (STAT3, phosphatidylinositol 3-kinase, Ras) in v-Src-expressing Ba/F3 cells.
- Assessed cell proliferation, apoptosis, and the expression of key regulatory molecules (Bcl-2, caspase-3, cyclins, c-myc).
Main Results:
- v-Src induced constitutive activation of STAT3, phosphatidylinositol 3-kinase, and Ras, leading to factor-independent proliferation.
- Inhibition of STAT3 (STAT3D) and phosphatidylinositol 3-kinase (Deltap85) reduced v-Src-dependent growth by ~60% and ~40%, respectively.
- Dominant-negative Ras (N17) induced apoptosis, down-regulated Bcl-2, activated caspase-3, and suppressed cell growth by ~85%, indicating Ras is crucial for survival.
Conclusions:
- v-Src-activated Ras and STAT3 pathways play distinct but overlapping roles in the transcriptional regulation of cell cycle molecules.
- The oncogenic activity of v-Src necessitates the simultaneous activation of multiple signaling pathways, with Ras being particularly vital for cell survival.