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C-Raf controlled pathways in the protection of tumor cells from apoptosis
Emily P Slater1, Thomas Stübig, Quek Choon Lau
1Institute of Molecular Biology and Tumor Research (IMT) Philipps-University, Emil-Mannkopff-Strasse 2, 35033 Marburg, Germany.
Abstract:
The Raf serine-threonine kinase is upregulated in many human tumors and plays a pivotal role in tumor cell proliferation and survival. Abrogation of c-Raf expression by specific antisense oligonucleotides (Raf-AS-ODN) efficiently blocks tumor cell growth and induces apoptosis in human cancer cells. The signaling pathways and molecular mechanisms c-Raf utilizes to mediate the survival of tumor cells are, however, not well understood. Here we show that apoptosis triggered by Raf depletion cannot be overcome by ectopic Bcl-2 expression and occurs in the absence of cytochrome c release, arguing against a direct impact of c-Raf on mitochondrial pathways of apoptosis regulation. We also show that c-Raf depletion leads to a clearly decreased expression of different epidermal growth factor (EGF) receptor ligands, suggesting that the autocrine stimulation of an EGF receptor-mediated survival pathway might be involved in the blockade of tumor cell apoptotis by c-Raf.
Insights
Inhibition of Raf kinase (c-Raf) blocks tumor cell growth by inducing apoptosis. This occurs independently of mitochondrial pathways and suggests a role for epidermal growth factor receptor (EGFR) signaling in c-Raf-mediated tumor cell survival.
Area of Science:
- Oncology
- Molecular Biology
- Cell Signaling
Background:
- Raf serine-threonine kinase (c-Raf) is upregulated in human tumors, promoting cancer cell proliferation and survival.
- Antisense oligonucleotides (Raf-AS-ODN) targeting c-Raf effectively inhibit tumor cell growth and induce apoptosis.
- The precise molecular mechanisms by which c-Raf promotes tumor cell survival are not fully elucidated.
Purpose of the Study:
- To investigate the signaling pathways and molecular mechanisms underlying c-Raf-mediated tumor cell survival.
- To determine if c-Raf impacts mitochondrial apoptosis pathways.
- To explore the potential involvement of epidermal growth factor receptor (EGFR) signaling in c-Raf's role.
Main Methods:
- Utilized antisense oligonucleotides (Raf-AS-ODN) to abrogate c-Raf expression in human cancer cells.
- Assessed apoptosis induction and its relation to Bcl-2 expression and cytochrome c release.
- Quantified the expression levels of epidermal growth factor (EGF) receptor ligands following c-Raf depletion.
Main Results:
- Apoptosis induced by c-Raf depletion was not rescued by ectopic Bcl-2 expression and occurred without cytochrome c release, indicating c-Raf does not directly regulate mitochondrial apoptosis.
- Depletion of c-Raf led to a significant decrease in the expression of various epidermal growth factor (EGF) receptor ligands.
- These findings suggest that c-Raf may maintain tumor cell survival by promoting an autocrine EGF receptor-mediated signaling pathway.
Conclusions:
- c-Raf-mediated tumor cell survival is not directly dependent on the mitochondrial apoptosis pathway.
- The abrogation of c-Raf expression impacts the expression of EGF receptor ligands, implicating EGFR signaling in c-Raf's pro-survival function.
- Targeting c-Raf may offer therapeutic strategies by disrupting EGFR-mediated autocrine survival loops in cancer cells.