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PKC and Raf-1 inhibition-related apoptotic signalling in N2a cells
Agnieszka Bronisz1, Barbara Gajkowska, Krystyna Domańska-Janik
1Department of Neurochemistry, Laboratory of Molecular Neurophatology, Medical Research Centre Polish Academy of Science, Pawińskiego, Warsaw, Poland.
Abstract:
In this study, a neuroblastoma N2a cell line was applied to investigate mechanisms of apoptosis induced either by selective inhibition of protein kinase C (PKC) by low amounts of staurosporine (STS(10) ) or by inhibition PI3-K after wortmannin (WM) treatment. We present evidence that, in the absence of serum in the medium, decreased phosphorylation of Raf-1 and BAD112, as well as Akt and BAD136, proteins and their translocation to mitochondria coincided with STS10 - or WM-induced apoptosis, respectively. Concomitantly, release of cytochrome c into the cytosol indicated a BCL-2-dependent mode of cell death after both treatments. Furthermore, in typical 'gain of function' experiments, cells with overexpression of permanently active Raf-1 or Akt transgenes displayed a significantly higher and independent resistance to either STS10 or WM. Thus, our results indicate that PKC/Raf-1/BAD112, as well as PI3-K/Akt/BAD136 signalling pathways, are both necessary for N2a cell survival and thus are unable to functionally substitute for each other as long as the cells do not receive additional signal(s) derived from serum. However, in the presence of serum, undefined trophic signal(s) can stimulate cross-talk between these two pathways at a level upstream from Raf-1 and Akt phosphorylation. In this case, only simultaneous inhibition of PKC and PI3-K is able to induce apoptosis.
Insights
Protein Kinase C (PKC) and PI3-K pathways are crucial for neuroblastoma cell survival. Inhibition of either pathway induces apoptosis unless serum provides cross-talk signals, requiring simultaneous inhibition for cell death.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Neuroblastoma is a pediatric cancer with complex survival mechanisms.
- Protein kinase C (PKC) and Phosphoinositide 3-kinase (PI3-K) are key signaling pathways involved in cell survival and proliferation.
- Understanding apoptosis induction in cancer cells is critical for developing targeted therapies.
Purpose of the Study:
- To investigate the distinct and overlapping roles of PKC and PI3-K signaling in neuroblastoma N2a cell apoptosis.
- To elucidate the mechanisms of apoptosis induced by selective inhibition of PKC or PI3-K.
- To determine the influence of serum on these signaling pathways and their cross-talk.
Main Methods:
- Utilized a neuroblastoma N2a cell line.
- Induced apoptosis via selective inhibition of PKC (staurosporine) or PI3-K (wortmannin).
- Analyzed protein phosphorylation (Raf-1, Akt) and translocation (BAD proteins) to mitochondria.
- Assessed cytochrome c release and BCL-2 dependency.
- Conducted 'gain of function' experiments with constitutively active Raf-1 or Akt.
Main Results:
- In serum-free conditions, inhibition of PKC or PI3-K led to decreased phosphorylation and mitochondrial translocation of specific proteins (Raf-1/BAD112, Akt/BAD136), inducing apoptosis.
- Cytochrome c release indicated a BCL-2-dependent cell death mechanism.
- Overexpression of active Raf-1 or Akt conferred resistance to individual pathway inhibition.
- Serum presence allowed for cross-talk between PKC and PI3-K pathways upstream of Raf-1 and Akt.
- Simultaneous inhibition of both PKC and PI3-K was required to induce apoptosis in the presence of serum.
Conclusions:
- PKC/Raf-1/BAD112 and PI3-K/Akt/BAD136 pathways are essential for N2a cell survival and cannot substitute for each other without serum.
- Serum-derived signals enable pathway cross-talk, modulating apoptosis sensitivity.
- Targeting both PKC and PI3-K pathways simultaneously may be a viable strategy for treating neuroblastoma, especially in serum-rich environments.