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Comparison of paclitaxel-, 5-fluoro-2'-deoxyuridine-, and epidermal growth factor (EGF)-induced apoptosis. Evidence
T J Kottke1, A L Blajeski, L M Martins
1Division of Oncology Research, Mayo Clinic, Mayo Graduate School, Rochester, Minnesota 55905, USA.
Abstract:
Epidermal growth factor (EGF), a hormone that stimulates proliferation of many cell types, induces apoptosis in some cell lines that overexpress the EGF receptor. To evaluate the mechanism of EGF-induced apoptosis, MDA-MB-468 breast cancer cells were examined by microscopy, flow cytometry, immunoblotting, enzyme assays, and affinity labeling after treatment with EGF, paclitaxel, or 5-fluoro-2'-deoxyuridine (5FUdR). Apoptosis induced by all three agents was accompanied by activation of caspases-3, -6, and -7, as indicated by disappearance of the corresponding zymogens from immunoblots, cleavage of substrate polypeptides in situ, and detection of active forms of these caspases in cytosol and nuclei using fluorogenic assays and affinity labeling. Further analysis indicated involvement of the cytochrome c/Apaf-1/caspase-9 pathway of caspase activation, but not the Fas/Fas ligand pathway. Interestingly, caspase activation was consistently lower after EGF treatment than after paclitaxel or 5FUdR treatment. Additional experiments revealed that the majority of cells detaching from the substratum after EGF (but not paclitaxel or 5FUdR) were morphologically normal and retained the capacity to readhere, suggesting that EGF-induced apoptosis involves cell detachment followed by anoikis. These observations not only indicate that EGF- and chemotherapy-induced apoptosis in this cell line involve the same downstream pathways but also suggest that detachment-induced apoptosis is responsible for the paradoxical antiproliferative effects of EGF.
Insights
Epidermal growth factor (EGF) triggers apoptosis in breast cancer cells via caspase activation and anoikis. This detachment-induced cell death explains EGF's paradoxical antiproliferative effects, distinct from chemotherapy.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Epidermal growth factor (EGF) stimulates cell proliferation but can induce apoptosis in cells overexpressing its receptor.
- Understanding the mechanisms of EGF-induced apoptosis is crucial for cancer therapy.
Purpose of the Study:
- To investigate the molecular mechanisms underlying EGF-induced apoptosis in MDA-MB-468 breast cancer cells.
- To compare EGF-induced apoptosis with apoptosis induced by chemotherapy agents (paclitaxel, 5FUdR).
Main Methods:
- Microscopy, flow cytometry, immunoblotting, enzyme assays, and affinity labeling were used.
- Analysis focused on caspase activation pathways (caspase-3, -6, -7, -9) and cell detachment.
- Cells were treated with EGF, paclitaxel, or 5-fluoro-2'-deoxyuridine (5FUdR).
Main Results:
- EGF, paclitaxel, and 5FUdR induced apoptosis via the cytochrome c/Apaf-1/caspase-9 pathway, not the Fas/Fas ligand pathway.
- Caspase activation was lower with EGF compared to chemotherapy agents.
- EGF treatment led to cell detachment followed by anoikis, with cells retaining viability.
Conclusions:
- EGF and chemotherapy induce apoptosis through common downstream pathways in this cell line.
- EGF-induced apoptosis is primarily driven by detachment-induced anoikis, explaining its antiproliferative effect.
- The findings highlight distinct mechanisms of apoptosis induction by growth factors versus chemotherapy.
