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ERbB-2 expression is rate-limiting for epidermal growth factor-mediated stimulation of ovarian cancer cell
S S Hsieh1, C Malerczyk, A Aigner
1Department of Pharmacology and Toxicology, Philipps-University Marburg, Germany.
Abstract:
Over-expression of the ErbB-2 proto-oncogene frequently coincides with an aggressive clinical course of certain human adenocarcinomas. The ErbB-2 receptor is a member of the ErbB family of growth factor receptors, and within this complex signaling network, ErbB-2-containing heterodimers are preferentially formed. To assess whether ErbB-2 is a critical component in epidermal growth factor (EGF)-mediated stimulation of tumor cell proliferation, we used as a model SK-OV-3 ovarian cancer cells, which over-express EGF receptor (EGFR) and ErbB-2 receptors. In these cells, we reduced ErbB-2 mRNA and protein expression by transfection with ErbB-2-targeted hammerhead ribozymes and generated cell lines expressing different levels of ErbB-2. In SK-OV-3 cells, ErbB-2 expression conferred a growth advantage and soft agar experiments revealed that ErbB-2 was rate-limiting for anchorage-independent growth. The induction of colony formation by EGF was completely abrogated in ErbB-2-depleted cells, despite unchanged expression levels and tyrosine phosphorylation of the EGFR. The duration of EGF-mediated c-Fos mRNA up-regulation was decreased in parallel with loss of ErbB-2 expression. Furthermore, the rate of spontaneous apoptosis was increased in ErbB-2-depleted cells. Our results demonstrate that in human ovarian cancer cells the EGFR-ErbB-2 heterodimer, and not the EGFR homodimer, can be rate-limiting for EGF-mediated proliferation, thus suggesting that the oncogenic activity of ErbB-2 in human tumors is due in part to its ability to increase the growth response to stroma-derived EGF-like growth factors.
Insights
Over-expression of ErbB-2 (ErbB-2 receptor tyrosine kinase) drives aggressive ovarian cancer by enhancing tumor cell proliferation. Targeting ErbB-2 may inhibit cancer growth, offering a potential therapeutic strategy.
Area of Science:
- Oncology
- Molecular Biology
- Cell Signaling
Background:
- Over-expression of the ErbB-2 proto-oncogene is linked to aggressive human adenocarcinomas.
- ErbB-2 is a member of the ErbB family of growth factor receptors, forming preferential heterodimers within signaling networks.
Purpose of the Study:
- To investigate if ErbB-2 is critical for epidermal growth factor (EGF)-mediated tumor cell proliferation.
- To assess the role of EGFR-ErbB-2 heterodimers in ovarian cancer cell growth.
Main Methods:
- Utilized SK-OV-3 ovarian cancer cells over-expressing EGF receptor (EGFR) and ErbB-2.
- Reduced ErbB-2 expression using ribozyme transfection, creating cell lines with varying ErbB-2 levels.
- Assessed anchorage-independent growth, EGF-induced proliferation, c-Fos mRNA expression, and spontaneous apoptosis.
Main Results:
- ErbB-2 expression conferred a growth advantage and was rate-limiting for anchorage-independent growth.
- EGF-induced colony formation was abrogated in ErbB-2-depleted cells, with unchanged EGFR levels and phosphorylation.
- EGF-mediated c-Fos mRNA up-regulation duration decreased with ErbB-2 loss, and spontaneous apoptosis increased.
Conclusions:
- The EGFR-ErbB-2 heterodimer, not the EGFR homodimer, is rate-limiting for EGF-mediated proliferation in ovarian cancer cells.
- ErbB-2's oncogenic activity may stem from enhancing tumor cell response to EGF-like growth factors.
- Targeting ErbB-2 could be a therapeutic strategy for ErbB-2-driven cancers.