Autocrine vascular endothelial growth factor signalling in breast cancer. Evidence from cell lines and primary breast cancer cultures in vitro
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Inhibition of angiogenesis has become a major target in experimental cancer therapies. Vascular endothelial growth factor (VEGF) and its receptors are essential for breast cancer progression and relevant targets in experimental anti-angiogenesis. VEGF, produced by carcinoma cells, acts in a paracrine fashion on endothelial cells and displays autocrine activity on carcinoma cells. Breast cancer cells express VEGF-A, VEGF-B, VEGF-C and their receptors VEGFR-1 (Flt-1), VEGFR-2 (Flk-1/KDR) and neuropilin (NP-1/NP-2). VEGF-A triggers cellular signalling, an invasive phenotype of certain breast cancer cell lines and influences cell survival. However, such an autocrine VEGF/VEGFR signalling loop remains to be established. We demonstrate production of VEGF-A in cell lines MDA-MB-468, T47d, MCF-7, HBL-100 and in a primary breast cancer culture. Moreover, these cells showed baseline VEGFR-2 tyrosine-phosphorylation that could be enhanced by VEGF-A stimulation. In addition, VEGF-A leads to increased phosphorylation of ERK1/2 and Akt indicating that VEGF-A stimulation plays a crucial role in the regulation of cell growth, apoptosis, survival and differentiation. Moreover, we have established a novel breast cancer cell culture MW1 that expresses high levels of VEGF-A. We demonstrate that VEGFR-2 on the surface of breast cancer cells is functional and is capable of being stimulated by external VEGF-A. VEGF-A production by and VEGFR-2 activation on the surface of breast cancer cells indicates the presence of a distinct autocrine signalling loop that enables breast cancer cells to promote their own growth and survival by phosphorylation and activation of VEGFR-2. Moreover, this autocrine loop represents an attractive therapeutic target.
Keywordsangiogenesis autocrine signalling breast cancer cell culture KDR VEGF
American Type Culture Collection
epidermal growth factor receptor
insulin-like growth factor receptor
vascular endothelial growth factor
vascular endothelial growth factor receptor
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We thank Stephanie Kliche, Guido Fellbrich, Lisa Wiesmüller, Shan Wang-Gorke as well as Ulrike Mayr-Beyrle, Stephen Ethier and Arthur Mercurio for valuable discussions and technical help. This study was supported in part by the Medical Faculty of the University of Ulm (to M.W.), by a Heisenberg Scholarship of the Deutsche Forschungsgemeinschaft (Wa734/5–1) and by a project grant of the Deutsche Forschungsgemeinschaft (priority research program ȁ8angiogenesisȁ9, Wa734/6–3) (both to J.W.).
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