Nerve growth factor promotes breast cancer angiogenesis by activating multiple pathways

We showed that both recombinant NGF and NGF produced by breast cancer cells stimulated angiogenesis in Matrigel plugs in immunodeficient mice. NGF strongly increased invasion, cord formation and the monolayer permeability of endothelial cells. Moreover, NGF-stimulated invasion was under the control of its tyrosine kinase receptor (TrkA) and downstream signaling pathways such as PI3K and ERK, leading to the activation of matrix metalloprotease 2 and nitric oxide synthase. Interestingly, NGF increased the secretion of VEGF in both endothelial and breast cancer cells. Inhibition of VEGF, with a neutralizing antibody, reduced about half of NGF-induced endothelial cell invasion and angiogenesis in vivo.Our findings provided direct evidence that NGF could be an important stimulator for breast cancer angiogenesis. Thus, NGF, as well as the activated signaling pathways, should be regarded as potential new targets for anti-angiogenic therapy against breast cancer.It is well established that tumor growth beyond the size of 1-2 mm is dependent upon angiogenesis [1]. This process is regulated by numerous proangiogenic factors which are secreted by tumor or surrounding stromal cells. Among these proangiogenic factors, vascular endothelial growth factor (VEGF) plays a pivotal role in tumor angiogenesis. VEGF promotes angiogenesis via its ability to stimulate permeability, growth, migration and invasion of endothelial cells, and to mobilize endothelial precursor cells from bone marrow [2-4]. Inhibition of VEGF reduces angiogenesis and tumor growth in vivo [5]. Conversely, VEGF overexpression is associated with increased microvessel density, tumor metastasis, and poor prognosis [6-8]. Among several VEGF isoforms, VEGF-A is the most predominant angiogenic factor, as its level is strongly associated with tumor progression and poor clinical outcome in many types of cancers including breast cancer [9-11].NGF has been studied most extensively for its role in regulating growth, developme