Reid Penny E, Brown Nicola J, Holen Ingunn
Academic Units of Clinical Oncology and Surgical Oncology, School of Medicine and Biomedical Sciences, University of Sheffield, Sheffield, UK.
Mol Cancer. 2009 Jul 15;8:49. doi: 10.1186/1476-4598-8-49.
Angiogenesis, the sprouting of capillaries from existing blood vessels, is central to tumour growth and progression, however the molecular regulation of this process remains to be fully elucidated. The secreted glycoprotein osteoprotegerin (OPG) is one potential pro-angiogenic factor, and clinical studies have demonstrated endothelial cells within a number of tumour types to express high levels of OPG compared to those in normal tissue. Additionally, OPG can increase endothelial cell survival, proliferation and migration, as well as induce endothelial cell tube formation in vitro. This study aims to elucidate the processes involved in the pro-angiogenic effects of OPG in vitro, and also how OPG levels may be regulated within the tumour microenvironment.
It has previously been demonstrated that OPG can induce tube formation on growth factor reduced matrigel. In this study, we demonstrate that OPG enhances the pro-angiogenic effects of VEGF and that OPG does not stimulate endothelial cell tube formation through activation of the VEGFR2 receptor. We also show that cell contact between HuDMECs and the T47D breast cancer cell line increases endothelial cell OPG mRNA and protein secretion levels in in vitro co-cultures. These increases in endothelial cell OPG secretion were dependent on alphanubeta3 ligation and NFkappaB activation. In contrast, the pro-angiogenic factors VEGF, bFGF and TGFbeta had no effect on HuDMEC OPG levels.
These findings suggest that the VEGF signalling pathway is not involved in mediating the pro-angiogenic effects of OPG on endothelial cells in vitro. Additionally, we show that breast cancer cells cause increased levels of OPG expression by endothelial cells, and that direct contact between endothelial cells and tumour cells is required in order to increase endothelial OPG expression and secretion. Stimulation of OPG secretion was shown to involve alphanubeta3 ligation and NFkappaB activation.
血管生成，即从现有血管中长出毛细血管，是肿瘤生长和进展的核心过程，然而这一过程的分子调控仍有待充分阐明。分泌型糖蛋白骨保护素（OPG）是一种潜在的促血管生成因子，临床研究表明，与正常组织中的内皮细胞相比，多种肿瘤类型中的内皮细胞表达高水平的OPG。此外，OPG可增加内皮细胞的存活、增殖和迁移，并在体外诱导内皮细胞形成管腔结构。本研究旨在阐明OPG在体外促血管生成作用所涉及的过程，以及肿瘤微环境中OPG水平可能如何被调控。
先前已证明OPG可在生长因子降低的基质胶上诱导管腔形成。在本研究中，我们证明OPG增强了VEGF的促血管生成作用，且OPG不会通过激活VEGFR2受体来刺激内皮细胞形成管腔结构。我们还表明，在体外共培养中，人真皮微血管内皮细胞（HuDMECs）与T47D乳腺癌细胞系之间的细胞接触会增加内皮细胞OPG的mRNA和蛋白分泌水平。内皮细胞OPG分泌的这些增加依赖于αβ3整合素连接和核因子κB（NFκB）激活。相比之下，促血管生成因子VEGF、碱性成纤维细胞生长因子（bFGF）和转化生长因子β（TGFβ）对HuDMEC的OPG水平没有影响。
这些发现表明，VEGF信号通路不参与介导OPG在体外对内皮细胞的促血管生成作用。此外，我们表明乳腺癌细胞会导致内皮细胞OPG表达水平升高，并且内皮细胞与肿瘤细胞之间需要直接接触才能增加内皮细胞OPG的表达和分泌。已表明OPG分泌的刺激涉及αβ3整合素连接和NFκB激活。
