Kranenburg Onno, Kroon-Batenburg Loes M J, Reijerkerk Arie, Wu Ya-Ping, Voest Emile E, Gebbink Martijn F B G
Department of Medical Oncology, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands.
FEBS Lett. 2003 Mar 27;539(1-3):149-55. doi: 10.1016/s0014-5793(03)00218-7.
Endostatin is a fragment of collagen XVIII that acts as an endogenous inhibitor of tumor angiogenesis and tumor growth. Anti-tumor effects have been described using both soluble and insoluble recombinant endostatin. However, differences in endostatin structure are likely to cause differences in bioactivity. In the present study we have investigated the structure and cellular effects of insoluble endostatin. We found that insoluble endostatin shows all the hallmarks of amyloid aggregates. Firstly, it binds Congo red and shows the characteristic apple-green birefringe when examined under polarized light. Secondly, electron microscopy shows that endostatin forms short unbranched fibrils. Thirdly, X-ray analysis shows the abundant presence of cross-beta sheets, the tertiary structure that underlies fibrillogenesis. None of these properties was observed when examining soluble endostatin. Soluble endostatin can be triggered to form cross-beta sheets following denaturation, indicating that endostatin is a protein fragment with an inherent propensity to form amyloid deposits. Like beta-amyloid, found in the brains of patients with Alzheimer's disease, amyloid endostatin binds to and is toxic to neuronal cells, whereas soluble endostatin has no effect on cell viability. Our results demonstrate a previously unrecognized functional difference between soluble and insoluble endostatin, only the latter acting as a cytotoxic amyloid substance.
内皮抑素是胶原蛋白XVIII的一个片段，作为肿瘤血管生成和肿瘤生长的内源性抑制剂。使用可溶性和不溶性重组内皮抑素均已描述了其抗肿瘤作用。然而，内皮抑素结构的差异可能会导致生物活性的差异。在本研究中，我们研究了不溶性内皮抑素的结构和细胞效应。我们发现不溶性内皮抑素显示出淀粉样聚集体的所有特征。首先，它与刚果红结合，在偏振光下检查时显示出特征性的苹果绿双折射。其次，电子显微镜显示内皮抑素形成短的无分支纤维。第三，X射线分析显示大量存在交叉β片层，这是纤维形成的三级结构。检查可溶性内皮抑素时未观察到这些特性中的任何一种。可溶性内皮抑素在变性后可被触发形成交叉β片层，表明内皮抑素是一种具有形成淀粉样沉积物固有倾向的蛋白质片段。与在阿尔茨海默病患者大脑中发现的β淀粉样蛋白一样，淀粉样内皮抑素与神经元细胞结合并对其有毒性，而可溶性内皮抑素对细胞活力没有影响。我们的结果证明了可溶性和不溶性内皮抑素之间以前未被认识到的功能差异，只有后者作为一种细胞毒性淀粉样物质起作用。
