Maeshima Y, Colorado P C, Kalluri R
Department of Medicine and the Cancer Center, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA.
J Biol Chem. 2000 Aug 4;275(31):23745-50. doi: 10.1074/jbc.C000186200.
Vascular basement membrane is an important regulator of angiogenesis and undergoes many alterations during angiogenesis and these changes are speculated to influence neovascularization. Recently, fragments of collagen molecules have been identified to possess anti-angiogenic activity. Tumstatin (alpha3(IV)NC1 domain) is one such novel molecule with distinct anti-tumor properties and possesses an N-terminal (amino acids 54-132) anti-angiogenic and a C-terminal (amino acids 185-203) anti-tumor cell activity (Maeshima, Y., et al. 2000) J. Biol. Chem. 275, 21340-21348). Previous studies have identified the 185-203 amino acid sequence as a ligand for alpha(v)beta(3) integrin (Shahan, T. A., et al. (1999) Cancer Res. 59, 4584-4590). In the present study, we found distinct additional RGD-independent alpha(v)beta(3) integrin binding site within 54-132 amino acids of tumstatin. This site is not essential for inhibition of tumor cell proliferation but necessary for the anti-angiogenic activity. A fragment of tumstatin containing 54-132 amino acid (tum-2) binds both endothelial cells and melanoma cells but only inhibited proliferation of endothelial cells, with no effect on tumor cell proliferation. A similar experiment with fragment of tumstatin containing the 185-203 amino acid (tum-4) demonstrates that it binds both endothelial cells and melanoma cells but only inhibits the proliferation of melanoma cells. The presence of cyclic RGD peptides did not affect the alpha(v)beta(3) integrin-mediated activity of tumstatin, although significant inhibition of endothelial cell binding to vitronectin was observed. The two distinct RGD-independent binding sites on tumstatin suggest unique alpha(v)beta(3) integrin-mediated mechanisms governing the two distinct anti-tumor properties of tumstatin.
血管基底膜是血管生成的重要调节因子，在血管生成过程中会发生许多改变，据推测这些变化会影响新血管形成。最近，已鉴定出胶原蛋白分子片段具有抗血管生成活性。肿瘤抑素（α3(IV)NC1结构域）就是这样一种具有独特抗肿瘤特性的新型分子，其N端（氨基酸54 - 132）具有抗血管生成活性，C端（氨基酸185 - 203）具有抗肿瘤细胞活性（前岛洋，等人，2000年，《生物化学杂志》275卷，21340 - 21348页）。先前的研究已确定185 - 203氨基酸序列是α(v)β(3)整合素的配体（沙汉，T.A.，等人，（1999年）《癌症研究》59卷，4584 - 4590页）。在本研究中，我们在肿瘤抑素的54 - 132氨基酸内发现了另外一个独特的不依赖RGD的α(v)β(3)整合素结合位点。该位点对于抑制肿瘤细胞增殖并非必需，但对于抗血管生成活性是必需的。包含54 - 132氨基酸的肿瘤抑素片段（tum - 2）既能结合内皮细胞也能结合黑色素瘤细胞，但仅抑制内皮细胞的增殖，对肿瘤细胞增殖无影响。用包含185 - 203氨基酸的肿瘤抑素片段（tum - 4）进行的类似实验表明，它既能结合内皮细胞也能结合黑色素瘤细胞，但仅抑制黑色素瘤细胞的增殖。环状RGD肽的存在并不影响肿瘤抑素的α(v)β(3)整合素介导的活性，尽管观察到内皮细胞与玻连蛋白的结合受到显著抑制。肿瘤抑素上两个不同的不依赖RGD的结合位点表明，存在独特的α(v)β(3)整合素介导的机制来调控肿瘤抑素的两种不同抗肿瘤特性。
