Prof. Dr. Gerd Bendas, Department of Pharmacy, Rheinische Friedrich Wilhelms University Bonn, An der Immenburg 4, 53121 Bonn, Germany, Tel.: +49 228 735250, Fax: +49 228 734692, E-mail:
Thromb Haemost. 2013 Nov;110(5):1046-54. doi: 10.1160/TH13-02-0158. Epub 2013 Sep 5.
The integrin VLA-4 is important for the metastatic dissemination of melanoma cells. We could recently show that heparin can block VLA-4 binding, which contributes, next to blocking P- and L-selectin, to the understanding of antimetastatic activities of heparin. The matricellular ligand Cyr61, secreted by numerous tumours, is responsible for increased tumourigenicity and metastasis. This has been attributed to Cyr61 binding to, and thus activating integrins. However, a VLA-4/Cyr61 axis has not yet been reported. Since Cyr61 possesses heparin binding capabilities, Cyr61 can be supposed as potential target for heparin to indirectly interfere with integrin functions. The present in vitro studies address (i) the existence of a Cyr61/VLA-4 axis and (ii) the functional relevance of heparin interference via Cyr61. The C-terminal module III of Cyr61 could be exposed as nanomolar affine binding site for VLA-4. A shRNA-based knockdown of Cyr61 in MV3 human melanoma cells reduced VLA-4-mediated cell binding to VCAM-1, migration on fibronectin, and integrin signalling functions significantly. Using a biosensor approach we provide insight into heparin interference with this process. The low-molecular-weight heparin tinzaparin, but not the pentasaccharide fondaparinux, binds module IV of Cyr61 with micromolar affinity. But tinzaparin cannot interfere with Cyr61 accumulation onto syndecan-4, indicating different Cyr61 binding sites for heparin and other GAGs. Nonetheless, tinzaparin affects the VLA-4 binding and signalling functions selectively via Cyr61 already at very low concentration most likely by blocking the cellular secreted free Cyr61. This study emphasises Cyr61 as promising, and hitherto not considered target for heparin to selectively influence integrin functions.
整合素 VLA-4 对于黑色素瘤细胞的转移扩散很重要。我们最近发现肝素可以阻断 VLA-4 的结合，除了阻断 P-和 L-选择素之外，这有助于理解肝素的抗转移活性。细胞外基质配体 Cyr61 由许多肿瘤分泌，是增加肿瘤发生和转移的原因。这归因于 Cyr61 与整合素结合并激活整合素。然而，目前尚未报道 VLA-4/Cyr61 轴。由于 Cyr61 具有肝素结合能力，因此可以推测 Cyr61 是肝素潜在的靶点，可间接干扰整合素的功能。本研究探讨了（i）Cyr61/VLA-4 轴的存在，以及（ii）通过 Cyr61 进行肝素干扰的功能相关性。Cyr61 的 C 端模块 III 可以作为与 VLA-4 结合的纳摩尔亲和结合位点暴露出来。MV3 人黑色素瘤细胞中的 Cyr61 的 shRNA 敲低显著降低了 VLA-4 介导的细胞与 VCAM-1 的结合、在纤维连接蛋白上的迁移以及整合素信号转导功能。我们使用生物传感器方法深入了解肝素对这一过程的干扰。低分子量肝素丁肝素，但不是戊糖依诺肝素，以微摩尔亲和力结合 Cyr61 的模块 IV。但是丁肝素不能干扰 Cyr61 积累到 syndecan-4 上，表明肝素和其他 GAG 对 Cyr61 具有不同的结合位点。尽管如此，丁肝素已经在非常低的浓度下通过阻断细胞分泌的游离 Cyr61 选择性地影响 VLA-4 的结合和信号转导功能。本研究强调了 Cyr61 是一种很有前途的、迄今尚未被认为是肝素选择性影响整合素功能的靶点。
