Tenascin-C (TNC) 在血小板促乳腺癌肺转移中的生物学作用研究

Recurrence and metastasis is the leading cause of death among breast cancer patients. With a high incidence and bad prognosis, the pulmonary metastasis in breast cancer is always a difficult and hot topic in recent years. Tenascin-C (TNC) is a tumor microenvironment-specific extracellular matrix glycoprotein with a high expression and link to malignancy in cancer. It has been shown that: 1. TNC can induce tumor cell migration and invasion by a mechanism that involves epithelial to mesenchymal transition (EMT) and TGF-β signaling. However, no information is available about how TNC activates this signaling pathway and what impact that would have on tumor cell dissemination, circulating tumor cells and extravasation into the lung parenchyma; 2. Convincing proof was provided that a transient interaction of platelets with circulating tumor cells can activate TGF-β signaling which then cause EMT and extravasation of the tumor cells into the lung parenchyma; 3. It has been reported that platelets can directly interact with TNC through different integrin. In addition, in the NeuNT breast cancer mouse model, we recently observed the appearance of metastatic lung lymphovascular invasion (LVI) attaching to the endothelium and extravasating into the lung parenchyma. Moreover, the LVIs are surrounded by platelets and an attached ECM coat of TNC. Hence, the aim of this project is to address whether TNC and platelets potentially function as accomplices in breast cancer lung metastasis. We will study the role of TNC on the attraction of tumor cells into a thrombus and on the recruitment of platelets into metastatic lung LVI as well as on the formation and extravasation of metastatic lung LVI. Furthermore, we will investigate the molecular mechanisms of the interplay between TNC and platelets in tumor cell EMT and extravasation. This project will explore the mechanism of tumor metastasis from a perspective of microenvironment of circulating tumor cells, and provide potential new strategies for clinical anti-tumor metastasis therapy.

乳腺癌复发转移是导致患者死亡的最主要原因。其中肺转移发生率最高,患者预后最差,是近年来研究的难点和热点。Tenascin-C（TNC）是一种在恶性肿瘤中特异性高表达的细胞外基质糖蛋白。有研究表明：1.TNC可以通过TGF-β信号通路导致肿瘤细胞上皮间充质转化（EMT），参与调节肿瘤细胞侵袭浸润，然而TNC如何激活此信号通路并促进肿瘤转移目前尚不明确；2.循环肿瘤细胞与血小板相互作用可以使TGF-β信号激活，导致EMT以及肿瘤细胞向肺实质的外渗；3.TNC可以通过不同整合素受体参与血小板的募集。另外，本课题组前期研究发现，在NeuNT乳腺癌小鼠中，肺血管瘤栓周围包绕着血小板以及富含TNC的细胞外基质成分。因此，本课题将探讨TNC在瘤栓形成、血小板聚集及肺血管瘤栓外渗中的作用，进而探讨TNC与血小板在TGF-β介导的乳腺癌细胞EMT及其向肺实质外渗中的分子机制,为临床抗肿瘤转移治疗提供新思路。

乳腺癌复发转移是导致患者死亡的最主要原因。其中肺转移发生率高,患者预后差, 如何阻止肺转移瘤栓向肺实质的外渗是研究热点。其正确动物模型的建立及内在理论基础的研究迫在眉睫。Tenascin-C(TNC)是一种在恶性肿瘤中特异性高表达的细胞外基质糖蛋白，与肿瘤转移存在密切联系，但是目前TNC通过何种机制促进转移尚不完全清楚，尤其对肿瘤转移过程中循环肿瘤细胞向肺实质的外渗有什么样的影响也未见报道。本项目通过建立野生型TNC+/+与基因敲除型TNC-/- MMTV-NeuNT乳腺癌小鼠模型以及MMTV背景小鼠NT193乳腺癌细胞原位种植瘤模型，研究了TNC促进乳腺癌肺转移的机制。本项目发现: 基质来源TNC参与了血管内肺转移瘤栓微环境的构成，为肿瘤细胞逃避机体免疫反应提供了物理屏障，促进了瘤栓中肿瘤细胞的存活。同时，TNC可以促使肺转移瘤栓中血小板的聚集，促使血小板胞内颗粒中的TGF-β释放，并通过TGF-β信号通路诱导肿瘤细胞上皮间充质转化，促进血管内肺转移瘤栓向肺实质的外渗，促进乳腺癌肺转移。该研究成果可以帮助我们发展针对乳腺癌患者循环肿瘤细胞的诊断工具，从而对乳腺癌患者的转移进行早期诊断。另外，我们发现，TNC通过结合趋化因子CXCL12，将肿瘤浸润CD8 T细胞(CD8 TIL)阻拦在癌巣外的基质中，减少了CD8 TIL向癌巣的浸润，促进肿瘤生长与转移。在临床标本中，TNC低表达患者侵入癌巣的CD8 TIL与留在肿瘤基质的CD8 TIL细胞比例明显高于TNC高表达患者。同时，TNC及CXCL12高表达，CD8 TIL低浸润的患者相比于其他患者预后更差，这些结果提示，TNC可能参与CD8 TIL的免疫调节，这一发现，为肿瘤患者的个体化免疫治疗提供了新的思路。同时，本项目中动物模型的建立，为研究乳腺癌复发转移提供了很好的临床前工具，为后续抗肿瘤转化研究提供帮助。