组织蛋白酶C（CTSC）在乳腺癌肺转移微环境调控中的作用与机制

Tumor microenvironment, composed of various cellular and non-cellular factors, plays important roles in cancer development and metastasis. Tumor-secretory proteins are the major mediators for tumor cells to adapt and modify microenvironment, arguing for the studies of secretory factors to understand tumor metastasis. Due to their friendly accessibility, secretory proteins also hold great promise for therapeutic application. In the preliminary work, we performed differential secretome analysis of breast cancer cells and identified a list of secretory proteins associated with breast-to-lung metastasis. Among them, the cysteine proteinase Cathepsin C (CTSC) was found to be obviously and unanimously upregulated in lung-tropic cancer cells. In addition, preliminary functional analyses showed that CTSC might facilitate the recruitment of Ly6G+ neutrophils in lung metastasis niche, lung colonization of cancer cells and myeloid cell infilteration in lung metastases. This study aims at understanding the function and mechanisms of CTSC in breast cancer lung metastasis and microenvironment regulation. We will take advantage of the cell and animal metastasis models in our group, as well as clinical analyses, to elucidate whether and how extracellular CTSC regulates breast cancer lung colonization. We will also study the role of CTSC to regulate the recruitment and function of neutrophils, as well as other stromal components in lung metastases. Further, we will find out the downstream molecular effectors of CTSC. Overall, the completion of this study will help understand how tumor cells interact and remodel the microenvironment during metastasis and may open new avenues for the prognosis and treatment of malignant breast cancer.

中性粒细胞、巨噬细胞等髓系细胞参与的肿瘤微环境在肿瘤转移过程中发挥重要作用，但具体调控机制尚未清晰。分泌蛋白是癌细胞与微环境互作的主要参与者，对肿瘤分泌蛋白的研究有重要的生物学意义及癌症诊疗的应用前景。在前期工作中，我们通过对乳腺癌细胞的分泌蛋白组学分析，发现组织蛋白酶C（CTSC）在乳腺癌肺转移过程中显著并一致性地上调，而且CTSC能促进播散到肺的癌细胞周围中性粒细胞的招募，导致肺转移灶形成的加速以及转移灶内髓系细胞浸润的增加。因此我们认为肿瘤分泌的CTSC可能通过调控肺部转移微环境促进乳腺癌的转移定殖。本项目深入研究CTSC在乳腺癌肺转移过程中的功能与机制，阐明CTSC对中性粒细胞及其他肿瘤微环境细胞招募及功能的影响，发现CTSC发挥作用的下游分子途径，分析CTSC及其下游分子与乳腺癌转移风险的临床相关性，为CTSC分子通路在肿瘤转移临床预后诊断和治疗中的应用提供分子靶点和理论基础。

中性粒细胞等免疫细胞参与的肿瘤微环境在肿瘤转移过程中发挥重要作用，但具体调控机制尚未清晰。在前期工作中，我们通过对乳腺癌细胞的分泌蛋白组学分析，发现组织蛋白酶C（CTSC）在乳腺癌肺转移过程中显著并一致性地上调，而且CTSC能促进播散到肺的癌细胞周围Ly6G+中性粒细胞的招募。在本项目中我们发现肿瘤分泌的CTSC能进一步激活中性粒细胞使之形成胞外诱捕网（NET），从而播散癌细胞肺转移定殖。在机制上，CTSC通过酶切激活中性粒细胞膜定位PR3促进中性粒细胞中IL-1β的成熟和释放，从而上调中性粒细胞NF-κB信号通路和IL-6、CCL3等细胞因子的分泌，进而招募更多的中性粒细胞。同时，CTSC通过PR3-IL-1β-p38/MAPK上调中性粒细胞ROS水平，诱导NET的形成。而NET降解肺转移微环境中抗肿瘤因子TSP-1，增强播散癌细胞的增殖。利用小分子抑制剂靶向CTSC后能显著抑制NET形成以及乳腺癌肺转移。项目主要研究成果发表于Cancer Cell，相关专利实现商业转化。

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