小细胞肺癌外泌体介导S100蛋白重塑血脑屏障微环境促进肿瘤脑转移的机制研究

Small cell lung cancer (SCLC) is the most aggressive histologic subtype of lung cancer, with a strong predilection for metastasizing early. However, the cellular and molecular basis of SCLC brain metastasis is poorly known. Some recent studies revealed that brain microvasculature was the primary soil for metastatic tumor cell attachment and growth in the brain. We previously found that SCLC cells acted on human brain microvascular endothelial cells (HBMEC) to induce disassembly of TJ that leading to increased endothelial permeability and SCLC cells transendothelial migration. These data suggested that brain microvasculature might play an important role in the SCLC extravasation into the brain parenchyma. Therefore, we compare the protein expression profile in exosome derived from SCLC cell co-cultured with HBMEC by protein mass spectrometry and S100A16 was identified as a candidate protein. Further results showed that S100A16 in SCLC exosome was associated with SCLC metastasis to the brain. Based on these results, our projects will be focused in the role of S100A16 of SCLC exosome in SCLC migration across the blood brain barrier and metastasis to the brain, including S100A16 potential clinical relevance, the detailed effects of S100A16 in SCLC exosome on the SCLC metastasis to brain. Finally, the possibility of S100A16 in SCLC exosome as an early warning factor in SCLC metastasis to brain will be evaluated by the detection of a large number of clinical samples. These works are necessary to improve a better understanding of the mechanisms of SCLC brain metastasis and provide a potential therapeutic target for SCLC brain metastasis. More importantly, these studies will provide the strong evidence to verify the theory of exosome-mediated organotropic metastasis.

小细胞肺癌（SCLC）具有对脑特异性转移的特点，具体机制尚不清楚。前期发现，SCLC可以将细胞膜下蛋白Annexin A1外分泌到细胞外，介导脑转移的发生。进一步利用蛋白质质谱分析，在SCLC分泌的外泌体中筛选到能够与其结合的S100家族蛋白——S100A16，初步结果提示其与SCLC脑转移有关。本项目拟研究：①明确SCLC外泌体中S100A16与SCLC脑转移的关系；②探明SCLC外泌体中S100A16介导SCLC与BBB相互作用迁移入脑的过程；③解析SCLC 外泌体中S100A16如何完成细胞间信息的传递以调控BBB组成细胞功能，帮助SCLC迁移入脑；④分析SCLC患者血清外泌体中S100A16在脑转移中的临床意义，评价其作为脑转移风险预测因子的可能性。本项目的完成可为“外泌体介导肿瘤器官特异性转移”提供实验佐证，丰富SCLC脑转移机制的研究，有望为防治SCLC脑转移提供潜在作用靶点。

小细胞肺癌（SCLC）具有对脑特异性转移的病理特点，具体机制尚不清楚。我们以肺癌外泌体及前期工作中获得的与脑转移相关的因子S100A16为研究对象，开展如下工作：从临床和实验室研究两个层面尝试证明S100A16为介导SCLC经血脑屏障转移入脑的相关因子；分析肺癌细胞外泌体对脑内组织细胞功能的影响及其如何实现在不同细胞间完成信息传递，帮助肺癌细胞迁移入脑。本项目研究的重要结果如下：其一，在原有课题研究内容上获得的研究结果:①SCLC脑转移过程中，来源于人脑微血管内皮细胞的外泌体被肺癌细胞摄取后诱导其过S100A16；升高的S100A16核转位后诱导线粒体内膜蛋白PHB1表达，维持线粒体功能稳定进而维系癌细胞在脑内的生存；②肺癌细胞外泌体被脑微血管内皮细胞摄取后诱导其释放wnt信号抑制分子Dkk-1，Dkk-1调控转移前微环境中小胶质细胞活化状态，削弱了小胶质细胞外界刺激的敏感性，而迁移入脑的肺癌细胞内Dkk-1表达逐渐减少则抵消这一抑制效应，使小胶质细胞易被活化为具有促癌作用的M2型细胞。其二，在研究过程中获得了两个新的研究生长点，开展了如下探索性工作：①利用全转录组基因测序技术结合生物信息学方法分析寻找脑转移后的肺癌细胞基因表达谱的变化规律，发现脑转移肺癌细胞获得了与神经细胞早期发育相关的基因表达谱，且细胞内氧代谢谱发生可塑性转变；对其中与个体胚胎发育密切相关且在氧代谢基因功能子集中的HOXB9进行探讨，结果提示HOXB9可能通过调控细胞周期影响肺癌细胞脑内成瘤的能力；②从探索早期肺癌发生的病因学出发，利用TCGA数据库中肺腺癌临床样本转录组基因测序数据，挖掘原位肺癌肿瘤微环境相关因子，并分析其与疾病病程关系，为进一步深入早期肺癌病因学研究开展探索性的工作。结果发现布鲁顿酪氨酸激酶BTK是肺癌发展的负向预后因子，也是其微环境重塑的潜在指示因子，这些结果部分解释了BTK抑制剂ibrutinib对于肺癌临床治疗的无效性，为肺癌免疫治疗提供潜在的实验线索。本项目获得的重要结果部分以标注资金资助形式已发表，尚有结果整理撰文发表中。