肿瘤细胞源性外泌体转运lincRNA-EPS调控NLRP6塑造小细胞肺癌转移前微环境

Widespread metastasis is the major cause of death for small-cell lung cacner (SCLC). Pre-metastatic niche forming in distant viscera is the prerequisite for metastasis. Alternative M2 activation of macrophage is the launch condition for pre-metastatic niche forming. Applicant’s previous study discovered SCLC cell can induce M2 phenotype switch of macrophage by enhance NLRP6 expression in circulating immature monocyte cell without contact directly. However, the mechanism how SCLC cells affect monocyte cells still remains unclear. Preliminary study showed tumor-derived exosome from SCLC cells can promote NLRP6 expression of monocyte and induce M2 phenotype switch of macrophage, which indicated that tumor-derived exosome from SCLC cells maybe the cause for pre-metastatic niche forming. LincRNA-EPS was found in these exosomes. LincRNA-EPS is a long non-coding RNA which is considered as a kind of inflammatory brakes gene. It has been proved can promote NLRP6 transcription by compressing chromatin near the immune response genes (IRGs). Therefore, we put forward the hypothesis of this study: Small cell lung cancer tumor cells secret exosomes containing lincRNA-EPS, which is transferred to circulation immature monocyte by exosomes to induce M2 phenotype switching of macrophage, and thus turn on the switch of pre-metastatic niche forming in distant viscera, finally promote the metastasis of SCLC. This study will explore the relationship of exosome, lincRNA-EPS and pre-metastatic niche forming, and extend the mechanism of metastasis in SCLC.

广泛转移是小细胞肺癌死亡率高的根本原因。巨噬细胞的替代激活是转移前微环境形成的起始条件。申请人前期研究发现小细胞肺癌细胞株通过NLRP6诱导单核细胞向替代激活的巨噬细胞分化，促进肿瘤转移。但小细胞肺癌细胞株促进单核细胞NLRP6表达的机制仍不明确。预实验发现小细胞肺癌细胞株来源的外泌体可以诱导单核细胞NLRP6的表达，且外泌体包含lincRNA-EPS。研究表明lincRNA-EPS是一种通过压缩染色质促进NLRP6转录的长链非编码RNA。由此提出本课题假设：小细胞肺癌肿瘤细胞来源的外泌体传导lincRNA-EPS至循环单核细胞，通过促进NLRP6表达诱导单核细胞向替代激活的巨噬细胞分化，由此开启塑造远隔器官转移前微环境，促进小细胞肺癌的转移。本研究的开展有利于探索外泌体、lincRNA-EPS、NLRP6和转移前微环境之间的关系，拓展小细胞肺癌转移的新机制。

转移仍然是小细胞肺癌(small cell lung cancer，SCLC)相关死亡的主要原因。越来越多的研究将肿瘤转移与以炎症反应、免疫抑制以及肿瘤源性外泌体为特征的转移前微环境联系起来。为了阐明SCLC中这些因素之间的关系，我们首先分析了72位SCLC患者的病理切片，并发现CD206+ M2型巨噬细胞与SCLC患者的转移状态和不良预后相关。接着我们构建了SCLC转移裸鼠模型，发现肺转移灶处浸润性巨噬细胞(MØ)转变为M2表型，并伴随NLRP6表达水平升高。肿瘤来源的外泌体是肿瘤微环境中肿瘤和免疫细胞的关键调节因子。因此，我们研究了SCLC来源的外泌体是否有助于MØ表型转换。我们的研究结果表明，SCLC来源的外泌体通过NLRP6/NF-κB通路诱导巨噬细胞M2表型转换，从而在体外和体内促进了SCLC转移。此外，沉默NLRP6抑制了SCLC外泌体诱导的巨噬细胞M2表型转换。因此，我们的研究结果揭示了一种SCLC转移的新的可能机制，即SCLC来源的外泌体通过激活抗炎反应诱导远处MØ的免疫抑制以促进全身转移。