轴突导向分子SEMA6A下调PLGF抑制肿瘤相关巨噬细胞M2型极化抗结直肠癌肝脏转移的机制研究

Tumor associated macrophages (TAMs) are a large component of the tumor microenvironment, which promote tumor cells invasion and metastasis, and they are related to malignant degree and poor prognosis. TAMs depolarization from M2 phenotype is considered to be a promising anti-metastasis strategy. Recent studies have been shown that SEMA6A, the axon guidance molecule is involved in immune response and inhibits tumor progression. However, whether SEMA6A regulates tumor metastasis via affecting inflammatory microenvironment is unclear. Our preliminary studies and database analysis suggested that a significant downregulation in SEMA6A expression in colorectal carcinoma tissues as compared with normal specimens, and loss of SEMA6A expression was negatively associated with distant metastasis and poor prognosis of colorectal carcinoma patients. SEMA6A overexpression colorectal carcinoma cells showed a significant decrease in liver metastatic foci and a less M2-TAMs infiltration when implanted in WT mice with downregulation of tumor cells-produced placenta growth factor (PLGF). Thus, we hypothesized that SEMA6A might block PLGF production via the receptor PlexinA4 of colorectal carcinoma cells, contributing to skewing TAMs polarization away from the M2- to a tumor-inhibiting M1-like phenotype, leading to suppressing liver metastasis of tumor cells. The goals of this project are: 1) to determine its role in liver metastasis of colorectal carcinoma cells, 2) to elucidate how SEMA6A inhibits tumor metastasis via regulating TAMs polarization. The proposed studies will provide new knowledge regarding mechanisms of TAMs polarization, thus addressing a fundamental issue for new approaches in antitumor drugs and tumor immunotherapy based on polarizing TAMs away from the M2 phenotype.

肿瘤相关巨噬细胞 (TAMs)是肿瘤微环境的重要组成部分，抑制TAMs的M2型极化是极具应用前景的抗肿瘤转移新策略。新近发现轴突导向分子SEMA6A参与免疫反应、抑制肿瘤进展。但SEMA6A是否通过重塑炎症微环境调控肿瘤转移不清楚。我们前期探索分析发现：结直肠癌组织中SEMA6A的表达水平下降，与肿瘤发生远处转移及患者生存期呈负相关，SEMA6A过表达的结直肠癌细胞肝脏转移显著抑制，M2型TAMs浸润减少，并下调细胞因子PLGF的合成。据此假设：SEMA6A与结直肠癌细胞表面PlexinA4受体结合，通过下调PLGF合成分泌，介导TAMs由M2型向M1型极化，通过增强抗肿瘤免疫效应，抑制结直肠癌肝脏转移。本申请将阐明SEMA6A通过重塑炎症微环境抑制结直肠癌肝脏转移，揭示其调节TAMs表型极化的分子机制。本研究将为开发基于抑制M2型极化的全新抗肿瘤转移药物及肿瘤免疫治疗提供重要的科学依据。

结直肠癌（Colorectal Cancer, CRC）是最常见的恶性肿瘤之一。目前，除了直接杀伤肿瘤细胞，通过调控肿瘤微环境，增强抗肿瘤免疫应答，被认为是极具应用前景的抗肿瘤新策略。轴突导向分子Semaphorin 6A（SEMA6A）是SEMA家族的跨膜糖蛋白，通过与受体结合来传导信号。研究发现SEMA6A广泛参与细胞迁移、血管生成、免疫反应及调控肿瘤等过程。尽管SEMA6A参与调节肿瘤的生物学行为，但是SEMA6A在CRC中的作用及机制仍不清楚。该项研究发现SEMA6A在CRC组织中表达下调，SEMA6A表达与患者预后呈显著正相关，是患者总生存期的独立预测因子。揭示了SEMA6A与受体结合，通过下调免疫抑制分子，增强抗肿瘤免疫效应，抑制肿瘤细胞的生长、侵袭和转移。此外，亚型分子SEMA6B和SEMA4C在CRC组织中表达大量增加，与患者的预后存活时间呈显著的负相关，均为CRC的独立预后因子。机制上，阐明了SEMA6B高表达通过促进肿瘤免疫抑制微环境的形成导致CRC患者的不良预后；SEMA4C通过诱导肿瘤细胞上皮-间质转化促进CRC的发展。同时，在肿瘤免疫标志物的研究中，我们阐明了免疫检查点分子IDO1联合T细胞标志物CD8A构成的分类器，可对CRC预后评估提供更加准确的预测指标，优于单独的CD8 T细胞浸润水平及CMS分类，是结肠癌预后诊断的独立影响因子。此外，进一步揭示了MATH算法可以准确对肿瘤异质性进行量化评价，对于肿瘤患者的风险分层、精准治疗及预后评估有重要的临床价值。本课题的完成提示：轴突导向分子SEMA6A、亚型分子SEMA6B、SEMA4C以及轴突导向受体—基因X，可能成为CRC免疫治疗的新的策略及治疗靶点，并且为CRC诊断、预后判断、分子分型及新的药物靶点的发现提供了重要的科学依据，这对于防治CRC的恶行进展及精准治疗具有重要的理论意义和实际价值。