Ⅰ型固有淋巴细胞分泌LTα3激活Troy受体并促进胃癌细胞干性的作用及机制研究

Innate lymphoid cells (ILCs) play essential roles for intestinal inflammation and epithelial regeneration, but it remains unclear how they contribute to tumor development. As indicated by our preliminary studies, type 1 ILCs (ILC1s) were the major ILCs infiltrated in gastric cancer tissues and their abundance was associated with stemness of primary cancer cells. We further demonstrated that soluble lymphotoxin (LTα3) released by ILC1s could promote Lgr5 transcription and the stem-like properties via its receptor Troy expressed by cancer cells in vitro. However the mechanisms underlying enhancement of Lgr5 transcription and cancer stemness remain unknown. We therefore hypothesize that infiltrating ILC1s may regulate self-renewal by releasing LTα3 to activate the receptor Troy on gastric cancer cells. Interaction between LTα3 and Troy activated NF-κB, which formed a complex with and activated β-catenin, leading to recruitment of a histone demethylase Jmjd2b to reduce H3K9me3 level in Lgr5 promoter and enhance Lgr5 expression and cancer stemness. We will establish genetically engineered mice that are deficient in adaptive immunity and depleted of either ILC1s or ILC1s-specific LTα3 to demonstrate the regulation of gastric cancer progression and cancer stemness by the innate effectors. Molecular techniques such as Chromatin Immunoprecipitation will be applied to study the epigenetic control of Lgr5 transcription by the NF-κB/β-catenin/Jmjd2b complex. Taken together, we will investigate the regulation of tumor progression and cancer stemness by innate immune cells, thereby providing novel therapeutic modalities and potential targets for treatment of gastric cancer.

固有淋巴细胞调控肠道炎症和上皮修复，但在肿瘤发生发展中的作用不详。我们发现I型固有淋巴细胞（ILC1s）在胃癌组织中增多且与肿瘤细胞干性密切相关；在体外ILC1s分泌淋巴毒素（LTα3）激活胃癌细胞Troy受体，促进Lgr5转录和肿瘤细胞干性，但机制不明。我们提出假说：ILC1s源性LTα3激活胃癌细胞Troy受体，Troy下游NF-κB活化后可能招募β-catenin和组蛋白去甲基化酶Jmjd2b形成复合物，从而降低Lgr5启动子H3K9me3水平，上调Lgr5转录，促进胃癌细胞获得干性。拟利用基因剔除小鼠，进一步在体内研究ILC1s和LTα3对胃癌进展和胃癌细胞干性的调控作用，染色质免疫共沉淀等技术探讨Troy受体下游NF-κB/β-catenin/Jmjd2b相互作用，调控Lgr5表达的表观遗传学机制，探索免疫微环境调控肿瘤进展和肿瘤细胞干性的机制，有望提供胃癌治疗的新思路和新靶点。

胃癌等消化系统肿瘤中存在一群具有干细胞样特性的肿瘤干细胞，独具自我更新能力，是肿瘤生长演进的“种子”。肿瘤间质微环境和肿瘤实质均在调控肿瘤细胞干性中发挥重要作用，但目前对免疫微环境如何影响肿瘤细胞干性，肿瘤细胞如何响应微环境信号刺激进而维持干性的机制均尚未完全阐明。本项目聚焦微环境中肿瘤细胞干性的调控机制，获得如下研究发现：1. 肿瘤微环境中的固有淋巴细胞（ILC1s）对维持胃癌细胞干性发挥重要作用；2. ILC1s源性LTα3结合胃癌细胞Troy受体促进胃癌细胞干性；3. Lgr5+胃癌细胞和肝癌细胞具有肿瘤干细胞特性，组蛋白去甲基化酶LSD1介导的Wnt信号通路激活，在维持Lgr5+肿瘤细胞干性中发挥关键作用；4. Hippo信号上游分子的异常DNA甲基化，也在维持gr5+肿瘤干自我更新中中发挥重要作用；5. 发现了一个对Wnt信号敏感的胃干细胞亚群；6. Wnt信号通过上调SMYD3，依赖组蛋白表观修饰机制，正反馈上调ASCL2表达，维持Lgr5+胃癌干细胞自我更新。综上所述，本项目发现在胃癌等消化系统肿瘤中，Lgr5+肿瘤细胞均有干细胞特征，进一步阐明微环境调控其自我更新的分子机制。我们还发现Wnt信号通过靶向SMYD3，上调ASCL2表达和胃癌细胞的新机制，提示肿瘤微环境中，表观遗传修饰酶SMYD3是靶向干预胃癌干细胞自我更新的潜在靶点之一。这些创新性发现为进一步阐明胃癌等消化系统肿瘤干细胞生物学特性调控机理，为从源头上根除肿瘤“种子细胞”，开发新的抗肿瘤治疗方式提供了试验依据，具有一定的临床转化价值。

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