Background: Tumor microenvironment (TME) is one of the important factors in tumorigenesis and progression, in which tumor-associated macrophages (TAMs) play an important role in non-small cell lung cancer (NSCLC) progression. However, the mechanism of TAMs in NSCLC progression remains unclear, so this study aimed to investigate the role of TAMs in NSCLC progression and to find potential therapeutic targets.
Methods: Gene Expression Profiling Interactive Analysis (GEPIA) database was used to analyze the expression of prostaglandin E2 receptor 4 (EP4) mRNA in NSCLC and normal lung tissues; the protein expression levels of cyclooxygenase-2 (COX-2), EP4, cluster of differentiation 86 (CD86), CD163 and CD31 were detected by immunohistochemistry (IHC) in 120 NSCLC tissues and 24 paracancerous tissues specimens. The nude mouse lung adenocarcinoma cell A549 and macrophage RAW264.7 co-transplanted tumor model was established. And the samples were collected by gavage with EP4 inhibitor E7046, and then stained with hematoxylin-eosin (HE), IHC, and immunofluorescence (IF), and then detected by Western blot for the epithelial mesenchymal transformation (EMT) of the tumor tissues of the nude mice in each group. Western blot was used to detect the expressions of EMT related protiens in each group of nude mice; full-length transcriptome sequencing was used to screen the key genes causing liver metastasis and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis was performed.
Results: EP4 mRNA expression level in NSCLC tissues was generally lower than that in normal lung tissues (P<0.05); COX-2, EP4, CD163, CD31 proteins were differentially expressed in NSCLC tissues and adjacent tissues, and differences were observed in many clinicopathological parameters of NSCLC patients; RAW264.7 shortened the latency period of tumorigenesis of A549 and promoted the proliferation of tumors and liver metastasis of tumors, and E7046 could reduce tumor cell proliferation activity, tumor tissue vascular density and M2-type macrophage infiltration in nude mice; IF staining showed that macrophages were mainly distributed around the metastatic foci of tumors; Western blot results showed that compared with A549 alone transplantation group, the relative expression of E-cadherin protein in tumor tissues of mice in A549 and RAW264.7 co-transplantation group was significantly decreased, and the difference was statistically significant (P<0.05), while the relative expression of N-cadherin protein was up-regulated, but the difference was not statistically significant (P>0.05); the main pathways enriched in the differential genes of the full-length transcriptome were the PI3K-AKT and MAPK signaling pathways.
Conclusions: During NSCLC development, the COX-2/PGE2/EP4 axis may promote tumor progression by inducing macrophage functional activation, and EP4 may be a potential new target for tumor immunotherapy. This study provides new perspectives and ideas for in-depth exploration of the mechanisms of NSCLC development, as well as a theoretical basis for the development of new therapeutic strategies for NSCLC.
【中文题目：COX-2/PGE2/EP4轴诱导巨噬细胞功能活化在NSCLC发展过程中的作用】 【中文摘要：背景与目的 肿瘤微环境（tumor microenvironment, TME）是肿瘤发生、发展的重要因素之一，其中肿瘤相关巨噬细胞（tumor-associated macrophages, TAMs）在非小细胞肺癌（non-small cell lung cancer, NSCLC）进展中起着重要作用。然而，TAMs在NSCLC发展过程中的作用机制仍不清楚，因此本研究旨在探讨TAMs在NSCLC发展过程中的作用，并寻找潜在的治疗靶点。方法 使用GEPIA（Gene Expression Profiling Interactive Analysis）数据库分析前列腺素E2受体4（prostaglandin E2 receptor 4, EP4）mRNA在NSCLC和正常肺组织中的表达情况；利用免疫组化（immunohistochemistry, IHC）方法检测120例NSCLC组织及24例癌旁组织标本中环氧合酶-2（cyclooxygenase-2, COX-2）、EP4、分化簇86（cluster of differentiation 86, CD86）、CD163、CD31的蛋白表达水平；建立裸鼠肺腺癌细胞A549与巨噬细胞RAW264.7共移植瘤模型，使用EP4抑制剂E7046灌胃，收集样本行苏木素-伊红（hematoxylin-eosin, HE）、IHC和免疫荧光（immunofluorescence, IF）染色，免疫印迹（Western blot）检测各组裸鼠肿瘤组织上皮间充质转化（epithelial-mesenchymal transformation, EMT）相关蛋白表达情况；全长转录组测序技术筛选引起肿瘤肝转移的关键基因并进行KEGG（Kyoto Encyclopedia of Genes and Genomes）富集分析。结果 EP4 mRNA在NSCLC组织中表达水平普遍低于正常肺组织（P<0.05） ；COX-2、EP4、CD163、CD31蛋白在NSCLC组织和癌旁组织中差异性表达且在NSCLC患者多项临床病理参数中存在差异；RAW264.7缩短了A549的成瘤潜伏期，促进肿瘤增殖及肿瘤肝转移，E7046可降低裸鼠肿瘤细胞增殖活性、肿瘤组织血管密度及M2型巨噬细胞浸润；IF染色显示巨噬细胞主要分布在肿瘤转移灶周围；Western blot结果显示与A549单独移植组相比，A549与RAW264.7共移植组小鼠肿瘤组织中E-钙黏蛋白（E-cadherin）相对表达量明显降低，差异具有统计学意义（P<0.05），N-钙黏蛋白（N-cadherin）相对表达量上调，但差异无统计学意义（P>0.05）；全长转录组差异基因主要富集的通路为PI3K-AKT、MAPK信号通路。结论 在NSCLC发生发展过程中，COX-2/PGE2/EP4轴可能通过诱导巨噬细胞功能活化来促进肿瘤的进展，EP4可能是具有潜力的肿瘤免疫治疗新靶点。本研究为深入探讨NSCLC的发生发展机制提供了新的视角和思路，同时为开发新的NSCLC治疗策略提供了理论依据。 】 【中文关键词：肺肿瘤；PGE2；EP4；巨噬细胞；肿瘤免疫】.
Keywords: EP4; Lung neoplasms; Macrophage; PGE2; Tumor immunity.