hsa_circ_0046523-miR-148a-3p-Smad2/PD-L1调控轴介导的肿瘤免疫抑制微环境促进胰腺癌侵袭转移

The immunosuppressive microenvironment is an important promoting factor for the immune evasion and metastases of cancer cells. Smad2 and PD-L1 can induce immunosuppressive microenvironment through activating TGF-β/Smad and PD-1/PD-L1 signaling pathways, respectively. Our previous studies indicated that Smad2 and PD-L1 were two direct targets of miR-148a-3p in pancreatic cancer. Meanwhile, hsa_circ_0046523 was aberrantly upregulation and could function as a miRNA sponge of miR-148a-3p. Therefore, we hypothesize there may be an hsa_circ_0046523-miR-148a-3p-Smad2/PD-L1 regulating axis in pancreatic cancer. This regulating axis might continuously upregulate Smad2 and PD-L1 expression, activate TGF-β/Smad and PD-1/PD-L1 signaling pathways which result in the induction of tumor immunosuppressive microenvironment, and promote invasion and metastases in pancreatic cancer. To test this hypothesis, we plan to evaluate the gene expression and their interactions of this hsa_circ_0046523-miR-148a-3p-Smad2/PD-L1 regulating axis in pancreatic cancer. The effects of introduction of immunosuppressive microenvironment through hsa_circ_0046523-miR-148a-3p-Smad2/PD-L1 regulating axis will also be evaluated in vitro and in vivo, as well as their regulatory relationships. The study might provide novel therapeutic targets for the treatment of pancreatic cancer through remodeling tumor immune microenvironment.

免疫抑制微环境是导致肿瘤细胞免疫逃逸和侵袭转移的重要因素。Smad2和PD-L1分别激活TGF-β/Smad和PD-1/PD-L1信号通路而诱导免疫抑制微环境。课题组前期研究发现：胰腺癌中miR-148a-3p可靶向调控Smad2和PD-L1，同时环状RNA46523异常表达上调并可能作为miRNA海绵吸附miR-148a-3p。故推测胰腺癌中存在环状RNA46523-miR-148a-3p-Smad2/PD-L1调控轴持续上调Smad2/PD-L1的表达，激活相关信号通路，介导肿瘤免疫抑制微环境，促进侵袭转移。本项目首先分析该调控轴中各分子在胰腺癌组织中表达的相关性及其与肿瘤免疫微环境的关系，然后经体外实验干预调控轴中各分子的表达，明确其上下游调控关系及其对胰腺癌恶行性的影响，最后经免疫健全小鼠胰腺原位移植瘤实验进一步体内验证。研究结果有望为重塑胰腺癌免疫微环境的靶向治疗提供新的切入点。

胰腺癌是一种极具侵袭性的消化系统恶性肿瘤，严重危害人类健康。深入研究胰腺癌免疫微环境的分子调控网络，进行有效干预逆转免疫抑制微环境，对抑制胰腺癌发生发展以及提高免疫治疗效果具有重要意义。PD-1/PD-L1作为T细胞免疫反应的协同刺激信号通路，是肿瘤免疫治疗的重要靶点。本项目采用多重荧光免疫组织化学方法检测胰腺癌组织中浸润性T细胞表型，结果表明：胰腺癌肿瘤微环境中免疫效应细胞减少，免疫抑制细胞增多；其中总T细胞、CD4+ Th、Tregs和PD-L1+ T细胞数量是胰腺癌预后的独立危险因素。同时，本项目研究结果显示hsa_circ_0046523在胰腺癌组织和胰腺癌细胞中高表达，其表达水平与miR-148a-3p的表达呈负相关，而与PD-L1的表达呈正相关；hsa_circ_0046523表达与胰腺癌患者肿瘤分化程度、T分期、淋巴结转移、TNM分期及预后密切相关。更为重要的是，hsa_circ_0046523可以促进胰腺癌细胞的增殖、迁移及侵袭能力，且可以介导胰腺癌免疫抑制微环境的形成，促进肿瘤细胞免疫逃逸；机制上，hsa_circ_0046523通过海绵吸附miR-148a-3p，上调胰腺癌细胞PD-L1的表达，促进肿瘤微环境中Tregs细胞浸润，并抑制CD4+ T细胞、CD8+ T细胞浸润，促进CD8+ T细胞的凋亡及耗竭，从而发挥免疫调节功能。总而言之，本研究明确了hsa_circ_0046523-miR-148a-3p-PD-L1调控轴的存在及其介导的免疫抑制微环境对胰腺癌侵袭转移的影响，有助于发掘胰腺癌临床诊治的新靶点。