CXCL12/CXCR4通过IER3调控胃癌PD-L1表达诱导T细胞凋亡的机制研究

Both activation of PD-L1/PD-1 and CXCL12/CXCR4 signaling pathways have inhibitory role of T cells, however, the interaction between them is unknown. Our original study showed that: CXCL12/CXCR4 increased PD-L1 expression and induced stronger T cells apoptosis, accompanied by upregulation of lncRNA-ASF and immediate early genes IER3 expression, and downregulation of miR-148b-3p. The inhibition of lncRNA-ASF or IER3 induced PD-L1 downregulation. In addition, lncRNA-ASF upregulated IER3 by competitively binding miR-148b-3p，which is the negative regulator of IER3 expression. Collectively, the aim of our study is to prove that lncRNA-ASF, a mediator of CXCL12/CXCR4 signaling in gastric cancer, as ceRNA, inhibited miR-148b-3p-mediated IER3 downregulation by competitively binding miR-148b-3p, which finally resulted in PD-L1 over-expression, and then induced T cells apoptosis. The result of the study will be helpful in illustrating the mechanisms by which CXCL12/CXCR4 regulates PD-L1 expression and promotes immune escape in gastric cancer.

PD-L1/PD-1和CXCL12/CXCR4通路均能抑制T细胞功能，但二者的相互作用不明。我们的原创性研究证实：1.CXCL12/CXCR4能上调胃癌PD-L1表达，更强的诱导T细胞凋亡，同时伴有lncRNA-ASF和即刻早起反应基因IER3上调，miR-148b-3p下调。2.抑制lncRNA-ASF或IER3表达则PDL1下调。3.lncRNA-ASF通过与miR-148b-3p结合，抑制miR-148b-3p对IER3的负靶向调节，从而提高IER3的表达。本研究旨在证实，CXCL12/CXCR4上调lncRNA-ASF，使其发挥ceRNA作用，解除miRNA-148b-3p对IER3的抑制，最终通过上调IER3，促进胃癌PD-L1表达，导致T细胞凋亡。本研究结果将为明确CXCL12/CXCR4通路如何通过调控PD-L1，强化胃癌的免疫逃逸提供科学依据。

胃癌是世界范围内常见恶性肿瘤之一。近年来，抗PD1单抗治疗已被批准作为晚期胃癌的一线治疗方案。然而，只有部分亚型胃癌患者可以从免疫治疗中获益。究其原因是缺乏有效的预测胃癌免疫治疗的生物标志物。本研究探讨了CXCL12/CXCR4如何调控胃癌PD-L1表达诱导免疫逃逸及胃癌转移的新机制。我们的原创性研究证实：1.CXCL12/CXCR4可以通过IER3上调胃癌PD-L1表达诱导T细胞凋亡。2.5-FU增加了胃癌来源的外泌体PD-L1。重要的是，在21例III-IV期胃癌患者血浆，经过2个、4和6个周期5-FU治疗中与基线水平相比，循环exosomal PD-L1显著上调。伴随着IFN-γ，TNF-α，IL-2，IL-6和GM-CSF下调。此外，与有反应者相比，无反应者循环外泌体PD-L1的增加更为显著。外泌体PD-L1还可诱导Jurkat T细胞凋亡并抑制外周血单个核细胞中的T细胞活化，这可以通过纳武利尤单抗部分逆转。这些结果提示5-FU诱导的外泌体PD-L1的上调可导致进展期胃癌在多周期化疗后的全身免疫抑制。3.CXCL12/CXCR4与EGF/EGFR信号通路轴通过NF-KB相互调控表达促进胃癌转移。在胃癌组织标本中检测发现，CXCR4与EGFR表达呈显著正相关，CXCR4与EGFR双阳性的胃癌患者预后最差。4.我们发现CXCL12/CXCR4通过NF-kB信号通路上调SERPINB3表达促进胃癌细胞浸润和迁移。5.我们在两个独立的GEO数据集中确定了晚期胃癌（AGC）的三种免疫相关亚型（Immunity_H、Immunity_M 和 Immunity_L），与Immunity-L相比，Immuntiy_H亚型表现出更高的免疫细胞浸润和免疫活性，预后良好。在核心网络基因中，ADAM like decysin 1（ADAMDEC1）被确定为与进展期胃癌良好预后高度相关的关键基因。进一步的实验验证表明ADAMDEC1缺乏可以上调胃癌PD-L1表达诱导Jurkat T细胞的凋亡。本研究结果明确了胃癌PD-L1表达调控及胃癌转移的新机制，将为判断胃癌的预后和靶向及免疫治疗疗效提供新的证据。