Department of Pathology, Ajou University School of Medicine, Suwon, South Korea.
Department of Pathology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, South Korea.
Int J Cancer. 2019 Aug 15;145(4):916-926. doi: 10.1002/ijc.32140. Epub 2019 Feb 8.
Notwithstanding remarkable treatment success with anti-PD-1 monoclonal antibody, oncogenic mechanism of PD-L1 regulation in gastric cancer (GC) remains poorly understood. We hypothesized that ARID1A might be related to tumor PD-L1 expression in GC. We found that tumor PD-L1 positivity was associated with loss of ARID1A and showed trend toward better survival of patients with various molecular subtypes of GC (experimental set, n = 273). Considering heterogeneous ARID1A expression, we validated this using whole tissue sections (n = 159) and found that loss of ARID1A was correlated with microsatellite instability-high (MSI-H), Epstein-Barr virus (EBV), and PD-L1 positivity. Furthermore, for patients with MSI-H tumors, the degree of PD-L1 expression was significantly higher in ARID1A-deficient tumors. After ARID1A knockdown in GC cell lines, total and membranous PD-L1 protein, and PD-L1 mRNA levels were increased based on Western blot, flow cytometry, and qRT-PCR, respectively. With IFN-γ treatment, PD-L1 expression was significantly increased both in ARID1A-deficient cancer cells and controls, but the increase was not more pronounced in the former. Loss of ARID1A increased PD-L1 via activating AKT signaling, while LY294002 (PI3K inhibitor) decreased PD-L1 levels. Furthermore, we found that 3 MSI-H tumors showing highest expression of PD-L1 had simultaneous KRAS mutation and loss of ARID1A, suggesting a possible synergistic role boosting PD-L1. Our results strongly indicate that loss of ARID1A is tightly associated with high PD-L1 expression in GC. These results would increase our understanding of the oncogenic mechanism of PD-L1 regulation in GC, and also help to find the optimal candidates for immunotherapy.
尽管抗 PD-1 单克隆抗体治疗取得了显著成功，但胃癌（GC）中 PD-L1 调节的致癌机制仍知之甚少。我们假设 ARID1A 可能与 GC 中的肿瘤 PD-L1 表达有关。我们发现肿瘤 PD-L1 阳性与 ARID1A 的缺失有关，并显示出各种 GC 分子亚型患者生存更好的趋势（实验集，n=273）。考虑到 ARID1A 表达的异质性，我们使用全组织切片（n=159）对此进行了验证，发现 ARID1A 的缺失与微卫星不稳定高（MSI-H）、EB 病毒（EBV）和 PD-L1 阳性相关。此外，对于 MSI-H 肿瘤患者，ARID1A 缺陷型肿瘤的 PD-L1 表达程度明显更高。在 GC 细胞系中敲低 ARID1A 后，通过 Western blot、流式细胞术和 qRT-PCR 分别检测到总 PD-L1 和膜 PD-L1 蛋白以及 PD-L1 mRNA 水平增加。用 IFN-γ 处理后，ARID1A 缺陷型癌细胞和对照细胞的 PD-L1 表达均显著增加，但前者的增加不更明显。ARID1A 的缺失通过激活 AKT 信号增加 PD-L1，而 LY294002（PI3K 抑制剂）降低 PD-L1 水平。此外，我们发现 3 个 MSI-H 肿瘤中 PD-L1 表达最高的同时存在 KRAS 突变和 ARID1A 缺失，表明可能存在协同作用，增强 PD-L1。我们的研究结果强烈表明，ARID1A 的缺失与 GC 中 PD-L1 的高表达密切相关。这些结果将提高我们对 GC 中 PD-L1 调节致癌机制的理解，也有助于找到免疫治疗的最佳候选者。
