The Shmunis School of Biomedicine and Cancer Research, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 6997801, Israel.
Cells. 2023 Sep 23;12(19):2338. doi: 10.3390/cells12192338.
PD-L1 has been characterized as an inhibitory immune checkpoint, leading to the suppression of potential anti-tumor immune activities in many cancer types. In view of the relatively limited efficacy of immune checkpoint blockades against PD-L1 in breast cancer, our recent study addressed the possibility that in addition to its immune-inhibitory functions, PD-L1 promotes the pro-metastatic potential of the cancer cells themselves. Indeed, our published findings demonstrated that PD-L1 promoted pro-metastatic functions of breast cancer cells in a cell-autonomous manner, both in vitro and in vivo. These functions fully depended on the integrity of the S283 intracellular residue of PD-L1. Here, using siRNAs and the S283A-PD-L1 variant, we demonstrate that the cell-autonomous pro-metastatic functions of PD-L1-tumor cell proliferation and invasion, and release of the pro-metastatic chemokine CXCL8-required the activation of STAT3 and STAT1 in luminal A and triple-negative breast cancer cells. The cell-autonomous pro-metastatic functions of PD-L1 were potently impaired upon inhibition of N-linked glycosylation (kifunensine). Site-specific mutants at each of the N-linked glycosylation sites of PD-L1 (N35, N192, N200, and N219) revealed that they were all required for PD-L1-induced pro-metastatic functions to occur; the N219 site was the main regulator of STAT3 and STAT1 activation, with accompanying roles for N192 and N200 (depending on the cell type). Using a T cell-independent mouse system, we found that cells expressing N35A-PD-L1 and N219A-PD-L1 had a significantly lower tumorigenic and metastatic potential than cells expressing WT-PD-L1. TCGA analyses revealed significant associations between reduced survival and high levels of α-mannosidase II (inferring on N-linked glycosylation) in breast cancer patients. These findings suggest that N-linked glycosylation of PD-L1 may be used to screen for patients who are at greater risk of disease progression, and that modalities targeting N-linked glycosylated PD-L1 may lead to the inhibition of its cell-autonomous pro-metastatic functions and to lower tumor progression in breast cancer.
PD-L1 被认为是一种抑制性免疫检查点，导致许多癌症类型中潜在的抗肿瘤免疫活性受到抑制。鉴于免疫检查点阻断对乳腺癌中 PD-L1 的疗效相对有限，我们最近的研究探讨了 PD-L1 除了具有免疫抑制功能外，是否还能促进癌细胞本身的促转移潜能。事实上，我们已发表的研究结果表明，PD-L1 以细胞自主的方式促进乳腺癌细胞的促转移功能，无论是在体外还是体内。这些功能完全依赖于 PD-L1 第 283 位丝氨酸残基的完整性。在这里，我们使用 siRNA 和 S283A-PD-L1 变体，证明 PD-L1 肿瘤细胞增殖和侵袭的细胞自主促转移功能，以及促转移趋化因子 CXCL8 的释放，需要在腔 A 和三阴性乳腺癌细胞中激活 STAT3 和 STAT1。PD-L1 的细胞自主促转移功能在 N 连接糖基化（kifunensine）抑制时受到强烈损害。PD-L1 的每个 N 连接糖基化位点（N35、N192、N200 和 N219）的特异性突变体表明，它们都需要 PD-L1 诱导的促转移功能发生；N219 位点是 STAT3 和 STAT1 激活的主要调节剂，同时 N192 和 N200 也发挥作用（取决于细胞类型）。使用 T 细胞非依赖性小鼠系统，我们发现表达 N35A-PD-L1 和 N219A-PD-L1 的细胞比表达 WT-PD-L1 的细胞具有更低的致瘤性和转移性潜力。TCGA 分析显示，在乳腺癌患者中，低生存率与 α-甘露糖苷酶 II 水平升高（暗示 N 连接糖基化）之间存在显著关联。这些发现表明，PD-L1 的 N 连接糖基化可用于筛选疾病进展风险较高的患者，靶向 N 连接糖基化 PD-L1 的方法可能会抑制其细胞自主促转移功能，并降低乳腺癌的肿瘤进展。
