Graduate School of Medical Science and Engineering, KAIST, Daejeon, Korea.
Department of Pathology, Yonsei University College of Medicine, Seoul, Korea.
Cancer Immunol Res. 2018 Mar;6(3):255-266. doi: 10.1158/2326-6066.CIR-17-0320. Epub 2018 Jan 30.
Activation of YAP, a Hippo pathway effector, is an important resistance mechanism to BRAF inhibitor (BRAFi) in melanoma. Emerging evidence also suggests that YAP is involved in suppression of the antitumor immune response. However, the potential direct impact of YAP activity on cytotoxic T-cell immune responses has not been explored yet. Here, we show that BRAFi-resistant melanoma cells evade CD8 T-cell immune responses in a PD-L1-dependent manner by activating YAP, which synchronously supports melanoma cell survival upon BRAF inhibition. PD-L1 expression is elevated in BRAFi-resistant melanoma cells, in which YAP is robustly activated, and YAP knockdown decreases PD-L1 expression. In addition, constitutively active YAP (YAP-5SA) increases PD-L1 expression by binding to an upstream enhancer of the PD-L1 gene and potentiating its transcription. Both BRAFi-resistant and YAP-5SA-expressing melanoma cells suppress the cytotoxic function and cytokine production of Melan-A-specific CD8 T cells, whereas anti-PD-1 antibody reverses the YAP-mediated T-cell suppression. Moreover, nuclear enrichment of YAP in clinical melanoma samples correlates with increased PD-L1 expression. Our findings show that YAP directly mediates evasion of cytotoxic T-cell immune responses in BRAFi-resistant melanoma cells by upregulating PD-L1, and targeting of YAP-mediated immune evasion may improve prognosis of melanoma patients. .
YAP 的激活是黑色素瘤对 BRAF 抑制剂(BRAFi)产生耐药的重要机制,Hippo 通路效应物。新出现的证据还表明,YAP 参与了抗肿瘤免疫反应的抑制。然而,YAP 活性对细胞毒性 T 细胞免疫反应的潜在直接影响尚未得到探索。在这里,我们表明,BRAFi 耐药的黑色素瘤细胞通过激活 YAP 以 PD-L1 依赖的方式逃避 CD8 T 细胞免疫反应,这同步支持了 BRAF 抑制时黑色素瘤细胞的存活。在 BRAFi 耐药的黑色素瘤细胞中,PD-L1 表达上调,YAP 被强烈激活,而 YAP 敲低则降低 PD-L1 表达。此外,组成性激活的 YAP(YAP-5SA)通过与 PD-L1 基因的上游增强子结合并增强其转录来增加 PD-L1 表达。BRAFi 耐药和 YAP-5SA 表达的黑色素瘤细胞均抑制 Melan-A 特异性 CD8 T 细胞的细胞毒性功能和细胞因子产生,而抗 PD-1 抗体逆转了 YAP 介导的 T 细胞抑制。此外,临床黑色素瘤样本中 YAP 的核富集与 PD-L1 表达增加相关。我们的研究结果表明,YAP 通过上调 PD-L1 直接介导 BRAFi 耐药黑色素瘤细胞逃避细胞毒性 T 细胞免疫反应,靶向 YAP 介导的免疫逃逸可能改善黑色素瘤患者的预后。
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