Membrane-Associated RING-CH 8 Functions as a Novel PD-L1 E3 Ligase to Mediate PD-L1 Degradation Induced by EGFR Inhibitors.
Membrane-Associated RING-CH 8 Functions as a Novel PD-L1 E3 Ligase to Mediate PD-L1 Degradation Induced by EGFR Inhibitors.
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DOI：
10.1158/1541-7786.mcr-21-0147
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发表时间：
2021-10
期刊：
影响因子：
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通讯作者：
Sun SY
中科院分区：
文献类型：
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作者：
Qian G;Guo J;Vallega KA;Hu C;Chen Z;Deng Y;Wang Q;Fan S;Ramalingam SS;Owonikoko TK;Wei W;Sun SY
程序性死亡配体1（PD-L1）在癌细胞上的表达是促成免疫抑制和免疫逃逸的关键机制。PD-L1表达也可能影响表皮生长因子受体（EGFR）靶向治疗的治疗结果（例如，与奥希替尼/AZD 9291）对抗EGFR突变型非小细胞肺癌（NSCLC），并且甚至可以在治疗期间改变，尽管机制在很大程度上不明确。本研究主要侧重于阐明奥希替尼诱导PD-L1降解的机制，以及验证奥希替尼降低EGFR突变型NSCLC细胞和肿瘤中PD-L1表达的作用。奥希替尼和其他EGFR抑制剂主要在EGFR突变型NSCLC和异种移植肿瘤中有效降低PD-L1水平。奥希替尼不仅降低了PD-L1 mRNA表达，还促进了PD-L1蛋白的蛋白酶体降解，表明转录和翻译后机制均导致了奥希替尼诱导的PD-L1降低。β-TrCP的敲低或GSK 3的抑制未能阻止奥希替尼诱导的PD-L1减少。相反，敲低编码膜结合E3泛素连接酶的膜相关RING-CH 8（MARCH 8）挽救了奥希替尼诱导的PD-L1减少。此外，MARCH 8表达的操纵相应地改变了PD-L1降解速率。重要的是，MARCH 8通过其N-末端区域与PD-L1相互作用，并在细胞中泛素化PD-L1。总的来说，这些结果强烈表明MARCH 8是一种先前未发现的E3泛素连接酶，负责PD-L1降解，包括奥希替尼诱导的PD-L1降解，建立了MARCH 8和PD-L1调控之间的新联系。
Expression of programmed death-ligand 1 (PD-L1) on cancer cells is a critical mechanism contributing to immunosuppression and immune escape. PD-L1 expression may also impact therapeutic outcomes of epidermal growth factor receptor (EGFR)-targeted therapy (e.g., with osimertinib/AZD9291) against EGFR mutant non-small cell lung cancers (NSCLCs) and can even be altered during the treatment albeit with largely undefined mechanisms. This study primarily focuses on elucidating the mechanism by which osimertinib induces PD-L1 degradation in addition to validating osimertinib’s effect on decreasing PD-L1 expression in EGFR mutant NSCLC cells and tumors. Osimertinib and other EGFR inhibitors effectively decreased PD-L1 levels primarily in EGFR mutant NSCLCs and xenografted tumors. Osimertinib not only decreased PD-L1 mRNA expression, but also prompted proteasomal degradation of PD-L1 protein, indicating both transcriptional and posttranslational mechanisms accounting for osimertinib-induced reduction of PD-L1. Knockdown of β-TrCP or inhibition of GSK3 failed to prevent PD-L1 reduction induced by osimertinib. Rather, knockdown of membrane-associated RING-CH 8 (MARCH8) that encodes a membrane-bound E3 ubiquitin ligase rescued osimertinib-induced PD-L1 reduction. Furthermore, manipulation of MARCH8 expression accordingly altered PD-L1 degradation rate. Critically, MARCH8 interacted with PD-L1 through its N-terminal region and also ubiquitinated PD-L1 in cells. Collectively, these results strongly suggest that MARCH8 is a previously undiscovered E3 ubiquitin ligase responsible for PD-L1 degradation including osimertinib-induced PD-L1 degradation, establishing a novel connection between MARCH8 and PD-L1 regulation.