Department of Laboratory Medicine, Shanghai East Hospital, Tongji University School of Medicine, Shanghai, China.
Key Laboratory of Cell Differentiation and Apoptosis of The Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
Cancer Med. 2018 Aug;7(8):4004-4011. doi: 10.1002/cam4.1675. Epub 2018 Jul 10.
The immune checkpoint protein programmed cell death ligand 1 (PD-L1) binds to PD1 to promote tumor cell escape from the killing effect of the immune system. However, there are few studies on the regulatory mechanisms of PD-L1 in tumors. Although PD-L1 has been reported to undergo ubiquitination in some cancers, its regulatory mechanisms in oral squamous cell carcinoma (OSCC) are unclear. Therefore, we aimed to investigate this phenomenon.
We examined the expression and function of USP9X and PD-L1 in human oral keratinocytes (HOK) and OSCC cell lines (HN4 and HN30) as the control and relevant cancer cells using western blotting, immunoprecipitation, immunohistochemistry (IHC), T-cell-mediated tumor cell killing assay, and liquid chromatography-mass spectrometry.
Programmed cell death ligand 1 was highly expressed in OSCC by the regulation of the ubiquitin-proteasome pathway. Furthermore, we discovered that ubiquitin-specific peptidase 9, X-linked (USP9X) could be combined with PD-L1 to induce its deubiquitination and stabilize its protein expression in OSCC.
Our data indicate that USP9X deubiquitinates and stabilizes PD-L1. Suppressing the expression of USP9X blocks tumor cell growth. The results provide a theoretical basis for USP9X as a therapeutic target.
免疫检查点蛋白程序性死亡配体 1（PD-L1）与 PD1 结合，促进肿瘤细胞逃避免疫系统的杀伤作用。然而，关于肿瘤中 PD-L1 的调控机制的研究较少。尽管已有研究报道 PD-L1 在某些癌症中发生泛素化，但在口腔鳞状细胞癌（OSCC）中其调控机制尚不清楚。因此，我们旨在研究这一现象。
我们使用 Western blot、免疫沉淀、免疫组织化学（IHC）、T 细胞介导的肿瘤细胞杀伤实验和液相色谱-质谱联用技术，检测人口腔角质细胞（HOK）和 OSCC 细胞系（HN4 和 HN30）中 USP9X 和 PD-L1 的表达和功能，作为对照和相关癌细胞。
通过泛素蛋白酶体通路的调控，PD-L1 在 OSCC 中高表达。此外，我们发现，X 连锁的泛素特异性肽酶 9（USP9X）可以与 PD-L1 结合，诱导其去泛素化，并稳定其在 OSCC 中的蛋白表达。
我们的数据表明，USP9X 去泛素化并稳定 PD-L1。抑制 USP9X 的表达可阻断肿瘤细胞的生长。这些结果为 USP9X 作为治疗靶点提供了理论依据。
