E3 Ubiquitin Ligase RNF125 Suppresses Immune Escape in Head and Neck Squamous Cell Carcinoma by Regulating PD-L1 Expression

Abstract

Head and neck squamous cell carcinoma (HNSCC) is a lethal malignancy. Given the essential roles of E3 ligases in cancer immunotherapies, this paper explored the effect of E3 ubiquitin ligase ring finger protein 125 (RNF125) on immune escape in HNSCC. After delivering overexpressed (oe)-RNF125, interferon-gamma, or oe-programmed death-ligand 1 (PD-L1) into HNSCC cells and cell culture with carboxyfluorescein succinimidyl ester-labeled CD8⁺ T cells, RNF125 and PD-L1 levels were determined via RT-qPCR and Western blot, with HNSCC cell behaviors assessed via colony formation assay, Transwell assays and flow cytometry, and inflammatory factors measured via ELISA. PD-L1 ubiquitination level and PD-L1's interaction with RNF125 were analyzed via co-immunoprecipitation. The in vivo action of RNF125 on HNSCC was validated via nude mouse tumorigenicity assay. Briefly, RNF125 was weakly expressed in HNSCC cells. RNF125 overexpression inhibited immune escape of HNSCC cells, evidenced by decreased TSCCA cell proliferation, migration, and invasion, increased CD8⁺ T cell proliferation, and elevated IL-2 and TNF-α levels. RNF125 downregulated PD-L1 in TSCCA cells and facilitated PD-L1 ubiquitinational degradation. PD-L1 overexpression partially abated RNF125-mediated suppression on TSCCA cell immune escape. Moreover, RNF125 suppressed tumorigenesis and tumor growth in vivo. Overall, RNF125 promoted PD-L1 ubiquitinational degradation, hence inhibiting immune escape in HNSCC.

Keywords: CD8+ T cells; E3 ubiquitin ligases; Head and neck squamous cell carcinoma; Immune escape; Programmed death-ligand 1; Ring finger protein 125; Ubiquitinational degradation.