METTL3‑mediated OTUB1 sustains PD‑L1 protein stability via deubiquitination and promotes immune evasion in oral squamous cell carcinoma.

Immune evasion facilitates the progression of oral squamous cell carcinoma (OSCC). This study investigates how METTL3-mediated OTUB1 modulates PD-L1 ubiquitination and promotes immune evasion in OSCC. OTUB1 expression was analyzed in tumor and adjacent normal tissues from OSCC patients. OTUB1 knockdown experiments were performed in HN-6 cells. The relationship between OTUB1 and PD-L1 was detected. OTUB1-knockdown HN-6 cells were co-cultured with activated PBMCs, and tumor immunity was subsequently assessed. Tumor growth and immunity were observed in a mouse model injected with HN-6 cells transfected with si-OTUB1 and oe-PD-L1. The mechanistic interaction among METTL3, YTHDF1, and OTUB1 was determined, as well as their action in mouse tumor models. OTUB1 was upregulated in OSCC and correlated with poor prognosis. Knocking down OTUB1 directly increased PD-L1 ubiquitination levels, downregulated PD-L1 protein abundance, and weakened the binding between tumor cells and PD-1. OSCC cells with OTUB1 knockdown were co-incubated with PBMCs, resulting in enhanced apoptosis of OSCC cells, increased CD4⁺/CD8⁺ T cell infiltration, reduced FoxP3⁺ Tregs, exhausted CD8⁺ T cell subsets, and elevated GzmB/IFN-γ production. METTL3 mediated m⁶A modification of OTUB1 mRNA, which enhanced the stability of OTUB1 mRNA and upregulated OTUB1 expression through the reader protein YTHDF1. In vivo experiments confirmed that METTL3 promoted OSCC progression and immune evasion via m