Notch1 Mutation Represents a Potential Therapeutic Target to Enhance Immune Recognition in Oral Squamous Cell Carcinoma.

Notch1, a tumor suppressor gene, is one of the most frequently mutated genes in head and neck squamous cell carcinoma (HNSCC). Therefore, it is clinically important to investigate the effects of Notch1 mutations on antitumor immunity in oral squamous cell carcinoma (OSCC), a subset of HNSCC. This study investigated Notch1 mutations and the expression of immune-related proteins. We also examined the influence of Notch1 mutations on the immune microenvironment using a public database. We examined the expression of Notch1-4 in OSCC cell lines using qPCR. After Notch1 knockdown, OSCC cell proliferation and migration were analyzed using CCK8 and wound healing assays, respectively. Localization of programmed cell death ligand 1 (PD-L1) was assessed by western blot and flow cytometry, while PD-L1 expression was evaluated by western blot. In the somatic mutation analysis of 47 OSCC patients, the relationship between tumor-infiltrating CD8+ T cells and PD-L1 expression was analyzed using immunohistochemical (IHC) staining. Furthermore, data from The Cancer Genome Atlas (TCGA) were analyzed using multiple online bioinformatics tools to compare the characteristics of Notch1 mutations in HNSCC. The expression of Notch1 varied depending on the OSCC cell line phenotype, and Notch1 mutation was significantly correlated with tumor growth but not with tumor infiltration. In Notch1 knockdown, PD-L1 expression on the tumor cell surface increased, while cytoplasmic PD-L1 expression decreased. Among the 47 OSCC patients analyzed, seven (14%) had Notch1 mutations. Of those, five patients (71%) exhibited high tumor-infiltrating CD8+ T cells and Notch1 mutation. Online bioinformatics analysis using the xCell algorithm revealed that Notch1-mutated tumors had significantly higher levels of naïve CD8+ T cells compared to Notch1 wild-type tumors. These findings highlight Notch1 mutation as a potential therapeutic target for immune recognition in OSCC.