Targeting Intratumoral Copper Inhibits Tumor Progression via p62-Mediated EZH2 Degradation and Potentiates Anti-PD-1 Immunotherapy in Oral Squamous Cell Carcinoma.

High copper levels are required for tumor initiation and progression, termed cuproplasia. However, its role and underlying mechanisms in oral squamous cell carcinoma (OSCC) remain poorly understood. It is find that copper and its transporter SLC31A1 accumulate extensively in OSCC. Blocking copper influx through SLC31A1 siRNA or copper chelators significantly represses OSCC both in vitro and in vivo. Single-cell RNA sequencing and multiplex immunohistochemical staining revealed that copper chelators specifically decrease the stem-like tumor epithelial cell subpopulation. Further investigation shows that intratumoral copper depletion reduces histone methyltransferase EZH2 expression at the protein level, but not at the mRNA level, as determined through a screen analysis of histone-modification enzymes. Mechanistically, it is discovered that silencing SLC31A1 and treating with copper chelators increase p62-mediated EZH2 ubiquitination at the Ub-K63 site by suppressing copper binding to SMURF2, an E3 ligase of EZH2, leading to its autophagic degradation. Additionally, combining copper chelators with anti-PD-1 treatment effectively suppresses tumor growth, and high levels of SLC31A1 are notably associated with non-response to anti-PD-1 treatment. In conclusion, the crucial role of copper in modulating EZH2 protein stability is demonstrated, and a new approach using copper chelators and anti-PD-1 therapy for OSCC patients is provided.