COPS4 encodes a core subunit of the COP9 signalosome (CSN), a multifunctional protein complex essential for cellular regulation. As a structural component of CSN, COPS4 maintains complex integrity and participates in deneddylation of cullin-containing E3 ubiquitin ligases, thereby modulating the ubiquitin-proteasome degradation pathway 1. The complex also associates with kinases like CK2 and PKD to phosphorylate regulatory proteins including p53, c-Jun, and IκBα, controlling their stability and function 2. COPS4 expression is significantly elevated in multiple cancer types including cholangiocarcinoma, hepatocellular carcinoma, esophageal squamous cell carcinoma, and head/neck cancers, where elevated levels correlate with advanced pathological stage, nodal involvement, and metastatic status 3. In breast cancer, COPS4 is a frequently recognized autoantigen, with elevated IgG responses associated with shorter recurrence-free survival and lower CD8+ T cell infiltration 4. Mechanistically, COPS4 knockdown in breast cancer cells reduces proliferation and induces apoptosis via modulation of CDK6 and Caspase3 expression 5. In prostate cancer, COPS4 prevents proteasomal degradation of soluble guanylyl cyclase α1 while promoting p53 degradation, supporting tumor survival 2. COPS4 dysregulation through gene amplification, mutations, and promoter hypomethylation drives overexpression in tumors 3, positioning it as a prognostic biomarker and potential therapeutic target across multiple malignancies.