Integrative Pan-Cancer Mapping of Proteasome Dependency Prioritizes PSMB5 and PSMB6 as Context-Dependent Vulnerability Biomarkers Linked to Immune Context

The prioritization of biomarkers that inform molecular-targeted cancer research remains challenging because tumor vulnerabilities are context-dependent. The ubiquitin–proteasome system is essential for cancer cell survival; however, the functional and biomarker-level relevance of individual proteasome subunits has not been systematically defined across cancer types. In this study, we performed an integrative pan-cancer analysis to prioritize proteasome subunits that function as context-dependent vulnerability biomarkers. We analyzed proteasome subunits and proteasome-associated genes across 54 cancer types by integrating large-scale CRISPR (n = 1178 cell lines) and RNAi (n = 707 cell lines) dependency datasets with transcriptomic, survival, immune infiltration, and co-essentiality network analyses. PSMB5 and PSMB6 were prioritized as robust cross-platform and cross-lineage dependency biomarkers, exhibiting reproducible and selective vulnerability patterns across diverse malignancies. Their dependency strength was quantitatively associated with immune-related signaling pathways, including MHC and interferon responses, and inversely correlated with key immune regulatory genes such as NLRC5 and IRF1. Co-essentiality network analysis revealed modular functional organization of proteasome-associated genes, supporting context-dependent roles rather than uniform essentiality. Importantly, the association between proteasome subunits and tumor immune context was externally validated through meta-analysis across 24 independent hepatocellular carcinoma cohorts, demonstrating reproducible correlations with CD4-positive T cell, CD8 T cell, and macrophage infiltration signatures. Functional validation further confirmed that siRNA-mediated knockdown of PSMB5 and PSMB6 significantly impaired proliferation across multiple hepatocellular carcinoma cell lines. Collectively, this study prioritizes PSMB5 and PSMB6 as consistently associated functional biomarkers that integrate genetic dependency and immune context, providing a data-driven framework for stratifying proteasome-targeted therapeutic strategies across cancers.