Psmb9, proteasome 20S subunit beta 9, is an immunoproteasome-specific subunit. Immunoproteasomes play crucial roles in cell processes such as cell survival or death decisions, the cell cycle, and cellular differentiation, and are also involved in antigen processing and presentation pathways [3,5].

In melanoma, overexpression of Psmb9 in SKCM cell lines inhibits cell proliferation and migration, suggesting it as a tumor-suppressor gene, potentially through activating CD8+ T cells, modulating IFN-γ secretion, and altering IFN-γ receptors [1]. In atherosclerosis, Psmb9 deficiency in Apoe-/-mice decreased atherosclerotic lesion size, plaque vulnerability, and vascular inflammation. PSMB8-AS1, a lncRNA, promotes vascular inflammation and atherosclerosis via upregulating Psmb9, which in turn elevates VCAM1 and ICAM1 expression via ZEB1 [2]. In coal workers' pneumoconiosis, silica exposure reduces Psmb9 expression causing cell apoptosis, while overexpression of Psmb9 abolishes this apoptosis, identifying Psmb9 as a susceptibility gene [4].

In conclusion, Psmb9 is essential in multiple biological processes and disease conditions. Gene-knockout mouse models, like Psmb9-deficient Apoe-/-mice, have provided valuable insights into its role in atherosclerosis. In melanoma and coal workers' pneumoconiosis, functional studies have also revealed its significance in tumor suppression and disease susceptibility respectively. Understanding Psmb9's function contributes to better comprehension of these disease mechanisms and may guide future therapeutic strategies.