HERC5/ISG15 Enhances Glioblastoma Stemness and Tumor Progression by mediating SERBP1protein stability.

Glioblastoma (GBM) is the most common malignant brain tumor, and has a low survival rate and a poor prognosis. Intensive studies of pathogenic mechanisms are essential for exploring therapeutic targets for GBM. In this study, the roles played by interferon-stimulated gene 15 (ISG15), HECT, RCC1-containing protein 5 (HERC5), and SERPINE1 mRNA binding protein 1 (SERBP1) in regulating GBM cell stemness were investigated. The real-time quantitative polymerase chain reaction (qPCR), western blotting (WB), and immunohistochemistry (IHC) were used to determine the expression levels of HERC5, ISG15, and SERBP1. Cell stemness was analyzed using a cell sphere formation assay. Colony formation and cell counting kit-8 (CCK-8) assays were performed to assess cell proliferation, Transwell assays used to evaluate cell migration and invasion, and flow cytometry was used to assess cell apoptosis after treatment with temozolomide. SERBP1 stability was assessed by a CHX chase assay. A co-immunoprecipitation (Co-IP) assay verified the binding of ISG15 and HERC5 onto SERBP1. Our results showed that HERC5 and ISG15 were highly expressed in GBM. HERC5 and ISG15 promoted the cell stemness of GBM, and increased cell proliferation, sphere formation, migration, invasion, and chemoresistance. Moreover, HERC5 and ISG15 played a synergistic role in promoting the cell stemness of GBM. We also found that HERC5/ISG15 promoted the stability of SERBP1, which also promoted the cell stemness of GBM. The tumor-promoting role of HERC5 and ISG15 was also confirmed in a subcutaneous xenograft tumor model. Collectively, HERC5/ISG15 was found to regulate GBM stemness and tumor progression by mediating SERBP1 protein stability. Our present study suggests a promising therapeutic target for GBM.