Interference with PSMB4 Expression Exerts an Anti-Tumor Effect by Decreasing the Invasion and Proliferation of Human Glioblastoma Cells

Background/aims: Glioblastoma (GBM) is a malignant brain tumor with a poor prognosis. Proteasome subunit beta type-4 (PSMB4) is an essential subunit that contributes to the assembly of the 20S Proteasome complex. However, the role of PSMB4 in glioblastomas remains to be clarified. The aim of this study was to investigate the role of PSMB4 in GBM tumor progression.

Methods: We first analyzed the PSMB4 protein and mRNA expression in 80 clinical brain specimens and 77 datasets from the National Center for Biotechnology Information (NCBI) Gene Expression Omnibus (GEO) database. Next, we inhibited the PSMB4 expression by siRNA in cellular and animal models to explore PSMB4's underlying mechanisms. The cell survival after siPSMB4 transfection was assayed by MTT assay. Annexin V and propidium iodide staining was used to monitor the Apoptosis by flow cytometric analysis. Moreover, the migration and invasion were evaluated by wound healing and Transwell assays. The expression of migration-related and invasion-related proteins after PSMB4 inhibition was detected by Western blotting. In addition, an orthotropic xenograft mouse model was used to assay the effect of PSMB4 knockdown in the in vivo study.

Results: Basis on the results of bioinformatics study, glioma patients with higher PSMB4 expression had a shorter survival time than those with lower PSMB4 expression. The staining of clinical brain tissues showed elevated PSMB4 expression in GBM tissues compared with normal brain tissues. The PSMB4 inhibition decreased proliferation, migration and invasion abilities in human GBM cells. Downregulated PSMB4 resulted in cell cycle arrest and Apoptosis in vitro. In an orthotropic xenograft mouse model, the glioma tumors progression was reduced when PSMB4 was down-regulated. The decreased PSMB4 enhanced the anti-tumor effect of temozolomide (TMZ) on tumor growth. In addition, the absence of PSMB4 decreased the expression of phosphorylated focal adhesion kinase and matrix metallopeptidase 9 in vivo.

Conclusion: PSMB4 inhibition in combination with TMZ may exert an anti-tumor effect by decreasing cell proliferation and invasion as well as by promoting Apoptosis in human glioblastoma cells. This research may improve the therapeutic efficacy of glioblastoma treatment.