Cell surface GRP78 regulates BACE2 via lysosome-dependent manner to maintain mesenchymal phenotype of glioma stem cells

BackgroundGlioma stem cells (GSCs) are considered the initial cells of gliomas, contributing to therapeutic resistance. Patient-derived GSCs well recapitulate the heterogeneity of their parent glioma tissues, which can be classified into different subtypes. Likewise, previous works identified GSCs as two distinct subtypes, mesenchymal (MES) and proneural (PN) subtypes, and with general recognition, the MES subtype is considered a more malignant phenotype characterized by high invasion and radioresistance. Therefore, understanding the mechanisms involved in the MES phenotype is necessary for glioblastoma treatment.MethodsData for bioinformatic analysis were obtained from The Cancer Genome Atlas (TCGA) and The Gene Expression Omnibus (GEO) database. An antibody was used to block cell surface glucose-regulated protein 78 (csGRP78). Apoptosis and cell cycle analyses were performed to evaluate radiation damage. Immunofluorescence staining was applied to assess protein expression and distribution. Mass spectrometry combined with bioinformatic analysis was used to screen downstream molecules. Intracranial GSC-derived xenografts were established for in vivo experiments.ResultsTotal GRP78 expression was associated with MES GSC stemness, and csGRP78 was highly expressed in MES GSCs. Targeting csGRP78 suppressed the self-renewal and radioresistance of MES GSCs in vitro and in vivo, accompanied by downregulation of the STAT3, NF-kappa B and C/EBP beta pathways. Mass spectrometry revealed the potential downstream beta -site APP-cleaving enzyme 2 (BACE2), which was regulated by csGRP78 via lysosomal degradation. Knockdown of BACE2 inactivated NF-kappa B and C/EBP beta and significantly suppressed the tumorigenesis and radioresistance of MES GSCs in vitro and in vivo.ConclusionsCell surface GRP78 was preferentially expressed in MES GSCs and played a pivotal role in MES phenotype maintenance. Thus, blocking csGRP78 in MES GSCs with a high-specificity antibody might be a promising novel therapeutic strategy.

Automated summary

Surface expression of glucose-regulated protein 78 (csGRP78) was found to be preferentially expressed in MES GSCs, and targeting csGRP78 effectively suppressed self-renewal and radioresistance of MES GSCs both in vitro and in vivo by downregulating STAT3, NF-kappa B, and C/EBP beta pathways, potentially through regulation of downstream molecule BACE2. These findings suggest that blocking csGRP78 with a high-specificity antibody could be a promising therapeutic strategy for glioblastoma treatment.