Moesin contributes to the unfavourable prognosis of glioblastoma multiforme possibly by modulating the immune checkpoint molecule B7-H3

Background and aims: Glioblastoma multiforme (GBM) is a highly malignant brain tumour and a leading cause of cancer-related deaths in children, adolescents, and young adults. Due to the limited efficacy of current therapies, novel strategies are needed to improve GBM outcomes. B7-H3 is an immune checkpoint molecule that drives tumour immune evasion and metastasis, contributing to poor prognosis in several cancers. Ezrin-radixin-moesin (ERM) support the plasma membrane localisation of transmembrane proteins as scaffolds. We aimed to elucidate the role of ERM in B7-H3 plasma membrane expression and analyse the prognostic significance of B7-H3 and ERM using cell lines and clinical databases derived from GBM patients. Methods: mRNA and protein expression, intracellular localisation, and molecular interaction of B7-H3 and ERM in human GBM cells were determined using quantitative RT-PCR, western blot, immunofluorescence, and co-immunoprecipitation, respectively. Plasma membrane expression and localisation of B7-H3 were measured five days after transfection with small interfering RNAs against each ERM. The expressions and prognostic impacts of B7-H3 and ERM in GBM tumour tissues were assessed using a clinical RNA-sequencing database. Results: Knockdown of moesin, but not ezrin or radixin, reduced plasma membrane localisation of B7-H3 without affecting its mRNA expression. B7-H3 colocalised and interacted with moesin in the plasma membrane of human GBM cells. B7-H3 and moesin expressions in tumour tissues were significantly higher than in normal brain tissues and associated with decreased disease-free survival time in GBM patients. Conclusions: Moesin contributes to the poor prognosis of GBM by acting as the dominant scaffold responsible for B7-H3 overexpression.