Secreted Phosphoprotein 1 (SPP1) Promotes Angiogenesis of Glioblastoma Through Up-regulating PSMA Expression Via Transcription Factor HIF-1α

Background: Glioblastoma multiforme (GBM) is a highly vascular-rich and devastatingly aggressive type of malignant brain tumors, thus anti-angiogenesis therapy plays an essential role in the treatment of GBM. Our previous study had showed that the prostate-specific membrane antigen (PSMA) promoted angiogenesis of GBM though interacting with Integrin β4 (ITGB4) and regulating NF-kB signaling pathway. This study aims to explore the upstream molecular mechanism of GBM regulating the expression of PSMA and promoting angiogenesis process.Methods: Human cytokine antibody array and bioinformatics were used to explore potential cytokines involved in regulating PSMA expression. Recombinant protein was applied and Western blot, qRT-PCR were assessed to verify that the contributing cytokine was SPP1. Expression levels, prognosis and receiver operation characteristic (ROC) curve of SPP1 were determined by bioinformatics to evaluate its clinical value. ELISA was conducted to evaluate the variation of SPP1 in the serum of GBM patients pre- and post-surgery. Potential transcription factor mediating the expression of PSMA was sifted through PROMO and JASPAR website. ChIP assay and dual luciferase were used to confirm that the transcription factor regulating PSMA expression was HIF-1α. Cellular migration and tube formation ability were assessed by scratch assay and tube formation assay in human umbilical vein endothelial cells (HUVECs).Results: We demonstrated that cytokine SPP1 secreted from GBM could regulate the expression of PSMA in HUVEC. SPP1 was abundantly expressed in the GBM, and the high expression of SPP1 is associated with poor prognosis. Recombinant protein SPP1 could promote migration and tube formation ability of HUVEC. The mechanistic study revealed that SPP1 regulated the expression of PSMA through transcription factor HIF1α. In addition, knockdown of HIF1α could reduce the expression of PSMA in HUVEC, and block the ability of SPP1 in promoting migration and tube formation of HUVEC. Furthermore, SPP1 and HIF1α both had a high value of clinical diagnosis with considerable sensitivity and specificity.Conclusions: In this study, we identified that upstream cytokine SPP1 secreted from GBM could upregulate PSMA expression in endothelial cells via transcription factor HIF1α, which constructs a positive chain in angiogenesis and provides promising candidates for targeted therapy of GBM.