Abstract
Background: Neuroglobin (Ngb) is a novel oxygen-binding or sensor protein that is present primarily in neurons and the brain. It plays a critical role in sensing oxygen and hypoxia signals and in transducing intracellular signaling pathways. However, the specific functions and mechanism of Ngb in the glioblastoma remain unclear. Methods: The expression of Ngb in glioma brain tissues and cells was measured by Western blot, immunohistochemical staining and retrieved from TCGA databases. Loss or gain of function assays, CCK-8 assay, scratch and transwell assay, transmission electron microscopy (TEM) analysis, acridine orange staining, evaluation of fluorescent LC3 puncta, and flow cytometry analysis were conducted to determine the effects of Ngb overexpression or knockdown on glioblastoma multiforme (GBM) cell proliferation, invasion and autophagy, and Ngb/EGFR interactions were verified by glutathione S-Transferase (GST) pull-down assay and co-immunoprecipitation (Co-IP), and the mechanism of Ngb on autophagy was investigated by Western blot. The animal model of glioma was further employed to assess the inhibitory effect of Ngb overexpression on GBM cell growth. Results: The study demonstrated that the expression of Ngb was significantly downregulated in glioma tissues and cell lines and that its downregulation was positively correlated with poor patient survival, further demonstrating that Ngb promoted belcin1 and LC3-dependent autophagy in the GBM cells. We found that inhibitory effect of Ngb on cellular invasion is associated with the suppression of EGFR/PI3K/AKT/m-TOR signaling. Furthermore, our study revealed that increasing Ngb expression in GBM cells notably decreased their ability to migrate and invade in vitro and suppressed tumor growth in vivo. The overexpression of Ngb resulted in cell cycle arrest at the S phase and increased apoptosis. Finally, our findings indicated that Ngb increased autophagy, which may inhibit the invasion of glioblastoma multiforme (GBM) by interaction with the amino acid 1-42 domains of Ngb with EGFR. Conclusions: In this study, our research findings indicated that Ngb promoted autophagy and suppressed the migration and invasion of GBM cells through inactivation of the EGFR/PI3K/AKT/m-TOR signaling pathway, highlighting that autophagy activation may suppress the invasion of GBM cells with low Ngb expression.