Golgi phosphoprotein 3 promotes glioma progression via inhibiting Rab5-mediated endocytosis and degradation of epidermal growth factor receptor

Background. Golgi phosphoprotein 3 (GOLPH3) is associated with worse prognosis of gliomas, but its role and mechanism in glioma progression remain largely unknown. This study aimed to explore the role and mechanism of GOLPH3 in glioma progression. Methods. The expression of GOLPH3 in glioma tissues was detected by quantitative PCR, immunoblotting, and immunohistochemistry. GOLPH3's effect on glioma progression was examined using cell growth assays and an intracranial glioma model. The effect of GOLPH3 on epidermal growth factor receptor (EGFR) stability, endocytosis, and degradation was examined by immunoblotting and immunofluorescence. The activity of Rab5 was checked by glutathione S-transferase pulldown assay. Results. GOLPH3 was upregulated in gliomas, and its downregulation inhibited glioma cell proliferation both in vitro and in vivo. Furthermore, GOLPH3 depletion dampened EGFR signaling by enhancing EGFR endocytosis, driving EGFR into late endosome and promoting lysosome-mediated degradation. Interestingly, GOLPH3 bound to Rab5 and GOLPH3 downregulation promoted the activation of Rab5. In addition, Rab5 depletion abolished the effect of GOLPH3 on EGFR endocytosis and degradation. Conclusion. Our results imply that GOLPH3 promotes glioma cell proliferation via inhibiting Rab5-mediated endocytosis and degradation of EGFR, thereby activating the phosphatidylinositol-3 kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) signaling pathway. We find a new mechanism by which GOLPH3 promotes tumor progression through regulating cell surface receptor trafficking. Extensive and intensive understanding of the role of GOLPH3 in glioma progression may provide an opportunity to develop a novel molecular therapeutic target for gliomas.