The Positive Feedback Loop Between RLIP76 and HIF-1α Promotes Glycolysis and Tumorigenesis in Glioma Cells Under Hypoxic Conditions

Abstract

BackgroundHypoxia is intimately associated with increased glycolysis in gliomas, and HIF-1α plays a critical role in this process. Here, we aim to show that RLIP76 is a novel target of HIF-1α and is involved in hypoxia-enhanced glycolysis in glioma cells. MethodsThe human glioma cell lines U87 and U251 were used to explore the interactions of RLIP76-HIF-1α and RLIP76-VHL using Western blot, a Biotin pull-down assay, Immunoprecipitation, and a Chromatin immunoprecipitation assay under hypoxia. U251 cells pretreated with hypoxia were used for tumor xenografts. ResultsRLIP76 is a novel target of HIF-1α and contributes to hypoxia-enhanced glycolysis in glioma cells. HIF-1α-induced RLIP76 can critically regulate the stability of HIF-1α by alleviating VHL-mediated HIF-1α ubiquitination under hypoxia. RLIP76 interacts with HIF-1α and VHL through an RLIP76 GAP-dependent mechanism. The GAP function of RLIP76 regulates its complex formation because of the dependence of RLIP76 GAP on interactions between RLIP76 and these proteins. RLIP76 knockdown results in decreased U251 cell growth after hypoxia pretreatment in vivo. ConclusionsThis study reveals a positive feedback loop between HIF-1α and RLIP76, suggesting that RLIP76 may undergo a complex series of GAP-dependent interactions with HIF-1α and VHL to protect HIF-1α from degradation while promoting glycolysis under hypoxic conditions. We indicate that RLIP76 is crucial for the regulation of hypoxia-enhanced glycolysis and may provide a new gene therapy approach for glioma patients.