Depletion of HIF‐1α‐mediated Mitochondrial Uncoupling Protein‐4 (UCP4) Expression Sensitizes Temozolomide (TMZ)‐Induced Apoptosis in Glioblastoma

Abstract

IntroductionMitochondrial Uncoupling Protein‐4 (UCP4) UCP4 is exclusively expressed in the brain and has been shown to promote cell proliferation and enhance resistance to mitochondrial toxins by shifting cellular ATP synthesis from oxidative phosphorylation (OxPhos) toward glycolysis. Notably, a recent study demonstrated that the expression of cerebral UCP4 was upregulated when the animals were exposed to acute high‐altitude hypoxia. This upregulation may facilitate the adaptation of malignant glioma cells to their hypoxic microenvironment, and contribute to the subsequent mitochondria remodeling and metabolic reprogramming. UCP4 has become an interesting focus in the regulation of oxidative stress in age‐related neurodegenerative diseases. However, the function and mechanism of UCP4 upregulation under hypoxia remains poorly defined in gliomas.MethodsThe human glioblastoma cell line, U373MG was used for this study. UCP4 expression level under hypoxia was detected using Western Blot. Glioma cell proliferation, anchorage‐independent growth and invasion were evaluated using MTT assay, BrdU incorporation, Soft‐agar colonogenic assay, and Matrigel invasion assay. To silent UCP4, U373MG cells were infected with shRNA against UCP4. LDH release assay was employed to assess whether targeting UCP4 could sensitize the Temozolomine (TMZ) – induced the apoptosis in U373MG cells. The Human UCP4 base promoter region was cloned for Luciferase reporter assays.ResultsHere, we showed that 1) Hypoxia increased UCP4 which promoted tumor progression in gliomas. 2) Knockdown of UCP4 decreased tumor progression and increased the cell sensitivity to TMZ chemotherapy. 3) HIF‐1α regulated UCP4 expression via binding to the UCP4 upstream consensus sequence, and silencing HIF‐1α decreases UCP4 expression.ConclusionsOur data suggested that hypoxia increased UCP4 expression which may contribute to cell adaptation to the hypoxic microenvironment. Targeting UCP4/HIF‐1α, or blocking HIF‐1α binding to UCP4 promoter in glioma cells may offer a new avenue for therapeutic intervention.Support or Funding InformationSupported by the award Florida Center for Brain Tumor Research UF10262 (PI: Zixi Jack Cheng).