title: Hypoxia-inducible factor-2α (HIF-2α), but not HIF-1α, is essential for hypoxic induction of class III β-tubulin expression in human glioblastoma cells.
abstract: Glioblastoma multiforme (GBM) is the deadliest form of primary brain cancer. Several reports have indicated aberrant levels of βIII-tubulin (βIII-t) in human GBM. βIII-t overexpression was linked to increasing malignancy in glial tumors and described to determine the onset of resistance to chemotherapy. Furthermore, a linkage was suggested between the induction of βIII-t expression and hypoxia, a hallmark of GBM. We investigated the role of hypoxia-inducible factor (HIF)-1α and HIF-2α in the regulation of the βIII-t gene (TUBB3) in GBM cells cultured in either normoxia or hypoxia. We report for the first time that HIF-2α, but not HIF-1α, is involved in hypoxia-induced βIII-t expression in GBM cells. By gene-reporter experiments and site-directed mutagenesis, we found that two overlapping hypoxia response elements located in the 3' UTR of the gene were involved in the activation of TUBB3. This occurred through an enhanced binding of HIF-2α to the 3' region, as revealed by an electrophoretic mobility shift assay. Conversely, the promoter of TUBB3 was shown to be inactive. In addition, we observed that HIF-1α exhibits a repressive effect on βIII-t expression in cells cultured in normoxia. These results show that both HIF-α isoforms have opposing effects on βIII-t expression in GBM cells. Finally, we observed that hypoxia-induced βIII-t expression is well correlated with the kinetics of HIF-2α protein stabilization. The evidence for a direct linkage between HIF-2α and increased expression of βIII-t by hypoxia suggests that an anti-HIF-2α strategy (i.e. by downregulating βIII-t) could be of potential interest for improving the treatment of GBM.
authors.affiliation: CNRS, UMR 6301 ISTCT, CERVOxy group, GIP Cyceron, Caen, France; CEA, DSV/I2BM, UMR 6301 ISTCT, Caen, France; Université de Basse-Normandie, UMR 6301 ISTCT, Caen, France; Normandie University, Caen, France.
authors.forename: Karim
authors.initials: K
authors.lastname: Bordji
authors.forename: Alexandra
authors.initials: A
authors.lastname: Grandval
authors.forename: Leilane
authors.initials: L
authors.lastname: Cuhna-Alves
authors.forename: Emmanuèle
authors.initials: E
authors.lastname: Lechapt-Zalcman
authors.forename: Myriam
authors.initials: M
authors.lastname: Bernaudin
mesh_terms: D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000502:physiology*; D001665:Binding Sites; D001932:Brain Neoplasms / Q000378:metabolism* / Q000473:pathology; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D005909:Glioblastoma / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000502:physiology; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D034741:RNA, Small Interfering / Q000235:genetics; D014404:Tubulin / Q000235:genetics*; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D034741:RNA, Small Interfering; D014404:Tubulin; D000099162:Endothelial PAS Domain-Containing Protein 1; C497442:HIF1A protein, human; C498585:TUBB3 protein, human
keywords: HIF-1α; HIF-2α; glioblastoma cells; hypoxia; βIII-tubulin