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

• Published in: The FEBS journal Vol. 281; no. 23; pp. 5220 - 5236
• Main Authors: Bordji, Karim, Grandval, Alexandra, Cuhna‐Alves, Leilane, Lechapt‐Zalcman, Emmanuèle, Bernaudin, Myriam
• Format: Journal Article
• Language: English
• Published: England Published by Blackwell Pub. on behalf of the Federation of European Biochemical Societies 01.12.2014; Wiley
• Subjects: Base Sequence; Basic Helix-Loop-Helix Transcription Factors - genetics; Basic Helix-Loop-Helix Transcription Factors - physiology; Binding Sites; brain; Brain Neoplasms - metabolism; Brain Neoplasms - pathology; Cell Hypoxia; Cell Line, Tumor; cultured cells; drug therapy; gel electrophoresis; genes; Glioblastoma - metabolism; Glioblastoma - pathology; glioblastoma cells; HIF‐1α; HIF‐2α; Humans; hypoxia; hypoxia-inducible factor 1; Hypoxia-Inducible Factor 1, alpha Subunit - genetics; Hypoxia-Inducible Factor 1, alpha Subunit - physiology; Life Sciences; Molecular Sequence Data; neoplasms; normoxia; promoter regions; Promoter Regions, Genetic; response elements; RNA, Small Interfering - genetics; site-directed mutagenesis; tubulin; Tubulin - genetics; βIII‐tubulin; hypoxia; HIF-1α; βIII-tubulin; HIF-2α; glioblastoma cells
• ISSN: 1742-464X; 1742-4658; 1742-4658
• DOI: 10.1111/febs.13062

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.