Cobalt stimulates HIF-1-dependent but inhibits HIF-2-dependent gene expression in liver cancer cells

• Published in: The international journal of biochemistry & cell biology 2013-11, Vol.45 (11), p.2359-2368
• Main Authors: Befani, Christina, Mylonis, Ilias, Gkotinakou, Ioanna-Maria, Georgoulias, Panagiotis, Hu, Cheng-Jun, Simos, George, Liakos, Panagiotis
• Format: Article
• Language: English
• Subjects: Activated; Activation; Amino Acids, Dicarboxylic - pharmacology; Basic Helix-Loop-Helix Transcription Factors - antagonists & inhibitors; Basic Helix-Loop-Helix Transcription Factors - genetics; Basic Helix-Loop-Helix Transcription Factors - metabolism; Cancer; Cell Hypoxia - drug effects; Cell Hypoxia - genetics; Cell Line, Tumor; Cell Nucleus - drug effects; Cell Nucleus - metabolism; Cobalt; Cobalt - pharmacology; Deferoxamine - pharmacology; EPO; erythropoietin; Erythropoietin - genetics; Erythropoietin - secretion; Gene expression; Gene Expression Regulation, Neoplastic - drug effects; Genes; HIF-2α; Humans; Hypoxia; hypoxia-inducible factor 1; Hypoxia-Inducible Factor 1, alpha Subunit - genetics; Hypoxia-Inducible Factor 1, alpha Subunit - metabolism; liver neoplasms; Liver Neoplasms - genetics; Liver Neoplasms - pathology; neoplasm cells; oxygen; Phosphoglycerate Kinase - genetics; Phosphoglycerate Kinase - metabolism; Promoter Regions, Genetic - genetics; Propanolamines - pharmacology; Protein Binding - drug effects; Protein Binding - genetics; protein synthesis; Proteins; Pyrrolidines - pharmacology; RNA, Messenger - genetics; RNA, Messenger - metabolism; secretion; SOD2; Superoxide Dismutase - genetics; tissues; transcription (genetics); Transcription, Genetic - drug effects; Upstream Stimulatory Factors - metabolism; USF2
• ISSN: 1357-2725; 1878-5875
• DOI: 10.1016/j.biocel.2013.07.025

Hypoxia-inducible factors (HIFs) are transcriptional regulators that mediate the cellular response to low oxygen. Although HIF-1 is usually considered as the principal mediator of hypoxic adaptation, several tissues and different cell types express both HIF-1 and HIF-2 isoforms under hypoxia or when treated with hypoxia mimetic chemicals such as cobalt. However, the similarities or differences between HIF-1 and HIF-2, in terms of their tissue- and inducer-specific activation and function, are not adequately characterized. To address this issue, we investigated the effects of true hypoxia and hypoxia mimetics on HIF-1 and HIF-2 induction and specific gene transcriptional activity in two hepatic cancer cell lines, Huh7 and HepG2. Both hypoxia and cobalt caused rapid induction of both HIF-1α and HIF-2α proteins. Hypoxia induced erythropoietin (EPO) expression and secretion in a HIF-2-dependent way. Surprisingly, however, EPO expression was not induced when cells were treated with cobalt. In agreement, both HIF-1- and HIF-2-dependent promoters (of PGK and SOD2 genes, respectively) were activated by hypoxia while cobalt only activated the HIF-1-dependent PGK promoter. Unlike cobalt, other hypoxia mimetics such as DFO and DMOG activated both types of promoters. Furthermore, cobalt impaired the hypoxic stimulation of HIF-2, but not HIF-1, activity and cobalt-induced HIF-2α interacted poorly with USF-2, a HIF-2-specific co-activator. These data show that, despite similar induction of HIF-1α and HIF-2α protein expression, HIF-1 and HIF-2 specific gene activating functions respond differently to different stimuli and suggest the operation of oxygen-independent and gene- or tissue-specific regulatory mechanisms involving additional transcription factors or co-activators.