151. NcoA2-Dependent Inhibition of HIF-1α Activation Is Regulated via AhR
- Author
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Chi Hao Tsai, Ching Hao Li, Yu Wen Cheng, Cheng Hui Lin, Po Lin Liao, Shih Hsuan Huang, and Jaw Jou Kang
- Subjects
Male ,Transcriptional Activation ,Aryl hydrocarbon receptor nuclear translocator ,Transcription, Genetic ,Cellular homeostasis ,Neovascularization, Physiologic ,Toxicology ,Transfection ,Transactivation ,Nuclear Receptor Coactivator 2 ,Basic Helix-Loop-Helix Transcription Factors ,Human Umbilical Vein Endothelial Cells ,Animals ,Humans ,Transcription factor ,Tube formation ,Cell Nucleus ,Mice, Inbred ICR ,biology ,Dose-Response Relationship, Drug ,Aryl Hydrocarbon Receptor Nuclear Translocator ,Cobalt ,Hep G2 Cells ,Aryl hydrocarbon receptor ,Hypoxia-Inducible Factor 1, alpha Subunit ,Molecular biology ,Cell Hypoxia ,Oxygen ,HEK293 Cells ,Gene Expression Regulation ,Receptors, Aryl Hydrocarbon ,Nuclear receptor coactivator 2 ,biology.protein ,Heterografts ,RNA Interference ,Signal transduction ,Protein Binding ,Signal Transduction - Abstract
High endogenous levels of aryl hydrocarbon receptor (AhR) contribute to hypoxia signaling pathway inhibition following exposure to the potent AhR ligand benzo[a]pyrene (B[a]P) and could alter cellular homeostasis and disease condition. Increasing evidence indicates that AhR might compete with AhR nuclear translocator (ARNT) for complex formation with hypoxia-inducible factor-1α (HIF-1α) for transactivation, which could alter several physiological variables. Nuclear receptor coactivator 2 (NcoA2) is a transcription coactivator that regulates transcription factor activation and inhibition of basic helix-loop-helix Per (Period)-ARNT-SIM (single-minded) (bHLH-PAS) family proteins, such as HIF-1α, ARNT, and AhR, through protein-protein interactions. In this study, we demonstrated that both hypoxia and hypoxia-mimic conditions decreased NcoA2 protein expression in HEK293T cells. Hypoxia response element (HRE) and xenobiotic-responsive element (XRE) transactivation also were downregulated with NcoA2 knockdown under hypoxic conditions. In addition, B[a]P significantly decreased NcoA2 protein expression be accompanied with AhR degradation. We next evaluated whether the absence of AhR could affect NcoA2 protein function under hypoxia-mimetic conditions. NcoA2 and HIF-1α nuclear localization decreased in both B[a]P-pretreated and AhR-knockdown HepG2 cells under hypoxia-mimic conditions. Interestingly, NcoA2 overexpression downregulated HRE transactivation by competing with HIF-1α and AhR to form protein complexes with ARNT. Both NcoA2 knockdown and overexpression inhibited endothelial cell tube formation in vitro. We also demonstrated using the in vivo plug assay that NcoA2-regulated vascularization decreased in mice. Taken together, these results revealed a biphasic role of NcoA2 between AhR and hypoxic conditions, thus providing a novel mechanism underlying the cross talk between AhR and hypoxia that affects disease development and progression.
- Published
- 2015