NcoA2-Dependent Inhibition of HIF-1α Activation Is Regulated via AhR.

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.

• Authors: Chi-Hao Tsai, Ching-Hao Li, Po-Lin Liao, Yu-Wen Cheng, Cheng-Hui Lin, Shih-Hsuan Huang, Jaw-Jou Kang
• Journal: Toxicological sciences : an official journal of the Society of Toxicology (Toxicol Sci) Vol. 148 Issue 2 Pg. 517-30 (Dec 2015) ISSN: 1096-0929 [Electronic] United States
• PMID: 26350169 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: © The Author 2015. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For Permissions, please e-mail: [email protected].

Chemical References

• AHR protein, human
• ARNT protein, human
• Basic Helix-Loop-Helix Transcription Factors
• HIF1A protein, human
• Hypoxia-Inducible Factor 1, alpha Subunit
• NCOA2 protein, human
• Nuclear Receptor Coactivator 2
• Receptors, Aryl Hydrocarbon
• Aryl Hydrocarbon Receptor Nuclear Translocator
• Cobalt
• cobaltous chloride
• Oxygen

Topics

• Animals
• Aryl Hydrocarbon Receptor Nuclear Translocator (metabolism)
• Basic Helix-Loop-Helix Transcription Factors (genetics, metabolism)
• Cell Hypoxia
• Cell Nucleus (drug effects, metabolism)
• Cobalt (pharmacology)
• Dose-Response Relationship, Drug
• Gene Expression Regulation
• HEK293 Cells
• Hep G2 Cells
• Heterografts
• Human Umbilical Vein Endothelial Cells (metabolism)
• Humans
• Hypoxia-Inducible Factor 1, alpha Subunit (genetics, metabolism)
• Male
• Mice, Inbred ICR
• Neovascularization, Physiologic
• Nuclear Receptor Coactivator 2 (genetics, metabolism)
• Oxygen (metabolism)
• Protein Binding
• RNA Interference
• Receptors, Aryl Hydrocarbon (genetics, metabolism)
• Signal Transduction
• Transcription, Genetic
• Transcriptional Activation
• Transfection