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Oxidative stress abolishes leptomycin B-sensitive nuclear export of transcription repressor Bach2 that counteracts
H Hoshino1, A Kobayashi, M Yoshida
1Department of Biochemistry, Tohoku University School of Medicine, Seiryo-machi 2-1, Sendai 980-8575, Japan.
Abstract:
The mammalian transcription activator Nrf2 plays critical roles in executing oxidative stress response by binding to the regulatory DNA sequence Maf recognition element. Bach2 is an Nrf2-related transcription repressor and a tissue-specific partner of the Maf oncoprotein family. We show here how Bach2 is regulated by an oxidative stress-sensitive conditional nuclear export. In cultured cells, Bach2 was localized in cytoplasm through its C-terminal evolutionarily conserved cytoplasmic localization signal (CLS). The CLS directed leptomycin B-sensitive nuclear export of reporter proteins, suggesting its dependence on the nuclear exporter Crm1/exportin 1. However, the CLS sequence does not bear a resemblance to the leucine-rich class of nuclear export signal, and mutagenesis analysis indicated that a stretch of nonhydrophobic amino acids is essential for its activity. Oxidative stressors aborted the CLS activity and induced nuclear accumulation of Bach2. Whereas oxidative stress is known to activate MARE-dependent transcription, overexpression of Bach2 in cultured cells silenced the inducibility of MARE. The results suggest that Bach2 mediates nucleocytoplasmic communication to couple oxidative stress and transcription repression in mammalian cells.
Insights
Bach2, a transcription repressor, is exported from the nucleus via a novel signal sensitive to oxidative stress. This mechanism links oxidative stress to transcription repression in mammalian cells.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- Nuclear factor erythroid 2-related factor 2 (Nrf2) is a key activator of the oxidative stress response.
- Bach2 is a repressor related to Nrf2 and partners with the Maf oncoprotein family.
- Oxidative stress response involves regulating transcription factors that bind to Maf recognition elements (MARE).
Purpose of the Study:
- To investigate the regulation of Bach2 by oxidative stress.
- To identify the mechanism of Bach2's nucleocytoplasmic transport.
- To determine Bach2's role in MARE-dependent transcription under oxidative stress.
Main Methods:
- Utilized cultured cells to study Bach2 localization and function.
- Employed reporter proteins and mutagenesis to analyze the cytoplasmic localization signal (CLS) of Bach2.
- Assessed the effect of oxidative stressors on Bach2 nuclear export and MARE inducibility.
Main Results:
- Bach2 is localized in the cytoplasm via a C-terminal CLS, dependent on Crm1/exportin 1.
- The Bach2 CLS is a novel non-leucine-rich nuclear export signal.
- Oxidative stress inhibits Bach2 export, causing nuclear accumulation and repression of MARE inducibility.
Conclusions:
- Bach2 is regulated by an oxidative stress-sensitive nuclear export mechanism.
- Bach2 acts as a mediator of nucleocytoplasmic communication linking oxidative stress to transcription repression.
- The findings reveal a novel pathway for controlling gene expression during oxidative stress.