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Mechanism of chemical activation of Nrf2

Yun Li1, Joseph D Paonessa, Yuesheng Zhang

  • 1Department of Cancer Prevention and Control, Roswell Park Cancer Institute, Buffalo, New York, United States of America.

Plos One
|May 5, 2012
PubMed

Insights

Chemical activators stabilize NF-E2 related factor-2 (Nrf2) by inhibiting its ubiquitination in the nucleus, not the cytoplasm. This process involves Nrf2 association with Keap1, challenging previous understanding of Nrf2 activation.

Area of Science:

  • Molecular Biology
  • Cellular Biology
  • Biochemistry

Background:

  • NF-E2 related factor-2 (Nrf2) is a key transcription factor for cytoprotective genes and a significant drug target for cancer prevention.
  • Nrf2 activators stabilize Nrf2 by blocking ubiquitination, a process previously thought to occur exclusively in the cytoplasm.
  • Kelch-like ECH-associated protein 1 (Keap1) is the primary repressor of Nrf2, orchestrating its ubiquitination and degradation.

Purpose of the Study:

  • To investigate the subcellular localization of Nrf2 ubiquitination inhibition by chemical activators.
  • To elucidate the mechanism by which chemopreventive agents activate Nrf2.
  • To challenge the established model of Nrf2 regulation by Keap1.

Main Methods:

  • Treatment of cells with chemical Nrf2 activators like 5,6-dihydrocyclopenta-1,2-dithiole-3-thione (CPDT) and sulforaphane (SF).
  • Analysis of Nrf2 ubiquitination status in cytoplasmic and nuclear fractions.
  • Assessment of Nrf2-Keap1 association and Nrf2 phosphorylation.
  • Investigating Keap1-dependent and independent Nrf2 degradation pathways.

Main Results:

  • Nrf2 ubiquitination inhibition by CPDT and SF occurs predominantly in the nucleus, not the cytoplasm.
  • Nrf2 activators promote Nrf2-Keap1 association, contrary to the dissociation hypothesis.
  • Activation appears to result from inhibition of Nrf2 phosphorylation at Ser40, potentially via Keap1 cysteine modification.
  • A Keap1-independent Nrf2 degradation pathway also exists.

Conclusions:

  • Chemopreventive Nrf2 activators function primarily in the nucleus to inhibit Nrf2 ubiquitination and degradation.
  • The mechanism involves enhanced Nrf2-Keap1 interaction and altered Keap1 conformation.
  • These findings necessitate a revised understanding of Nrf2 regulation and therapeutic targeting.

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