SPBP is a sulforaphane induced transcriptional coactivator of NRF2 regulating expression of the autophagy receptor p62/SQSTM1

PLoS One. 2014 Jan 9;9(1):e85262. doi: 10.1371/journal.pone.0085262. eCollection 2014.

Abstract

Organisms exposed to oxidative stress respond by orchestrating a stress response to prevent further damage. Intracellular levels of antioxidant agents increase, and damaged components are removed by autophagy induction. The KEAP1-NRF2 signaling pathway is the main pathway responsible for cell defense against oxidative stress and for maintaining the cellular redox balance at physiological levels. Sulforaphane, an isothiocyanate derived from cruciferous vegetables, is a potent inducer of KEAP1-NRF2 signaling and antioxidant response element driven gene expression. In this study, we show that sulforaphane enhances the expression of the transcriptional coregulator SPBP. The expression curve peaks 6-8 hours post stimulation, and parallels the sulforaphane-induced expression of NRF2 and the autophagy receptor protein p62/SQSTM1. Reporter gene assays show that SPBP stimulates the expression of p62/SQSTM1 via ARE elements in the promoter region, and siRNA mediated knock down of SPBP significantly decreases the expression of p62/SQSTM1 and the formation of p62/SQSTM1 bodies in HeLa cells. Furthermore, SPBP siRNA reduces the sulforaphane induced expression of NRF2, and the expression of the autophagy marker protein LC3B. Both these proteins contain ARE-like elements in their promoter regions. Over-expressed SPBP and NRF2 acts synergistically on the p62/SQSTM1 promoter and colocalize in nuclear speckles in HeLa cells. Collectively, these results suggest that SPBP is a coactivator of NRF2, and hence may be important for securing enhanced and sustained expression of NRF2 induced genes such as proteins involved in selective autophagy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / genetics*
  • Adaptor Proteins, Signal Transducing / metabolism
  • Anticarcinogenic Agents / pharmacology*
  • Autophagy / drug effects
  • Gene Expression Regulation, Neoplastic / drug effects*
  • HeLa Cells
  • Humans
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism
  • Isothiocyanates / pharmacology*
  • Kelch-Like ECH-Associated Protein 1
  • Microtubule-Associated Proteins / genetics
  • Microtubule-Associated Proteins / metabolism
  • NF-E2-Related Factor 2 / genetics*
  • NF-E2-Related Factor 2 / metabolism
  • Promoter Regions, Genetic
  • RNA, Small Interfering / genetics
  • RNA, Small Interfering / metabolism
  • Sequestosome-1 Protein
  • Signal Transduction
  • Sulfoxides
  • Transcription Factors / antagonists & inhibitors
  • Transcription Factors / genetics*
  • Transcription Factors / metabolism
  • Transcription, Genetic

Substances

  • Adaptor Proteins, Signal Transducing
  • Anticarcinogenic Agents
  • Intracellular Signaling Peptides and Proteins
  • Isothiocyanates
  • KEAP1 protein, human
  • Kelch-Like ECH-Associated Protein 1
  • MAP1LC3B protein, human
  • Microtubule-Associated Proteins
  • NF-E2-Related Factor 2
  • NFE2L2 protein, human
  • RNA, Small Interfering
  • SQSTM1 protein, human
  • Sequestosome-1 Protein
  • Sulfoxides
  • TCF20 protein, human
  • Transcription Factors
  • sulforaphane

Grant support

This work was supported by the Norwegian Research Council, Familien Blix Fond and the Norwegian Cancer Society to Prof. Terje Johansen. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.