Sp1 is a substrate of Keap1 and regulates the activity of CRL4AWDR23 ubiquitin ligase toward Nrf2

Ferbian Milas Siswanto; Ami Oguro; Susumu Imaoka

doi:10.1016/j.jbc.2021.100704

Sp1 is a substrate of Keap1 and regulates the activity of CRL4A^WDR23 ubiquitin ligase toward Nrf2

J Biol Chem. 2021 Jan-Jun:296:100704. doi: 10.1016/j.jbc.2021.100704. Epub 2021 Apr 23.

Authors

Ferbian Milas Siswanto¹, Ami Oguro², Susumu Imaoka³

Affiliations

¹ Department of Biomedical Chemistry, School of Science and Technology, Kwansei Gakuin University, Sanda, Japan.
² Department of Biomedical Chemistry, School of Science and Technology, Kwansei Gakuin University, Sanda, Japan; Program of Biomedical Science, Graduate School of Integrated Sciences for Life, Hiroshima University, Hiroshima, Japan.
³ Department of Biomedical Chemistry, School of Science and Technology, Kwansei Gakuin University, Sanda, Japan. Electronic address: imaoka@kwansei.ac.jp.

Abstract

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a critical transcription factor that orchestrates cellular responses to oxidative stress. Because the dysregulation of Nrf2 has been implicated in many diseases, precise regulation of its protein level is crucial for maintaining homeostasis. Kelch-like-ECH-associated protein 1 (Keap1) and WD40 repeat protein 23 (WDR23) directly regulate Nrf2 levels via similar but distinct proteasome-dependent pathways. WDR23 forms a part of the WDR23-Cullin 4A-RING ubiquitin ligase complex (CRL4A^WDR23), whereas Keap1 serves as a substrate adaptor for the Cullin 3-containing ubiquitin ligase complex. However, the mechanisms underlying crosstalk between these Keap1 and WDR23 pathways for the regulation of Nrf2 levels have not been investigated. Here, we showed that knockdown (KD) of Keap1 upregulated the expression of Cullin4A (CUL4A) in a specificity protein 1 (Sp1)-dependent manner. We also revealed that Sp1 interacted with Keap1, leading to ubiquitination of Sp1. Increases in Sp1 by Keap1 KD triggered Sp1 binding to the fourth Sp1 binding site (Sp1_M4) within the -230/+50 region of the CUL4A gene. We also demonstrated that the overexpression and KD of Sp1 reduced and increased Nrf2 protein levels, respectively. These effects were abrogated by the WDR23 KD, suggesting that Sp1 also regulates Nrf2 levels via the ubiquitin ligase complex CRL4A^WDR23. In conclusion, we discovered Sp1 as a novel substrate of Keap1 and provided evidence that Sp1 regulates the expression of CUL4A. We revealed a novel role for Sp1 in mediating crosstalk between two independent regulators of Nrf2 protein levels.

Keywords: Cullin 4A-RING ligase; Cullin4A; DNA damage-binding protein 1; Kelch-like ECH-associated protein 1; Ring-box 1; WD40 repeat protein 23; gene regulation; nuclear factor 2 (erythroid-derived 2-like factor); oxidative stress; posttranslational regulation; specificity protein 1.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Cell Line, Tumor
Gene Expression Regulation
Humans
Kelch-Like ECH-Associated Protein 1 / metabolism*
Kinetics
NF-E2-Related Factor 2 / metabolism*
Sp1 Transcription Factor / metabolism*
Ubiquitin-Protein Ligases / metabolism*

Substances

IL17RB protein, human
Kelch-Like ECH-Associated Protein 1
NF-E2-Related Factor 2
NFE2L2 protein, human
Sp1 Transcription Factor
Ubiquitin-Protein Ligases