The β-TrCP-Mediated Pathway Cooperates with the Keap1-Mediated Pathway in Nrf2 Degradation In Vivo

ABSTRACT

Nrf2 activates cytoprotective gene expression, and Nrf2 activity is regulated through at least two protein degradation pathways: the Keap1-mediated and β-TrCP-mediated pathways. To address the relative contributions of these pathways, we generated knock-in mouse lines expressing an Nrf2^SA mutant that harbored two substitution mutations of serine residues interacting with β-TrCP. The homozygous (Nrf2^SA/SA) mice grew normally, with Nrf2 levels comparable to those of wild-type (WT) mice under unstressed conditions. However, when Keap1 activity was suppressed, high levels of Nrf2 accumulated in Nrf2^SA/SA macrophages compared with that in WT macrophages. We crossed Nrf2^SA/SA mice with mice in which Keap1 was knocked down to two different levels. We found that the Nrf2^SA/SA mutation induced higher Nrf2 activity when the Keap1 level was strongly reduced, and these mice showed severe growth retardation. However, activation and growth retardation were not evident when Keap1 was moderately suppressed. These increases in Nrf2 activity induced by the Nrf2^SA mutation caused severe hyperplasia and hyperkeratosis in the esophageal epithelium but did not cause abnormalities in the other tissues/organs examined. These results indicate that the β-TrCP-mediated pathway cooperates with the Keap1-mediated pathway to regulate Nrf2 activity, which is apparent when the Keap1-mediated pathway is profoundly suppressed.

KEYWORDS:

• β-TrCP
• Keap1
• Nrf2
• degradation

Declaration of Interests

The authors declare no conflict of interest.

ACKNOWLEDGMENTS

We thank Eriko Naganuma, Hiromi Suda, Keiko Tateno, Haruka Kobayashi, Makiko Hayashi, and the Biomedical Research Core of Tohoku University Graduate School of Medicine for technical support.

This work was supported in part by AMED-P-CREATE (JP21cm0106101 to M.Y.) from the Japan Agency for Medical Research and Development (AMED) and KAKENHI 19H05649 (to M.Y.) and 20K08747 (to M.S.) from the Japan Society for the Promotion of Science (JSPS).