Abstract
Free radicals generated by oxidative stress cause damage that can contribute to numerous chronic diseases. Mammalian cells respond to this damage by increased transcription of cytoprotective phase II genes, which are regulated by NRF2. Previously, it has been shown that NRF2 protein levels increase after oxidative stress because its negative regulator, KEAP1, loses its ability to bind NRF2 and cause its proteasome-mediated degradation during oxidative stress. Here, we show that CRIF1, a protein previously known as cell cycle regulator and transcription cofactor, is also able to negatively regulate NRF2 protein stability. However, in contrast to KEAP1, which regulates NRF2 stability only under normal reducing conditions, CRIF1 regulates NRF2 stability and its target gene expression under both reducing and oxidative stress conditions. Thus, CRIF1-NRF2 interactions and their consequences are redox-independent. In addition, we found that CRIF1, unlike KEAP1 (which only interacts with N-terminal region of NRF2), physically interacts with both N- and C-terminal regions of NRF2 and promotes NRF2 ubiquitination and subsequent proteasome-mediated NRF2 protein degradation.