Degradation of the transcription factor Nrf2 in promyelocytic leukemia‐nuclear bodies

Abstract

The cellular abundance of the redox‐sensitive transcription factor Nrf2 is controlled by Keap1, an inhibitory protein that functions as a substrate adaptor for ubiquitylation of Nrf2 by the Cullin3/RING box1 (Cul3‐Rbx1) E3 ubiquitin ligase complex, thereby targeting Nrf2 for proteasome‐dependent degradation in the cytoplasm. Nrf2 can also be degraded in the nucleus but mechanistic details are lacking. Here, we show that promyelocytic leukemia‐nuclear body (PML‐NB)‐enriched preparations of HepG2 cells treated with arsenic trioxide (ATO) contained modified (sumoylated) Nrf2 and the poly‐SUMO‐specific ubiquitin E3 ligase RNF4, but not Keap1. Overexpressing RNF4 decreased the steady‐state levels of Nrf2 whereas the catalytically inactive RNF4 did not. The proteasomal inhibitor MG‐132 interfered with this RNF4‐induced decrease. In MG‐132‐treated cells, the content of ubiquitylated Nrf2 was higher in cells transfected with wild‐type RNF4 than in cells transfected with catalytically inactive RNF4. RNF4 also decreased the half‐life of Nrf2, measured in PML‐NB‐enriched fractions prepared from ATO‐treated cells. Given that treatment with ATO enhances SUMO‐2/3 attachment to Nrf2, these data suggest that RNF4 induces poly‐ubiquitylation of poly‐sumoylated Nrf2, leading to its degradation by proteasomes in PML‐NBs.Supported by NIH grants #5T32HL007737, 2 SD1MD000104 and SC1CA143985