Sirtuin 2 regulates cellular iron homeostasis via deacetylation of transcription factor NRF2

Xiaoyan Yang,Konrad T Sawicki,Chunlei Chen,David Gius,Jason S Shapiro,Paul W Burridge,Seong-Hoon Park,Meng Shang,Hsiang-Chun Chang,Conrad L Epting,Mitchell Knutson,Supak Jenkitkasemwong,Lisa D Wilsbacher,Hossein Ardehali,Athanassios Vassilopoulos

doi:10.1172/jci88574

Abstract

SIRT2 is a cytoplasmic sirtuin that plays a role in various cellular processes, including tumorigenesis, metabolism, and inflammation. Since these processes require iron, we hypothesized that SIRT2 directly regulates cellular iron homeostasis. Here, we have demonstrated that SIRT2 depletion results in a decrease in cellular iron levels both in vitro and in vivo. Mechanistically, we determined that SIRT2 maintains cellular iron levels by binding to and deacetylating nuclear factor erythroid-derived 2-related factor 2 (NRF2) on lysines 506 and 508, leading to a reduction in total and nuclear NRF2 levels. The reduction in nuclear NRF2 leads to reduced ferroportin 1 (FPN1) expression, which in turn results in decreased cellular iron export. Finally, we observed that Sirt2 deletion reduced cell viability in response to iron deficiency. Moreover, livers from Sirt2-/- mice had decreased iron levels, while this effect was reversed in Sirt2-/- Nrf2-/- double-KO mice. Taken together, our results uncover a link between sirtuin proteins and direct control over cellular iron homeostasis via regulation of NRF2 deacetylation and stability.

Highlights

Iron is an integral component of numerous proteins, free iron is a major source of ROS and cellular injury [1]
Infection with lenti-Sirt2-WT, but not lenti-Sirt2DN, reversed iron deficiency in Sirt2–/– mouse embryonic fibroblasts (MEFs) (Figure 1G). These results indicate that SIRT2 regulates cellular iron homeostasis at least in part through its deacetylation activity
Since nuclear factor erythroid-derived 2–related factor 2 (NRF2) activity was regulated by SIRT2 and SIRT2 is localized to the cytoplasm, we proposed that SIRT2 interacts with either NRF2 or Kelch-like ECH-associated protein 1 (KEAP1) to alter their activity

Summary

Introduction

Iron is an integral component of numerous proteins, free iron is a major source of ROS and cellular injury [1]. Under iron-deficient conditions, the iron-regulatory proteins IRP1 and IRP2 are activated to modulate the mRNA stability or translation rates of key iron transporters by binding to iron response elements (IREs) in the 3′- or 5′-UTRs of target mRNAs [2, 3]. IRP1/2 binding to the 5′-UTR of ferritin (Ftl) and ferroportin (Fpn1) mRNAs results in reduced translation rates, which leads to the mobilization of iron stores and reduced iron export, respectively. Interaction of IRP1/2 with the 3′-UTR stabilizes target mRNAs, such as the iron importer transferrin receptor 1 (Tfrc), and enhances iron uptake [2]. Iron homeostasis is controlled by other signaling pathways such as HIF, which regulates cellular iron import through transcriptional upregulation of Tfrc by binding to HIF-responsive elements in the promoter

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