Lysine 68 acetylation directs MnSOD as a tetrameric detoxification complex versus a monomeric tumor promoter

Yueming Zhu,Melissa E Stauffer,Seong-Hoon Park,Elizabeth L Tran,Guoxiang Liu,Robert Hart,Joseph O’ Brien,Marcelo Bonini,Angela E Dean,David Gius,Xianghui Zou,Karla J F Satchell,Haiyan Jiang,Nobuo Horikoshi,Matthew B Kieffer,Yucheng Gao,Songhua Quan

doi:10.1038/s41467-019-10352-4

Abstract

Manganese superoxide dismutase (MnSOD) functions as a tumor suppressor; however, once tumorigenesis occurs, clinical data suggest MnSOD levels correlate with more aggressive human tumors, implying a potential dual function of MnSOD in the regulation of metabolism. Here we show, using in vitro transformation and xenograft growth assays that the MnSOD-K68 acetylation (Ac) mimic mutant (MnSODK68Q) functions as a tumor promoter. Interestingly, in various breast cancer and primary cell types the expression of MnSODK68Q is accompanied with a change of MnSOD’s stoichiometry from a known homotetramer complex to a monomeric form. Biochemical experiments using the MnSOD-K68Q Ac-mimic, or physically K68-Ac (MnSOD-K68-Ac), suggest that these monomers function as a peroxidase, distinct from the established MnSOD superoxide dismutase activity. MnSODK68Q expressing cells exhibit resistance to tamoxifen (Tam) and cells selected for Tam resistance exhibited increased K68-Ac and monomeric MnSOD. These results suggest a MnSOD-K68-Ac metabolic pathway for Tam resistance, carcinogenesis and tumor progression.

Highlights

Manganese superoxide dismutase (MnSOD) functions as a tumor suppressor; once tumorigenesis occurs, clinical data suggest MnSOD levels correlate with more aggressive human tumors, implying a potential dual function of MnSOD in the regulation of metabolism
This raises a key biological question: what is the in vivo impact of MnSOD-Ac and how do elevated, and/or aberrant, stoichiometric levels disrupt normal mitochondrial metabolism leading to cellular damage and/or a tumor-permissive murine phenotype? Interestingly, female mice lacking Sirt[3] spontaneously develop estrogen-positive (ER + ), poorly differentiated, high Ki-67 mammary gland tumors that appear to be similar to human luminal B breast malignancies, which are often diagnosed in older women[2,5,7,15]
Correlative findings in human tumor samples suggest that while MnSOD may function as a tumor suppressor (TS) during the early stages of tumor initiation, once tumorigenesis progresses, MnSOD levels positively correlate with more aggressive human tumors[20], suggesting that specific isoforms of MnSOD, including potentially the acetylated form of MnSOD, may function as a tumor promoter

Summary

Introduction

Manganese superoxide dismutase (MnSOD) functions as a tumor suppressor; once tumorigenesis occurs, clinical data suggest MnSOD levels correlate with more aggressive human tumors, implying a potential dual function of MnSOD in the regulation of metabolism. Mice lacking Sirt[3], and containing acetylated MnSOD (MnSOD-Ac), developed tumors[7], implying that SIRT3 may function as a tumor suppressor (TS) This raises a key biological question: what is the in vivo impact of MnSOD-Ac and how do elevated, and/or aberrant, stoichiometric levels disrupt normal mitochondrial metabolism leading to cellular damage and/or a tumor-permissive murine phenotype? Mice that have a monoallelic knockout for MnSOD (MnSOD+/−) exhibit decreased MnSOD activity, increased oxidative stress, and decreased life span, as well as aging-related phenotypes, especially carcinogenesis[16] This in vitro and in vivo evidence supports the possibility that there is a link between the mitochondrial acetylome, as directed by SIRT3, and ROS detoxification, mitochondrial metabolism, and carcinogenesis; rigorous mechanistic data supporting this intriguing idea has been limited. We show that the homotetramer is a TS, whereas the monomer, as modeled by enforced MnSODK68Q expression, functions as a tumor promoter

Methods

Results

Conclusion