1、Articleshttps:/doi.org/10.1038/s41556-018-0178-01Department of Experimental Radiation Oncology,The University of Texas MD Anderson Cancer Center,Houston,TX,USA.2Division of Biostatistics,Dan L.Duncan Cancer Center and Department of Molecular and Cellular Biology,Baylor College of Medicine,Houston,TX
2、,USA.3Department of Translational Molecular Pathology,The University of Texas MD Anderson Cancer Center,Houston,TX,USA.4Department of Cancer Biology,Cleveland Clinic Lerner Research Institute,Cleveland,OH,USA.5The University of Texas MD Anderson UT Health Graduate School of Biomedical Sciences,Houst
3、on,TX,USA.6Department of Molecular and Cellular Oncology,The University of Texas MD Anderson Cancer Center,Houston,TX,USA.7Graduate Institute of Biomedical Sciences and Center for Molecular Medicine,China Medical University,Taichung,Taiwan.8Present address:Institute of Biology,Westlake University,Ha
4、ngzhou,Zhejiang Province,China.9Present address:Guangdong Key Laboratory of Liver Disease Research,The Third Affiliated Hospital of Sun Yat-Sen University,Guangzhou,China.10These authors contributed equally:Yilei Zhang,Jiejun Shi.*e-mail:WL1bcm.edu;bganmdanderson.orgTo survive,cancer cells require a
5、n adequate supply of nutrients,such as amino acids,to maintain redox homeostasis and to meet their biosynthetic and bioenergetic needs1,2.Nutrient depletion induces metabolic stress and eventually provokes cell death,including apoptosis and other non-apoptotic forms of regu-lated cell death3,4.Cance
6、r cells engage strategies of metabolic adapta-tion,including inactivation of apoptosis pathways,to survive under metabolic stress conditions and to allow tumour progression5,6.It is conceivable that non-apoptotic cell death pathways are also dys-regulated in cancer,although the underlying mechanisms
7、 remain much less understood.Ferroptosis is a recently identified metabolic stress-induced non-apoptotic form of regulated cell death that is caused by cys-tine depletion and overproduction of lipid-based reactive oxygen species(ROS),particularly lipid hydroperoxide,in an iron-depen-dent manner711.S
8、olute carrier family 7 member 11(SLC7A11,also called xCT),the catalytic subunit of the cystine/glutamate antiporter system xc,is the major transporter of extracellular cys-tine1214.Correspondingly,cystine depletion or drugs that block SLC7A11-mediated cystine uptake,such as erastin,induce ferrop-tos
9、is7.Intracellular cystine is rapidly converted to cysteine,which subsequently serves as the rate-limiting precursor for glutathione synthesis.Glutathione peroxidase 4(GPX4)utilizes reduced gluta-thione(GSH)to reduce lipid hydroperoxides to lipid alcohols,to protect cells against membrane lipid perox
10、idation and inhibit fer-roptosis15,16.Ferroptosis is morphologically,genetically and bio-chemically distinct from other forms of regulated cell death,such as apoptosis and necroptosis7.It is well established that cell death,most notably apoptosis,plays important roles in tumour suppression17,18.Howe
11、ver,the roles and regulatory mechanisms of ferroptosis in tumour biology remain largely unexplored.BRCA1-associated protein 1(BAP1)encodes a nuclear deubiq-uitinating(DUB)enzyme that interacts with several transcriptional factors and chromatin-modifying enzymes,such as FOXK1/2,ASXL1/2,OGT,HCFC1 and
12、KDM1B,and plays an important role in the epigenetic regulation of gene transcription1925.BAP1 and its associated proteins form the polycomb repressive deubiquitinase(PRDUB)complex,which mainly functions to remove monoubiq-uitin from ubiquitinated histone 2A at lysine 119(H2Aub)26.It has been shown t
13、hat this type of histone modification regulates gene transcription through epigenetic mechanisms2729.BAP1 is a tumour suppressor gene with frequent inactivating mutations and deletions in a variety of sporadic human cancers,including uveal melanoma(UVM),renal cell carcinoma,mesothelioma and cholangi
14、ocar-cinoma19,3033.However,the mechanisms by which BAP1 exerts its tumour suppression function,particularly the extent to which BAP1 regulation of H2Aub levels on chromatin and corresponding transcriptional targets plays a role in its tumour suppression func-tion,remain unclear.In this study,we cond
15、uct integrative analyses to achieve a comprehensive identification of BAP1-regulated target genes and relevant biological processes in cancer cells,and identify a BAP1-mediated epigenetic mechanism that links ferroptosis to tumour suppression.ResultsGenome-wide analyses link BAP1 to metabolism-relat
16、ed biologi-cal processes.We conducted unbiased genome-wide analyses to char-acterize BAP1-dependent H2Aub occupancies and corresponding BAP1 links metabolic regulation of ferroptosis to tumour suppressionYilei Zhang1,10,Jiejun Shi 2,10,Xiaoguang Liu1,Li Feng3,Zihua Gong1,4,Pranavi Koppula1,5,Kapil S
17、irohi 1,Xu Li1,8,Yongkun Wei6,Hyemin Lee1,Li Zhuang1,Gang Chen3,Zhen-Dong Xiao1,9,Mien-Chie Hung5,6,7,Junjie Chen1,5,Peng Huang3,5,Wei Li 2*and Boyi Gan 1,5,6*The roles and regulatory mechanisms of ferroptosis(a non-apoptotic form of cell death)in cancer remain unclear.The tumour suppressor BRCA1-as
18、sociated protein 1(BAP1)encodes a nuclear deubiquitinating enzyme to reduce histone 2A ubiquitination(H2Aub)on chromatin.Here,integrated transcriptomic,epigenomic and cancer genomic analyses link BAP1 to metabolism-related biological processes,and identify cystine transporter SLC7A11 as a key BAP1 t
19、arget gene in human cancers.Functional studies reveal that BAP1 decreases H2Aub occupancy on the SLC7A11 promoter and represses SLC7A11 expression in a deubiq-uitinating-dependent manner,and that BAP1 inhibits cystine uptake by repressing SLC7A11 expression,leading to elevated lipid peroxidation and
20、 ferroptosis.Furthermore,we show that BAP1 inhibits tumour development partly through SLC7A11 and fer-roptosis,and that cancer-associated BAP1 mutants lose their abilities to repress SLC7A11 and to promote ferroptosis.Together,our results uncover a previously unappreciated epigenetic mechanism coupl
21、ing ferroptosis to tumour suppression.NAtuRe CeLL BioLoGY|VOL 20|OCTOBER 2018|11811192| CeLL BioLogytranscriptional alterations in the genome.To this end,we established UMRC6 cells(a BAP1-deficient renal cancer cell line)with stable expression of an empty vector(EV),BAP1 wild type(WT)and a BAP1 C91A
22、 DUB-inactive mutant34.We confirmed that re-expres-sion of BAP1 WT,but not its C91A mutant,in UMRC6 cells decreased global H2Aub levels(Fig.1a).We then performed H2Aub chroma-tin immunoprecipitation coupled with high-throughput sequencing(ChIPseq)analyses in these cells.Our ChIPseq analyses revealed
23、 that re-expression of BAP1 WT,but not its C91A mutant,resulted in significant reduction of genome-wide H2Aub occupancies in UMRC6 cells(Fig.1b,c).Distribution analysis showed that more than half of H2Aub bindings in EV/WT/C91A cells were detected at promoter or gene body regions(Supplementary Fig.1
24、a).BAP1 WT,but not BAP1 C91A,cells showed decreases of H2Aub occu-pancies at promoter,gene body and intergenic regions(Fig.1d and Supplemenary Fig.1b).Overall,we identified more than 5,000 genes with reduced H2Aub occupancies in BAP1 WT cells compared with EV cells(Fig.1e;false discovery rate(FDR)1.
25、5,FDR 1.6-fold,1,494 genes 2-fold,and 101 genes 2.5-fold).GSEA revealed,in all three analyses,that genes with BAP1-dependent H2Aub reduction were enriched with BAP1-upregulated genes;indeed,the more strin-gent the cutoff we used,the more significant the correlation(see Fig.1g for 101 genes,normalize
26、d enrichment score=1.61,FDR=0;see Supplementary Fig.1d for 1,494 genes,normalized enrich-ment score=1.52,FDR=0;see Supplementary Fig.1e for 5,837 genes,normalized enrichment score=1.22,FDR=0).Thus,our analysis was consistent with the prevailing model that H2Aub cor-relates with transcriptional repre
27、ssion28.It is also worth noting that the fold changes in H2Aub binding on promoters of the genes that were differentially regulated by BAP1 were more pronounced than those in the total set of 5,837 genes(Fig.1d,h,i and Supplementary Fig.1b,f,g;with the following median log2-fold change of H2Aub on B
28、AP1 re-expression:0.44 for all 5,837 genes versus 1.03 for BAP1-downregulated genes versus 0.96 for BAP1-upregulated genes).Thus,BAP1-dependent H2Aub de-ubiquitination correlates with BAP1-mediated transcriptional alteration.Heatmap analysis of the H2Aub profile around transcriptional start sites(TS
29、Ss)revealed that the genes that were upregulated or downregulated by BAP1 dis-played reduced H2Aub signals centred on TSSs on re-expression of BAP1 WT,but not C91A(Fig.1j).Gene ontology(GO)analysis of 354 BAP1-upregulated and 187 BAP1-downregulated genes revealed that,while BAP1-upregulated genes we
30、re enriched in diverse cellular processes(Supplementary Fig.1h and Supplementary Table 1),the genes that were downregu-lated by BAP1 showed striking enrichment in metabolism-related biological processes,among which response to oxidative stress was the most significantly enriched(Fig.1k and Supplemen
31、tary Table 1).Together,our genome-wide analyses suggested that BAP1-mediated de-ubiquitination of H2Aub is associated with both transcriptional activation and repression of gene targets involved in different bio-logical processes(see Discussion),and linked BAP1-repressed genes to metabolism.Cancer g
32、enomic analyses link SLC7A11 to BAP1-mediated tumour suppression in human cancers.Next,we studied the potential relevance of BAP1-regulated genes to BAP1-mediated tumour suppression in human cancers through analysis of The Cancer Genome Atlas(TCGA)data sets.Because we conducted our genome-wide analy
33、ses in a renal cancer cell line,we focused on the TCGA Kidney Clear Cell Carcinoma(KIRC)data set35 in our initial analysis.Specifically,we subjected the list of 541 genes(187 BAP1-downregulated and 354 BAP1-upregulated genes with reduced H2Aub occupancies;Fig.1f)to a series of computational analyses
34、,including(1)expression correlation with BAP1 in KIRC,(2)comparison of expression in KIRC and normal kidneys and(3)patient survival prediction in KIRC(Fig.2a).We aimed to identify BAP1-downregulated target genes(1)whose expression is inversely correlated with that of BAP1 in KIRC,(2)that are upregul
35、ated in KIRC compared with normal kidneys,and(3)whose upregulation correlates with shorter patient survival,and vice versa.Such analy-ses identified 20 BAP1-downregulated and 26 BAP1-upregulated genes that satisfied all three criteria,among which SLC7A11 was the only downregulated gene,whereas Shroo
36、m3 and PARD3B were the upregulated genes that showed statistical significance in all three analyses(Supplementary Table 2).Notably,SLC7A11 was among the top genes identified in our RNAseq and H2Aub ChIPseq analyses(Fig.1j and Supplementary Fig.1c),and also among the genes involved in response to oxi
37、dative stress,the most significantly enriched biological process of BAP1-downregulated genes from the GO analysis(Supplementary Table 1).We therefore focused on SLC7A11 in the follow-up studies.As shown in Fig.2b-d,our analyses revealed that SLC7A11 expression inversely correlated with BAP1 expressi
38、on in KIRC,that SLC7A11 exhibited higher expression in KIRC than in normal kidneys,and that higher expression of SLC7A11 predicted shorter survival in KIRC patients.We then extended the same analyses of SLC7A11 to other TCGA data sets.Such analyses revealed that BAP1 expression inversely correlated
39、with SLC7A11 expression not only in KIRC,but also in several other human cancers,including kidney papillary cell carcinoma(KIRP),UVM,pheochromocy-toma and paraganglioma(PCPG)and breast invasive carcinoma(BRCA)3639(Fig.2e).Consistent with this,we observed an inverse correlation between BAP1 and SLC7A
40、11 levels across a panel of cancer cell lines(Fig.2f).Further comparison of the expres-sion levels of SLC7A11 in KIRP,PCPG,BRCA and correspond-ing normal tissues showed that SLC7A11 is upregulated in these cancers(Fig.2g).(Note that there was no normal tissue control for UVM in the TCGA or GTEx data
41、bases,so we were unable to conduct the analysis for UVM.)Correspondingly,BAP1 is mutated/deleted(in UVM,KIRC and KIRP)or downregulated(in PCPG and BRCA)in these tumour types with SLC7A11 high expression (Fig.2h,i).Finally,we showed that,in KIRP and UVM,patients with high SLC7A11 expression had short
42、er overall survival than did patients with low SLC7A11 expression,whereas UVM patients with lower BAP1 expression had significantly shorter overall survival (Fig.2j-l).In KIRP and UVM,the combination of high SLC7A11 and low BAP1 expression predicted even worse clinical outcomes than either parameter
43、 alone(Fig.2m,n).Together,our analyses identified SLC7A11 as one of the most relevant target genes in BAP1-mediated tumour suppression in human cancers,and revealed that BAP1 and SLC7A11 expression levels show an inverse correlation and predict clinical outcomes in human cancers.BAP1 suppresses SLC7
44、A11 expression and reduces H2Aub occupancy on the SLC7A11 promoter.The aforementioned com-putational analyses prompted detailed mechanistic studies on how BAP1 regulates SLC7A11.UMRC6 cells,the BAP1-deficient cell line used in our RNAseq and H2Aub ChIPseq analyses,exhibited high SLC7A11 expression(F
45、ig.2f).We confirmed that NAtuRe CeLL BioLoGY|VOL 20|OCTOBER 2018|11811192| CeLL BioLogyH2AubH2AUMRC6BAP1-actinH2Aub binding profileNormalized occupancy5 kbTSSTES5 kb2345EVWTC91AFold change of normalizedH2Aub occupancyC91A/EVWT/EV0.51.01.5P 1.5,FDR 2.5-fold H2Aub reduction were positively enriched in
46、 BAP1-upregulated genes.h,i,Box plots of log2-fold changes of H2Aub occupancies in promoter and gene body regions for 187 genes(h)and 354 genes(i),as shown in f.j,Left three panels,Heatmaps showing the H2Aub profile around the TSS of 187 downregulated and 354 upregulated genes(f)in EV,BAP1 WT and C9
47、1A cells,in decreasing order.Right panel,Heatmap showing expression levels of the corresponding genes in EV and BAP1 WT cells.k,GO analysis for the 187 downregulated genes.Top annotation clusters are shown according to their enrichment scores(log10(P value).*Positive regulation of glucose import in
48、response to insulin stimulus.Fishers exact test.Box and whisker plots show centre line at median,box limits at 25th/75th centiles and whiskers 1.5 interquartile range(IQR).Unprocessed blots are presented in Supplementary Fig.7.NAtuRe CeLL BioLoGY|VOL 20|OCTOBER 2018|11811192| CeLL BioLogyre-expressi
49、on of BAP1 WT,but not its C91A mutant,in UMRC6 cells decreased SLC7A11 expression(Fig.3a-c),suggesting that BAP1-mediated repression of SLC7A11 expression requires BAP1s DUB activity.Similarly,BAP1 re-expression in NCI-H226 cells,a BAP1-deficient mesothelioma cell line with high SLC7A11 expres-sion(
50、Fig.2f),also repressed SLC7A11 expression(Supplementary Fig.2a,b).Conversely,BAP1 deficiency by CRISPR technology increased SLC7A11 expression in several BAP1-proficient renal cancer cells with low SLC7A11 levels,including 786-O,Caki1 and ACHN cells(Fig.3d,e and Supplementary 2c-f).Importantly,res-t