蛋白质翻译后修饰SUMOylation在肿瘤微环境中的功能作用

目前肿瘤仍然是人类生存中无法克服的一大难题,治疗方案多种多样,但还未找到一种行之有效的方法。随着越来越多的研究发现,人们把治疗肿瘤的目光投向了一种新的领域——肿瘤微环境(tumor microenvironment,TME),指癌细胞周围各种基质细胞的动态和复杂的环境。TME是宿主免疫系统和肿瘤之间的关键交互区域,TME内的细胞相互影响并与癌细胞相互作用以影响癌细胞的侵袭、肿瘤的生长和转移,是治疗癌症的一个全新的方向。在TME复杂的环境中,蛋白质的翻译后修饰(post-translational modification,PTMs)被证明在TME中发挥着重要的作用。PTMs通过调节蛋白质的结构、空间定位和相互作用调控其功能。在PTMs中有一种可逆的翻译后修饰被称为SUMOylation,是通过小泛素样修饰物(small ubiquitin-like modifier,SUMO)靶向赖氨酸残基修饰的翻译后修饰,是细胞过程中普遍存在的调控机制。SUMOylation广泛参与致癌、DNA损伤反应、癌细胞增殖、转移和凋亡,在TME中发挥举足轻重的作用。本综述旨在总结蛋白质的SUMOylation动态修饰对多种免疫细胞的影响,从而探究其在TME中发挥的作用。

Cardiac-targeted PIASy gene silencing mediates deSUMOylation of caveolin-3 and prevents ischemia/reperfusion-induced Na_(v)1.5 downregulation and ventricular arrhythmias

Background:Abnormal myocardial voltage-gated sodium channel 1.5(Nav1.5)expression and function cause lethal ventricular arrhythmias during myocardial ischemia–reperfusion(I/R).Protein inhibitor of activated STAT Y(PIASy)-mediated caveolin-3(Cav-3)small ubiquitin-related modifier(SUMO)modification affects Cav-3 binding to the Nav1.5.PIASy activity is increased after myocardial I/R,but it is unclear whether this is attributable to plasma membrane Nav1.5 downregulation and ventricular arrhythmias.Methods:Using recombinant adeno-associated virus subtype 9(AAV9),rat cardiac PIASy was silenced using intraventricular injection of PIASy short hairpin RNA(shRNA).After two weeks,rat hearts were subjected to I/R and electrocardiography was performed to assess malignant arrhythmias.Tissues from peri-infarct areas of the left ventricle were collected for molecular biological measurements.Results:PIASy was upregulated by I/R(P<0.01),with increased SUMO2/3 modification of Cav-3 and reduced membrane Nav1.5 density(P<0.01).AAV9-PIASy shRNA intraventricular injection into the rat heart down-regulated PIASy after I/R,at both mRNA and protein levels(P<0.05 vs.Scramble-shRNA+I/R group),decreased SUMO-modified Cav-3 levels,enhanced Cav-3 binding to Nav1.5,and prevented I/R-induced decrease of Nav1.5 and Cav-3co-localization in the intercalated disc and lateral membrane.PIASy silencing in rat hearts reduced I/R-induced fatal arrhythmias,which was reflected by a modest decrease in the duration of ventricular fibrillation(VF;P<0.05 vs.Scramble-shRNA+I/R group)and a significantly reduced arrhythmia score(P<0.01 vs.Scramble-shRNA+I/R group).The anti-arrhythmic effects of PIASy silencing were also evidenced by decreased episodes of ventricular tachycardia(VT),sustained VT and VF,especially at the time 5–10 min after ischemia(P<0.05 vs.Scramble-shRNA+IR group).Using in vitro human embryonic kidney 293 T(HEK293T)cells and isolated adult rat cardiomyocyte models exposed to hypoxia/reoxygenation(H/R),we confirmed that increased PIASy promoted Cav-3 modification by SUMO2/3 and Nav1.5/Cav-3 dissociation after H/R.Mutation of SUMO consensus lysine sites in Cav-3(K38R or K144R)altered the membrane expression levels of Nav1.5 and Cav-3 before and after H/R in HEK293T cells.Conclusions:I/R-induced cardiac PIASy activation increased Cav-3 SUMOylation by SUMO2/3 and dysregulated Nav1.5-related ventricular arrhythmias.Cardiac-targeted PIASy silencing mediated Cav-3 deSUMOylation and partially prevented I/R-induced Nav1.5 downregulation in the plasma membrane of cardiomyocytes,and subsequent ventricular arrhythmias in rats.PIASy was identified as a potential therapeutic target for life-threatening arrhythmias in patients with ischemic heart diseases.

大鼠脑缺血中SUMOylation化的特异性蛋白的表达

目的探讨大鼠脑缺血中SUMOylation化的特异性蛋白TIF1β的表达。方法将9只SD大鼠随机分为三组:MCAO脑缺血组(采用线栓法制作MCAO大鼠模型)、正常对照组、假手术组,每组3只。选取大脑中动脉闭塞6 h后的脑缺血大鼠脑组织,取样部位为缺血周边区;正常对照组和假手术组则取相同部位脑组织,采用Western Blot法分别测定三组SUMO2/3、TIF1β蛋白的表达情况。结果 MCAO脑缺血组SUMO2/3、TIF1β表达量显著升高(P<0.01)。结论大鼠脑缺血中TIF1β的SUMO修饰可能参与其病理生理过程。

SUMOylation and deacetylation affect NF-κB p65 activity induced by high glucose in human lens epithelial cells

AIM: To explore the effects of IκBα SUMOylation and NF-κB p65 deacetylation on NF-κB p65 activity induced by high glucose in cultured human lens epithelial cells(HLECs).METHODS: HLECs(SRA01/04) were cultured with 5.5, 25, and 50 mmol/L glucose media for 24 h, and with 50 mmol/L glucose media for 0, 12, and 24 h respectively. SUMO1 and SIRT1 expressions were detected by reverse transcriptionpolymerase chain reaction(RT-PCR) and Western blot(WB). IκBα and NF-κB p65 expressions were detected by WB. With NAC, DTT, MG132 or Resveratrol(RSV) treatment, SUMO1 and SIRT1 expressions were detected by WB. Protein expression localizations were examined by immunofluorescence and co-immunofluorescence. The effects of SUMO1 or SIRT1 overexpression, as well as MG132 and RSV, on the nuclear expression and activity of IκBα and NF-κB p65 were analyzed by immunoblot and dual luciferase reporter gene assay.RESULTS: SUMO1 and SIRT1 expressions were influenced by high glucose in mRNA and protein levels, which could be blocked by NAC or DTT. SUMO1 was down-regulated by using MG132, and SIRT1 was up-regulated under RSV treatment. IκBα nuclear expression was attenuated and NF-κB p65 was opposite under high glucose, while IκBα and NF-κB p65 location was transferred to the nucleus. SUMO1 or SIRT1 overexpression and MG132 or RSV treatment affected the nuclear expression and activity of IκBα and NF-κB p65 under high glucose condition.CONCLUSION: IκBα SUMOylation and NF-κB p65 deacetylation affect NF-κB p65 activity in cultured HLECs under high glucose, and presumably play a significant role in controlling diabetic cataract.

Influence of Sox protein SUMOylation on neural development and regeneration

SRY-related HMG-box(Sox) transcription factors are known to regulate central nervous system development and are involved in several neurological diseases.Post-translational modification of Sox proteins is known to alter their functions in the central nervous system.Among the different types of post-translational modification,small ubiquitin-like modifier(SUMO) modification of Sox proteins has been shown to modify their transcriptional activity.Here,we review the mechanisms of three Sox proteins in neuronal development and disease,along with their transcriptional changes under SUMOylation.Across three species,lysine is the conserved residue for SUMOylation.In Drosophila,SUMOylation of Sox N plays a repressive role in transcriptional activity,which impairs central nervous system development.However,de SUMOylation of Sox E and Sox11 plays neuroprotective roles,which promote neural crest precursor formation in Xenopus and retinal ganglion cell differentiation as well as axon regeneration in the rodent.We further discuss a potential translational therapy by SUMO site modification using AAV gene transduction and Clustered regularly interspaced short palindromic repeats-Cas9 technology.Understanding the underlying mechanisms of Sox SUMOylation,especially in the rodent system,may provide a therapeutic strategy to address issues associated with neuronal development and neurodegeneration.

Function and clinical significance of SUMOylation in type Ⅰ endometrial carcinoma

Objective This study elucidated the function and role of SUMOylation in type Ⅰ endometrial carcinoma.Methods Fifty type Ⅰ endometrial carcinoma cases and para-cancer tissue samples were collected.The expression levels of ubiquitin-conjugating enzyme E2I(Ube2 i,Ubc9) and small ubiquitin-like modifier 1(SUMO1)/sentrin-specific peptidase 1(SENP1) proteins were examined using immunohistochemistry and the correlation with clinicopathological parameters was analyzed.Results Ubc9 expression in type Ⅰ endometrial carcinoma tissues was significantly higher than that in the para-cancer tissues;in contrast,the expression of the SENP1 protein was markedly lower than that in the para-cancer tissues.Ubc9 and SENP1 expression levels were negatively correlated and were associated with tumor differentiation,but not age,depth of invasion,tumor stage,and lymph node metastasis.Conclusion SUMOylation modification plays a major role in the pathogenesis and development of type Ⅰ endometrial carcinoma.Thus,it could be a potential target for the treatment of endometrial cancer.

Drugging SUMOylation for neuroprotection and oncotherapy

Recently there have been exciting research advances in neuroprotective therapies for ischemic stroke. In the past, the search for neu- roprotective agents has been fraught with failure at the clinical trials stage due to numerous factors, including subject heterogeneity and improper therapeutic windows （Tymianski, 2017）. Moreover, it is becoming clearer that the complex and evolving pathobiology of stroke requires multimodal therapeutic approaches capable of modulating the numerous axes that contribute to ischemia/reperfusion damage, rather than targeting a single axis （Bernstock et al., 2018a）. With the success of recent endovascular thrombectomy （EVT） trials, it has been suggested that clinical trials of EVT with adjunct neuroprotection can overcome past difficulties and maximize the effect size by using imaging to reduce patient heterogeneity （i. e., selecting those with large vessel occlusions, small ischemic cores, and good collateral circulation）, restoring perfusion using better EVT devices, and enrolling patients in the correct therapeutic window （i.e., when they still have salvageable brain tissue） （Tymianski, 2017）. Considering the opportunity that this represents for new, better clinical trials of neuroprotective agents, the search is on for high-potential compounds that may be investigated in these future studies.

构建SUMOylation相关基因的结直肠癌患者临床预后模型

目的筛选与SUMOylation过程密切相关的基因,并构建结直肠癌的预后基因表达模型。方法从癌症基因组图谱(The Cancer Genome Atlas,TCGA)数据库中下载与结直肠癌相关的转录组数据和临床资料,结合基因集富集分析(Gene Set Enrichment Analysis,GSEA)数据库,筛选SUMOylation过程中与结直肠癌预后相关的基因。采用单因素COX回归和逐步回归进一步筛选关键基因,构建预后模型,并且计算模型风险评分,即SUMO-score。通过校准曲线和临床决策曲线评价该模型的可行性和准确性。结果筛选获得SUMOylation过程中与结直肠癌预后相关的18个基因,并根据基因签名的风险评分将患者分为高风险组和低风险组。结果显示,高风险组患者的预后显著差于低风险组(P<0.001)。多因素分析表明,SUMO-score可作为结直肠癌的独立预测因素。将SUMO-score与临床病理特征相结合,构建列线图预测模型。校准曲线显示,该模型具有良好的拟合度,提示其具有较高的预测能力。结论本研究构建了一个基于SUMOylation过程相关基因的风险模型,可用于预测结直肠癌预后。

SIZ1-mediated SUMOylation of CPSF100 promotes plant thermomorphogenesis by controlling alternative polyadenylation

Under warm temperatures,plants adjust their morphologies for environmental adaption via precise gene expression regulation.However,the function and regulation of alternative polyadenylation(APA),an important fine-tuning of gene expression,remains unknown in plant thermomorphogenesis.In this study,we found that SUMOylation,a critical post-translational modification,is induced by a long-term treat-ment at warm temperatures via a SUMO ligase SIZ1 in Arabidopsis.Disruption of SIZ1 altered the global usage of polyadenylation signals and affected the APA dynamic of thermomorphogenesis-related genes.CPSF100,a key subunit of the CPSF complex for polyadenylation regulation,is SUMOylated by SIZ1.Importantly,we demonstrated that SUMOylation is essential for the function of CPSF1oo in genome-wide polyadenylation site choice during thermomorphogenesis.Further analyses revealed that the SUMO conjugation on CPSF100 attenuates its interaction with two isoforms of its partner CPSF30,increasing the nuclear accumulation of CPsF1oo for polyadenylation regulation.In summary,our study uncovers a regulatory mechanism of APA via SiZ1-mediated SUMOylation in plant thermomorpho-genesis.

SUMOylation-modified Pelota-Hbs1 RNA surveillance complex restricts the infection of potyvirids in plants

RNA quality control nonsense-mediated decay is involved in viral restriction in both plants and animals.However,it is not known whether two other RNA quality control pathways,nonstop decay and no-go decay,are capable of restricting viruses in plants.Here,we show that the evolutionarily conserved Pelota–Hbs1 complex negatively regulates infection of plant viruses in the family Potyviridae(termed potyvirids),the largest group of plant RNA viruses that accounts for more than half of the viral crop damage worldwide.Pelota enables the recognition of the functional G1-2A6-7 motif in the P3 cistron,which is conserved in almost all potyvirids.This allows Pelota to target the virus and act as a viral restriction factor.Furthermore,Pelota interacts with the SUMO E2-conjugating enzyme SCE1 and is SUMOylated in planta.Blocking Pelota SUMOylation disrupts the ability to recruit Hbs1 and inhibits viral RNA degradation.These findings reveal the functional importance of Pelota SUMOylation during the infection of potyvirids in plants.

SUMOylation facilitates the assembly of a Nuclear Factor-Y complex to enhance thermotolerance in Arabidopsis

Heat stress(HS) has serious negative effects on plant development and has become a major threat to agriculture. A rapid transcriptional regulatory cascade has evolved in plants in response to HS. Nuclear Factor-Y(NF-Y) complexes are critical for this mechanism, but how NF-Y complexes are regulated remains unclear.In this study, we identified NF-YC10(NF-Y subunit C10), a central regulator of the HS response in Arabidopsis thaliana, as a substrate of SUMOylation, an important post-translational modification. Biochemical analysis showed that the SUMO ligase SIZ1(SAP AND MIZ1 DOMAINCONTAINING LIGASE1) interacts with NF-YC10and enhances its SUMOylation during HS. The SUMOylation of NF-YC10 facilitates its interaction with and the nuclear translocation of NF-YB3, in which the SUMO interaction motif(SIM)is essential for its efficient association with NF-YC10. Further functional analysis indicated that the SUMOylation of NF-YC10 and the SIM of NF-YB3 are critical for HS-responsive gene expression and plant thermotolerance. These findings uncover a role for the SIZ1-mediated SUMOylation of NF-YC10 in NF-Y complex assembly under HS, providing new insights into the role of a post-translational modification in regulating transcription during abiotic stress responses in plants.

Downregulation of cardiac PIASy inhibits Cx43 SUMOylation and ameliorates ventricular arrhythmias in a rat model of myocardial ischemia/reperfusion injury

Background:Dysfunction of the gap junction channel protein connexin 43(Cx43)contributes to myocardial ischemia/reperfusion(I/R)-induced ventricular arrhythmias.Cx43 can be regulated by small ubiquitin-like modifier(SUMO)modification.Protein inhibitor of activated STAT Y(PIASy)is an E3 SUMO ligase for its target proteins.However,whether Cx43 is a target protein of PIASy and whether Cx43 SUMOylation plays a role in I/R-induced arrhythmias are largely unknown.Methods:Male Sprague-Dawley rats were infected with PIASy short hairpin ribonucleic acid(shRNA)using recombinant adeno-associated virus subtype 9(rAAV9).Two weeks later,the rats were subjected to 45 min of left coronary artery occlusion followed by 2 h reperfusion.Electrocardiogram was recorded to assess arrhythmias.Rat ventricular tissues were collected for molecular biological measurements.Results:Following 45 min of ischemia,QRS duration and QTc intervals statistically significantly increased,but these values decreased after transfecting PIASy shRNA.PIASy downregulation ameliorated ventricular arrhythmias induced by myocardial I/R,as evidenced by the decreased incidence of ventricular tachycardia and ventricular fibrillation,and reduced arrythmia score.In addition,myocardial I/R statistically significantly induced PIASy expression and Cx43 SUMOylation,accompanied by reduced Cx43 phosphorylation and plakophilin 2(PKP2)expression.Moreover,PIASy downregulation remarkably reduced Cx43 SUMOylation,accompanied by increased Cx43 phosphorylation and PKP2 expression after I/R.Conclusion:PIASy downregulation inhibited Cx43 SUMOylation and increased PKP2 expression,thereby improving ventricular arrhythmias in ischemic/reperfused rats heart.

MYC promotes global transcription in part by controlling P-TEFb complex formation via DNA-binding independent inhibition of CDK9 SUMOylation

MYC is an oncogenic transcription factor with a novel role in enhancing global transcription when overexpressed. However, how MYC promotes global transcription remains controversial. Here, we used a series of MYC mutants to dissect the molecular basis for MYC-driven global transcription. We found that MYC mutants deficient in DNA binding or known transcriptional activation activities can still promote global transcription and enhance serine 2 phosphorylation(Ser2P) of the RNA polymerase(Pol) II Cterminal domain(CTD), a hallmark of active elongating RNA Pol II. Two distinct regions within MYC can promote global transcription and Ser2P of Pol II CTD. The ability of various MYC mutants to promote global transcription and Ser2P correlates with their ability to suppress CDK9 SUMOylation and enhance positive transcription elongation factor b(P-TEFb) complex formation. We showed that MYC suppresses CDK9 SUMOylation by inhibiting the interaction between CDK9 and SUMO enzymes including UBC9 and PIAS1. Furthermore, MYC's activity in enhancing global transcription positively contributes to its activity in promoting cell proliferation and transformation. Together, our study demonstrates that MYC promotes global transcription, at least in part, by promoting the formation of the active P-TEFb complex via a sequence-specific DNA-binding activity-independent manner.

Cellular gp96 upregulates AFP expression by blocking NR5A2 SUMOylation and ubiquitination in hepatocellular carcinoma

Alpha-fetoprotein (AFP) is the most widely used biomarker for the diagnosis of hepatocellular carcinoma (HCC). However, asubstantial proportion of HCC patients have either normal or marginally increased AFP levels in serum, and the underlyingmechanisms are not fully understood. In the present study, we provided in vitro and in vivo evidence that heat shock protein gp96promoted AFP expression at the transcriptional level in HCC. NR5A2 was identified as a key transcription factor for the AFP gene, andits stability was enhanced by gp96. A further mechanistic study by co-immunoprecipitation, GST pull-down, and molecular dockingshowed gp96 and the SUMO E3 ligase RanBP2 competitively binding to NR5A2 at the sites spanning from aa 507 to aa 539. Thebinding of gp96 inhibited SUMOylation, ubiquitination, and subsequent degradation of NR5A2. In addition, clinical analysis of HCCpatients indicated that gp96 expression in tumors was positively correlated with serum AFP levels. Therefore, our study uncovered anovel mechanism that gp96 regulates the stability of its client proteins by directly affecting their SUMOylation and ubiquitination.These findings will help in designing more accurate AFP-based HCC diagnosis and progression monitoring approaches.

Sortilin-induced lipid accumulation and atherogenesis are suppressed by HNF1b SUMOylation promoted by flavone of Polygonatum odoratum

This study aims to investigate the impact of hepatocyte nuclear factor 1β(HNF1b)on macrophage sortilin-mediated lipid metabolism and aortic atherosclerosis and explore the role of the flavone of Polygonatum odoratum(PAOA-flavone)-promoted small ubiquitin-related modifier(SUMO)modification in the atheroprotective efficacy of HNF1b.HNF1b was predicted to be a transcriptional regulator of sortilin expression via bioinformatics,dual-luciferase reporter gene assay,and chromatin immunoprecipitation.HNF1b overexpression decreased sortilin expression and cellular lipid contents in THP-1 macrophages,leading to a depression in atherosclerotic plaque formation in low-density lipoprotein(LDL)receptor-deficient(LDLR−/−)mice.Multiple SUMO1-modified sites were identified on the HNF1b protein and co-immunoprecipitation confirmed its SUMO1 modification.The SUMOylation of HNF1b protein enhanced the HNF1b-inhibited effect on sortilin expression and reduced lipid contents in macrophages.PAOA-flavone treatment promoted SUMO-activating enzyme subunit 1(SAE1)expression and SAE1-catalyzed SUMOylation of the HNF1b protein,which prevented sortilin-mediated lipid accumulation in macrophages and the formation of atherosclerotic plaques in apolipoprotein E-deficient(ApoE−/−)mice.Interference with SAE1 abrogated the improvement in lipid metabolism in macrophage cells and atheroprotective efficacy in vivo upon PAOA-flavone administration.In summary,HNF1b transcriptionally suppressed sortilin expression and macrophage lipid accumulation to inhibit aortic lipid deposition and the development of atherosclerosis.This anti-atherosclerotic effect was enhanced by PAOA-flavone-facilitated,SAE1-catalyzed SUMOylation of the HNF1b protein.

Sumoylation of hypoxia inducible factor-1α and its significance in cancer

Hypoxia-inducible factor-1(HIF-1)is a key heterodimeric transcription factor for the cellular adaptive response to hypoxia,a common feature of the microenvironment in solid tumors.The transcriptional activity,protein stabilization,protein-protein interactions and cellular localization of HIF-1α,an oxygen-sensitive subunit of HIF-1,are mainly modulated by various post-translational modifications.Recently,we reported that polycomb chromobox 4(Cbx4)governs the transcriptional activity of HIF-1αby enhancing its sumoylation at K391 and K477,through which Cbx4 potentiates angiogenesis of hepatocellular carcinoma.This review summarizes the current knowledge of HIF-1α sumoylation and its roles in the pathogenesis of cancer.

SUMOylation of RIG-I positively regulates the type I interferon signaling

Retinoic acid-inducible gene-I(RIG-I)functions as an intracellular pattern recognition receptor(PRR)that recognizes the 5'-triphosphate moiety of single-stranded RNA viruses to initiate the innate immune response.Previous studies have shown that Lys63-linked ubiquitylation is required for RIG-I activation and the downstream anti-viral type I interferon(IFN-I)induction.Herein we reported that,RIG-I was also modified by small ubiquitin-like modifier-1(SUMO-1).Functional analysis showed that RIG-I SUMOylation enhanced IFN-I production through increased ubiquitylation and the interaction with its downstream adaptor molecule Cardif.Our results therefore suggested that SUMOylation might serve as an additional regulatory tier for RIG-I activation and IFN-I signaling.

Writing and erasing MYC ubiquitination and SUMOylation

The transcription factor c-MYC(MYC thereafter)controls diverse transcription programs and plays a key role in the development of many human cancers.Cells develop multiple mechanisms to ensure that MYC levels and activity are precisely controlled in normal physiological context.As a short half-lived protein,MYC protein levels are tightly regulated by the ubiquitin proteasome system.Over a dozen of ubiquitin ligases have been found to ubiquitinate MYC whereas a number of deubiquitinating enzymes counteract this process.Recent studies show that SUMOylation and deSUMOylation can also regulate MYC protein stability and activity.Interestingly,evidence suggests an intriguing crosstalk between MYC ubiquitination and SUMOylation.Deregulation of the MYC ubiquitination-SUMOylation regulatory network may contribute to tumorigenesis.This review is intended to provide the current understanding of the complex regulation of the MYC biology by dynamic ubiquitination and SUMOylation and their crosstalk.

A CK2-RNF4 interplay coordinates non-canonical SUMOylation and degradation of nuclear receptor FXR

Farnesoid X receptor （FXR） is a ligand-activated nuclear receptor that plays a central role in regulating genes involved in bile acid homeostasis, and fat and glucose metabolism. Here, we demonstrate a post-translational interplay between FXR phosphoryl- ation, SUMOylation, and ubiquitination that directs the receptor into an activation-degradation pathway in hepatocytes. We iden- tify a non-canonical SUMOylation motif termed pSuM that conjugates SUM02 at Lys-325 of FXR under the direct control of casein kinase 2 （CK2）, which provides the required negative charge for Ubc9 and PIAS1 to perform SUMOylation, by phosphorylating Ser-327. Lys-325 SUMOylation is indispensable to the promotion of efficient ligand activation and transcriptional coactivation of FXR. Constitutive pSuM activation using a phospho-mimic Ser-327 mutant or catalytic CK2 expression strongly induces SUM02 conjugation, which directs FXR ubiquitination and proteasome-dependent degradation. We also determine that such SUMOylation-dependent ubiquitination of FXR is mediated by the E3 ubiquitin ligase RNF4, which is required to achieve maximal induction of FXR and optimal up- or downregulation of responsive genes involved in bile acid homeostasis and liver regeneration. Our findings identify a highly regulated atypical SUMO conjugation motif that serves to coordinate FXR transcriptional compe- tence, thereby expanding the intricate dynamics of the SUMOylation process used by incoming signals to govern metabolic gene regulation.

Chromatin-associated SUMOylation controls the transcriptional switch between plant development and heat stress responses

The post-translational protein modification known as SUMOylation has conserved roles in the heat stress responses of various species.The functional connection between the global regulation of gene expression and chromatin-associatedSUMOylation in plant cells isunknown.Here,weuncovereda genome-wide relationship between chromatin-associated SUMOylation and transcriptional switches in Arabidopsis thaliana grown at room temperature,exposed to heat stress,and exposed to heat stress followed by recovery.The small ubiquitin-like modifier(SUMO)-associated chromatin sites,characterized by whole-genome ChIP-seq,were generally associated with active chromatin markers.In response to heat stress,chromatin-associated SUMO signals increased at promoter-transcriptional start site regions and decreased in gene bodies.RNAseq analysis supported the role of chromatin-associatedSUMOylation in transcriptional activation during rapid responses to high temperature.Changes inSUMOsignals on chromatinwere associated with the upregulation of heat-responsivegenesandthedownregulation ofgrowth-relatedgenes.Disruption of theSUMOligasegene SIZ1 abolished SUMOsignals on chromatin and attenuated rapid transcriptional responses to heat stress.The SUMO signal peaks were enriched in DNA elements recognized by distinct groups of transcription factors under different temperature conditions.These observations provide evidence that chromatin-associated SUMOylation regulates the transcriptional switch between development and heat stress response in plant cells.