SUMO wrestling with type 1 diabetes

Exploring potential targets for natural product therapy of DN: the role of SUMOylation

Diabetic nephropathy (DN) is a common and serious micro-vascular complication of diabetes and a leading cause of end-stage renal disease globally. This disease primarily affects middle-aged and elderly individuals, especially those with a diabetes history of over 10 years and poor long-term blood glucose control. Small ubiquitin-related modifiers (SUMOs) are a group of reversible post-translational modifications of proteins that are widely expressed in eukaryotes. SUMO proteins intervene in the progression of DN by modulating various signaling cascades, such as Nrf2-mediated oxidative stress, NF-κB, TGF-β, and MAPK pathways. Recent advancements indicate that natural products regulating SUMOylation hold promise as targets for intervening in DN. In a previous article published in 2022, we reviewed the mechanisms by which SUMOylation intervenes in renal fibrosis and presented a summary of some natural products with therapeutic potential. Therefore, this paper will focus on DN. The aim of this review is to elucidate the mechanism of action of SUMOylation in DN and related natural products with therapeutic potential, thereby summarising the targets and candidate natural products for the treatment of DN through the modulation of SUMOylation, such as ginkgolic acid, ginkgolide B, resveratrol, astragaloside IV, etc., and highlighting that natural product-mediated modulation of SUMOylation is a potential therapeutic strategy for the treatment of DN as a potential therapeutic strategy.

Ubiquitin-conjugating enzyme E2 for regulating autophagy in diabetic cardiomyopathy: A mini-review

The prevalence of diabetic cardiomyopathy (DCM) increases year by year with the increase in the prevalence of diabetes mellitus (DM), which is one of the most serious cardiovascular complications of DM and a major cause of death in diabetic patients. Although the pathological molecular features of DCM have not been fully elucidated, increasing evidence suggests that impaired autophagy in cardiomyocytes plays a nonnegligible role in the development of DCM. It has been shown that SUMOylation [SUMO = small ubiquitin-like modifier], a post-translational modification of proteins, and its associated ubiquitin-proteasome system mediates protein quality control in the heart and plays an important role in the proteotoxic environment of the heart. Specifically, the expression of ubiquitin-conjugating enzyme E2 (Ubc9), the only SUMO-E2 enzyme, exerts a positive regulatory effect on autophagy in cardiomyocytes with potential cardioprotective effects. This review focuses on the role that autophagy plays in DCM and the potential for Ubc9-regulated autophagy pathways to ameliorate DCM, highlighting the potential of Ubc9 as an interventional target in DCM and providing new insights into the pathogenesis of the disease.

Regulation of insulin secretion by the post-translational modifications

Post-translational modification (PTM) has a significant impact on cellular signaling and function regulation. In pancreatic β cells, PTMs are involved in insulin secretion, cell development, and viability. The dysregulation of PTM in β cells is clinically associated with the development of diabetes mellitus. Here, we summarized current findings on major PTMs occurring in β cells and their roles in insulin secretion. Our work provides comprehensive insight into understanding the mechanisms of insulin secretion and potential therapeutic targets for diabetes from the perspective of protein PTMs.

SUMOylation of ERp44 enhances Ero1α ER retention contributing to the pathogenesis of obesity and insulin resistance

OBJECTIVE

As the only E2 conjugating enzyme for the SUMO system, Ubc9-mediated SUMOylation has been recognized to regulate diverse biological processes, but its impact on adipocytes relevant to obesity and insulin resistance is yet to be elucidated.

METHODS

We established adipocyte-specific Ubc9 deficient mice to explore the effects of Ubc9 on obesity and metabolic disorders induced by high-fat diet (HFD) in adult mice. The molecular targets of SUMOylation were explored by liquid chromatography-mass spectrometry, and the regulatory mechanism of SUMOylation in T2D was analyzed.

RESULTS

Adipocyte-specific depletion of Ubc9 (AdipoQ-Cre-Ubc9^fl/fl, Ubc9^AKO) protected mice from HFD-induced obesity, insulin resistance, and hepatosteatosis. The Ubc9^AKO mice were featured by the reduced HFD-induced endoplasmic reticulum (ER) stress and inflammatory response. Mechanically, over nutrition rendered adipocytes to undergo a SUMOylation turnover characterized by the change of SUMOylation levels and substrates. ERp44 displayed the highest change in terms of SUMOylation levels of substrates involved in ER-related functions. The lack of ERp44 SUMOylation at lysine 76 (K76) located within the thioredoxin (TRX)-like domain by Ubc9 deficiency enhanced its degradation and suppressed its covalent binding to Ero1α, an oxidase that exists in the ER but lacks ER retention motif, thereby alleviating endoplasmic reticulum stress by promoting Ero1α secretion.

CONCLUSIONS

Our data suggest that modulation of ERp44 SUMOylation in adipocytes could be a feasible strategy against obesity and insulin resistance in clinical settings.

Small-molecule inhibitors targeting small ubiquitin-like modifier pathway for the treatment of cancers and other diseases

SUMOylation is a key post-translational modification that involves the covalent attachment of small ubiquitin-like modifier (SUMO) to the lysine residues of target proteins. The well-balanced SUMOylation is essential for normal cellular behaviors, while disturbance of SUMOylation is associated with various cancers and other diseases. Herein, we summarize the structures and biological functions of proteins involved in the SUMOylation process, their dysregulation in human diseases, and the discovery of small-molecular inhibitors targeting this pathway. In addition, we highlight the emerging trends in this field.

SUMO1 Deficiency Exacerbates Neurological and Cardiac Dysfunction after Intracerebral Hemorrhage in Aged Mice

Small ubiquitin-like modifier 1 (SUMO1) reduces cardiac hypertrophy and induces neuroprotective effects. Previous studies have found that intracerebral hemorrhage (ICH) provokes cardiac deficit in the absence of primary cardiac diseases in mice. In this study, we tested the hypothesis that SUMO1 deficiency leads to worse brain and heart dysfunction after ICH and SUMO1 plays a key role in regulating brain-heart interaction after ICH in aged mice. Aged (18-20 months) female SUMO1 null (SUMO1-/-) mice and wild-type (WT) C57BL/6 J mice were randomly divided into four groups (n = 8/group): (1) WT-sham group, (2) SUMO1-/--sham group, (3) WT-ICH group, and (4) SUMO1-/--ICH group. Cardiac function was measured by echocardiography. Neurological and cognitive functional tests were performed. Mice were sacrificed at 10 days after ICH for histological and immunohistochemically staining. Compared with WT-sham mice, WT-ICH mice exhibited (1) significantly (P < 0.05) decreased SUMO1 expression in heart tissue, (2) evident neurological and cognitive dysfunction as well as brain white matter deficits, (3) significantly increased cardiac dysfunction, and (4) inflammatory factor expression in the heart and brain. Compared with WT-ICH mice, SUMO1-/--ICH mice exhibited significantly increased: (1) brain hemorrhage volume, worse neurological and cognitive deficits, and increased white matter deficits; (2) cardiac dysfunction and cardiac fibrosis; (3) inflammatory response both in heart and brain tissue. Aged SUMO1-deficient female mice subjected to ICH not only exhibit increased neurological and cognitive functional deficit but also significantly increased cardiac dysfunction and inflammatory cell infiltration into the heart and brain. These data suggest that SUMO1 plays an important role in brain-heart interaction.

Reduction of Glut1 in the Neural Retina But Not the RPE Alleviates Polyol Accumulation and Normalizes Early Characteristics of Diabetic Retinopathy

Hyperglycemia is a key determinant for development of diabetic retinopathy (DR). Inadequate glycemic control exacerbates retinopathy, while normalization of glucose levels delays its progression. In hyperglycemia, hexokinase is saturated and excess glucose is metabolized to sorbitol by aldose reductase via the polyol pathway. Therapies to reduce retinal polyol accumulation for the prevention of DR have been elusive because of low sorbitol dehydrogenase levels in the retina and inadequate inhibition of aldose reductase. Using systemic and conditional genetic inactivation, we targeted the primary facilitative glucose transporter in the retina, Glut1, as a preventative therapeutic in diabetic male and female mice. Unlike WT diabetics, diabetic Glut1 ^+/- mice did not display elevated Glut1 levels in the retina. Furthermore, diabetic Glut1 ^+/- mice exhibited ameliorated ERG defects, inflammation, and oxidative stress, which was correlated with a significant reduction in retinal sorbitol accumulation. Retinal pigment epithelium-specific reduction of Glut1 did not prevent an increase in retinal sorbitol content or early hallmarks of DR. However, like diabetic Glut1 ^+/- mice, reduction of Glut1 specifically in the retina mitigated polyol accumulation and diminished retinal dysfunction and the elevation of markers for oxidative stress and inflammation associated with diabetes. These results suggest that modulation of retinal polyol accumulation via Glut1 in photoreceptors can circumvent the difficulties in regulating systemic glucose metabolism and be exploited to prevent DR.SIGNIFICANCE STATEMENT Diabetic retinopathy affects one-third of diabetic patients and is the primary cause of vision loss in adults 20-74 years of age. While anti-VEGF and photocoagulation treatments for the late-stage vision threatening complications can prevent vision loss, a significant proportion of patients do not respond to anti-VEGF therapies, and mechanisms to stop progression of early-stage symptoms remain elusive. Glut1 is the primary facilitative glucose transporter for the retina. We determined that a moderate reduction in Glut1 levels, specifically in the retina, but not the retinal pigment epithelium, was sufficient to prevent retinal polyol accumulation and the earliest functional defects to be identified in the diabetic retina. Our study defines modulation of Glut1 in retinal neurons as a targetable molecule for prevention of diabetic retinopathy.

SUMOylation of Enzymes and Ion Channels in Sensory Neurons Protects against Metabolic Dysfunction, Neuropathy, and Sensory Loss in Diabetes

Diabetic peripheral neuropathy (DPN) is a highly frequent and debilitating clinical complication of diabetes that lacks therapies. Cellular oxidative stress regulates post-translational modifications, including SUMOylation. Here, using unbiased screens, we identified key enzymes in metabolic pathways and ion channels as novel molecular targets of SUMOylation that critically regulated their activity. Sensory neurons of diabetic patients and diabetic mice demonstrated changes in the SUMOylation status of metabolic enzymes and ion channels. In support of this, profound metabolic dysfunction, accelerated neuropathology, and sensory loss were observed in diabetic gene-targeted mice selectively lacking the ability to SUMOylate proteins in peripheral sensory neurons. TRPV1 function was impaired by diabetes-induced de-SUMOylation as well as by metabolic imbalance elicited by de-SUMOylation of metabolic enzymes, facilitating diabetic sensory loss. Our results unexpectedly uncover an endogenous post-translational mechanism regulating diabetic neuropathy in patients and mouse models that protects against metabolic dysfunction, nerve damage, and altered sensory perception.

SUMOylation, a multifaceted regulatory mechanism in the pancreatic beta cells

SUMOylation is an evolutionarily conserved post-translational modification (PTM) that regulates protein subcellular localization, stability, conformation, transcription and enzymatic activity. Recent studies indicate that SUMOylation plays a key role in insulin gene expression, glucose metabolism and insulin exocytosis under physiological conditions in the pancreatic beta cells. Furthermore, SUMOylation is implicated in beta cell survival and recovery following exposure to oxidative stress, ER stress and inflammatory mediators under pathological situations. SUMOylation is closely regulated by the cellular redox status, and it collaborates with other PTMs such as phosphorylation, ubiquitination, and NEDDylation, to maintain beta cellular homeostasis. We hereby provide an update on recent findings regarding the role of SUMOylation in the regulation of pancreatic beta cell viability and function, and discuss its potential implication in beta cell senescence and RNA processing (e.g., pre-mRNA splicing and mRNA methylation). Through which we intend to provide novel insights into this fundamental biological process regarding both maintenance of beta cell viability and functionality, and beta cell dysfunction in diabetes mellitus.

Loss of ubiquitin-conjugating enzyme E2 (Ubc9) in macrophages exacerbates multiple low-dose streptozotocin-induced diabetes by attenuating M2 macrophage polarization

Type 1 diabetes (T1D) is characterized by the selective autoimmune destruction of the islet β cells, and macrophages play a significant role in this process. Small ubiquitin-like modification (SUMOylation) is an important posttranslational modification involved in T1D pathogenesis, but its function in macrophages remains unexplored. We presently developed and used macrophage-specific ubiquitin-conjugating enzyme E2 (Ubc9) knockout (LyzM-Cre-Ubc9^fl/fl, KO) mice to address the impact of SUMOylation on macrophage function in a T1D model. We observed that blocking Ubc9 in macrophages exacerbated multiple-low dose streptozotocin (MLD-STZ)-induced diabetes. Specifically, after STZ treatment, blood glucose levels were consistently elevated in the KO mice. The KO mice exhibited a higher diabetes incidence than WT controls (85% vs. 55%, P < 0.01) along with a higher insulitis severity. The loss of Ubc9 impaired macrophage energy metabolism and attenuated macrophage M2 program, thereby enhancing T cell activation. Pancreas-resident macrophages, rather than migrant macrophages, played a predominant role in MLD-STZ-induced diabetes. Mechanistically, Ubc9-mediated SUMOylation of interferon regulator factor 4 (IRF4) enhanced its nuclear localization and stability, thereby transcribing IL-4 and arginase 1 (Arg1) to promote the macrophage M2 program. Ubc9-mediated SUMOylation modulates T1D risk at least in part by regulating macrophage function. Modulation of disturbed SUMOylation process in macrophages, either through cell adoptive transfer or targeted drug-delivery, could help to establish a tolerant pancreatic microenvironment and promote inflammation resolution in early insulitis stage, thus hindering T1D progression.

HseSUMO: Sumoylation site prediction using half-sphere exposures of amino acids residues

Background

Post-translational modifications are viewed as an important mechanism for controlling protein function and are believed to be involved in multiple important diseases. However, their profiling using laboratory-based techniques remain challenging. Therefore, making the development of accurate computational methods to predict post-translational modifications is particularly important for making progress in this area of research.

Results

This work explores the use of four half-sphere exposure-based features for computational prediction of sumoylation sites. Unlike most of the previously proposed approaches, which focused on patterns of amino acid co-occurrence, we were able to demonstrate that protein structural based features could be sufficiently informative to achieve good predictive performance. The evaluation of our method has demonstrated high sensitivity (0.9), accuracy (0.89) and Matthew’s correlation coefficient (0.78–0.79). We have compared these results to the recently released pSumo-CD method and were able to demonstrate better performance of our method on the same evaluation dataset.

Conclusions

The proposed predictor HseSUMO uses half-sphere exposures of amino acids to predict sumoylation sites. It has shown promising results on a benchmark dataset when compared with the state-of-the-art method.

The extracted data of this study can be accessed at https://github.com/YosvanyLopez/HseSUMO.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5206-8) contains supplementary material, which is available to authorized users.

SumSec: Accurate Prediction of Sumoylation Sites Using Predicted Secondary Structure

Post Translational Modification (PTM) is defined as the modification of amino acids along the protein sequences after the translation process. These modifications significantly impact on the functioning of proteins. Therefore, having a comprehensive understanding of the underlying mechanism of PTMs turns out to be critical in studying the biological roles of proteins. Among a wide range of PTMs, sumoylation is one of the most important modifications due to its known cellular functions which include transcriptional regulation, protein stability, and protein subcellular localization. Despite its importance, determining sumoylation sites via experimental methods is time-consuming and costly. This has led to a great demand for the development of fast computational methods able to accurately determine sumoylation sites in proteins. In this study, we present a new machine learning-based method for predicting sumoylation sites called SumSec. To do this, we employed the predicted secondary structure of amino acids to extract two types of structural features from neighboring amino acids along the protein sequence which has never been used for this task. As a result, our proposed method is able to enhance the sumoylation site prediction task, outperforming previously proposed methods in the literature. SumSec demonstrated high sensitivity (0.91), accuracy (0.94) and MCC (0.88). The prediction accuracy achieved in this study is 21% better than those reported in previous studies. The script and extracted features are publicly available at: https://github.com/YosvanyLopez/SumSec.

Both conditional ablation and overexpression of E2 SUMO-conjugating enzyme (UBC9) in mouse pancreatic beta cells result in impaired beta cell function

AIMS/HYPOTHESIS

Post-translational attachment of a small ubiquitin-like modifier (SUMO) to the lysine (K) residue(s) of target proteins (SUMOylation) is an evolutionary conserved regulatory mechanism. This modification has previously been demonstrated to be implicated in the control of a remarkably versatile regulatory mechanism of cellular processes. However, the exact regulatory role and biological actions of the E2 SUMO-conjugating enzyme (UBC9)-mediated SUMOylation function in pancreatic beta cells has remained elusive.

METHODS

Inducible beta cell-specific Ubc9 (also known as Ube2i) knockout (KO; Ubc9^Δbeta) and transgenic (Ubc9^Tg) mice were employed to address the impact of SUMOylation on beta cell viability and functionality. Ubc9 deficiency or overexpression was induced at 8 weeks of age using tamoxifen. To study the mechanism involved, we closely examined the regulation of the transcription factor nuclear factor erythroid 2-related factor 2 (NRF2) through SUMOylation in beta cells.

RESULTS

Upon induction of Ubc9 deficiency, Ubc9^Δbeta islets exhibited a 3.5-fold higher accumulation of reactive oxygen species (ROS) than Ubc9^f/f control islets. Islets from Ubc9^Δbeta mice also had decreased insulin content and loss of beta cell mass after tamoxifen treatment. Specifically, at day 45 after Ubc9 deletion only 40% of beta cell mass remained in Ubc9^Δbeta mice, while 90% of beta cell mass was lost by day 75. Diabetes onset was noted in some Ubc9^Δbeta mice 8 weeks after induction of Ubc9 deficiency and all mice developed diabetes by 10 weeks following tamoxifen treatment. In contrast, Ubc9^Tg beta cells displayed an increased antioxidant ability but impaired insulin secretion. Unlike Ubc9^Δbeta mice, which spontaneously developed diabetes, Ubc9^Tg mice preserved normal non-fasting blood glucose levels without developing diabetes. It was noted that SUMOylation of NRF2 promoted its nuclear expression along with enhanced transcriptional activity, thereby preventing ROS accumulation in beta cells.

CONCLUSIONS/INTERPRETATION

SUMOylation function is required to protect against oxidative stress in beta cells; this mechanism is, at least in part, carried out by the regulation of NRF2 activity to enhance ROS detoxification. Homeostatic SUMOylation is also likely to be essential for maintaining beta cell functionality.

The strategies for identification and quantification of SUMOylation

SUMOylation is a post-translational modification that plays critical roles in a multitude of cellular processes including transcription, cellular localization, DNA repair and cell cycle progression. Similar to ubiquitin, the small ubiquitin-like modifiers (SUMOs) are covalently attached to the epsilon amino group of lysine residues in the substrates. To understand the regulation and the dynamics of post-translational modifications (PTMs), the identification and quantification of SUMOylation is strictly needed. Although numerous proteomic approaches have been developed to identify hundreds of SUMO target proteins, the number of SUMOylation signatures identified from endogenous modified proteins is limited, and the identification of precise acceptor sites remains a challenge due to the low abundance of in vivo SUMO-modified proteins and the high activity of SUMO-specific proteases in cell lysates. In particular, very few sensitive strategies are available for accurate quantification of SUMO target proteins. Within the past decade, mass spectrometry-based strategies have been the most popular technologies for proteome-wide studies of SUMOylation. Recently, some new approaches such as single-molecule detection have been introduced. In this review, we summarize the strategies that have been exploited for enrichment, purification and identification of SUMOylation substrates and acceptor sites as well as ultrasensitive quantification of SUMOylation. We highlight the emerging trends in this field as well.

Fine tuning of vitamin D receptor (VDR) activity by post-transcriptional and post-translational modifications

Vitamin D receptor (VDR) is a member of the nuclear receptor (NR) superfamily of ligand-activated transcription factors. Activated VDR is responsible for maintaining calcium and phosphate homeostasis, and is required for proper cellular growth, cell differentiation and apoptosis. The expression of both phases I and II drug-metabolizing enzymes is also regulated by VDR, therefore it is clinically important.

Post-translational modifications of NRs have been known as an important mechanism modulating the activity of NRs and their ability to drive the expression of target genes. The aim of this mini review is to summarize the current knowledge about post-transcriptional and post-translational modifications of VDR.

Predicting protein lysine phosphoglycerylation sites by hybridizing many sequence based features

Post-translational modification (PTM) is essential for many biological processes. Covalent and generally enzymatic modification of proteins can impact the activity of proteins. Modified proteins would have more complex structures and functions. Knowing whether a specific residue is modified or not is significant to unravel the function and structure of this protein. As experimental approaches to discover protein PTM sites are always costly and time consuming, computational prediction methods are desirable alternative methods. Lysine phosphoglycerylation is a type of newly discovered PTM that is related to glycolytic process and glucose metabolism. Since the lysine phosphoglycerylation process requires no catalytic enzyme, its site selectivity mechanism is still not fully understood. In this study, we designed a novel computational method, namely PhoglyPred, to identify lysine phosphoglycerylation sites. By utilizing several different protein sequence descriptors, PhoglyPred achieved an overall accuracy of 90.3% in a Jackknife test, which is better than other state-of-the-art predictors. By analyzing the importance of different features using the F-score, we found several important sequence features, which may benefit future studies in understanding the site selectivity mechanism of lysine phosphoglycerylation.

SUMO1/UBC9‑decreased Nox1 activity inhibits reactive oxygen species generation and apoptosis in diabetic retinopathy

Diabetic retinopathy (DR) is an increasing global health concern that causes vision loss and blindness. Reactive oxygen species (ROS) are considered to be a principal cause of DR. An important source of ROS is the oxidization of NADPH. In the present study, NADPH oxidase 1 (Nox1)-expressing human retinal epithelial cell (HREC) lines were generated and infected with small ubiquitin-like modifier 1 (SUMO1) and/or ubiquitin conjugating enzyme E2 I (UBC9) lentiviral pGMLV constructs. The viabilities, apoptotic capacities and ROS production levels of the HREC lines were quantified using Hoechst 33258, annexin V/propidium iodide and dichlorodihydrofluorescein diacetate assays, respectively. Additionally, rat DR models were established. From these models, the apoptotic capacities of retinal tissues were visualized using terminal deoxynucleotidyl transferase dUTP nick end labeling assays, and the pathologies were evaluated. The mRNA and protein expression levels of SUMO1, UBC9 and Nox1 were analyzed using reverse transcription-quantitative polymerase chain reaction and western blot analyses, respectively. Compared with controls, the relative mRNA levels of SUMO1 and UBC9 were significantly upregulated, and the Nox1 levels significantly downregulated, in cells infected with SUMO1 or UBC9 alone or in combination. The ROS production and apoptosis rates of cells and retinal tissues were decreased. In addition, pathological symptoms in DR tissues improved when they were simultaneously transfected with SUMO1 and UBC9 via intraocular injection. In conclusion, the SUMO1/UBC9 axis may regulate Nox1-mediated DR by inhibiting ROS generation and apoptosis in rat and cellular model systems.

The Roles of SUMO in Metabolic Regulation

Protein modification with the small ubiquitin-related modifier (SUMO) can affect protein function, enzyme activity, protein-protein interactions, protein stability, protein targeting and cellular localization. SUMO influences the function and regulation of metabolic enzymes within pathways, and in some cases targets entire metabolic pathways by affecting the activity of transcription factors or by facilitating the translocation of entire metabolic pathways to subcellular compartments. SUMO modification is also a key component of nutrient- and metabolic-sensing mechanisms that regulate cellular metabolism. In addition to its established roles in maintaining metabolic homeostasis, there is increasing evidence that SUMO is a key factor in facilitating cellular stress responses through the regulation and/or adaptation of the most fundamental metabolic processes, including energy and nucleotide metabolism. This review focuses on the role of SUMO in cellular metabolism and metabolic disease.

Cross-talk between sumoylation and phosphorylation in mouse spermatocytes

The meiotic G2/M1 transition is mostly regulated by posttranslational modifications, however, the cross-talk between different posttranslational modifications is not well-understood, especially in spermatocytes. Sumoylation has emerged as a critical regulatory event in several developmental processes, including reproduction. In mouse oocytes, inhibition of sumoylation caused various meiotic defects and led to aneuploidy. However, the role of sumoylation in male reproduction has only begun to be elucidated. Given the important role of several SUMO targets (including kinases) in meiosis, in this study, the role of sumoylation was addressed by monitoring the G2/M1 transition in pachytene spermatocytes in vitro upon inhibition of sumoylation. Furthermore, to better understand the cross-talk between sumoylation and phosphorylation, the activity of several kinases implicated in meiotic progression was also assessed upon down-regulation of sumoylation. The results of the analysis demonstrate that inhibition of sumoylation with ginkgolic acid (GA) arrests the G2/M1 transition in mouse spermatocytes preventing chromosome condensation and disassembling of the synaptonemal complex. Our results revealed that the activity of PLK1 and the Aurora kinases increased during the G2/M1 meiotic transition, but was negatively regulated by the inhibition of sumoylation. In the same experiment, the activity of c-Abl, the ERKs, and AKT were not affected or increased after GA treatment. Both the AURKs and PLK1 appear to be "at the right place, at the right time" to at least, in part, explain the meiotic arrest obtained in the spermatocyte culture.

Protein post-translational modifications: In silico prediction tools and molecular modeling

Post-translational modifications (PTMs) occur in almost all proteins and play an important role in numerous biological processes by significantly affecting proteins' structure and dynamics. Several computational approaches have been developed to study PTMs (e.g., phosphorylation, sumoylation or palmitoylation) showing the importance of these techniques in predicting modified sites that can be further investigated with experimental approaches. In this review, we summarize some of the available online platforms and their contribution in the study of PTMs. Moreover, we discuss the emerging capabilities of molecular modeling and simulation that are able to complement these bioinformatics methods, providing deeper molecular insights into the biological function of post-translational modified proteins.

Heat Shock Proteins and Diabetes

Diabetes is a chronic disease, and its prevalence continues to rise and can increase the risk for the progression of microvascular (such as nephropathy, retinopathy and neuropathy) and also macrovascular complications. Diabetes is a condition in which the oxidative stress and inflammation rise. Heat shock proteins (HSPs) are a highly conserved family of proteins that are expressed by all cells exposed to environmental stress, and they have diverse functions. In patients with diabetes, the expression and levels of HSPs decrease, but these chaperones can aid in improving some complications of diabetes, such as oxidative stress and inflammation. (The suppression of some HSPs is associated with a generalized increase in tissue inflammation.) In this review, we summarize the current understanding of HSPs in diabetes as well as their complications, and we also highlight their potential role as therapeutic targets in diabetes.

Inhibition of CDK1 activity by sumoylation

Sumoylation (a covalent modification by Small Ubiquitin-like Modifiers or SUMO proteins) has been implicated in the regulation of various cellular events including cell cycle progression. We have recently identified CDK1, a master regulator of mitosis and meiosis, as a SUMO target both in vivo and in vitro, supporting growing evidence concerning a close cross talk between sumoylation and phosphorylation during cell cycle progression. However, any data regarding the effect of sumoylation upon CDK1 activity have been missing. In this study, we performed a series of in vitro experiments to inhibit sumoylation by three different means (ginkgolic acid, physiological levels of oxidative stress, and using an siRNA approach) and assessed the changes in CDK1 activity using specific antibodies and a kinase assay. We have also tested for an interaction between SUMO and active and/or inactive CDK1 isoforms in addition to having assessed the status of CDK1-interacting sumoylated proteins upon inhibition of sumoylation. Our data suggest that inhibition of sumoylation increases the activity of CDK1 probably through changes in sumoylated status and/or the ability of specific proteins to bind CDK1 and inhibit its activity.

The role of adipose-derived inflammatory cytokines in type 1 diabetes

Adipose tissue dysfunction correlates with the development of diabetes. Mice with an adipocyte-specific deletion of the SUMO-specific protease SENP1 develop symptoms of type-1 diabetes mellitus (T1DM). Peri-pancreatic adipocytes (PATs) exert both systemic and paracrine effects on pancreases function. Our recent studies report that PATs of SENP1-deficient mice have increased proinflammatory cytokine production compared with other adipose depots. Proinflammatory cytokines produced from PATs not only have direct cytotoxic effects on pancreatic islets, but also increase CCL5 expression in adjacent pancreatic islets, which induces persistent inflammation in pancreases by acquisition of Th1 and Th17 effector T cell subsets. Small ubiquitin-like modifier (SUMO) can post-translationally conjugate to cellular proteins (SUMOylation) and modulate their biological functions. Several components in SUMOylation associate with T1DM susceptibility. We find that SUMOylation of NF-κB essential molecule NEMO augments NF-κB activity, NF-κB-dependent cytokine production and pancreatic inflammation. NF-κB inhibitor should provide therapeutic approach to block PAT inflammation and ameliorate the T1DM phenotype. We further propose that adipocytes in PATs may play a primary role in establishing pancreatic immune regulation at onset of diabetes, providing new insights into the molecular pathogenesis of type 1 diabetes.

Protein Modifications as Manifestations of Hyperglycemic Glucotoxicity in Diabetes and Its Complications

Diabetes and its complications are hyperglycemic toxicity diseases. Many metabolic pathways in this array of diseases become aberrant, which is accompanied with a variety of posttranslational protein modifications that in turn reflect diabetic glucotoxicity. In this review, we summarize some of the most widely studied protein modifications in diabetes and its complications. These modifications include glycation, carbonylation, nitration, cysteine S-nitrosylation, acetylation, sumoylation, ADP-ribosylation, O-GlcNAcylation, and succination. All these posttranslational modifications can be significantly attributed to oxidative stress and/or carbon stress induced by diabetic redox imbalance that is driven by activation of pathways, such as the polyol pathway and the ADP-ribosylation pathway. Exploring the nature of these modifications should facilitate our understanding of the pathological mechanisms of diabetes and its associated complications.

Systematic Analysis of the Genetic Variability That Impacts SUMO Conjugation and Their Involvement in Human Diseases

Protein function has been observed to rely on select essential sites instead of requiring all sites to be indispensable. Small ubiquitin-related modifier (SUMO) conjugation or sumoylation, which is a highly dynamic reversible process and its outcomes are extremely diverse, ranging from changes in localization to altered activity and, in some cases, stability of the modified, has shown to be especially valuable in cellular biology. Motivated by the significance of SUMO conjugation in biological processes, we report here on the first exploratory assessment whether sumoylation related genetic variability impacts protein functions as well as the occurrence of diseases related to SUMO. Here, we defined the SUMOAMVR as sumoylation related amino acid variations that affect sumoylation sites or enzymes involved in the process of connectivity, and categorized four types of potential SUMOAMVRs. We detected that 17.13% of amino acid variations are potential SUMOAMVRs and 4.83% of disease mutations could lead to SUMOAMVR with our system. More interestingly, the statistical analysis demonstrates that the amino acid variations that directly create new potential lysine sumoylation sites are more likely to cause diseases. It can be anticipated that our method can provide more instructive guidance to identify the mechanisms of genetic diseases.

Can your protein be sumoylated? A quick summary and important tips to study SUMO-modified proteins

A diverse set of SUMO target proteins has been identified. Therefore, there is a growing interest in studying sumoylation and SUMO interactions in cells. When the sumoylation of a protein or a SUMO interaction is suspected, a standard co-immunoprecipitation analysis using anti-SUMO and anti-target protein antibody is usually performed as a first step. However, the identification of endogenous sumoylated proteins is challenging because of the activity of isopeptidases, and often only a small fraction of a target protein is sumoylated at a given time. Here, we briefly summarize several important steps to ensure a successful co-immunoprecipitation analysis to detect possible sumoylation.

Immune response to chemically modified proteome

Both enzymatic and nonenzymatic PTMs of proteins involve chemical modifications. Some of these modifications are prerequisite for the normal functioning of cell, while other chemical modifications render the proteins as "neo-self" antigens, which are recognized as "non-self" leading to aberrant cellular and humoral immune responses. However, these modifications could be a secondary effect of autoimmune diseases, as in the case of type I diabetes, hyperglycemia leads to protein glycation. The enigma of chemical modifications and immune response is akin to the "chick-and-egg" paradox. Nevertheless, chemical modifications regulate immune response. In some of the well-known autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, and multiple sclerosis, chemically modified proteins act as autoantigens forming immune complexes. In some instances, chemical modifications are also involved in regulating immune response during pathogen infection. Further, the usefulness of proteomic analysis of immune complexes is briefly discussed.

Advances in our understanding of the pathophysiology of Type 1 diabetes: lessons from the NOD mouse

T1D (Type 1 diabetes) is an autoimmune disease caused by the immune-mediated destruction of pancreatic β-cells. Studies in T1D patients have been limited by the availability of pancreatic samples, a protracted pre-diabetic phase and limitations in markers that reflect β-cell mass and function. The NOD (non-obese diabetic) mouse is currently the best available animal model of T1D, since it develops disease spontaneously and shares many genetic and immunopathogenic features with human T1D. Consequently, the NOD mouse has been extensively studied and has made a tremendous contribution to our understanding of human T1D. The present review summarizes the key lessons from NOD mouse studies concerning the genetic susceptibility, aetiology and immunopathogenic mechanisms that contribute to autoimmune destruction of β-cells. Finally, we summarize the potential and limitations of immunotherapeutic strategies, successful in NOD mice, now being trialled in T1D patients and individuals at risk of developing T1D.

SUMO: a (oxidative) stressed protein

Redox species are produced during the physiological cellular metabolism of a normal tissue. In turn, their presence is also attributed to pathological conditions including neurodegenerative diseases. Many are the molecular changes that occur during the unbalance of the redox homeostasis. Interestingly, posttranslational protein modifications (PTMs) play a remarkable role. In fact, several target proteins are modified in their activation, localization, aggregation, and expression after the cellular stress. Among PTMs, protein SUMOylation represents a very important molecular modification pathway during "oxidative stress". It has been reported that this ubiquitin-like modification is a fine sensor for redox species. Indeed, SUMOylation pathway efficiency is affected by the exposure to oxidative species in a different manner depending on the concentration and time of application. Thus, we here report updated evidence that states the role of SUMOylation in several pathological conditions, and we also outline the key involvement of c-Jun N-terminal kinase and small ubiquitin modifier pathway cross talk.

SUMOhunt: Combining Spatial Staging between Lysine and SUMO with Random Forests to Predict SUMOylation

Modification with SUMO protein has many key roles in eukaryotic systems which renders the identification of its target proteins and sites of considerable importance. Information regarding the SUMOylation of a protein may tell us about its subcellular localization, function, and spatial orientation. This modification occurs at particular and not all lysine residues in a given protein. In competition with biochemical means of modified-site recognition, computational methods are strong contenders in the prediction of SUMOylation-undergoing sites on proteins. In this research, physicochemical properties of amino acids retrieved from AAIndex, especially those involved in docking of modifier and target proteins and optimal presentation of target lysine, in combination with sequence information and random forest-based classifier presented in WEKA have been used to develop a prediction model, SUMOhunt, with statistics significantly better than all previous predictors. In this model 97.56% accuracy, 100% sensitivity, 94% specificity, and 0.95 MCC have been achieved which shows that proposed amino acid properties have a significant role in SUMO attachment. SUMOhunt will hence bring great reliability and efficiency in SUMOylation prediction.

Sequence motifs of myelin membrane proteins: towards the molecular basis of diseases

The shortest sequence of amino acids in protein containing functional and structural information is a "motif." To understand myelin protein functions, we intensively searched for motifs that can be found in myelin proteins. Some myelin proteins had several different motifs or repetition of the same motif. The most abundant motif found among myelin proteins was a myristoylation motif. Bovine MAG held 11 myristoylation motifs and human myelin basic protein held as many as eight such motifs. PMP22 had the fewest myristoylation motifs, which was only one; rat PMP22 contained no such motifs. Cholesterol recognition/interaction amino-acid consensus (CRAC) motif was not found in myelin basic protein. P2 protein of different species contained only one CRAC motif, except for P2 of horse, which had no such motifs. MAG, MOG, and P0 were very rich in CRAC, three to eight motifs per protein. The analysis of motifs in myelin proteins is expected to provide structural insight and refinement of predicted 3D models for which structures are as yet unknown. Analysis of motifs in mutant proteins associated with neurological diseases uncovered that some motifs disappeared in P0 with mutation found in neurological diseases. There are 2,500 motifs deposited in a databank, but 21 were found in myelin proteins, which is only 1% of the total known motifs. There was great variability in the number of motifs among proteins from different species. The appearance or disappearance of protein motifs after gaining point mutation in the protein related to neurological diseases was very interesting.

Polymorphism M55V in gene encoding small ubiquitin-like modifier 4 (SUMO4) protein associates with susceptibility to type 1 (and type 2) diabetes

BACKGROUND

The association between small ubiquitin-like modifier 4 (SUMO4) gene polymorphism and type 1 diabetes mellitus (T1DM) or type 2 diabetes mellitus (T2DM) has been investigated in several studies. We conducted a meta-analysis to evaluate the association of SUMO4 gene polymorphism with T1DM and T2DM susceptibility.

METHODS

A meta-analysis was performed on the published studies before August 2011. The association of SUMO4 M55V polymorphism with T1DM and T2DM was evaluated. Meta-analysis was performed for genotypes AA versus GG, AA versus AG, AA versus AG + GG and A allele versus G allele in a fixed/random effect model. The combined odds ratio (OR) with 95% confidence interval (95% CI) was calculated to estimate the strength of the association.

RESULTS

Sixteen case-control studies including 9190 cases and 10 456 healthy controls were included. T1DM patients were divided into Asian and Caucasian subgroup. We detected a significant association of SUMO4 M55V polymorphism with T1DM in Asian population (A versus G: OR = 0.79, 95%CI = 0.72-0.86, p = 0.000) and a significant association of SUMO4 M55V polymorphism with T1DM in Caucasian population (A versus G: OR = 0.84, 95%CI = 0.73-0.97, p = 0.007). Included T2DM patients were all Asian. Meanwhile, a significant association of SUMO4 M55V polymorphism with T2DM was also found (A versus G: OR = 0.86, 95%CI = 0.79-0.94, p = 0.001).

CONCLUSIONS

Our study demonstrates significant associations of SUMO4 M55V polymorphism with T1DM in Asian and Caucasian population and with T2DM in Asian population.

Association between the SUMO4 M55V (A163G) polymorphism and susceptibility to type 1 diabetes: a meta-analysis

OBJECTIVE

The aim of this study was to determine whether the SUMO4 M55V (A163G) polymorphism confers susceptibility to type 1 diabetes (T1D).

METHODS

A meta-analysis was conducted on the association between the SUMO4 M55V polymorphism and T1D using; (1) allelic contrast (G vs. A), and the (2) recessive (GG vs. GA+AA), (3) dominant (GG+GA vs. AA), and (4) additive models (GG vs. AA).

RESULTS

Thirteen separate studies were considered in the meta-analysis, which in total included 5915 patients and 6660 controls, and five European and eight Asian sample populations. Europeans had a higher prevalence of the G allele than Asians (50.4% vs. 30.2%). Meta-analysis of the SUMO4 M55V polymorphism showed an association between T1D and the SUMO4 G allele in all study subjects (OR=1.236, 95% CI=1.112-1.373, p=7.9×10(-6)), and stratification by ethnicity indicated a highly significant association between the SUMO4 G allele and T1D in Asians (OR=1.303, 95% CI=1.169-1.452, p=1.78×10(-7)) and a marginal association with T1D in Europeans (OR=1.177, 95% CI=1.000-1.386, p=0.050). Furthermore, significant associations were found between the SUMO4 M55V polymorphism and T1D and all study subjects, Europeans, and Asians using the dominant model (OR=1.239, 95% CI=1.144-1.342, p=1.4×10(-8); OR=1.156, 95% CI=1.051-1.271, p=0.003; OR=1.461, 95% CI=1.262-1.691, p=3.8×10(-8), respectively).

CONCLUSIONS

This meta-analysis indicates that the SUMO4 M55V polymorphism confers susceptibility to T1D in Asians and Europeans.

Decreased catalytic function with altered sumoylation of DNA topoisomerase I in the nuclei of scleroderma fibroblasts

Introduction

Sumoylation is involved in nucleolus-nucleoplasm transport of DNA topoisomerase I (topo I), which may associate with changes of cellular and topo I functions. Skin fibroblasts of patients with systemic sclerosis (SSc) exhibit profibrotic cellular changes. The aims of this study were to examine the catalytic function and sumoylation of topo I in the nuclei of SSc fibroblasts, a major cell type involved in the fibrotic process.

Methods

Eleven pairs of fibroblast strains obtained from nonlesional skin biopsies of SSc patients and age/sex/ethnicity-matched normal controls were examined for catalytic function of nuclear topo I. Immunoprecipitation (IP)-Western blots were used to examine sumoylation of fibroblast topo I. Real-time quantitative RT-PCR was used to measure transcript levels of SUMO1 and COL1A2 in the fibroblasts.

Results

Topo I in nuclear extracts of SSc fibroblasts generally showed a significantly lower efficiency than that of normal fibroblasts in relaxing equivalent amounts of supercoiled DNA. Increased sumoylation of topo I was clearly observed in 7 of 11 SSc fibroblast strains. Inhibition of SUMO1 with SUMO1 siRNA improved the catalytic efficiency of topo I in the SSc fibroblasts. In contrast, sumoylation of recombinant topo I proteins reduced their catalytic function.

Conclusions

The catalytic function of topo I was decreased in SSc fibroblasts, to which increased sumoylation of topo I may contribute.

Identification of SUMOylated proteins in neuroblastoma cells after treatment with hydrogen peroxide or ascorbate

The small ubiquitin-like modifier (SUMO) proteins have been implicated in the pathology of a number of diseases, including neurodegenerative diseases. The conjugation machinery for SUMOylation consists of a number of proteins which are redox sensitive. Here, under oxidative stress (100 μM hydrogen peroxide), antioxidant (100 μM ascorbate) or control conditions 169 proteins were identified by electrospray ionisation fourier transform ion cyclotron resonance mass spectrometry. The majority of these proteins (70%) were found to contain SUMOylation consensus sequences. From the remaining proteins a small number (12%) were found to contain possible SUMO interacting motifs. The proteins identified included DNA and RNA binding proteins, structural proteins and proteasomal proteins. Several of the proteins identified under oxidative stress conditions had previously been identified as SUMOylated proteins, thus validating the method presented.

Association of SUMO4 M55V polymorphism with type 1 diabetes in Chinese children

OBJECTIVE

A functional polymorphism at codon 55 of the small ubiquitin like modifier 4 (SUMO4) gene (methionine to valine; M55V) was recently found to be associated with type 1 diabetes mellitus mainly in Asian populations (T1D). In the present study, we aimed to investigate whether this locus also contributes to the genetic susceptiblity to type 1 diabetes in Chinese.

RESEARCH DESIGN AND METHODS

A case-control study was performed using genomic DNA samples from 165 unrelated Chinese childhood T1D subjects and 160 normal blood donors. The SUMO4 M55V single nucleotide polymorphism (SNP) was genotyped using polymerase chain reaction (PCR) amplification followed by digestion with the restriction enzyme Mse I.

RESULTS

The frequencies of SUMO4 163G allele were significantly increased in T1D patients (38. 2% vs. healthy control subjects 28.7%, P < 0.05, OR = 1.51, 95% CI 1.03-2.13). SUMO4 163 GG genotype was also significantly increased in the T1D patients (17% vs. healthy control subjects 8%, P < 0.05).

CONCLUSIONS

This study indicates that the SUMO4 gene M55V variant is associated with the genetic susceptibility of T1D in Chinese children.

SUMO proteins are involved in the stress response during spermatogenesis and are localized to DNA double-strand breaks in germ cells

Small ubiquitin-like modifiers (SUMO) proteins have been implicated in cellular stress response in different tissues, but whether sumoylation has a similar role during spermatogenesis is currently unknown. In this study, changes in the levels of both free SUMO isoforms and high-molecular weight (HMW) SUMO conjugates were monitored before and after the induction of different types of cellular stresses. Using cell lines and primary cells freshly isolated from mouse testes, significant changes were detected in the levels of SUMO1 and SUMO2/3 conjugates following short exposure of the cells to heat stress and oxidative stress. While high concentrations of H(2)O(2) caused an increase in protein sumoylation, low concentrations of H(2)O(2) mostly caused protein desumoylation. Immunofluorescence studies localized SUMO to the sites of DNA double-strand breaks in stressed germ cells and during meiotic recombination. To study the effect of oxidative stress in vivo, animals exposed to tobacco smoke for 12 weeks were used. Changes in sumoylation of HMW proteins were consistent with their oxidative damage in the tobacco-exposed mice. Our results are consistent with the important roles of different SUMO isoforms in stress responses in germ cells. Furthermore, this study identified topoisomerase 2 alpha as one of the targets of sumoylation during normal spermatogenesis and under stress.

SUMOylation and cell signalling

SUMOylation is a highly transient post-translational protein modification. Attachment of SUMO to target proteins occurs via a number of specific activating and ligating enzymes that form the SUMO-substrate complex, and other SUMO-specific proteases that cleave the covalent bond, thus leaving both SUMO and target protein free for the next round of modification. SUMO modification has major effects on numerous aspects of substrate function, including subcellular localisation, regulation of their target genes, and interactions with other molecules. The modified SUMO-protein complex is a very transient state, and it thus facilitates rapid response and actions by the cell, when needed. Like phosphorylation, acetylation and ubiquitination, SUMOylation has been associated with a number of cellular processes. In addition to its nuclear role, important sides of mitochondrial activity, stress response signalling and the decision of cells to undergo senescence or apoptosis, have now been shown to involve the SUMO pathway. With ever increasing numbers of reports linking SUMO to human disease, like neurodegeneration and cancer metastasis, it is highly likely that novel and equally important functions of components of the SUMOylation process in cell signalling pathways will be elucidated in the near future.

Analyses of multiple single-nucleotide polymorphisms in the SUMO4/IDDM5 region in affected sib-pair families with type I diabetes

Previous studies suggested that the SUMO4 gene, located in the IDDM5 interval on chromosome 6q25, was associated with type I diabetes (T1D) and several other autoimmune diseases. Subsequent analyses of the SUMO4 variants with T1D suggested that the association was stronger and more consistent in the Asian populations. In addition, considerable heterogeneity has been observed in the Caucasian populations. In this report, a 40-kb genomic interval including the SUMO4 gene was tagged with 15 single-nucleotide polymorphisms. A total of 2317 affected sib-pair families from the Type I Diabetes Genetic Consortium were genotyped using both the Illumina and Sequenom genotyping platforms. In these Caucasian families, we found little evidence supporting an association between SUMO4 and T1D.

SUMOylation of the mitochondrial fission protein Drp1 occurs at multiple nonconsensus sites within the B domain and is linked to its activity cycle

Dynamin-related protein (Drp) 1 is a key regulator of mitochondrial fission and is composed of GTP-binding, Middle, insert B, and C-terminal GTPase effector (GED) domains. Drp1 associates with mitochondrial fission sites and promotes membrane constriction through its intrinsic GTPase activity. The mechanisms that regulate Drp1 activity remain poorly understood but are likely to involve reversible post-translational modifications, such as conjugation of small ubiquitin-like modifier (SUMO) proteins. Through a detailed analysis, we find that Drp1 interacts with the SUMO-conjugating enzyme Ubc9 via multiple regions and demonstrate that Drp1 is a direct target of SUMO modification by all three SUMO isoforms. While Drp1 does not harbor consensus SUMOylation sequences, our analysis identified2 clusters of lysine residues within the B domain that serve as noncanonical conjugation sites. Although initial analysis indicates that mitochondrial recruitment of ectopically expressed Drp1 in response to staurosporine is unaffected by loss of SUMOylation, we find that Drp1 SUMOylation is enhanced in the context of the K38A mutation. This dominant-negative mutant, which is deficient in GTP binding and hydrolysis, does not associate with mitochondria and prevents normal mitochondrial fission. This finding suggests that SUMOylation of Drp1 is linked to its activity cycle and is influenced by Drp1 localization.

SUMO proteases: redox regulation and biological consequences

Small-ubiquitin modifier (SUMO) has emerged as a novel modification system that governs the activities of a wide spectrum of protein substrates. SUMO-specific proteases (SENP) are of particular interest, as they are responsible for both the maturation of SUMO precursors and for their deconjugation. The interruption of SENPs has been implicated in embryonic defects and carcinoma cells, indicating that a proper balance of SUMO conjugation and deconjugation is crucial. Recent advances in molecular and cellular biology have highlighted the distinct subcellular localization, and endopeptidase and isopeptidase activities of SENPs, suggesting that they are nonredundant. A better understanding of the molecular basis of SUMO recognition and hydrolytic cleavage has been obtained from the crystal structures of SENP-substrate complexes. While a number of proteomic studies have shown an upregulation of sumoylation, attention is now increasingly being directed towards the regulatory mechanism of sumoylation, in particular the oxidative effect. Findings on the oxidation-induced intermolecular disulfide of E1-E2 ligases and SENP1/2 have improved our understanding of the mechanism by which modification is switched up or down. More intriguingly, a growing body of evidence suggests that sumoylation cross-talks with other modifications, and that the upstream and downstream signaling pathway is co-regulated by more than one modifier.

Characterization of a negative feedback network between SUMO4 expression and NFkappaB transcriptional activity

Previously, we have demonstrated evidence suggesting that SUMO4 negatively regulates NFkappaB transcriptional activity, probably through sumoylation of IkappaBalpha. Here, we present data indicating that SUMO4 possesses the capacity to conjugate to IkappaBalpha. Luciferase reporter assays in 3T3 cells deficient for IkappaBalpha further demonstrated that SUMO4 regulates NFkappaB signaling dependent on its sumoylation of IkappaBalpha. More importantly, a putative NFkappaB binding motif has been characterized within the SUMO4 promoter. Subsequent promoter reporter assays revealed that SUMO4 promoter with disrupted NFkappaB binding motif failed to response to NFkappaB specific IL-1beta stimulation. ChIP assays showed that NFkappaB binds to SUMO4 promoter and activates its transcription. Together, our data suggest that SUMO4 may act as a negative feedback regulator to prevent excessive activation of NFkappaB. Given the importance of NFkappaB signaling in immune response, SUMO4 could play a role to tightly control the potency of immune response to prevent autoimmunity.