Disruption of SUMO-specific protease 2 induces mitochondria mediated neurodegeneration

Astragaloside IV combined with ligustrazine ameliorates abnormal mitochondrial dynamics via Drp1 SUMO/deSUMOylation in cerebral ischemia-reperfusion injury

OBJECTIVES

Astragaloside IV (AST IV) and ligustrazine (Lig), the main ingredients of Astragali Radix and Chuanxiong Rhizoma respectively, have demonstrated significant benefits in treatment of cerebral ischemia -reperfusion injury (CIRI); however, the mechanisms underlying its benificial effects remain unclear. SUMO-1ylation and deSUMO-2/3ylation of dynamin-related protein 1 (Drp1) results in mitochondrial homeostasis imbalance following CIRI, which subsequently aggravates cell damage. This study investigates the mechanisms by which AST IV combined with Lig protects against CIRI, focusing on the involvement of SUMOylation in mitochondrial dynamics.

METHODS

Rats were administrated AST IV and Lig for 7 days, and middle cerebral artery occlusion was established to mimic CIRI. Neural function, cerebral infarction volume, cerebral blood flow, cognitive function, cortical pathological lesions, and mitochondrial morphology were measured. SH-SY5Y cells were subjected to oxygen-glucose deprivation/reoxygenation (OGD/R) injury. Mitochondrial membrane potential and lactic dehydrogenase (LDH), reactive oxygen species (ROS), and adenosine triphosphate (ATP) levels were assessed with commercial kits. Moreover, co-immunoprecipitation (Co-IP) was used to detect the binding of SUMO1 and SUMO2/3 to Drp1. The protein expressions of Drp1, Fis1, MFF, OPA1, Mfn1, Mfn2, SUMO1, SUMO2/3, SENP1, SENP2, SENP3, SENP5, and SENP6 were measured using western blot.

RESULTS

In rats with CIRI, AST IV and Lig improved neurological and cognitive functions, restored CBF, reduced brain infarct volume, and alleviated cortical neuron and mitochondrial damage. Moreover, in SH-SY5Y cells, the combination of AST IV and Lig enhanced cellular viability, decreased release of LDH and ROS, increased ATP content, and improved mitochondrial membrane potential. Furthermore, AST IV combined with Lig reduced the binding of Drp1 with SUMO1, increased the binding of Drp1 with SUMO2/3, suppressed the expressions of Drp1, Fis1, MFF, and SENP3, and increased the expressions of OPA1, Mfn1, Mfn2, SENP1, SENP2, and SENP5. SUMO1 overexpression promoted mitochondrial fission and inhibited mitochondrial fusion, whereas SUMO2/3 overexpression suppressed mitochondrial fission. AST IV combined with Lig could reverse the effects of SUMO1 overexpression while enhancing those of SUMO2/3 overexpression.

CONCLUSIONS

This study posits that the combination of AST IV and Lig has the potential to reduce the SUMO-1ylation of Drp1, augment the SUMO-2/3ylation of Drp1, and thereby exert a protective effect against CIRI.

A polypeptide derived from pilose antler ameliorates CUMS-induced depression-like behavior by SENP2-PLCβ4 signaling axis

Neurogenesis is known to be closely associated with depression. We aimed to investigate whether a polypeptide monomer derived from pilose antler (polypeptide sequence LSALEGVFYP, PAP) exerts an antidepressant effect by influencing neurogenesis, and to elucidate the mechanism of its antidepressant action. Behavioral tests were performed to observe the antidepressant effect of PAP. Neurogenesis in the dentate gyrus (DG) region of hippocampus was observed by immunofluorescence. The expression of key proteins of Sentrin/SUMO-specific proteases 2 (SENP2)- Phosphoinositide-specific phospholipase C beta 4 (PLCβ4) pathway was accessed by co-immunoprecipitation (Co-IP), and the calcium homeostasis associated proteins were observed via Western blot (WB). Subsequently, temozolomide (TMZ) pharmacologically blocked neurogenesis to verify the antidepressant effect of PAP on neurogenesis. The mechanism of PAP antidepressant effect was verified by constructing a sh-SENP2 virus vector to silence SENP2 protein. Finally, corticosterone (CORT)-induced PC12 cell model was used to verify whether PAP was involved in the process of deconjugated PLCβ4 SUMOylated. The results showed that PAP improved depression-like behavior and neurogenesis induced by chronic unpredictable mild stimulation (CUMS). In addition, PAP acted on SENP2-PLCβ4 pathway to deconjugate the SUMOylation of PLCβ4 and affect calcium homeostasis. Pharmacological blockade of neurogenesis by TMZ treatment impaired the antidepressant efficacy of PAP. Knockout of SENP2 in the CUMS model attenuated the antidepressant response of PAP, and the impaired neurogenesis was not ameliorated by PAP treatment. In summary, PAP acted on the SENP2-PLCβ4 signaling pathway to inhibit the SUMOylation of PLCβ4 and maintain calcium homeostasis, thereby protecting neurogenesis and playing an antidepressant role.

The PML hub: An emerging actor of leukemia therapies

PML assembles into nuclear domains that have attracted considerable attention from cell and cancer biologists. Upon stress, PML nuclear bodies modulate sumoylation and other post-translational modifications, providing an integrated molecular framework for the multiple roles of PML in apoptosis, senescence, or metabolism. PML is both a sensor and an effector of oxidative stress. Emerging data has demonstrated its key role in promoting therapy response in several hematological malignancies. While these membrane-less nuclear hubs can enforce efficient cancer cell clearance, their downstream pathways deserve better characterization. PML NBs are druggable and their known modulators may have broader clinical utilities than initially thought.

Possible molecular mechanisms underlying the development of atherosclerosis in cancer survivors

Cancer survivors undergone treatment face an increased risk of developing atherosclerotic cardiovascular disease (CVD), yet the underlying mechanisms remain elusive. Recent studies have revealed that chemotherapy can drive senescent cancer cells to acquire a proliferative phenotype known as senescence-associated stemness (SAS). These SAS cells exhibit enhanced growth and resistance to cancer treatment, thereby contributing to disease progression. Endothelial cell (EC) senescence has been implicated in atherosclerosis and cancer, including among cancer survivors. Treatment modalities for cancer can induce EC senescence, leading to the development of SAS phenotype and subsequent atherosclerosis in cancer survivors. Consequently, targeting senescent ECs displaying the SAS phenotype hold promise as a therapeutic approach for managing atherosclerotic CVD in this population. This review aims to provide a mechanistic understanding of SAS induction in ECs and its contribution to atherosclerosis among cancer survivors. We delve into the mechanisms underlying EC senescence in response to disturbed flow and ionizing radiation, which play pivotal role in atherosclerosis and cancer. Key pathways, including p90RSK/TERF2IP, TGFβR1/SMAD, and BH4 signaling are explored as potential targets for cancer treatment. By comprehending the similarities and distinctions between different types of senescence and the associated pathways, we can pave the way for targeted interventions aim at enhancing the cardiovascular health of this vulnerable population. The insights gained from this review may facilitate the development of novel therapeutic strategies for managing atherosclerotic CVD in cancer survivors.

Mitochondrial SENP2 regulates the assembly of SDH complex under metabolic stress

Succinate dehydrogenase (SDH) is a heterotetrameric enzyme complex belonging to the mitochondrial respiratory chain and uniquely links the tricarboxylic acid (TCA) cycle with oxidative phosphorylation. Cancer-related SDH mutations promote succinate accumulation, which is regarded as an oncometabolite. Post-translational modifications of SDH complex components are known to regulate SDH activity, although the contribution of SUMOylation remains unclear. Here, we show that SDHA is SUMOylated by PIAS3 and deSUMOylated by SENP2, events dictating the assembly and activity of the SDH complex. Moreover, CBP acetylation of SENP2 negatively regulates its deSUMOylation activity. Under glutamine deprivation, CBP levels decrease, and the ensuing SENP2 activation and SDHA deSUMOylation serve to concurrently dampen the TCA cycle and electron transport chain (ETC) activity. Along with succinate accumulation, this mechanism avoids excessive reactive oxygen species (ROS) production to promote cancer cell survival. This study elucidates a major function of mitochondrial-localized SENP2 and expands our understanding of the role of SUMOylation in resolving metabolic stress.

miRNA-27a is essential for bone remodeling by modulating p62-mediated osteoclast signaling

The ability to simultaneously modulate a set of genes for lineage-specific development has made miRNA an ideal master regulator for organogenesis. However, most miRNA deletions do not exhibit obvious phenotypic defects possibly due to functional redundancy. miRNAs are known to regulate skeletal lineages as the loss of their maturation enzyme Dicer impairs bone remodeling processes. Therefore, it is important to identify specific miRNA essential for bone homeostasis. We report the loss of MIR27a causing severe osteoporosis in mice. MIR27a affects osteoclast-mediated bone resorption but not osteoblast-mediated bone formation during skeletal remodeling. Gene profiling and bioinformatics further identify the specific targets of MIR27a in osteoclast cells. MIR27a exerts its effects on osteoclast differentiation through modulation of Squstm1/p62 whose mutations have been linked to Paget's disease of bone. Our findings reveal a new MIR27a-p62 axis necessary and sufficient to mediate osteoclast differentiation and highlight a therapeutic implication for osteoporosis.

Protein sumoylation in normal and cancer stem cells

Stem cells with the capacity of self-renewal and differentiation play pivotal roles in normal tissues and malignant tumors. Whereas stem cells are supposed to be genetically identical to their non-stem cell counterparts, cell stemness is deliberately regulated by a dynamic network of molecular mechanisms. Reversible post-translational protein modifications (PTMs) are rapid and reversible non-genetic processes that regulate essentially all physiological and pathological process. Numerous studies have reported the involvement of post-translational protein modifications in the acquirement and maintenance of cell stemness. Recent studies underscore the importance of protein sumoylation, i.e., the covalent attachment of the small ubiquitin-like modifiers (SUMO), as a critical post-translational protein modification in the stem cell populations in development and tumorigenesis. In this review, we summarize the functions of protein sumoylation in different kinds of normal and cancer stem cells. In addition, we describe the upstream regulators and the downstream effectors of protein sumoylation associated with cell stemness. We also introduce the translational studies aiming at sumoylation to target stem cells for disease treatment. Finally, we propose future directions for sumoylation studies in stem cells.

SUMO control of nervous system development

In the last decades, the post-translational modification system by covalent attachment of the SUMO polypeptide to proteins has emerged as an essential mechanism controlling virtually all the physiological processes in the eukaryotic cell. This includes vertebrate development. In the nervous system, SUMO plays crucial roles in synapse establishment and it has also been linked to a variety of neurodegenerative diseases. However, to date, the involvement of the modification of specific targets in key aspects of nervous system development, like patterning and differentiation, has remained largely elusive. A number of recent works confirm the participation of target-specific SUMO modification in critical aspects of nervous system development. Here, we review pioneering and new findings demonstrating the essential role SUMO plays in neurogenesis and other facets of neurodevelopment, which will help to precisely understand the variety of mechanisms SUMO utilizes to control most fundamental processes in the cell.

Discovery of a Dual SENP1 and SENP2 Inhibitor

SUMOylation is a reversible post–translational modification (PTM) involving covalent attachment of small ubiquitin-related modifier (SUMO) proteins to substrate proteins. Dysregulation of SUMOylation and deSUMOylation results in cellular malfunction and is linked to various diseases, such as cancer. Sentrin-specific proteases (SENPs) were identified for the maturation of SUMOs and the deconjugation of SUMOs from their substrate proteins. Hence, this is a promising target tackling the dysregulation of the SUMOylation process. Herein, we report the discovery of a novel protein-protein interaction (PPI) inhibitor for SENP1-SUMO1 by virtual screening and subsequent medicinal chemistry optimization of the hit molecule. The optimized inhibitor ZHAWOC8697 showed IC₅₀ values of 8.6 μM against SENP1 and 2.3 μM against SENP2. With a photo affinity probe the SENP target was validated. This novel SENP inhibitor represents a new valuable tool for the study of SUMOylation processes and the SENP-associated development of small molecule-based treatment options.

SUMOylation and Major Depressive Disorder

Since the discovery of the small ubiquitin-like modifier (SUMO) protein in 1995, SUMOylation has been considered a crucial post-translational modification in diverse cellular functions. In neurons, SUMOylation has various roles ranging from managing synaptic transmitter release to maintaining mitochondrial integrity and determining neuronal health. It has been discovered that neuronal dysfunction is a key factor in the development of major depressive disorder (MDD). PubMed and Google Scholar databases were searched with keywords such as 'SUMO', 'neuronal plasticity', and 'depression' to obtain relevant scientific literature. Here, we provide an overview of recent studies demonstrating the role of SUMOylation in maintaining neuronal function in participants suffering from MDD.

SUMOylation in peripheral tissues under low perfusion-related pathological states

SUMOylation is described as a posttranslational protein modification (PTM) that is involved in the pathophysiological processes underlying several conditions related to ischemia- and reperfusion-induced damage. Increasing evidence suggests that, under low oxygen levels, SUMOylation might be part of an endogenous mechanism, which is triggered by injury to protect cells within the central nervous system. However, the role of ischemia-induced SUMOylation in the periphery is still unclear. This article summarizes the results of recent studies regarding SUMOylation profiles in several diseases characterized by impaired blood flow to the cardiorenal, gastrointestinal, and respiratory systems. Our review shows that although ischemic injury per se does not always increase SUMOylation levels, as seen in strokes, it seems that in most cases the positive modulation of protein SUMOylation after peripheral ischemia might be a protective mechanism. This complex relationship warrants further investigation, as the role of SUMOylation during hypoxic conditions differs from organ to organ and is still not fully elucidated.

Identification of Natural Products as SENP2 Inhibitors for Targeted Therapy in Heart Failure

Aims: Sentrin-specific protease -2 (SENP2) is involved in deSUMOylation. Increased deSUMOylation in murine hearts by SENP2 upregulation resulted in cardiac dysfunction and congenital heart defects. Natural compounds via regulating cell proliferation and survival, induce cell cycle cessation, cell death, apoptosis, and producing reactive oxygen species and various enzyme systems cause disease prevention. Then, natural compounds can be suitable inhibitors and since SENP2 is a protein involved in heart disease, so our aim was inhibition of SENP2 by natural products for heart disease treatment. Material and methods: Molecular docking and molecular dynamics simulation of natural products i.e. Gallic acid (GA), Caffeic acid (CA), Thymoquinone (TQ), Betanin, Betanidin, Fisetin, and Ebselen were done to evaluate the SENP2 inhibitory effect of these natural products. The toxicity of compounds was also predicted. Results: The results showed that Betanin constituted a stable complex with SENP2 active site as it revealed low RMSD, high binding energy, and hydrogen bonds. Further, as compared to Ebselen, Betanin demonstrated low toxicity, formed a stable complex with SENP2 via four to seven hydrogen bonds, and constituted more stable MD plots. Therefore, depending upon the outcomes presented herein, Betanin significantly inhibited SENP2 and hence may be considered as a suitable natural compound for the treatment of heart failure. Further clinical trials must be conducted to validate its use as a potential SENP2 inhibitor.

Natural Products Against Renal Fibrosis via Modulation of SUMOylation

Renal fibrosis is the common and final pathological process of kidney diseases. As a dynamic and reversible post-translational modification, SUMOylation and deSUMOylation of transcriptional factors and key mediators significantly affect the development of renal fibrosis. Recent advances suggest that SUMOylation functions as the promising intervening target against renal fibrosis, and natural products prevent renal fibrosis via modulating SUMOylation. Here, we introduce the mechanism of SUMOylation in renal fibrosis and therapeutic effects of natural products. This process starts by summarizing the key mediators and enzymes during SUMOylation and deSUMOylation and its regulation role in transcriptional factors and key mediators in renal fibrosis, then linking the mechanism findings of SUMOylation and natural products to develop novel therapeutic candidates for treating renal fibrosis, and concludes by commenting on promising therapeutic targets and candidate natural products in renal fibrosis via modulating SUMOylation, which highlights modulating SUMOylation as a promising strategy for natural products against renal fibrosis.

SENP2 regulates mitochondrial function and insulin secretion in pancreatic β cells

Increasing evidence has shown that small ubiquitin-like modifier (SUMO) modification plays an important role in metabolic regulation. We previously demonstrated that SUMO-specific protease 2 (SENP2) is involved in lipid metabolism in skeletal muscle and adipogenesis. In this study, we investigated the function of SENP2 in pancreatic β cells by generating a β cell-specific knockout (Senp2-βKO) mouse model. Glucose tolerance and insulin secretion were significantly impaired in the Senp2-βKO mice. In addition, glucose-stimulated insulin secretion (GSIS) was decreased in the islets of the Senp2-βKO mice without a significant change in insulin synthesis. Furthermore, islets of the Senp2-βKO mice exhibited enlarged mitochondria and lower oxygen consumption rates, accompanied by lower levels of S616 phosphorylated DRP1 (an active form of DRP1), a mitochondrial fission protein. Using a cell culture system of NIT-1, an islet β cell line, we found that increased SUMO2/3 conjugation to DRP1 due to SENP2 deficiency suppresses the phosphorylation of DRP1, which possibly induces mitochondrial dysfunction. In addition, SENP2 overexpression restored GSIS impairment induced by DRP1 knockdown and increased DRP1 phosphorylation. Furthermore, palmitate treatment decreased phosphorylated DRP1 and GSIS in β cells, which was rescued by SENP2 overexpression. These results suggest that SENP2 regulates mitochondrial function and insulin secretion at least in part by modulating the phosphorylation of DRP1 in pancreatic β cells.

SUMO-specific Isopeptidases Tuning Cardiac SUMOylation in Health and Disease

SUMOylation is a transient posttranslational modification with small-ubiquitin like modifiers (SUMO1, SUMO2 and SUMO3) covalently attached to their target-proteins via a multi-step enzymatic cascade. SUMOylation modifies protein-protein interactions, enzymatic-activity or chromatin binding in a multitude of key cellular processes, acting as a highly dynamic molecular switch. To guarantee the rapid kinetics, SUMO target-proteins are kept in a tightly controlled equilibrium of SUMOylation and deSUMOylation. DeSUMOylation is maintained by the SUMO-specific proteases, predominantly of the SENP family. SENP1 and SENP2 represent family members tuning SUMOylation status of all three SUMO isoforms, while SENP3 and SENP5 are dedicated to detach mainly SUMO2/3 from its substrates. SENP6 and SENP7 cleave polySUMO2/3 chains thereby countering the SUMO-targeted-Ubiquitin-Ligase (StUbL) pathway. Several biochemical studies pinpoint towards the SENPs as critical enzymes to control balanced SUMOylation/deSUMOylation in cardiovascular health and disease. This study aims to review the current knowledge about the SUMO-specific proteases in the heart and provides an integrated view of cardiac functions of the deSUMOylating enzymes under physiological and pathological conditions.

SUMOylation as a Therapeutic Target for Myocardial Infarction

Myocardial infarction is a prevalent and life-threatening cardiovascular disease. The main goal of existing interventional therapies is to restore coronary reperfusion while few are designed to ameliorate the pathology of heart diseases via targeting the post-translational modifications of those critical proteins. Small ubiquitin-like modifier (SUMO) proteins are recently discovered to form a new type of protein post-translational modifications (PTM), known as SUMOylation. SUMOylation and deSUMOylation are dynamically balanced in the maintenance of various biological processes including cell division, DNA repair, epigenetic transcriptional regulation, and cellular metabolism. Importantly, SUMOylation plays a critical role in the regulation of cardiac functions and the pathology of cardiovascular diseases, especially in heart failure and myocardial infarction. This review summarizes the current understanding on the effects of SUMOylation and SUMOylated proteins in the pathophysiology of myocardial infarction and identifies the potential treatments against myocardial injury via targeting SUMO. Ultimately, this review recommends SUMOylation as a key therapeutic target for treating cardiovascular diseases.

SUMOylation modification-mediated cell death

SUMOylation dynamically conjugates SUMO molecules to the lysine residue of a substrate protein, which depends on the physiological state of the cell and the attached SUMO isoforms. A prominent role of SUMOylation in molecular pathways is to govern the cellular death process. Herein, we summarize the association between SUMOylation modification events and four types of cellular death processes: apoptosis, autophagy, senescence and pyroptosis. SUMOylation positively or negatively regulates a certain cellular death pattern depending on specific conditions including the attached SUMO isoforms, disease types, substrate proteins and cell context. Moreover, we also discuss the possible role of SUMOylation in ferroptosis and propose a potential role of the SUMOylated GPX4 in the regulation of ferroptosis. Mapping the exact SUMOylation network with cellular death contributes to develop novel SUMOylation-targeting disease therapeutic strategies.

BMPR1A maintains skeletal stem cell properties in craniofacial development and craniosynostosis

Skeletal stem cells from the suture mesenchyme, which are referred to as suture stem cells (SuSCs), exhibit long-term self-renewal, clonal expansion, and multipotency. These SuSCs reside in the suture midline and serve as the skeletal stem cell population responsible for calvarial development, homeostasis, injury repair, and regeneration. The ability of SuSCs to engraft in injury site to replace the damaged skeleton supports their potential use for stem cell-based therapy. Here, we identified BMPR1A as essential for SuSC self-renewal and SuSC-mediated bone formation. SuSC-specific disruption of Bmpr1a in mice caused precocious differentiation, leading to craniosynostosis initiated at the suture midline, which is the stem cell niche. We found that BMPR1A is a cell surface marker of human SuSCs. Using an ex vivo system, we showed that SuSCs maintained stemness properties for an extended period without losing the osteogenic ability. This study advances our knowledge base of congenital deformity and regenerative medicine mediated by skeletal stem cells.

Inhibition of Drp1 SUMOylation by ALR protects the liver from ischemia-reperfusion injury

Hepatic ischemic reperfusion injury (IRI) is a common complication of liver surgery. Although an imbalance between mitochondrial fission and fusion has been identified as the cause of IRI, the detailed mechanism remains unclear. Augmenter of liver regeneration (ALR) was reported to prevent mitochondrial fission by inhibiting dynamin-related protein 1 (Drp1) phosphorylation, contributing partially to its liver protection. Apart from phosphorylation, Drp1 activity is also regulated by small ubiquitin-like modification (SUMOylation), which accelerates mitochondrial fission. This study aimed to investigate whether ALR-mediated protection from hepatic IRI might be associated with an effect on Drp1 SUMOylation. Liver tissues were harvested from both humans and from heterozygous ALR knockout mice, which underwent IRI. The SUMOylation and phosphorylation of Drp1 and their modulation by ALR were investigated. Hepatic Drp1 SUMOylation was significantly increased in human transplanted livers and IRI-livers of mice. ALR-transfection significantly decreased Drp1 SUMOylation, attenuated the IRI-induced mitochondrial fission and preserved mitochondrial stability and function. This study showed that the binding of transcription factor Yin Yang-1 (YY1) to its downstream target gene UBA2, a subunit of SUMO-E1 enzyme heterodimer, was critical to control Drp1 SUMOylation. By interacting with YY1, ALR inhibits its nuclear import and dramatically decreases the transcriptional level of UBA2. Consequently, mitochondrial fission was significantly reduced, and mitochondrial function was maintained. This study showed that the regulation of Drp1 SUMOylation by ALR protects mitochondria from fission, rescuing hepatocytes from IRI-induced apoptosis. These new findings provide a potential target for clinical intervention to reduce the effects of IRI during hepatic surgery.

The role of SUMOylation during development

During the development of multicellular organisms, transcriptional regulation plays an important role in the control of cell growth, differentiation and morphogenesis. SUMOylation is a reversible post-translational process involved in transcriptional regulation through the modification of transcription factors and through chromatin remodelling (either modifying chromatin remodelers or acting as a ‘molecular glue’ by promoting recruitment of chromatin regulators). SUMO modification results in changes in the activity, stability, interactions or localization of its substrates, which affects cellular processes such as cell cycle progression, DNA maintenance and repair or nucleocytoplasmic transport. This review focuses on the role of SUMO machinery and the modification of target proteins during embryonic development and organogenesis of animals, from invertebrates to mammals.

Forebrain excitatory neuron-specific SENP2 knockout mouse displays hyperactivity, impaired learning and memory, and anxiolytic-like behavior

Sentrin/SUMO-specific protease 2 (SENP2) is a member of SENPs family involved in maturation of SUMO precursors and deSUMOylation of specific target, and is highly expressed in the central nervous system (CNS). Although SENP2 has been shown to modulate embryonic development, fatty acid metabolism, atherosclerosis and epilepsy, the function of SENP2 in the CNS remains poorly understood. To address the role of SENP2 in the CNS and its potential involvement in neuropathology, we generated SENP2 conditional knockout mice by crossing floxed SENP2 mice with CaMKIIα-Cre transgenic mice. Behavioral tests revealed that SENP2 ablation induced hyper-locomotor activity, anxiolytic-like behaviors, spatial working memory impairment and fear-associated learning defect. In line with these observations, our RNA sequencing (RNA-seq) data identified a variety of differential expression genes that are particularly enriched in locomotion, learning and memory related biologic process. Taken together, our results indicated that SENP2 plays a critical role in emotional and cognitive regulation. This SENP2 conditional knockout mice model may help reveal novel mechanisms that underlie a variety of neuropsychiatric disorders associated with anxiety and cognition.

The role of mitochondria-associated membranes in cellular homeostasis and diseases

Mitochondria and endoplasmic reticulum (ER) are fundamental in the control of cell physiology regulating several signal transduction pathways. They continuously communicate exchanging messages in their contact sites called MAMs (mitochondria-associated membranes). MAMs are specific microdomains acting as a platform for the sorting of vital and dangerous signals. In recent years increasing evidence reported that multiple scaffold proteins and regulatory factors localize to this subcellular fraction suggesting MAMs as hotspot signaling domains. In this review we describe the current knowledge about MAMs' dynamics and processes, which provided new correlations between MAMs' dysfunctions and human diseases. In fact, MAMs machinery is strictly connected with several pathologies, like neurodegeneration, diabetes and mainly cancer. These pathological events are characterized by alterations in the normal communication between ER and mitochondria, leading to deep metabolic defects that contribute to the progression of the diseases.

The requirement of SUMO2/3 for SENP2 mediated extraembryonic and embryonic development

Small ubiquitin‐related modifier (SUMO)‐specific protease 2 (SENP2) is essential for the development of healthy placenta. The loss of SENP2 causes severe placental deficiencies and leads to embryonic death that is associated with heart and brain deformities. However, tissue‐specific disruption of SENP2 demonstrates its dispensable role in embryogenesis and the embryonic defects are secondary to placental insufficiency. SENP2 regulates SUMO1 modification of Mdm2, which controls p53 activities critical for trophoblast cell proliferation and differentiation. Here we use genetic analyses to examine the involvement of SUMO2 and SUMO3 for SENP2‐mediated placentation. The results indicate that hyper‐SUMOylation caused by SENP2 deficiency can be compensated by reducing the level of SUMO modifiers. The placental deficiencies caused by the loss of SENP2 can be alleviated by the inactivation of gene encoding SUMO2 or SUMO3. Our findings demonstrate that SENP2 genetically interacts with SUMO2 and SUMO3 pivotal for the development of three major trophoblast layers. The alleviation of placental defects in the SENP2 knockouts further leads to the proper formation of the heart structures, including atrioventricular cushion and myocardium. SUMO2 and SUMO3 modifications regulate placentation and organogenesis mediated by SENP2.

Genetic analyses reveal that hyper sumoylation caused by SENP2 deficiency can be compensated by reducing the level of SUMO modifiers. The placental deficiencies caused by the loss of SENP2 can be alleviated by the inactivation of gene encoding SUMO2 or SUMO3. SENP2 genetically interacts with SUMO2 and SUMO3 pivotal for the development of three major trophoblast layers. The alleviation of placental defects in the SENP2 knockouts further leads to the proper formation of the heart structures, including atrioventricular cushion and myocardium. Protein modification by SUMO2 and SUMO3 is essential for SENP2‐mediated placentation and organogenesis.

Localization Analysis of Seven De-sumoylation Enzymes (SENPs) in Ocular Cell Lines

PURPOSE

It is now well established that protein sumoylation acts as an important regulatory mechanism modulating functions over three thousand proteins. In the vision system, protein conjugation with SUMO peptides can regulate differentiation of multiple ocular tissues. Such regulation is often explored through analysis of biochemical and physiological changes with various cell lines in vitro. We have recently analyzed the expression levels of both mRNAs and proteins for seven de-sumoylation enzymes (SENPs) in five major ocular cell lines. In continuing the previous study, here we have determined their cellular localization of the seven de-sumoylation enzymes (SENP1, 2, 3, 5, 6, 7 and 8) in the above 5 major ocular cell lines using immunocytochemistry.

METHODS

The 5 major ocular cell lines were cultured in Dulbecco's modified Eagle's medium (DMEM) containing fetal bovine serum (FBS) or rabbit serum (RBS) and 1% Penicillin- Streptomycin. The localization of the 7 major de-sumoylation enzymes (SENPs) in the 5 major ocular cell lines were determined with immunohistochemistry. The images were captured with a Zeiss LSM 880 confocal microscope.

RESULTS

1) The SENP1 was localized in both cytoplasm and nucleus of 3 human ocular cell lines, FHL124, HLE and ARPE-19; In N/N1003A and αTN4-1, SENP 1 was more concentrated in the cytoplasm. SENP1 appears in patches; 2) SENP2 was distributed in both cytoplasm and nucleus of all ocular cell lines in patches. In HLE and ARPE-19 cells, SENP2 level was higher in nucleus than in cytoplasm; 3) SENP3 was almost exclusively concentrated in the nuclei in all ocular cells except for N/N1003A cells. In the later cells, a substantial amount of SENP3 was also detected in the cytoplasm although nuclear SENP3 level was higher than the cytoplasmic SENP3 level. SENP3 appeared in obvious patches in the nuclei; 4) SENP5 was dominantly localized in the cytoplasm (cellular organelles) near nuclear membrane or cytoplasmic membrane ; 5) SENP6 was largely concentrated in the nuclei of all cell lines except for αTN4-1 cells. In the later cells, a substantial amount of SENP6 was also detected in the cytoplasm although nuclear SENP6 level was higher than the cytoplasmic SENP6 level. 6) SENP7 has an opposite localization pattern between human and animal cell lines. In human cell lines, a majority of SENP7 was localized in nuclei whereas in mouse and rabbit lens epithelial cells, most SENP7 was distributed in the cytoplasm. SENP8 was found present in human cell lines. The 3 human ocular cell lines had relatively similar distribution pattern. In FHL124 and ARPE-19 cells, SENP8 was detected only in the cytoplasm, but in HLE cells, patches of SENP8 in small amount was also detected in the nuclei.

CONCLUSIONS

Our results for the first time defined the differential distribution patterns of seven desumoylation enzymes (SENPs) in 5 major ocular cell lines. These results help to understand the different functions of various SENPs in maintaining the homeostasis of protein sumoylation patterns during their functioning processes.

Intracellular and Intercellular Mitochondrial Dynamics in Parkinson's Disease

The appearance of alpha-synuclein-positive inclusion bodies (Lewy bodies) and the loss of catecholaminergic neurons are the primary pathological hallmarks of Parkinson's disease (PD). However, the dysfunction of mitochondria has long been recognized as a key component in the progression of the disease. Dysfunctional mitochondria can in turn lead to dysregulation of calcium homeostasis and, especially in dopaminergic neurons, raised mean intracellular calcium concentration. As calcium binding to alpha-synuclein is one of the important triggers of alpha-synuclein aggregation, mitochondrial dysfunction will promote inclusion body formation and disease progression. Increased reactive oxygen species (ROS) resulting from inefficiencies in the electron transport chain also contribute to the formation of alpha-synuclein aggregates and neuronal loss. Recent studies have also highlighted defects in mitochondrial clearance that lead to the accumulation of depolarized mitochondria. Transaxonal and intracytoplasmic translocation of mitochondria along the microtubule cytoskeleton may also be affected in diseased neurons. Furthermore, nanotube-mediated intercellular transfer of mitochondria has recently been reported between different cell types and may have relevance to the spread of PD pathology between adjacent brain regions. In the current review, the contributions of both intracellular and intercellular mitochondrial dynamics to the etiology of PD will be discussed.

The synaptic balance between sumoylation and desumoylation is maintained by the activation of metabotropic mGlu5 receptors

Sumoylation is a reversible post-translational modification essential to the modulation of neuronal function, including neurotransmitter release and synaptic plasticity. A tightly regulated equilibrium between the sumoylation and desumoylation processes is critical to the brain function and its disruption has been associated with several neurological disorders. This sumoylation/desumoylation balance is governed by the activity of the sole SUMO-conjugating enzyme Ubc9 and a group of desumoylases called SENPs, respectively. We previously demonstrated that the activation of type 5 metabotropic glutamate receptors (mGlu5R) triggers the transient trapping of Ubc9 in dendritic spines, leading to a rapid increase in the overall synaptic sumoylation. However, the mechanisms balancing this increased synaptic sumoylation are still not known. Here, we examined the diffusion properties of the SENP1 enzyme using a combination of advanced biochemical approaches and restricted photobleaching/photoconversion of individual hippocampal spines. We demonstrated that the activation of mGlu5R leads to a time-dependent decrease in the exit rate of SENP1 from dendritic spines. The resulting post-synaptic accumulation of SENP1 restores synaptic sumoylation to initial levels. Altogether, our findings reveal the mGlu5R system as a central activity-dependent mechanism to maintaining the homeostasis of sumoylation at the mammalian synapse.

Zinc-Induced SUMOylation of Dynamin-Related Protein 1 Protects the Heart against Ischemia-Reperfusion Injury

Background

Zinc plays a role in mitophagy and protects cardiomyocytes from ischemia/reperfusion injury. This study is aimed at investigating whether SUMOylation of Drp1 is involved in the protection of zinc ion on cardiac I/R injury.

Methods

Mouse hearts were subjected to 30 minutes of regional ischemia followed by 2 hours of reperfusion (ischemia/reoxygenation (I/R)). Infarct size and apoptosis were assessed. HL-1 cells were subjected to 24 hours of hypoxia and 6 hours of reoxygenation (hypoxia/reoxygenation (H/R)). Zinc was given 5 min before reperfusion for 30 min. SENP2 overexpression plasmid (Flag-SENP2), Drp1 mutation plasmid (Myc-Drp1 4KR), and SUMO1 siRNA were transfected into HL-1 cells for 48 h before hypoxia. Effects of zinc on SUMO family members were analyzed by Western blotting. SUMOylation of Drp1, apoptosis and the collapse of mitochondrial membrane potential (ΔΨm), and mitophagy were evaluated.

Results

Compared with the control, SUMO1 modification level of proteins in the H/R decreased, while this effect was reversed by zinc. In the setting of H/R, zinc attenuated myocardial apoptosis, which was reversed by SUMO1 siRNA. Similar effects were observed in SUMO1 KO mice exposed to H/R. In addition, the dynamin-related protein 1 (Drp1) is a target protein of SUMO1. The SUMOylation of Drp1 induced by zinc regulated mitophagy and contributed to the protective effect of zinc on H/R injury.

Conclusions

SUMOylation of Drp1 played an essential role in zinc-induced cardio protection against I/R injury. Our findings provide a promising therapeutic approach for acute myocardial I/R injury.

Mitochondrial Proteolysis and Metabolic Control

Mitochondria are metabolic hubs that use multiple proteases to maintain proteostasis and to preserve their overall quality. A decline of mitochondrial proteolysis promotes cellular stress and may contribute to the aging process. Mitochondrial proteases have also emerged as tightly regulated enzymes required to support the remarkable mitochondrial plasticity necessary for metabolic adaptation in a number of physiological scenarios. Indeed, the mutation and dysfunction of several mitochondrial proteases can cause specific human diseases with severe metabolic phenotypes. Here, we present an overview of the proteolytic regulation of key mitochondrial functions such as respiration, lipid biosynthesis, and mitochondrial dynamics, all of which are required for metabolic control. We also pay attention to how mitochondrial proteases are acutely regulated in response to cellular stressors or changes in growth conditions, a greater understanding of which may one day uncover their therapeutic potential.

Role of GTPases in the regulation of mitochondrial dynamics in Parkinson's disease

Mitochondria are highly dynamic organelle that undergo frequent fusion and division, and the balance of these opposing processes regulates mitochondrial morphology, distribution, and function. Mitochondrial fission facilitates the replication and distribution of mitochondria during cell division, whereas the fusion process including inner and outer mitochondrial membrane fusion allows the exchange of intramitochondrial material between adjacent mitochondria. Despite several GTPase family proteins have been implicated as key modulators of mitochondrial dynamics, the mechanisms by which these proteins regulate mitochondrial homeostasis and function remain not clearly understood. Neuronal function and survival are closely related to mitochondria dynamics, and disturbed mitochondrial fission/fusion may influence neurotransmission, synaptic maintenance, neuronal survival and function. Recent studies have shown that mitochondrial dysfunction caused by aberrant mitochondrial dynamics plays an essential role in the pathogenesis of both sporadic and familial Parkinson's disease (PD). Collectively, we review the molecular mechanism of known GTPase proteins in regulating mitochondrial fission and fusion, but also highlight the causal role for mitochondrial dynamics in PD pathogenesis.

Mitochondrial Retrograde Signaling in Mammals Is Mediated by the Transcriptional Cofactor GPS2 via Direct Mitochondria-to-Nucleus Translocation

As most of the mitochondrial proteome is encoded in the nucleus, mitochondrial functions critically depend on nuclear gene expression and bidirectional mito-nuclear communication. However, mitochondria-to-nucleus communication pathways in mammals are incompletely understood. Here, we identify G-Protein Pathway Suppressor 2 (GPS2) as a mediator of mitochondrial retrograde signaling and a transcriptional activator of nuclear-encoded mitochondrial genes. GPS2-regulated translocation from mitochondria to nucleus is essential for the transcriptional activation of a nuclear stress response to mitochondrial depolarization and for supporting basal mitochondrial biogenesis in differentiating adipocytes and brown adipose tissue (BAT) from mice. In the nucleus, GPS2 recruitment to target gene promoters regulates histone H3K9 demethylation and RNA POL2 activation through inhibition of Ubc13-mediated ubiquitination. These findings, together, reveal an additional layer of regulation of mitochondrial gene transcription, uncover a direct mitochondria-nuclear communication pathway, and indicate that GPS2 retrograde signaling is a key component of the mitochondrial stress response in mammals.

Proteases: Pivot Points in Functional Proteomics

Proteases drive the life cycle of all proteins, ensuring the transportation and activation of newly minted, would-be proteins into their functional form while recycling spent or unneeded proteins. Far from their image as engines of protein digestion, proteases play fundamental roles in basic physiology and regulation at multiple levels of systems biology. Proteases are intimately associated with disease and modulation of proteolytic activity is the presumed target for successful therapeutics. "Proteases: Pivot Points in Functional Proteomics" examines the crucial roles of proteolysis across a wide range of physiological processes and diseases. The existing and potential impacts of proteolysis-related activity on drug and biomarker development are presented in detail. All told the decisive roles of proteases in four major categories comprising 23 separate subcategories are addressed. Within this construct, 15 sets of subject-specific, tabulated data are presented that include identification of proteases, protease inhibitors, substrates, and their actions. Said data are derived from and confirmed by over 300 references. Cross comparison of datasets indicates that proteases, their inhibitors/promoters and substrates intersect over a range of physiological processes and diseases, both chronic and pathogenic. Indeed, "Proteases: Pivot Points …" closes by dramatizing this very point through association of (pro)Thrombin and Fibrin(ogen) with: hemostasis, innate immunity, cardiovascular and metabolic disease, cancer, neurodegeneration, and bacterial self-defense.

Amplification of Glyceronephosphate O-Acyltransferase and Recruitment of USP30 Stabilize DRP1 to Promote Hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death worldwide, and the underlying pathophysiology of HCC is highly complex. In this study, we report that, in a bioinformatic screen of 2,783 genes encoding metabolic enzymes, GNPAT, which encodes the enzyme glyceronephosphate O-acyltransferase, is amplified, upregulated, and highly correlated with poor clinical outcome in human patients with HCC. High GNPAT expression in HCC was due to its amplification and transcriptional activation by the c-Myc/KDM1A complex. GNPAT compensated the oncogenic phenotypes in c-Myc-depleted HCC cells. Mechanistically, GNPAT recruited the enzyme USP30, which deubiquitylated and stabilized dynamin-related protein 1 (DRP1), thereby facilitating regulation of mitochondrial morphology, lipid metabolism, and hepatocarcinogenesis. Inhibition of GNPAT and DRP1 dramatically attenuated lipid metabolism and hepatocarcinogenesis. Furthermore, DRP1 mediated the oncogenic phenotypes driven by GNPAT. Taken together, these results indicate that GNPAT and USP30-mediated stabilization of DRP1 play a critical role in the development of HCC.Significance: This study identifies and establishes the role of the enzyme GNPAT in liver cancer progression, which may serve as a potential therapeutic target for liver cancer. Cancer Res; 78(20); 5808-19. ©2018 AACR.

Mitochondrial dynamics: overview of molecular mechanisms

Mitochondria are highly dynamic organelles undergoing coordinated cycles of fission and fusion, referred as ‘mitochondrial dynamics’, in order to maintain their shape, distribution and size. Their transient and rapid morphological adaptations are crucial for many cellular processes such as cell cycle, immunity, apoptosis and mitochondrial quality control. Mutations in the core machinery components and defects in mitochondrial dynamics have been associated with numerous human diseases. These dynamic transitions are mainly ensured by large GTPases belonging to the Dynamin family. Mitochondrial fission is a multi-step process allowing the division of one mitochondrion in two daughter mitochondria. It is regulated by the recruitment of the GTPase Dynamin-related protein 1 (Drp1) by adaptors at actin- and endoplasmic reticulum-mediated mitochondrial constriction sites. Drp1 oligomerization followed by mitochondrial constriction leads to the recruitment of Dynamin 2 to terminate membrane scission. Inner mitochondrial membrane constriction has been proposed to be an independent process regulated by calcium influx. Mitochondrial fusion is driven by a two-step process with the outer mitochondrial membrane fusion mediated by mitofusins 1 and 2 followed by inner membrane fusion, mediated by optic atrophy 1. In addition to the role of membrane lipid composition, several members of the machinery can undergo post-translational modifications modulating these processes. Understanding the molecular mechanisms controlling mitochondrial dynamics is crucial to decipher how mitochondrial shape meets the function and to increase the knowledge on the molecular basis of diseases associated with morphology defects. This article will describe an overview of the molecular mechanisms that govern mitochondrial fission and fusion in mammals.

Site-specific characterization of endogenous SUMOylation across species and organs

Small ubiquitin-like modifiers (SUMOs) are post-translational modifications that play crucial roles in most cellular processes. While methods exist to study exogenous SUMOylation, large-scale characterization of endogenous SUMO2/3 has remained technically daunting. Here, we describe a proteomics approach facilitating system-wide and in vivo identification of lysines modified by endogenous and native SUMO2. Using a peptide-level immunoprecipitation enrichment strategy, we identify 14,869 endogenous SUMO2/3 sites in human cells during heat stress and proteasomal inhibition, and quantitatively map 1963 SUMO sites across eight mouse tissues. Characterization of the SUMO equilibrium highlights striking differences in SUMO metabolism between cultured cancer cells and normal tissues. Targeting preferences of SUMO2/3 vary across different organ types, coinciding with markedly differential SUMOylation states of all enzymes involved in the SUMO conjugation cascade. Collectively, our systemic investigation details the SUMOylation architecture across species and organs and provides a resource of endogenous SUMOylation sites on factors important in organ-specific functions.

Proteomics is a powerful method to study protein SUMOylation, but system-wide insights into endogenous SUMO2/3 modification events are still sparse. Here, the authors develop a more sensitive SUMO proteomics approach, providing detailed maps of endogenous SUMO2/3 sites in human cells and mouse tissues.

SUMO1/sentrin/SMT3 specific peptidase 2 modulates target molecules and its corresponding functions

Small ubiquitin-like modifier (SUMOylation) is a reversible post-translational modification, which plays important roles in numerous biological processes. SUMO could be covalently attached to target proteins in an isopeptide bond manner that occurs via a lysine ε-amino group on the target proteins and the glycine on SUMO C-terminus. This covalent binding could affect the subcellular localization and stability of target proteins. SUMO modification can be reversed by members of the Sentrin/SUMO-specific proteases (SENPs) family, which are highly evolutionarily conserved from yeast to human. SENP2, a member of the SENPs family, mainly plays a physiological function in the nucleus. SENP2 can promote maturity of the SUMO and deSUMOylate for single-SUMO modified or poly-SUMO modified proteins. SENP2 can affect the related biological processes through its peptidase activity or the amino terminal transcriptional repression domain. It plays important roles by inhibiting or activating some molecular functions. Therefore, the research achievements of SENP2 are reviewed in order to understand its related functions and the underlying molecular mechanisms and provide a clue for future research on SENP2.

The SUMO-specific isopeptidase SENP2 is targeted to intracellular membranes via a predicted N-terminal amphipathic α-helix

Sumoylation regulates a wide range of essential cellular functions, many of which are associated with activities in the nucleus. Although there is also emerging evidence for the involvement of the small ubiquitin-related modifier (SUMO) at intracellular membranes, the mechanisms by which sumoylation is regulated at membranes is largely unexplored. In this study, we report that the SUMO-specific isopeptidase, SENP2, uniquely associates with intracellular membranes. Using in vivo analyses and in vitro binding assays, we show that SENP2 is targeted to intracellular membranes via a predicted N-terminal amphipathic α-helix that promotes direct membrane binding. Furthermore, we demonstrate that SENP2 binding to intracellular membranes is regulated by interactions with the nuclear import receptor karyopherin-α. Consistent with membrane association, biotin identification (BioID) revealed interactions between SENP2 and endoplasmic reticulum, Golgi, and inner nuclear membrane-associated proteins. Collectively, our findings indicate that SENP2 binds to intracellular membranes where it interacts with membrane-associated proteins and has the potential to regulate their sumoylation and membrane-associated functions.

SENP1 and SENP2 regulate SUMOylation of amyloid precursor protein

Amyloid β, a key molecule in the pathogenesis of Alzheimer's disease (AD), is produced from amyloid precursor protein (APP) by the cleavage of secretases. APP is SUMOylated near the cleavage site of β-secretase. SUMOylation of APP reduces amyloid β production, but its regulatory system is still unclear. SUMOylation, a modification at a lysine residue of a target protein, is mediated by activating, conjugating, and ligating enzymes and is reversed by a family of sentrin/SUMO-specific proteases (SENPs). Here, we found that both SENP1 and SENP2 induced de-SUMOylation of APP. Using quantitative PCR, we also found that expression of SENP1 but not SENP2 increased in an age-dependent manner only in female mice. The results of immunoblot analyses showed that the protein expression was consistent with the PCR results. Females, compared to males, have a higher incidence of AD in humans and show more aggressive amyloid pathology in AD mouse models. Our results provide a clue to understanding the role of SUMOylation in the sex difference in AD pathogenesis.

SUMO-specific proteases and isopeptidases of the SENP family at a glance

The ubiquitin-related SUMO system controls many cellular signaling networks. In mammalian cells, three SUMO forms (SUMO1, SUMO2 and SUMO3) act as covalent modifiers of up to thousands of cellular proteins. SUMO conjugation affects cell function mainly by regulating the plasticity of protein networks. Importantly, the modification is reversible and highly dynamic. Cysteine proteases of the sentrin-specific protease (SENP) family reverse SUMO conjugation in mammalian cells. In this Cell Science at a Glance article and the accompanying poster, we will summarize how the six members of the mammalian SENP family orchestrate multifaceted deconjugation events to coordinate cell processes, such as gene expression, the DNA damage response and inflammation.

Extranuclear SUMOylation in Neurons

Post-translational modification of substrate proteins by SUMO conjugation regulates a diverse array of cellular processes. While predominantly a nuclear protein modification, there is a growing appreciation that SUMOylation of proteins outside the nucleus plays direct roles in controlling synaptic transmission, neuronal excitability, and adaptive responses to cell stress. Furthermore, alterations in protein SUMOylation are observed in a wide range of neurological and neurodegenerative diseases, and several extranuclear disease-associated proteins have been shown to be directly SUMOylated. Here, focusing mainly on SUMOylation of synaptic and mitochondrial proteins, we outline recent developments and discoveries, and present our opinion as to the most exciting avenues for future research to define how SUMOylation of extranuclear proteins regulates neuronal and synaptic function.

SUMOylation, aging and autophagy in neurodegeneration

Protein homeostasis is essential for the wellbeing of several cellular systems. Post-translational modifications (PTM) coordinate various pathways in response to abnormal aggregation of proteins in neurodegenerative disease states. In the presence of accumulating misfolded proteins and toxic aggregates, the small ubiquitin-like modifier (SUMO) is associated with various substrates, including chaperones and other recruited factors, for refolding and for clearance via proteolytic systems, such as the ubiquitin-proteasome pathway (UPS), chaperone-mediated autophagy (CMA) and macroautophagy. However, these pathological aggregates are also known to inhibit both the UPS and CMA, further creating a toxic burden on cells. This review suggests that re-routing cytotoxic aggregates towards selective macroautophagy by modulating the SUMO pathway could provide new mechanisms towards neuroprotection.

Sumoylation of TCF21 downregulates the transcriptional activity of estrogen receptor-alpha

Aberrant estrogen receptor-α (ERα) signaling is recognized as a major contributor to the development of breast cancer. However, the molecular mechanism underlying the regulation of ERα in breast cancer is still inconclusive. In this study, we showed that the transcription factor 21 (TCF21) interacted with ERα, and repressed its transcriptional activity in a HDACs-dependent manner. We also showed that TCF21 could be sumoylated by the small ubiquitin-like modifier SUMO1, and this modification could be reversed by SENP1. Sumoylation of TCF21 occurred at lysine residue 24 (K24). Substitution of K24 with arginine resulted in complete abolishment of sumoylation. Sumoylation stabilized TCF21, but did not affect its subcellular localization. Sumoylation of TCF21 also enhanced its interaction with HDAC1/2 without affecting its interaction with ERα. Moreover, sumoylation of TCF21 promoted its repression of ERα transcriptional activity, and increased the recruitment of HDAC1/2 to the pS2 promoter. Consistent with these observations, sumoylation of TCF21 could inhibit the growth of ERα-positive breast cancer cells and decreased the proportion of S-phase cells in the cell cycle. These findings suggested that TCF21 might act as a negative regulator of ERα, and its sumoylation inhibited the transcriptional activity of ERα through promoting the recruitment of HDAC1/2.

SUMO targeting of a stress-tolerant Ulp1 SUMO protease

SUMO proteases of the SENP/Ulp family are master regulators of both sumoylation and desumoylation and regulate SUMO homeostasis in eukaryotic cells. SUMO conjugates rapidly increase in response to cellular stress, including nutrient starvation, hypoxia, osmotic stress, DNA damage, heat shock, and other proteotoxic stressors. Nevertheless, little is known about the regulation and targeting of SUMO proteases during stress. To this end we have undertaken a detailed comparison of the SUMO-binding activity of the budding yeast protein Ulp1 (ScUlp1) and its ortholog in the thermotolerant yeast Kluyveromyces marxianus, KmUlp1. We find that the catalytic UD domains of both ScUlp1 and KmUlp1 show a high degree of sequence conservation, complement a ulp1Δ mutant in vivo, and process a SUMO precursor in vitro. Next, to compare the SUMO-trapping features of both SUMO proteases we produced catalytically inactive recombinant fragments of the UD domains of ScUlp1 and KmUlp1, termed ScUTAG and KmUTAG respectively. Both ScUTAG and KmUTAG were able to efficiently bind a variety of purified SUMO isoforms and bound immobilized SUMO1 with nanomolar affinity. However, KmUTAG showed a greatly enhanced ability to bind SUMO and SUMO-modified proteins in the presence of oxidative, temperature and other stressors that induce protein misfolding. We also investigated whether a SUMO-interacting motif (SIM) in the UD domain of KmULP1 that is not conserved in ScUlp1 may contribute to the SUMO-binding properties of KmUTAG. In summary, our data reveal important details about how SUMO proteases target and bind their sumoylated substrates, especially under stress conditions. We also show that the robust pan-SUMO binding features of KmUTAG can be exploited to detect and study SUMO-modified proteins in cell culture systems.

The desumoylating enzyme sentrin-specific protease 3 contributes to myocardial ischemia reperfusion injury

Sentrin-specific protease 3 (SENP3), a member of the desumoylating enzyme family, is known as a redox sensor and could regulate multiple cellular signaling pathways. However, its implication in myocardial ischemia reperfusion (MIR) injury is unclear. Here, we observed that SENP3 was expressed and upregulated in the mouse heart depending on reactive oxygen species (ROS) production in response to MIR injury. By utilizing siRNA-mediated cardiac specific gene silencing, SENP3 knockdown was demonstrated to significantly reduce MIR-induced infarct size and improve cardiac function. Mechanistic studies indicated that SENP3 silencing ameliorated myocardial apoptosis mainly via suppression of endoplasmic reticulum (ER) stress and mitochondrial-mediated apoptosis pathways. By contrast, adenovirus-mediated cardiac SENP3 overexpression significantly exaggerated MIR injury. Further molecular analysis revealed that SENP3 promoted mitochondrial translocation of dynamin-related protein 1 (Drp1) in reperfused myocardium. In addition, mitochondrial division inhibitor-1 (Mdivi-1), a pharmacological inhibitor of Drp1, significantly attenuated the exaggerated mitochondrial abnormality and cardiac injury by SENP3 overexpression after MIR injury. Taken together, we provide the first direct evidence that SENP3 upregulation pivotally contributes to MIR injury in a Drp1-dependent manner, and suggest that SENP3 suppression may hold therapeutic promise for constraining MIR injury.

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.

Rap1b Is an Effector of Axin2 Regulating Crosstalk of Signaling Pathways During Skeletal Development

Recent identification and isolation of suture stem cells capable of long-term self-renewal, clonal expanding, and differentiating demonstrate their essential role in calvarial bone development, homeostasis, and injury repair. These bona fide stem cells express a high level of Axin2 and are able to mediate bone regeneration and repair in a cell autonomous fashion. The importance of Axin2 is further demonstrated by its genetic inactivation in mice causing skeletal deformities resembling craniosynostosis in humans. The fate determination and subsequent differentiation of Axin2+ stem cells are highly orchestrated by a variety of evolutionary conserved signaling pathways including Wnt, FGF, and BMP. These signals are often antagonistic of each other and possess differential effects on osteogenic and chondrogenic cell types. However, the mechanisms underlying the interplay of these signaling transductions remain largely elusive. Here we identify Rap1b acting downstream of Axin2 as a signaling interrogator for FGF and BMP. Genetic analysis reveals that Rap1b is essential for development of craniofacial and body skeletons. Axin2 regulates Rap1b through modulation of canonical BMP signaling. The BMP-mediated activation of Rap1b promotes chondrogenic fate and chondrogenesis. Furthermore, by inhibiting MAPK signaling, Rap1b mediates the antagonizing effect of BMP on FGF to repress osteoblast differentiation. Disruption of Rap1b in mice not only enhances osteoblast differentiation but also impairs chondrocyte differentiation during intramembranous and endochondral ossifications, respectively, leading to severe defects in craniofacial and body skeletons. Our findings reveal a dual role of Rap1b in development of the skeletogenic cell types. Rap1b is critical for balancing the signaling effects of BMP and FGF during skeletal development and disease. © 2017 American Society for Bone and Mineral Research.

Dynamin-related protein-1 as potential therapeutic target in various diseases

Mitochondria can interchange morphology due to their dynamic nature. It can exist in either fragmented disconnected arrangement or elongated interconnected mitochondrial networks due to fission and fusion, respectively. The recent studies have revealed the remarkable and unexpected insights into the physiological impact and molecular regulation of mitochondrial morphology. The balance between fission and fusion governs the faith of the cell. The active targeting of DRP 1 to the outer mitochondrial membrane (OMM) is done by non-GTPase receptor proteins such as mitochondrial fission factor, mitochondrial fission protein 1 and mitochondrial elongation factor 1. The active targeting of DRP 1 to OMM leads to the fission of mitochondria. However, the imbalance of DRP 1-dependent mitochondrial fission and modulation of equilibrium of fission and fusion has been documented to be involved in several cardiovascular and neurodegenerative disorders. In this review, we are focusing on the active participation of DRP 1 in various diseases and also the factors responsible for the activation of DRP 1 for its action.