SUMO2 rescues neuronal and glial cells from the toxicity of P301L Tau mutant

Introduction

Abnormal intracellular accumulation of Tau aggregates is a hallmark of Alzheimer's disease (AD) and other Tauopathies, such as Frontotemporal dementia (FTD). Tau deposits primarily affect neurons, but evidence indicates that glial cells may also be affected and contribute distinctively to disease progression. Cells can respond to toxic insults by orchestrating global changes in posttranslational modifications of their proteome. Previous studies suggest that SUMOylation, a posttranslational modification consisting of conjugation of SUMO (Small ubiquitin-like modifier) to target proteins, was decreased in the hippocampus of AD patients and in animal model of AD compared with controls. This decrease in SUMOylation was correlated with increased Tau pathology and cognitive decline. Other studies have reported increased levels of SUMO in AD brains. The goal of our study was to evaluate whether SUMO conjugation modifies the neurodegenerative disease pathology associated with the aggregation-prone mutant TauP301L, in neurons and in glial cells.

Methods

We used viral approaches to express mutant TauP301L and SUMO2 in the hippocampus of wild-type mice. We assessed Tau distribution by immunostaining and Tau aggregation by insolubility assays followed by western blotting. We assessed neuronal toxicity and performed cell count and shape descriptor analyses on astrocytes and microglial cells.

Results

We found that mutant TauP301L, when expressed exclusively in neurons, is toxic not only to neurons but also to glial cells, and that SUMO2 counteracts TauP301L toxicity in neurons as well as in glia.

Discussion

Our results uncover an endogenous neuroprotective mechanism, whereby SUMO2 conjugation reduces Tau neuropathology and protects against toxic effects of Tau in glial cells.

Small ubiquitin-related modifier (SUMO)ylation of SIRT1 mediates (-)-epicatechin inhibited- differentiation of cardiac fibroblasts into myofibroblasts

CONTEXT

(-)-Epicatechin (EPI) is a crucial substance involved in the protective effects of flavanol-rich foods. Previous studies have indicated EPI has a cardioprotective effect, but the molecular mechanisms in inhibition of cardiac fibrosis are unclear.

OBJECTIVE

We evaluated the effect of EPI in preventing cardiac fibrosis and the underlying molecular mechanism related to the SIRT1-SUMO1/AKT/GSK3β pathway.

MATERIALS AND METHODS

Cardiac fibrosis mice model was established with transaortic constriction (TAC). Male C57BL/6 mice were randomly separated into 4 groups. Mice received 1 mg/kg/day of EPI or vehicle orally for 4 weeks. The acutely isolated cardiac fibroblasts were induced to myofibroblasts with 1 µM angiotensin II (Ang II). The cardiac function was measured with the ultrasonic instrument. Histological analysis of mice's hearts was determined with H&E or Masson method. The protein level of fibrosis markers, SUMOylation of SIRT1, and AKT/GSK3β pathway were quantified by immunofluorescence and western blot.

RESULTS

EPI treatment (1 mg/kg/day) could reverse the TAC-induced decline in LVEF (TAC, 61.28% ± 1.33% vs. TAC + EPI, 74.00% ± 1.64%), LVFS (TAC, 28.16% ± 0.89% vs. TAC + EPI, 37.18% ± 1.29%). Meantime, we found that 10 µM EPI blocks Ang II-induced transformation of cardiac fibroblasts into myofibroblasts. The underlying mechanism of EPI-inhibited myofibroblasts transformation involves activation of SUMOylation of SIRT1 through SP1. Furthermore, SUMOylation of SIRT1 inhibited Ang II-induced fibrogenic effect via the AKT/GSK3β pathway.

CONCLUSION

EPI plays a protective effect on cardiac fibrosis by regulating the SUMO1-dependent modulation of SIRT1, which provides a theoretical basis for use in clinical therapies.

Downregulation of SUMO2 inhibits hepatocellular carcinoma cell proliferation, migration and invasion

This study aimed to evaluate the prognostic value and biological function of small ubiquitin‐like modifier 2 (SUMO2) in hepatocellular carcinoma (HCC). SUMO2 expression in HCC tissues was markedly higher than that in normal liver tissues, and patients with high SUMO2 expression had significantly shorter median overall survival than those with low SUMO2 expression. Furthermore, SUMO2 expression was closely correlated with lymph node metastasis and vascular invasion and was a predictor of poor prognosis. The knockdown of SUMO2 in two HCC cell lines (SMMC‐7721 and Bel‐7404) dramatically suppressed their proliferation, migration and invasion. Western blot analysis showed that the downregulation of SUMO2 significantly reduced the expression of Ki‐67, matrix metalloproteinase‐9 (MMP‐9) and vascular endothelial growth factor (VEGF) in SMMC‐7721 and Bel‐7404 cells. Similarly, quantitative reverse transcription–PCR revealed consistently decreased expression of MMP‐9 and VEGF. Our data suggest that SUMO2 promotes proliferation, migration and invasion of HCC cells via mechanisms involving MMP‐9 and VEGF. Therefore, SUMO2 may be a prognostic factor and a promising therapeutic target for patients with HCC.

Nuclear Nrf2 Activity in Laryngeal Carcinoma is Regulated by SENP3 After Cisplatin-Induced Reactive Oxygen Species Stress

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a nuclear transcription factor that is activated by reactive oxygen species (ROS). Recent studies reported that hyperactivation of the Nrf2 pathway creates an environment that favors the survival of normal as well as malignant cells, protecting them against oxidative stress, chemotherapeutic agents, and radiotherapy. SUMO1/sentrin/SMT3 specific peptidase 3 (SENP3) reverses sumoylation of small ubiquitin-like modifier (SUMO)-conjugates. We demonstrated that Nrf2 was detected in the nuclei of laryngeal carcinoma cells, but not in cells of tissues surrounding the cancer, which correlated with the appearance of SENP3 in the nuclei. Silencing of Nrf2 in laryngeal carcinoma cell line Hep-2 significantly reduced cell viability and enhanced apoptosis rates under cisplatin, 5-fluorouracil (5-FU) and phenethyl isothiocyanate (PEITC) exposure. Cisplatin exposure induced ROS stress in Hep-2 cells in a time-dependent manner and was accompanied by increased Nrf2 and SENP3 protein accumulations, an effect reversed by the addition of the antioxidant N-acetyl-cysteine (NAC). Silencing of SENP3 led to reduced Nrf2 protein levels, whereas overexpression of SENP3 led to concomitant enhanced transcription of the Nrf2 target genes HO-1, NQO1, GCLC and GSTM1. Immunoprecipitation showed that overexpressed Nrf2 and SENP3 could be precipitated together, indicating that they were intracellular bound to each other. Our data identified intranuclear activation of Nrf2 is triggered by cisplatin-induced ROS development through the activity of SENP3. These findings provide novel insights into the Nrf2 reduced cancer cell response to the chemotherapy of laryngeal carcinoma.

Fish SUMO3 functions as a critical antiviral molecule against iridovirus and nodavirus

Protein SUMOylation (SUMO is small ubiquitin-related modifier) is a dynamic process that is strictly regulated under physiological and pathological conditions. We previously cloned and characterized two SUMO homologue genes (EcSUMO1 and EcSUMO2) from orange-spotted grouper (Epinephelus coioides). In the present study, the SUMO3 homologue from E. coioides (EcSUMO3) was cloned and its possible roles in fish immunity were analyzed. The open reading frame of EcSUMO3 contains 285 base pairs encoding a 94 amino acid protein with a predicted molecular mass of 10.73 kDa. The protein sequence of EcSUMO3 revealed similar domains with mammals, including the UBQ (ubiquitin-like proteins) domain, the hydrophobic surface, the Ulp1-Smt3 interaction sites, a VKTE motif and the C-terminal Gly residues. EcSUMO3 shares 46.83% and 89.58% identity with EcSUMO1 and EcSUMO2, respectively, and it shares 94%, 98%, and 98% identity with SUMO3 from Oreochromis niloticus, Danio rerio, and Homo sapiens, respectively. Quantitative real-time polymerase chain reaction analysis indicated that EcSUMO3 was constitutively expressed in all of the analyzed tissues in healthy grouper. EcSUMO3 expression levels were remarkably (p < 0.01) up-regulated in grouper spleen (GS) cells in response to stimulation with red-spotted grouper nervous necrosis virus (RGNNV) and Singapore grouper iridovirus (SGIV). EcSUMO3 was distributed in both the cytoplasm and nucleus in GS cells. EcSUMO3 enhanced SGIV and RGNNV replication during viral infection in vitro. These results are important for better understanding of the SUMO pathway in fish and provide insights into the regulatory mechanism of viral infection in E. coioides under farmed conditions.

Preliminary evidence of reductive stress in human cytotoxic T cells following exercise

This study investigated immunophenotypic differences in intracellular thiol redox state of peripheral blood mononuclear cells (PBMCs) isolated from trained [ n = 9, means ± SD: age 28 ± 5 yr; (body mass index) BMI 23.2 ± 2.6 kg/m2; V̇o2max (maximal oxygen intake)56.9 ± 6.1 ml·kg−1·min−1] and recreationally active (RA, n = 11, means ± SD: age 27 ± 6 yr; BMI 24.2 ± 3.7 kg/m2; V̇o2max 45.1 ± 6.4 ml·kg−1·min−1) participants before and after a maximal aerobic exercise tolerance test. Blood samples were taken before (Pre), during (sample acquired at 70% maximum heart rate), immediately after (Post + 0), and 15 min postexercise (Post + 15). PBMCs were isolated, and reduced thiol analysis [fluorescein-5 maleimide (F5M)] by immunophenotype [cluster of differentiation (CD)3+, CD4+, and CD8+] was performed using flow cytometry. A significant increase in cellular F5M fluorescence was observed in CD3+ T cells at Post + 0, with changes driven to a greater extent by CD8+ T cells (fold change in both groups CD4: +2.3, CD8: +2.8; P < 0.05). Further analysis revealed a population of highly reduced CD8+ T cells (CD8+T-reduced+) that significantly increased from Pre to Post + 0 in RA participants only (RA: +272 cell/µl, P < 0.05). To understand these results further, CD8+T-reduced+ and CD8+T-reduced− cells were analyzed for immunophenotype in response to the same exercise protocol ( n = 6, means ± SD: age 24 ± 5 yr; BMI 25.7 ± 4.1 kg·m−2; V̇o2max 41.33 ± 7.63 ml·kg−1·min−1). CD8+T-reduced+ had significantly less lymphoid homing potential (chemokine receptor type 7) Post + 0 compared with Pre. This study is the first, to our knowledge, to demonstrate that lymphocyte populations become more reductive in response to acute exercise.

NEW & NOTEWORTHY The study presented provides the first evidence to suggest that cytotoxic T cells become transiently reductive in healthy individuals following a single bout of cycling. Detection of these cells was enabled via the use of a flow cytometric assay that incorporates the thiol reactive probe fluorescein-5 maleimide. Using this method, transient reductive stress in viable T cells is permissible and provides the basis for further research in the area of exercise immunology.

SUMO in the DNA Double-Stranded Break Response: Similarities, Differences, and Cooperation with Ubiquitin

In recent years, our knowledge of the varied role that ubiquitination plays in promoting signal amplification, novel protein interactions, and protein turnover has progressed rapidly. This is particularly remarkable in the examination of how DNA double-stranded breaks (DSBs) are repaired, with many components of the ubiquitin (Ub) conjugation, de-conjugation, and recognition machinery now identified as key factors in DSB repair. In addition, a member of the Ub-like family, small Ub-like modifier (SUMO), has also been recognised as integral for efficient repair. Here, we summarise our emerging understanding of SUMOylation both as a distinct modification and as a cooperative modification with Ub, using the cellular response to DNA DSBs as the primary setting to compare these modifications.

SUMOylation and SENP3 regulate STAT3 activation in head and neck cancer

Hyperphosphorylation of signal transducer and activator of transcription 3 (STAT3) has been found in various types of human cancers, including head and neck cancer (HNC). Although smoking is critical in the development and progression of HNC, how tobacco components activate STAT3 is unclear. We demonstrated that exposure of HNC cell lines to a tobacco extract induced a rapid Y705 phosphorylation of STAT3 and a rapid increase in the SUMO protease SENP3 that depended on a simultaneous increase in reactive oxygen species. We identified that SUMOylation at the lysine 451 site facilitated STAT3 binding to the phosphatase TC45 through an SUMO-interacting motif of TC45. SENP3 could thus enhance STAT3 phosphorylation by de-conjugating the SUMO2/3 modification of STAT3. Knocking-down of SENP3 greatly impaired basal and induced STAT3 phosphorylation by tobacco extract or interleukin 6. A correlation between SENP3 protein levels and STAT3 Y705 phosphorylation levels in human laryngeal carcinoma specimens was found, which was more significant in the specimens derived from the smoker patients and with poor clinicopathological parameters. Our data identified SUMOylation as a previously undescribed post-translational modification of STAT3 and SENP3 as a critical positive modulator of tobacco- or cytokine-induced STAT3 activation. These findings provide novel insights into the hyperphosphorylation of STAT3 in development of HNC.

Quantitative proteomics study of the neuroprotective effects of B12 on hydrogen peroxide-induced apoptosis in SH-SY5Y cells

B12 belongs to the coumarin class of compounds that have been shown to have various physiological and pharmacological activities including anti-inflammatory, antibacterial, and antioxidant. In the present study, we characterised the neuroprotective effects of B12 against H₂O₂-induced neuronal cell damage in SH-SY5Y cells. Protein expression profiling in combination with pathway analysis was deployed to investigate the molecular events associated with the neuroprotective effects in human neuronal cells using a label-free quantitative proteomics approach. A total of 22 proteins were significantly differentially expressed in H₂O₂-damaged cells with or without B12 treatment. Bioinformatics analysis using the Cytoscape platform indicated that poly pyrimidine tract binding protein 1 (PTBP1) was highly associated with the protective effect, and western blotting verified that PTBP1 was up-regulated in H₂O₂ + B12 treatment group, compared with the H₂O₂ treated group. PTBP RNAi experiments knocked down PTBP expression, which cancelled out the protective effect of B12 on cell viability. Thus, we infer that B12 neuroprotective activity involves up-regulation of PTBP1 and its associated signalling networks following H₂O₂-induced apoptosis in SH-SY5Y cells. B12 or related compounds may prove to be useful therapeutic agents for the treatment of neurodegenerative diseases such as Alzheimer’s and Parkinson’s.

SENP3 regulates the global protein turnover and the Sp1 level via antagonizing SUMO2/3-targeted ubiquitination and degradation

SUMOylation is recently found to function as a targeting signal for the degradation of substrates through the ubiquitin-proteasome system. RNF4 is the most studied human SUMO-targeted ubiquitin E3 ligase. However, the relationship between SUMO proteases, SENPs, and RNF4 remains obscure. There are limited examples of the SENP regulation of SUMO2/3-targeted proteolysis mediated by RNF4. The present study investigated the role of SENP3 in the global protein turnover related to SUMO2/3-targeted ubiquitination and focused in particular on the SENP3 regulation of the stability of Sp1. Our data demonstrated that SENP3 impaired the global ubiquitination profile and promoted the accumulation of many proteins. Sp1, a cancer-associated transcription factor, was among these proteins. SENP3 increased the level of Sp1 protein via antagonizing the SUMO2/3-targeted ubiquitination and the consequent proteasome-dependent degradation that was mediated by RNF4. De-conjugation of SUMO2/3 by SENP3 attenuated the interaction of Sp1 with RNF4. In gastric cancer cell lines and specimens derived from patients and nude mice, the level of Sp1 was generally increased in parallel to the level of SENP3. These results provided a new explanation for the enrichment of the Sp1 protein in various cancers, and revealed a regulation of SUMO2/3 conjugated proteins whose levels may be tightly controlled by SENP3 and RNF4.

Oxidative stress response and Nrf2 signaling in aging

Increasing oxidative stress, a major characteristic of aging, has been implicated in a variety of age-related pathologies. In aging, oxidant production from several sources is increased, whereas antioxidant enzymes, the primary lines of defense, are decreased. Repair systems, including the proteasomal degradation of damaged proteins, also decline. Importantly, the adaptive response to oxidative stress declines with aging. Nrf2/EpRE signaling regulates the basal and inducible expression of many antioxidant enzymes and the proteasome. Nrf2/EpRE activity is regulated at several levels, including transcription, posttranslation, and interactions with other proteins. This review summarizes current studies on age-related impairment of Nrf2/EpRE function and discusses the changes in Nrf2 regulatory mechanisms with aging.

Adenovirus E4-ORF3 Targets PIAS3 and Together with E1B-55K Remodels SUMO Interactions in the Nucleus and at Virus Genome Replication Domains

Adenovirus E4-ORF3 and E1B-55K converge in subverting critical overlapping cellular pathways to facilitate virus replication. Here, we show that E1B-55K and E4-ORF3 induce sumoylation and the assembly of SUMO2/3 viral genome replication domains. Using a conjugation-deficient SUMO2 construct, we demonstrate that SUMO2/3 is recruited to E2A viral genome replication domains through noncovalent interactions. E1B-55K and E4-ORF3 have critical functions in inactivating MRN and ATM to facilitate viral genome replication. We show that ATM kinase inhibitors rescue ΔE1B-55K/ΔE4-ORF3 viral genome replication and that the assembly of E2A domains recruits SUMO2/3 independently of E1B-55K and E4-ORF3. However, the morphology and organization of SUMO2/3-associated E2A domains is strikingly different from that in wild-type Ad5-infected cells. These data reveal that E1B-55K and E4-ORF3 specify the nuclear compartmentalization and structure of SUMO2/3-associated E2A domains, which could have important functions in viral replication. We show that E4-ORF3 specifically targets and sequesters the cellular E3 SUMO ligase PIAS3 but not PIAS1, PIAS2, or PIAS4. The assembly of E4-ORF3 into a multivalent nuclear matrix is required to target PIAS3. In contrast to MRN, PIAS3 is targeted by E4-ORF3 proteins from disparate adenovirus subgroups. Our studies reveal that PIAS3 is a novel and evolutionarily conserved target of E4-ORF3 in human adenovirus infections. Furthermore, we reveal that viral proteins not only disrupt but also usurp SUMO2/3 to transform the nucleus and assemble novel genomic domains that could facilitate pathological viral replication.

IMPORTANCE

SUMO is a key posttranslational modification that modulates the function, localization, and assembly of protein complexes. In the ever-escalating host-pathogen arms race, viruses have evolved strategies to subvert sumoylation. Adenovirus is a small DNA tumor virus that is a global human pathogen and key biomedical agent in basic research and therapy. We show that adenovirus infection induces global changes in SUMO localization and conjugation. Using virus and SUMO mutants, we demonstrate that E1B-55K and E4-ORF3 disrupt and usurp SUMO2/3 interactions to transform the nucleus and assemble highly structured and compartmentalized viral genome domains. We reveal that the cellular E3 SUMO ligase PIAS3 is a novel and conserved target of E4-ORF3 proteins from disparate adenovirus subgroups. The induction of sumoylation and SUMO2/3 viral replication domains by early viral proteins could play an important role in determining the outcome of viral infection.

De-SUMOylation of FOXC2 by SENP3 promotes the epithelial-mesenchymal transition in gastric cancer cells

The impact of cellular oxidative stress in promoting the epithelial-mesenchymal transition (EMT) has been noticed. Our previous study shows that SENP3, a redox-sensitive SUMO2/3-specific protease, accumulates in a variety of cancers, but whether SENP3 and SUMOylation involve in the regulation of EMT is unclear. The present study uncovers a novel role of SENP3 in promoting the EMT process in gastric cancer via regulating an EMT-inducing transcription factor, forkhead box C2 (FOXC2). We demonstrate that the expression of mesenchymal marker genes and cell migration ability are enhanced in SENP3-overexpressing gastric cancer cells and attenuated in SENP3-knockdown cells. A nude mouse model and a set of patient's specimens suggest the correlation between SENP3 and gastric cancer metastasis. Biochemical assays identify FOXC2 as a substrate of SENP3. Meanwhile N-cadherin is verified as a target gene of FOXC2, which is transcriptionally activated by a SUMO-less FOXC2. Additionally, reactive oxygen species-induced de-SUMOylation of FOXC2 can be blocked by silencing endogenous SENP3. In conclusion, SENP3, which is increased in gastric cancer cells, potentiates the transcriptional activity of FOXC2 through de-SUMOylation, in favor of the induction of specific mesenchymal gene expression in gastric cancer metastasis.

Transcriptional regulation of heterogeneous nuclear ribonucleoprotein K gene expression

Heterogeneous nuclear ribonucleoprotein K (hnRNP K) is importantly involved in the regulation of development, DNA damage response, and several human diseases. The molecular mechanisms that control the expression of hnRNP K are largely unknown. In the present study, we investigated the detailed mechanism of the transcriptional regulation of human hnRNP K gene. Two activating and one repressive elements located in the proximal segment of the transcriptional initiation site were identified in hnRNP K gene. A 19 bp-region was responsible for the inhibitory activities of the repressor element. Twenty proteins were identified by DNA-affinity purification and mass spectrometry analyses as binding partners of the primary activating element in the hnRNP K promoter. Chromatin immunoprecipitation and EMSA analysis confirmed the binding of Sp1 with hnRNP K promoter. Sp1 enhanced the promoter activity, increased the expression of hnRNP K, and reduced the mRNA level of angiotensinogen, a gene known to be negatively regulated by hnRNP K. In summary, the current study characterized the promoter elements that regulate the transcription of human hnRNP K gene, identified 20 proteins that bind to the primary activating element of hnRNP K promoter, and demonstrated a functional effect of Sp1 on hnRNP K transcription.

CR6-interacting factor 1 is a key regulator in Aβ-induced mitochondrial disruption and pathogenesis of Alzheimer's disease

Mitochondrial dysfunction, often characterized by massive fission and other morphological abnormalities, is a well-known risk factor for Alzheimer's disease (AD). One causative mechanism underlying AD-associated mitochondrial dysfunction is thought to be amyloid-β (Aβ), yet the pathways between Aβ and mitochondrial dysfunction remain elusive. In this study, we report that CR6-interacting factor 1 (Crif1), a mitochondrial inner membrane protein, is a key player in Aβ-induced mitochondrial dysfunction. Specifically, we found that Crif1 levels were downregulated in the pathological regions of Tg6799 mice brains, wherein overexpressed Aβ undergoes self-aggregation. Downregulation of Crif1 was similarly observed in human AD brains as well as in SH-SY5Y cells treated with Aβ. In addition, knockdown of Crif1, using RNA interference, induced mitochondrial dysfunction with phenotypes similar to those observed in Aβ-treated cells. Conversely, Crif1 overexpression prevented Aβ-induced mitochondrial dysfunction and cell death. Finally, we show that Aβ-induced downregulation of Crif1 is mediated by enhanced reactive oxygen species (ROS) and ROS-dependent sumoylation of the transcription factor specificity protein 1 (Sp1). These results identify the ROS-Sp1-Crif1 pathway to be a new mechanism underlying Aβ-induced mitochondrial dysfunction and suggest that ROS-mediated downregulation of Crif1 is a crucial event in AD pathology. We propose that Crif1 may serve as a novel therapeutic target in the treatment of AD.

Design, synthesis, and biological evaluation of shikonin and alkannin derivatives as potential anticancer agents via a prodrug approach

To minimize the cytotoxicity of shikonin and alkannin that arises through the generation of reactive oxygen species (ROS) and alkylation of the naphthazarin ring, two series of novel core-scaffold-modified shikonin and alkannin derivatives were designed. These derivatives, which differ in their configurational and positional isomerism (R-, S-, and 2- and 6-isomers) were synthesized in high enantiomeric excess (>99 % ee). The selectivity of the dimethylated derivatives was significantly higher than the parent shikonin in vitro, but some side effects were still observed in vivo. Surprisingly, the dimethylated diacetyl derivatives with poor anticancer activity in vitro showed tumor-inhibiting effects similar to paclitaxel without any toxicity in vivo. The anticancer activity of these derivatives is in agreement with their low ROS generation and alkylating capacity, emphasizing their potential as prodrugs. This strategy provides means to address the nonspecific cytotoxicity of naphthazarin analogues toward normal cells.

Synthesis and evaluation of novel alkannin and shikonin oxime derivatives as potent antitumor agents

A set of forty alkannin and shikonin oxime derivatives were firstly designed and synthesized. Their cytotoxicities against three kinds of tumor cells and a normal cell line were tested and compared with alkannin and shikonin. The cell-based investigation demonstrated that some oxime derivatives were more or comparatively effective to the lead compounds, especially their selective and excellent antitumor activities towards K562 cells with no toxicity in normal cells. We may conclude that oximate modification to the mother nucleus of alkannin and shikonin is an available approach to acquire potent antitumor agents.

Aberrant sumoylation signaling evoked by reactive oxygen species impairs protective function of Prdx6 by destabilization and repression of its transcription

Loss of the cytoprotective protein peroxiredoxin 6 (Prdx6) in cells that are aging or under oxidative stress is known to be linked to the pathobiology of many age-related diseases. However, the mechanism by which Prdx6 activity goes awry is largely unknown. Using Prdx6-deficient (Prdx6(-/-) ) cells as a model for aging or redox active cells, human/mouse lens epithelial cells (LECs) facing oxidative stress and aging lenses, we found a significant increase in the levels of small ubiquitin-like modifier (Sumo)1 conjugates. These cells displayed increased levels of Sumo1 and reduced the expression of Prdx6. Specifically, we observed that Prdx6 is a target for aberrant sumoylation signaling, and that Sumo1 modification reduces its cellular abundance. LECs overexpressing Sumo1 showed reduced expression and activity of Prdx6 and its transactivator specificity protein 1 (Sp1), mRNA and protein with increased levels of reactive oxygen species; those cells were vulnerable to oxidative stress-induced cell death. A significant reduction in Prdx6, Sp1 protein and mRNA expression was observed in redox active Prdx6(-/-) cells and in aging lenses/LECs. The reduction was correlated with increased expression of Sumo1 and enrichment of the inactive form (dimeric) of Sumo-specific protease (Senp)1. Experiments with Sumo1-fused Prdx6 and Prdx6 promoter-linked to chloramphenicol acetyltransferase reporter gene constructs indicated that Sumo1 dysregulated Prdx6 activity by reducing its abundance and attenuating its transcription; in contrast, the delivery of Senp1 or Prdx6 reversed the process. The data show that reactive oxygen species-evoked aberrant sumoylation signaling affects Prdx6 activity by reducing Prdx6 abundance, as well as transcription. The findings of the present study may provide a foundation for a strategy to repair deleterious oxidative signaling generated by a reduced activity of Prdx6.

Arsenic exposure triggers a shift in microRNA expression

Exposure to inorganic Arsenic (iAs) through drinking water is a major public health problem affecting most countries. iAs has been classified by the International Agency for Research on Cancer as Group 1: "Carcinogenic to humans". Although numerous studies have shown the related adverse effects of iAs, sensitive appropriate biomarkers for studies of environmental epidemiology are still required. The present work aims at investigate the role of microRNAs (miRNAs), powerful negative regulators of gene expression, playing a key role in many physiological and pathological cellular processes, in iAs exposure. To this end, we analyzed miRNA changes in expression profile triggered by iAs exposure in Jurkat cell line. We used microarray technology to profile the expression of miRNAs following 2 μmol/L sodium arsenite treatment at different time points. Moreover, we performed phenotypic analysis of iAs treated cells. Real Time Polymerase Chain Reaction (RT-PCR) was used to validate miRNA microarray data and to assay expression modulation of selected relevant mRNAs. Finally, bioinformatics techniques were applied to reconstruct iAs-relevant molecular pathways and miRNA regulatory networks from the expression data. We report miRNAs modulated after iAs treatment in Jurkat cells. In particular, we highlight 36 miRNAs exhibiting consistent dysregulation and particularly a panel of 8 miRNAs which we also validated by RT-PCR analysis. Computational analysis of lists of putative target genes for these 8 miRNAs points to an involvement in arsenic-response pathways, for a subset of them, that were analyzed by RT-PCR. Furthermore, iAs exposure reveals induction of cell cycle progression and the failure of apoptosis, supporting the idea of iAs carcinogenic activity. Our study provides a list of miRNAs whose expression levels are affected by iAs treatment, corroborating the importance of proceeding with the hunt for specific subset of miRNAs, which can serve as potential biomarkers of iAs effects with useful diagnostic value.

Nuclear pool of phosphatidylinositol 4 phosphate 5 kinase 1α is modified by polySUMO-2 during apoptosis

Phosphatidylinositol 4 phosphate 5 kinase 1α (PIP5K) is mainly localized in the cytosol and plasma membrane. Studies have also indicated its prominent association with nuclear speckles. The exact nature of this nuclear pool of PIP5K is not clear. Using biochemical and microscopic techniques, we have demonstrated that the nuclear pool of PIP5K is modified by SUMO-1 in HEK-293 cells stably expressing PIP5K. Moreover, this SUMOylated pool of PIP5K increased during apoptosis. PolySUMO-2 chain conjugated PIP5K was detected by pull-down experiment using affinity-tagged RNF4, a polySUMO-2 binding protein, during late apoptosis.

Effects of radiation on the epidermal growth factor receptor pathway in the heart

PURPOSE

Radiation-induced heart disease (RIHD) is a serious side-effect of thoracic radiotherapy. The epidermal growth factor receptor (EGFR) pathway is essential for the function and survival of cardiomyocytes. Hence, agents that target the EGFR pathway are cardiotoxic. Tocotrienols protect from radiation injury, but may also enhance the therapeutic effects of EGFR pathway inhibitors in cancer treatment. This study investigated the effects of local irradiation on the EGFR pathway in the heart and tests whether tocotrienols may modify radiation-induced changes in this pathway.

METHODS

Male Sprague-Dawley rats received image-guided localized heart irradiation with 21 Gy. Twenty four hours before irradiation, rats received a single dose of tocotrienol-enriched formulation or vehicle by oral gavage. At time points from 2 h to 9 months after irradiation, left ventricular expression of EGFR pathway mediators was studied.

RESULTS

Irradiation caused a decrease in the expression of epidermal growth factor (EGF) and neuregulin-1 (Nrg-1) mRNA from 6 h up to 10 weeks, followed by an upregulation of these ligands and the receptor erythroblastic leukemia viral oncogene homolog (ErbB)4 at 6 months. In addition, the upregulation of Nrg-1 was statistically significant up to 9 months after irradiation. A long-term upregulation of ErbB2 protein did not coincide with changes in transcription or post-translational interaction with the chaperone heat shock protein 90 (HSP90). Pretreatment with tocotrienols prevented radiation-induced changes at 2 weeks.

CONCLUSIONS

Local heart irradiation causes long-term changes in the EGFR pathway. Studies have to address how radiation may interact with cardiotoxic effects of EGFR inhibitors.

Starting and stopping SUMOylation. What regulates the regulator?

A large number of proteins are modified post-translationally by the ubiquitin-like protein (Ubl) SUMO. This process, known as sumoylation, regulates the function, localisation and activity of target proteins as part of normal cellular metabolism, e.g., during development, and through the cell cycle, as well as in response to a range of stresses. In order to be effective, the sumoylation pathway itself must also be regulated. This review describes how the SUMOylation process is regulated. In particular, regulation of the SUMO conjugation and deconjugation machinery at the level of transcription and by post-translational modifications is discussed.

Promyelocytic leukemia (PML) protein plays important roles in regulating cell adhesion, morphology, proliferation and migration

PML protein plays important roles in regulating cellular homeostasis. It forms PML nuclear bodies (PML-NBs) that act like nuclear relay stations and participate in many cellular functions. In this study, we have examined the proteome of mouse embryonic fibroblasts (MEFs) derived from normal (PML^+/+) and PML knockout (PML^−/−) mice. The aim was to identify proteins that were differentially expressed when MEFs were incapable of producing PML. Using comparative proteomics, total protein were extracted from PML^−/− and PML^+/+ MEFs, resolved by two dimensional electrophoresis (2-DE) gels and the differentially expressed proteins identified by LC-ESI-MS/MS. Nine proteins (PML, NDRG1, CACYBP, CFL1, RSU1, TRIO, CTRO, ANXA4 and UBE2M) were determined to be down-regulated in PML^−/− MEFs. In contrast, ten proteins (CIAPIN1, FAM50A, SUMO2 HSPB1 NSFL1C, PCBP2, YWHAG, STMN1, TPD52L2 and PDAP1) were found up-regulated. Many of these differentially expressed proteins play crucial roles in cell adhesion, migration, morphology and cytokinesis. The protein profiles explain why PML^−/− and PML^+/+ MEFs were morphologically different. In addition, we demonstrated PML^−/− MEFs were less adhesive, proliferated more extensively and migrated significantly slower than PML^+/+ MEFs. NDRG1, a protein that was down-regulated in PML^−/− MEFs, was selected for further investigation. We determined that silencing NDRG1expression in PML^+/+ MEFs increased cell proliferation and inhibited PML expression. Since NDRG expression was suppressed in PML^−/− MEFs, this may explain why these cells proliferate more extensively than PML^+/+ MEFs. Furthermore, silencing NDRG1expression also impaired TGF-β1 signaling by inhibiting SMAD3 phosphorylation.

The biphasic redox sensing of SENP3 accounts for the HIF-1 transcriptional activity shift by oxidative stress

AIM

To investigate the mechanisms underlying the biphasic redox regulation of hypoxia-inducible factor-1 (HIF-1) transcriptional activity under different levels of oxidative stress caused by reactive oxidative species (ROS).

METHODS

HeLa cells were exposed to different concentrations of H(2)O(2) as a simple model for mild and severe oxidative stress. Luciferase reporter assay and/or quantitative real-time PCR were used to investigate the transcriptional activity. Immunoblot was used to detect protein expression. Chromatin immunoprecipitation assay was used to detect HIF-1/DNA binding. The interaction of p300 with HIF-1α or with SENP3, and the SUMO2/3 conjugation states of p300 were examined by coimmunoprecipitation.

RESULTS

HIF-1 transcriptional activity in HeLa cells was enhanced by low doses (0.05-0.5 mmol/L) of H(2)O(2), but suppressed by high doses (0.75-8.0 mmol/L) of H(2)O(2). The amount of co-activator p300 bound to HIF-1α in HeLa cells was increased under mild oxidative stress, but decreased under severe oxidative stress. The ROS levels differentially modified cysteines 243 and 532 in the cysteine protease SENP3, regulating the interaction of SENP3 with p300 to cause different SUMOylation of p300, thus shifting HIF-1 transcriptional activity.

CONCLUSION

The shift of HIF-1 transactivation by ROS is correlated with and dependent on the biphasic redox sensing of SENP3 that leads to the differential SENP3/p300 interaction and the consequent fluctuation in the p300 SUMOylation status.

Sequential posttranslational modifications program FEN1 degradation during cell-cycle progression

We propose that cell-cycle-dependent timing of FEN1 nuclease activity is essential for cell-cycle progression and the maintenance of genome stability. After DNA replication is complete at the exit point of the S phase, removal of excess FEN1 may be crucial. Here, we report a mechanism that controls the programmed degradation of FEN1 via a sequential cascade of posttranslational modifications. We found that FEN1 phosphorylation stimulated its SUMOylation, which in turn stimulated its ubiquitination and ultimately led to its degradation via the proteasome pathway. Mutations or inhibitors that blocked the modification at any step in this pathway suppressed FEN1 degradation. Critically, the presence of SUMOylation- or ubiquitination-defective, nondegradable FEN1 mutant protein caused accumulation of Cyclin B, delays in the G1 and G2/M phases, and polyploidy. These findings may represent a newly identified regulatory mechanism used by cells to ensure precise cell-cycle progression and to prevent transformation.

Redox sensing by proteins: oxidative modifications on cysteines and the consequent events

SIGNIFICANCE

Reactive oxygen species (ROS) are not only essential for the cell's normal functions, but also mediate many pathological effects. When cells experience oxidative stress, proteins are modulated by redox changes and ultimately generate novel signaling patterns. It remains elusive how proteins are modulated, rather than simply damaged, by ROS and then mediate the diverse cellular responses.

RECENT ADVANCES

During the past decade, researchers frequently used "redox sensor" for proteins. However, the term "redox sensing" has not been clearly defined to date. Thiols of cysteines are subjected to oxidative modifications. The conformation changes and the various types of post-translational modifications (PTMs) may result from thiol oxidation of the same protein or other proteins. The molecular effects of redox sensing include changes in protein activity, abundance, localization, and interaction with other biomacromolecules.

CRITICAL ISSUES

We discuss the emerging concept of cysteine-based redox sensing, emphasizing "sensing redox changes by proteins using their thiols." ROS are an input, and the conformation changes and/or the other PTMs after thiol oxidation are the output of redox sensing. Among dozens of redox sensing proteins listed in this article, SENP3 and caspase-9, which have been investigated in our work, are given particular attention. We also introduce the notion of biphasic and compartment-specific redox sensing by nuclear factor kappa B.

FUTURE DIRECTIONS

Understanding chemical modifications and conformational changes following protein redox sensing requires more studies in mass spectrometry and crystallography. Redox-indicative probes in live cells and tissues will help monitor redox-related biological and pathological progresses.