PIAS proteins modulate transcription factors by functioning as SUMO-1 ligases

A stress-dependent TDP-43 SUMOylation program preserves neuronal function

Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD) are overwhelmingly linked to TDP-43 dysfunction. Mutations in TDP-43 are rare, indicating that the progressive accumulation of exogenous factors - such as cellular stressors - converge on TDP-43 to play a key role in disease pathogenesis. Post translational modifications such as SUMOylation play essential roles in response to such exogenous stressors. We therefore set out to understand how SUMOylation may regulate TDP-43 in health and disease. We find that TDP-43 is regulated dynamically via SUMOylation in response to cellular stressors. When this process is blocked in vivo, we note age-dependent TDP-43 pathology and sex-specific behavioral deficits linking TDP-43 SUMOylation with aging and disease. We further find that SUMOylation is correlated with human aging and disease states. Collectively, this work presents TDP-43 SUMOylation as an early physiological response to cellular stress, disruption of which may confer a risk for TDP-43 proteinopathy.

Role of long non-coding RNAs and natural products in prostate cancer: insights into key signaling pathways

Prostate cancer (PC) ranks among the most prevalent cancers in males. Recent studies have highlighted intricate connections between long non-coding RNAs (lncRNAs), natural products, and cellular signaling in PC development. LncRNAs, which are RNA transcripts without protein-coding function, influence cell growth, programmed cell death, metastasis, and resistance to treatments through pathways like PI3K/AKT, WNT/β-catenin, and androgen receptor signaling. Certain lncRNAs, including HOTAIR and PCA3, are associated with PC progression, with potential as diagnostic markers. Natural compounds, such as curcumin and resveratrol, demonstrate anticancer effects by targeting these pathways, reducing tumor growth, and modulating lncRNA expression. For instance, curcumin suppresses HOTAIR levels, hindering PC cell proliferation and invasion. The interaction between lncRNAs and natural compounds may open new avenues for therapy, as these substances can simultaneously impact multiple signaling pathways. These complex interactions offer promising directions for developing innovative PC treatments, enhancing diagnostics, and identifying new biomarkers for improved prevention and targeted therapy. This review aims to map the multifaceted relationship among natural products, lncRNAs, and signaling pathways in PC pathogenesis, focusing on key pathways such as AR, PI3K/AKT/mTOR, WNT/β-catenin, and MAPK, which are crucial in PC progression and therapy resistance. Regulation of these pathways by natural products and lncRNAs could lead to new insights into biomarker identification, preventive measures, and targeted PC therapies.

Central role of SUMOylation in the regulation of chromatin interactions and transcriptional outputs of the androgen receptor in prostate cancer cells

The androgen receptor (AR) is pivotal in prostate cancer (PCa) progression and represents a critical therapeutic target. AR-mediated gene regulation involves intricate interactions with nuclear proteins, with many mediating and undergoing post-translational modifications that present alternative therapeutic avenues. Through chromatin proteomics in PCa cells, we identified SUMO ligases together with nuclear receptor coregulators and pioneer transcription factors within the AR's protein network. Intriguingly, this network displayed a significant association with SUMO2/3. To elucidate the influence of SUMOylation on AR chromatin interactions and subsequent gene regulation, we inhibited SUMOylation using ML-792 (SUMOi). While androgens generally facilitated the co-occupancy of SUMO2/3 and AR on chromatin, SUMOi induced divergent effects dependent on the type of AR-binding site (ARB). SUMOi augmented AR's pioneer-like binding on inaccessible chromatin regions abundant in androgen response elements (AREs) and diminished its interaction with accessible chromatin regions sparse in AREs yet rich in pioneer transcription factor motifs. The SUMOi-impacted ARBs divergently influenced AR-regulated genes; those associated with AR-mediated activation played roles in negative regulation of cell proliferation, while those with AR-mediated repression were involved in pattern formation. In conclusion, our findings underscore the pervasive influence of SUMOylation in shaping AR's role in PCa cells, potentially unveiling new therapeutic strategies.

ZMIZ2 facilitates hepatocellular carcinoma progression via LEF1 mediated activation of Wnt/β-catenin pathway

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the most common malignancies with a high lethality rate. ZMIZ2 is a transcriptional co-activator implicated in various human diseases. However, the role and molecular mechanism of ZMIZ2 in HCC remains to be elucidated.

METHODS

The expression and prognostic value of ZMIZ2 in HCC was excavated from public databases and explored by bioinformatic analysis. Then the expression of ZMIZ2 and related genes was further validated by quantitative RT-PCR, western blotting, and immunohistochemistry. Loss and gain-of-function experiments were performed in vitro and in vivo to investigate the function of ZMIZ2 in HCC. In addition, transcriptome sequencing and immunoprecipitation was conducted to explore the potential molecular mechanisms of ZMIZ2.

RESULTS

ZMIZ2 was highly expressed in HCC and associated with poor prognosis. Silencing ZMIZ2 significantly inhibited HCC cell proliferation, cell cycle process, migration, and invasion in vitro, and also inhibited the progression of HCC in vivo. Additionally, ZMIZ2 expression was correlated with immune cell infiltration in HCC samples. Somatic mutation analysis showed that ZMIZ2 and TP53 mutations jointly affected the progression of HCC. Mechanistically, ZMIZ2 interacted with LEF1 to regulate malignant progression of HCC by activating the Wnt/β-catenin pathway.

CONCLUSION

ZMIZ2 was overexpressed in HCC and associated with poor prognosis. The overexpression of ZMIZ2 was corelated with malignant phenotype, and it facilitated HCC progression via LEF1-mediated activation of the Wnt/β-catenin pathway. Furthermore, ZMIZ2 could be served as a prognostic biomarker and a new therapeutic target for HCC.

MYB regulates the SUMO protease SENP1 and its novel interaction partner UXT, modulating MYB target genes and the SUMO landscape

SUMOylation is a post-translational modification frequently found on nuclear proteins, including transcription factors (TFs) and coactivators. By controlling the activity of several TFs, SUMOylation may have far-reaching effects. MYB is an example of a developmental TF subjected to SUMO-mediated regulation, through both SUMO conjugation and SUMO binding. How SUMO affects MYB target genes is unknown. Here, we explored the global effect of reduced SUMOylation of MYB on its downstream gene programs. RNA-Seq in K562 cells after MYB knockdown and rescue with mutants having an altered SUMO status revealed a number of differentially regulated genes and distinct gene ontology term enrichments. Clearly, the SUMO status of MYB both quantitatively and qualitatively affects its regulome. The transcriptome data further revealed that MYB upregulates the SUMO protease SENP1, a key enzyme that removes SUMO conjugation from SUMOylated proteins. Given this role of SENP1 in the MYB regulome, we expanded the analysis, mapped interaction partners of SENP1, and identified UXT as a novel player affecting the SUMO system by acting as a repressor of SENP1. MYB inhibits the expression of UXT suggesting that MYB is able not only to control a specific gene program directly but also indirectly by affecting the SUMO landscape through SENP1 and UXT. These findings suggest an autoactivation loop whereby MYB, through enhancing SENP1 and reducing UXT, is itself being activated by a reduced level of repressive SUMOylation. We propose that overexpressed MYB, seen in multiple cancers, may drive this autoactivation loop and contribute to oncogenic activation of MYB.

A protein inhibitor of activated STAT (CgPIAS) negatively regulates the expression of ISGs by inhibiting STAT activation in oyster Crassostrea gigas

The protein inhibitor of activated STAT (PIAS) family proteins act as the important negative regulators in janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathway, which can be also involved in regulating the expression of interferon-stimulated genes (ISGs). In the present study, a PIAS homologue (designated as CgPIAS) was identified from oyster Crassostrea gigas. The open reading frame (ORF) of CgPIAS cDNA was of 1887 bp encoding a peptide of 628 amino acid residues. The CgPIAS protein contains a conserved scaffold attachment factor A/B/acinus/PIAS (SAP) domain, a Pro-Ile-Asn-Ile-Thr (PINIT) motif, a RING-finger-like zinc-binding domain (RLD) and two SUMO-interaction Motifs (SIMs). The deduced amino acid sequence of CgPIAS shared 74.58-81.36% similarity with other PIAS family members in the RLD domain. The mRNA transcripts of CgPIAS were detected in all the tested tissues with highest level in haemocytes (32.98-fold of mantles, p < 0.001). After poly (I:C) and recombinant Interferon-like protein (rCgIFNLP) stimulation, the mRNA expression of CgPIAS in haemocytes significantly up-regulated to the highest level at 48 h (7.38-fold, p < 0.001) and at 24 h (13.08-fold, p < 0.01), respectively. Moreover, the nuclear translocation of CgPIAS was observed in haemocytes after poly (I:C) stimulation. Biolayer Interferometry (BLI) assay revealed that the recombinant protein CgPIAS-RLD could interact with the recombinant protein CgSTAT in vitro with the K_D value of 3.88 × 10^-8 M. In the CgPIAS-RNAi oysters, the green signals of CgSTAT protein in nucleus of haemocytes increased compared with that in NC-RNAi group, and the mRNA expression of myxovirus resistance (CgMx1), oligoadenylate synthase-like proteins (CgOASL), CgViperin and IFN-induced protein 44-like (CgIFI44L-1) in haemocytes significantly increased at 12 h after poly (I:C) stimulation, which were 2.39-fold (p < 0.05), 2.18-fold (p < 0.001), 1.74-fold (p < 0.05), and 2.89-fold (p < 0.01) of that in control group, respectively. The above results indicated that CgPIAS negatively regulated the ISG expression by inhibiting STAT activation in oyster C. gigas.

Role of SUMOylation in Neurodegenerative Diseases

Neurodegenerative diseases (NDDs) are irreversible, progressive diseases with no effective treatment. The hallmark of NDDs is the aggregation of misfolded, modified proteins, which impair neuronal vulnerability and cause brain damage. The loss of synaptic connection and the progressive loss of neurons result in cognitive defects. Several dysregulated proteins and overlapping molecular mechanisms contribute to the pathophysiology of NDDs. Post-translational modifications (PTMs) are essential regulators of protein function, trafficking, and maintaining neuronal hemostasis. The conjugation of a small ubiquitin-like modifier (SUMO) is a reversible, dynamic PTM required for synaptic and cognitive function. The onset and progression of neurodegenerative diseases are associated with aberrant SUMOylation. In this review, we have summarized the role of SUMOylation in regulating critical proteins involved in the onset and progression of several NDDs.

SENP2 Promotes VSMC Phenotypic Switching via Myocardin De-SUMOylation

Myocardin is a master regulator of smooth muscle cell (SMC) differentiation, which induces the expression of smooth-muscle-specific genes through its direct association with serum response factor (SRF). During the past two decades, significant insights have been obtained regarding the regulatory control of myocardin expression and transcriptional activity at the transcriptional, post-transcriptional, and post-translational levels. However, whether and how SUMOylation plays important roles in modulating myocardin function remain elusive. In this study, we found that myocardin is modified by SUMO-1 at lysine 573, which can be reversibly de-conjugated by SENP2. SUMO-1 modification promotes myocardin protein stability, whereas SENP2 facilitates its proteasome-dependent degradation. Moreover, we found that PIAS4 is the SUMO E3 ligase that enhances the SUMOylation and protein stability of myocardin. Most importantly, we found that SENP2 promotes phenotypic switching of VSMC. We therefore concluded that SENP2 promotes VSMC phenotypic switching via de-SUMOylation of myocardin and regulation of its protein stability.

LINC00893 inhibits the progression of prostate cancer through miR-3173-5p/SOCS3/JAK2/STAT3 pathway

Background

Prostate cancer (PCa) is one of the most common malignant tumors in the male urinary system. In recent years, the morbidity and mortality of PCa have been increasing due to the limited effects of existing treatment strategies. Long non-coding RNA (lncRNA) LINC00893 was reported to inhibit the proliferation and metastasis of papillary thyroid cancer cells, but its role in PCa has not been reported. This study aims to investigate the role and underlying mechanism of LINC00893 in regulating the progression of PCa cells.

Methods

We first compared LINC00893 expression levels between PCa tissues and normal prostate tissues through TCGA database. The relative LINC00893 expression levels were further validated in 66 pairs of PCa tissues and para-cancerous normal tissues, as well as in PCa cell lines. Gain-of-function experiment was performed by transfecting PCa cell with LINC00893 expression vector, and CCK (Cell count kit)-8, 5-Ethynyl-2′-deoxyuridine (EdU) incorporation, colony information and transwell assays were conducted to assess the functional phenotypes. Dual-luciferase reporter, RNA-binding protein immunoprecipitation (RIP) and RNA pull-down assays were performed to evaluate the molecular interactions.

Results

LINC00893 was downregulated in PCa tissues and cell lines, and patients with low expression of LINC00893 were associated with a poorer overall survival rate. LINC00893 overexpression hindered the proliferation, epithelial-mesenchymal transition (EMT) as well as the migratory ability of PCa cells, and suppressed the tumorigenesis of PCa cells in nude mice. We further demonstrated that LINC00893 acted as a sponge for miR-3173-5p and inhibited its activity, which in turn regulated the suppressor of cytokine signaling 3 (SOCS3)/Janus Kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling axis.

Conclusions

Our study demonstrated that LINC00893 suppresses the progression of PCa cells through targeting miR-3173-5p/SOCS3/JAK2/STAT3 axis. Our data uncovers a novel tumor-suppressor role of LINC00893 in PCa, which may serve as a potential strategy for targeted therapy in PCa.

Grapical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-022-02637-4.

Site-specific SUMOylation of viral polymerase processivity factor: a way of localizingtoND10 subnuclear domains for restricted and self-controlled reproduction of herpesvirus

Lytic replication of human cytomegalovirus (HCMV), a member of β-herpesvirus, is a highly complicated and organized process that requires its DNA polymerase processivity factor, UL44, the first-reported HCMV replication protein subjected to SUMO post-translational modification (PTM). SUMOylation plays a pleiotropic role in protein functions of host cells and infecting viruses. Particularly, formation of herpesviral replication compartments (RCs) upon infection is induced in proximity to ND10 subnuclear domains, the host cell’s intrinsic antiviral immune devices and hot SUMOylation spots, relying just on SUMOylation of their protein components to become mature and functional in restriction of the viral replication. In this study, to unveil the exact role of SUMO PTM on UL44 involved in HCMV replication, we screened and identified PIAS3, an annotated E3 SUMO ligase, as a novel UL44-interacting protein engaged in cellular SUMOylation pathway. Co-existence of PIAS3 could enhance the UBC9-based SUMO modification of UL44 specifically at its conserved ⁴¹⁰lysine residue lying within the single canonical ψKxE SUMO Conjugation Motif (SCM). Intriguingly, we found this SCM-specific SUMOylation contributes to UL44 co-localization and interaction with subnuclear ND10 domains during infection, which in turn exerts an inhibitory effect on HCMV replication and growth. Together, these results highlight the importance of SUMOylation in regulating viral protein subnuclear localization, representing a novel way of utilizing ND10-based restriction to achieve the self-controlled slower replication and reproduction of herpesviruses.

Dissecting multiple roles of SUMOylation in prostate cancer

Protein modification with small ubiquitin-like modifiers (SUMOs) plays dual roles in prostate cancer (PCa) tumorigenesis and development. Any intermediary of the SUMO conjugation cycle going awry may forfeit the balance between tumorigenic potential and anticancer effects. Deregulated SUMOylation on the androgen receptor and oncoproteins also takes part in this pathological process, as exemplified by STAT3/NF-κB and tumor suppressors such as PTEN and p53. Here, we outline recent developments and discoveries of SUMOylation in PCa and present an overview of its multiple roles in PCa tumorigenesis/promotion and suppression, while elucidating its potential as a therapeutic target for PCa.

Dalhat M, Abdullah O, Kaleem M, Hosawi S, A Al-Abbasi F, Wu W, Choudhry H, Alhosin M. Targeting Post-Translational Modifications of the p73 Protein: A Promising Therapeutic Strategy for Tumors

The tumor suppressor p73 is a member of the p53 family and is expressed as different isoforms with opposing properties. The TAp73 isoforms act as tumor suppressors and have pro-apoptotic effects, whereas the ΔNp73 isoforms lack the N-terminus transactivation domain and behave as oncogenes. The TAp73 protein has a high degree of similarity with both p53 function and structure, and it induces the regulation of various genes involved in the cell cycle and apoptosis. Unlike those of the p53 gene, the mutations in the p73 gene are very rare in tumors. Cancer cells have developed several mechanisms to inhibit the activity and/or expression of p73, from the hypermethylation of its promoter to the modulation of the ratio between its pro- and anti-apoptotic isoforms. The p73 protein is also decorated by a panel of post-translational modifications, including phosphorylation, acetylation, ubiquitin proteasomal pathway modifications, and small ubiquitin-related modifier (SUMO)ylation, that regulate its transcriptional activity, subcellular localization, and stability. These modifications orchestrate the multiple anti-proliferative and pro-apoptotic functions of TAp73, thereby offering multiple promising candidates for targeted anti-cancer therapies. In this review, we summarize the current knowledge of the different pathways implicated in the regulation of TAp73 at the post-translational level. This review also highlights the growing importance of targeting the post-translational modifications of TAp73 as a promising antitumor strategy, regardless of p53 status.

Identification and Allelic Variants Associated With Cold Tolerance of PmPIAS in Pinctada fucata martensii

The protein inhibitor of activated STAT (PIAS) functions in diverse aspects, including immune response, cell apoptosis, cell differentiation, and proliferation. In the present study, the PIAS in the pearl oyster Pinctada fucata martensii was characterized. The sequence features of PmPIAS were similar to that of other PIAS sequences with PIAS typical domains, including SAP, Pro-Ile-Asn-Ile-Thr (PINIT), RLD domain, AD, and S/T-rich region. Homologous analysis showed that PmPIAS protein sequence showed the conserved primary structure compared with other species. Ribbon representation of PIAS protein sequences also showed a conserved structure among species, and the PINIT domain and RLD domain showed the conserved structure compared with the sequence of Homo sapiens. The expression pattern of PmPIAS in different tissues showed significant high expression in the gonad. PmPIAS also exhibited a significantly higher expression in the 1 and 2 days after cold tolerance stress (17°C) and showed its potential in the cold tolerance. The SNP analysis of the exon region of PmPIAS obtained 18 SNPs, and among them, 11 SNPs showed significance among different genotypes and alleles between cold tolerance selection line and base stock, which showed their potential in the breeding for cold tolerance traits.

SUMOylation regulates the protein network and chromatin accessibility at glucocorticoid receptor-binding sites

Glucocorticoid receptor (GR) is an essential transcription factor (TF), controlling metabolism, development and immune responses. SUMOylation regulates chromatin occupancy and target gene expression of GR in a locus-selective manner, but the mechanism of regulation has remained elusive. Here, we identify the protein network around chromatin-bound GR by using selective isolation of chromatin-associated proteins and show that the network is affected by receptor SUMOylation, with several nuclear receptor coregulators and chromatin modifiers preferring interaction with SUMOylation-deficient GR and proteins implicated in transcriptional repression preferring interaction with SUMOylation-competent GR. This difference is reflected in our chromatin binding, chromatin accessibility and gene expression data, showing that the SUMOylation-deficient GR is more potent in binding and opening chromatin at glucocorticoid-regulated enhancers and inducing expression of target loci. Blockage of SUMOylation by a SUMO-activating enzyme inhibitor (ML-792) phenocopied to a large extent the consequences of GR SUMOylation deficiency on chromatin binding and target gene expression. Our results thus show that SUMOylation modulates the specificity of GR by regulating its chromatin protein network and accessibility at GR-bound enhancers. We speculate that many other SUMOylated TFs utilize a similar regulatory mechanism.

The SUMOylation pathway suppresses arbovirus replication in Aedes aegypti cells

Mosquitoes are responsible for the transmission of many clinically important arboviruses that cause significant levels of annual mortality and socioeconomic health burden worldwide. Deciphering the mechanisms by which mosquitoes modulate arbovirus infection is crucial to understand how viral-host interactions promote vector transmission and human disease. SUMOylation is a post-translational modification that leads to the covalent attachment of the Small Ubiquitin-like MOdifier (SUMO) protein to host factors, which in turn can modulate their stability, interaction networks, sub-cellular localisation, and biochemical function. While the SUMOylation pathway is known to play a key role in the regulation of host immune defences to virus infection in humans, the importance of this pathway during arbovirus infection in mosquito vectors, such as Aedes aegypti (Ae. aegypti), remains unknown. Here we characterise the sequence, structure, biochemical properties, and tissue-specific expression profiles of component proteins of the Ae. aegypti SUMOylation pathway. We demonstrate significant biochemical differences between Ae. aegypti and Homo sapiens SUMOylation pathways and identify cell-type specific patterns of SUMO expression in Ae. aegypti tissues known to support arbovirus replication. Importantly, depletion of core SUMOylation effector proteins (SUMO, Ubc9 and PIAS) in Ae. aegypti cells led to enhanced levels of arbovirus replication from three different families; Zika (Flaviviridae), Semliki Forest (Togaviridae), and Bunyamwera (Bunyaviridae) viruses. Our findings identify an important role for mosquito SUMOylation in the cellular restriction of arboviruses that may directly influence vector competence and transmission of clinically important arboviruses.

Half the world’s population is at risk of infection from arboviruses transmitted by mosquitoes. Deciphering the viral-host interactions that influence the outcome of arbovirus infection in mosquitoes is beneficial to the development of future vector control strategies to limit arbovirus transmission and viral emergence within the human population. Similar to humans, mosquitoes possess different immune pathways to limit the replication of arboviruses. While the Small Ubiquitin-like MOdifier (SUMO) pathway is known to play an important role in the regulation of immune defences to viral infection in humans, the influence of this pathway during arbovirus infection in mosquito cells is currently unknown. Here we define the conservation, biochemical activity, and tissue distribution of the core effector proteins of the Aedes aegypti SUMOylation pathway. We show that the mosquito SUMOylation pathway plays a broadly antiviral role against a wide range of clinically important arboviruses, including Zika, Semliki Forest, and Bunyamwera viruses. Our findings identify SUMOylation as an important component of the antiviral response to arbovirus infection in mosquito cells.

A complementary study approach unravels novel players in the pathoetiology of Hirschsprung disease

Hirschsprung disease (HSCR, OMIM 142623) involves congenital intestinal obstruction caused by dysfunction of neural crest cells and their progeny during enteric nervous system (ENS) development. HSCR is a multifactorial disorder; pathogenetic variants accounting for disease phenotype are identified only in a minority of cases, and the identification of novel disease-relevant genes remains challenging. In order to identify and to validate a potential disease-causing relevance of novel HSCR candidate genes, we established a complementary study approach, combining whole exome sequencing (WES) with transcriptome analysis of murine embryonic ENS-related tissues, literature and database searches, in silico network analyses, and functional readouts using candidate gene-specific genome-edited cell clones. WES datasets of two patients with HSCR and their non-affected parents were analysed, and four novel HSCR candidate genes could be identified: ATP7A, SREBF1, ABCD1 and PIAS2. Further rare variants in these genes were identified in additional HSCR patients, suggesting disease relevance. Transcriptomics revealed that these genes are expressed in embryonic and fetal gastrointestinal tissues. Knockout of these genes in neuronal cells demonstrated impaired cell differentiation, proliferation and/or survival. Our approach identified and validated candidate HSCR genes and provided further insight into the underlying pathomechanisms of HSCR.

An in vitro Förster resonance energy transfer-based high-throughput screening assay identifies inhibitors of SUMOylation E2 Ubc9

SUMOylation is one of the posttranslational modifications that mediate cellular activities such as transcription, DNA repair, and signal transduction and is involved in the cell cycle. However, only a limited number of small molecule inhibitors have been identified to study its role in cellular processes. Here, we report a Förster resonance energy transfer (FRET) high-throughput screening assay based on the interaction between E2 Ubc9 and E3 PIAS1. Of the 3200 compounds screened, 34 (1.1%) showed higher than 50% inhibition and 4 displayed dose-response inhibitory effects. By combining this method with a label-free surface plasmon resonance (SPR) assay, false positives were excluded leading to discovering WNN0605-F008 and WNN1062-D002 that bound to Ubc9 with K_D values of 1.93 ± 0.62 and 5.24 ± 3.73 μM, respectively. We examined the effect of the two compounds on SUMO2-mediated SUMOylation of RanGAP1, only WNN0605-F008 significantly inhibited RanGAP1 SUMOylation, whereas WNN1062-D002 did not show any inhibition. These compounds, with novel chemical scaffolds, may serve as the initial material for developing new SUMOylation inhibitors.

Yellow Fever Virus Down-Regulates mRNA Expression of SOCS1 in the Initial Phase of Infection in Human Cell Lines

Flaviviruses are constantly evolving diverse immune evasion strategies, and the exploitation of the functions of suppressors of cytokine signalling (SOCS) and protein inhibitors of activated STATs (PIAS) to favour virus replication has been described for Dengue and Japanese encephalitis viruses but not for yellow fever virus (YFV), which is still of global importance despite the existence of an effective vaccine. Some mechanisms that YFV employs to evade host immune defence has been reported, but the expression patterns of SOCS and PIAS in infected cells is yet to be determined. Here, we show that SOCS1 is down-regulated early in YFV-infected HeLa and HEK 293T cells, while SOCS3 and SOCS5 are not significantly altered, and PIAS mRNA expression appears to follow a rise-dip pattern akin to circadian-controlled genes. We also demonstrate that YFV evades interferon-β application to produce comparable viral titres. This report provides initial insight into the in vitro expression dynamics of SOCS and PIAS upon YFV infection and a basis for further investigation into SOCS/PIAS expression and how these modulate the immune response in animal models.

SUMOylation stabilizes hSSB1 and enhances the recruitment of NBS1 to DNA damage sites

Human single-stranded DNA-binding protein 1 (hSSB1) is required for the efficient recruitment of the MRN complex to DNA double-strand breaks and is essential for the maintenance of genome integrity. However, the mechanism by which hSSB1 recruits NBS1 remains elusive. Here, we determined that hSSB1 undergoes SUMOylation at both K79 and K94 under normal conditions and that this modification is dramatically enhanced in response to DNA damage. SUMOylation of hSSB1, which is specifically fine-tuned by PIAS2α, and SENP2, not only stabilizes the protein but also enhances the recruitment of NBS1 to DNA damage sites. Cells with defective hSSB1 SUMOylation are sensitive to ionizing radiation, and global inhibition of SUMOylation by either knocking out UBC9 or adding SUMOylation inhibitors significantly enhances the sensitivity of cancer cells to etoposide. Our findings reveal that SUMOylation, as a novel posttranslational modification of hSSB1, is critical for the functions of this protein, indicating that the use of SUMOylation inhibitors (e.g., 2-D08 and ML-792) may be a new strategy that would benefit cancer patients being treated with chemo- or radiotherapy.

Duck PIAS2 Promotes H5N1 Avian Influenza Virus Replication Through Its SUMO E3 Ligase Activity

The protein inhibitor of the activated STAT2 (PIAS2) has been implicated in many cellular processes and can also regulate viral replication in mammals. However, the role of PIAS2 in the highly pathogenic avian influenza virus (HPAIV) H5N1 replication in ducks is still unclear. Through liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay, we identified that duck PIAS2 (duPIAS2) was one protein that interacted with the nucleoprotein (NP) from the H5N1 HPAIV strain of DK212. Through confocal microscopy images and Co-IP assay, we confirmed NP could interact with duPIAS2. Overexpression of duPIAS2 in primary duck embryo fibroblast (DEF) cells was shown to promote DK212 replication, and knockdown of duPIAS2 could repress DK212 replication. We further found duPIAS2 could promote NP SUMOylation through duck SUMO1 (duSUMO1), and the potential SUMOylation sites of NP were at lysines 7, 48, and 87. Furthermore, duPIAS2 promoted the replication of DK212, here relying on the activity of its SUMO E3 ligase. Duck SENP1 (duSENP1), a deSUMOylation enzyme, could repress NP SUMOylation and also inhibit DK212 replication. Together, we identified duPIAS2 could interact with NP and that duPIAS2 promoted H5N1 HPAIV replication, which might be related to NP SUMOylation.

Molecular mechanisms in SUMO conjugation

The small ubiquitin-like modifier (SUMO) is a post-translational modifier that can regulate the function of hundreds of proteins inside the cell. SUMO belongs to the ubiquitin-like family of proteins that can be attached to target proteins by a dedicated enzymatic cascade pathway formed by E1, E2 and E3 enzymes. SUMOylation is involved in many cellular pathways, having in most instances essential roles for their correct function. In this review, we want to highlight the latest research on the molecular mechanisms that lead to the formation of the isopeptidic bond between the lysine substrate and the C-terminus of SUMO. In particular, we will focus on the recent discoveries on the catalytic function of the SUMO E3 ligases revealed by structural and biochemical approaches. Also, we will discuss important questions regarding specificity in SUMO conjugation, which it still remains as a major issue due to the small number of SUMO E3 ligases discovered so far, in contrast with the large number of SUMO conjugated proteins in the cell.

Chordate PIAS proteins act as conserved repressors of the TRAF6 self-polyubiquitination

In mammals, PIAS proteins are important SUMO E3 ligases and act as versatile regulators of over sixty different proteins, including components from the NF-κB pathways. But the PIAS functions are not well-understood due to complicated molecular mechanisms and multiple gene paralogs with overlapping roles, which is especially true in lower vertebrates where dedicated studies are scarce. As a basal chordate with a single PIAS gene, amphioxus is a convenient model to study PIAS from the evolutionary perspective. TRAF6 is a critical adaptor of the NF-κB pathways but it is not known whether TRAF6 is regulated by PIAS. Here we discover that in mammalian cells, amphioxus PIAS inhibited NF-κB activation by co-localizing and binding with TRAF6. The interaction relied on the N-terminal SAP and PINIT domains of PIAS. TRAF6 is an E3 ubiquitin ligase, which initiates downstream NF-κB signaling by promoting its self-ubiquitination. Both amphioxus SUMO1 and Ubc9 (SUMO E2 ligase) could suppress TRAF6 self-ubiquitination and NF-κB activation, suggesting that the SUMOylation activity competed away the ubiquitination activity of TRAF6. However, we show that the wild-type PIAS and the mutant PIAS without SUMO E3 ligase activity both could inhibit TRAF6-mediated NF-κB activation by reducing TRAF6 self-ubiquitination. This implies that SUMO ligase activity is not the only mechanism for PIAS to negatively regulate TRAF6. Finally, we tested the interactions between human PIAS1-4 and TRAF6. It reveals that human PIAS1, 3 and 4, but not 2, were able to repress NF-κB activation by reducing TRAF6 self-ubiquitination. Taken together, our study discovers a conserved regulatory interaction between chordate PIAS and TRAF6. It therefore sheds light on the complicated role of PIAS in immune regulation, and may help to understand the PIAS functions in other lower chordate taxa, such as jawless and jawed fishes.

The role of JAK/STAT signaling pathway and its inhibitors in diseases

The JAK/STAT signaling pathway is an universally expressed intracellular signal transduction pathway and involved in many crucial biological processes, including cell proliferation, differentiation, apoptosis, and immune regulation. It provides a direct mechanism for extracellular factors-regulated gene expression. Current researches on this pathway have been focusing on the inflammatory and neoplastic diseases and related drug. The mechanism of JAK/STAT signaling is relatively simple. However, the biological consequences of the pathway are complicated due to its crosstalk with other signaling pathways. In addition, there is increasing evidence indicates that the persistent activation of JAK/STAT signaling pathway is closely related to many immune and inflammatory diseases, yet the specific mechanism remains unclear. Therefore, it is necessary to study the detailed mechanisms of JAK/STAT signaling in disease formation to provide critical reference for clinical treatments of the diseases. In this review, we focus on the structure of JAKs and STATs, the JAK/STAT signaling pathway and its negative regulators, the associated diseases, and the JAK inhibitors for the clinical therapy.

Su(var)2-10 and the SUMO Pathway Link piRNA-Guided Target Recognition to Chromatin Silencing

Regulation of transcription is the main mechanism responsible for precise control of gene expression. Whereas the majority of transcriptional regulation is mediated by DNA-binding transcription factors that bind to regulatory gene regions, an elegant alternative strategy employs small RNA guides, Piwi-interacting RNAs (piRNAs) to identify targets of transcriptional repression. Here, we show that in Drosophila the small ubiquitin-like protein SUMO and the SUMO E3 ligase Su(var)2-10 are required for piRNA-guided deposition of repressive chromatin marks and transcriptional silencing of piRNA targets. Su(var)2-10 links the piRNA-guided target recognition complex to the silencing effector by binding the piRNA/Piwi complex and inducing SUMO-dependent recruitment of the SetDB1/Wde histone methyltransferase effector. We propose that in Drosophila, the nuclear piRNA pathway has co-opted a conserved mechanism of SUMO-dependent recruitment of the SetDB1/Wde chromatin modifier to confer repression of genomic parasites.

SUMO3 modification by PIAS1 modulates androgen receptor cellular distribution and stability

Background

Abnormal reactivation of androgen receptor (AR) signaling in castration-resistant prostate cancer (CRPC) mainly results from overexpression and down-regulation of AR. Sumoylation of AR can influence its function. However, regulation of AR sumoylation by SUMO E3 ligases PIASs to modify AR distribution and stability are not well understood.

Methods

We assessed the potential effect of SUMO3 modification on AR intracellular localization by immunostaining in AR-negative prostate cancer DU145 cells, and detected the effect of PIAS1/SUMO3 overexpression on AR sumoylation related degradation. Then we characterized AR sumoylation sites involved modified by SUMO3, and the key residue of PIAS1 involved in itself sumoylation and further mediated AR sumoylation (sumo3-conjugated), translocation and degradation. Finally we detected the recognition of PIAS1 (sumoylation ligase) to MDM2, a ubiquin ligase mediated AR degradation.

Results

We demonstrate that SUMO E3 ligase PIAS1, along with SUMO3, mediates AR cytosolic translocation and subsequent degradation via a ubiquitin-proteasome pathway. Although AR sumoylation occurs prior to ubiquitination, the SUMO-acceptor lysine 386 on AR, together with ubiquitin-acceptor lysine 845, contribute to PIAS1/SUMO3-induced AR nuclear export, ubiquitination and subsequent degradation. Moreover, PIAS1 itself is modified by SUMO3 overexpression, and mutation of SUMO-acceptor lysine 117 on PIAS1 can impair AR cytoplasmic distribution, demonstrating the essential role of sumoylated PIAS1 in AR translocation. We further determine that sumoylated PIAS1 interacts with AR lysine 386 and 845 to form a binary complex. Consistent with the effect on AR distribution, SUMO3 modification of PIAS1 is also required for AR ubiquitination and degradation by recruiting ubiquitin E3 ligase MDM2.

Conclusion

Taken together, SUMO3 modification of PIAS1 modulates AR cellular distribution and stability. Our study provided the evidence the crosstalk between AR sumoylation and ubquitination mediated by PIAS1 and SUMO3.

Posttranslational regulation of androgen dependent and independent androgen receptor activities in prostate cancer

Prostate cancer (PCa) is the most commonly diagnosed cancer among men in western countries. Androgen receptor (AR) signaling plays key roles in the development of PCa. Androgen deprivation therapy (ADT) remains the standard therapy for advanced PCa. In addition to its ligand androgen, accumulating evidence indicates that posttranscriptional modification is another important mechanism to regulate AR activities during the progression of PCa, especially in castration resistant prostate cancer (CRPC). To date, a number of posttranscriptional modifications of AR have been identified, including phosphorylation (e.g. by CDK1), acetylation (e.g. by p300 and recognized by BRD4), methylation (e.g. by EZH2), ubiquitination (e.g. by SPOP), and SUMOylation (e.g. by PIAS1). These modifications are essential for the maintenance of protein stability, nuclear localization and transcriptional activity of AR. This review summarizes posttranslational modifications that influence androgen-dependent and -independent activities of AR, PCa progression and therapy resistance. We further emphasize that in addition to androgen, posttranslational modification is another important way to regulate AR activity, suggesting that targeting AR posttranslational modifications, such as proteolysis targeting chimeras (PROTACs) of AR, represents a potential and promising alternate for effective treatment of CRPC. Potential areas to be investigated in the future in the field of AR posttranslational modifications are also discussed.

Functional characterization of a protein inhibitor of activated STAT (PIAS) gene in Litopenaeus vannamei

Protein inhibitor of activated STAT (PIAS) plays a critical role in the feedback modulation of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway as a negative regulator in mammals and Drosophila, but the function of PIAS in crustaceans is still unclear. In this study, a PIAS termed LvPIAS was cloned and characterized from Litopenaeus vannamei. The full length of LvPIAS was 3065 bp, including a 2361 bp open reading frame (ORF) coding for a protein of 786 aa. LvPIAS expression was most abundant in muscle and could respond to the challenge of LPS, Vibrio parahaemolyticus, Staphhylococcus aureus, Poly I: C and white spot syndrome virus (WSSV). LvPIAS could be induced by the transcription factor LvSTAT, but LvPIAS could inhibit the transcriptional activity of LvSTAT to the LvPIAS promoter conversely, which indicated that there was a negative feedback loop between LvSTAT and LvPIAS. Furthermore, RNAi-mediated knockdown of LvPIAS shrimps showed higher survival rate to WSSV infection than those in the control group (dsGFP injection), suggesting that LvPIAS may play a negatively role against WSSV infection.

Sumoylation of BRI1-EMS-SUPPRESSOR 1 (BES1) by the SUMO E3 Ligase SIZ1 Negatively Regulates Brassinosteroids Signaling in Arabidopsis thaliana

Brassinosteroids (BRs), a group of plant steroid hormones, participate in the regulation of plant growth and developmental processes. BR functions through the BES1/BZR1 family of transcription factors, however, the regulation of the BES1 activity by post-translational modifications remains largely unknown. Here, we present evidence that the SUMO E3 ligase SIZ1 negatively regulates BR signaling pathway. T-DNA insertion mutant siz1-2 shows BL (Brassinolide, the most active BR) hypersensitivity and BRZ (Brassinazole, a BR biosynthesis inhibitor) insensitivity during hypocotyl elongation. In addition, expression of BES1-dependent BR-response genes is hyper-regulated in siz1-2 seedlings. The siz1-2bes1-D double mutant exhibits longer hypocotyl than bes1-D. Moreover, SIZ1 physically interacts with BES1 in vivo and in vitro and mediates the sumoylation of BES1. A K302R substitution in BES1 blocks its sumoylation mediated by SIZ1 in plants, indicating that K302 is the principal site for SUMO conjugation. Consistently, we find that sumoylation inhibits BES1 protein stability and activity. Taken together, our data show that the sumoylation of BES1 via SIZ1 negatively regulates the BR signaling pathway.

Suppressors of Cytokine Signaling and Protein Inhibitors of Activated Signal Transducer and Activator of Transcriptions As Therapeutic Targets in Flavivirus Infections

Flaviviruses cause significant human diseases putting more than 400 million people at risk annually worldwide. Because of migration and improved transportation, these viruses can be found on all continents (except Antarctica). Although a majority of the viruses are endemic in the tropics, a few [West Nile virus (WNV) and tick-borne encephalitis virus (TBEV)] have shown endemicity in Europe and North America. Currently, there are vaccines for the Yellow fever virus, Japanese encephalitis virus, and TBEV, but there is no effective vaccine and/or therapy against all other flaviviruses. Although there are intensive efforts to develop vaccines for Zika viruses, dengue viruses, and WNVs, there is the need for alternative or parallel antiviral therapeutic approaches. Suppressors of cytokine signaling (SOCS) and protein inhibitors of activated signal transducer and activator of transcription (STATs; PIAS), both regulatory proteins of the Janus kinase/STAT signaling pathway, have been explored as therapeutic targets in herpes simplex and vaccinia viruses, as well as in cancer therapy. In this review, we briefly describe the function of SOCS and PIAS and their therapeutic potential in flaviviral infections. [Figure: see text].

The Epstein-Barr Virus Oncoprotein, LMP1, Regulates the Function of SENP2, a SUMO-protease

Epstein-Barr virus (EBV) latent membrane protein-1 (LMP1) activates numerous signal transduction pathways using its C-terminal activating regions. We reported that LMP1 increased global levels of sumoylated proteins, which aided the oncogenic nature of LMP1. Because increased protein sumoylation is detected in numerous cancers, we wanted to elucidate additional mechanisms by which LMP1 modulates the sumoylation machinery. Results indicated that SUMO-protease activity decreased in a LMP1-dependent manner, so we hypothesized that LMP1 inhibits SUMO-protease activity, resulting in reduced de-sumoylation of cellular proteins, which contributes to the detected accumulation of sumoylated proteins in EBV-positive lymphomas. Focusing on SENP2, findings revealed that LMP1 expression corresponded with increased sumoylation of SENP2 at K48 and K447 in a CTAR-dependent manner. Interestingly, independent of LMP1-induced sumoylation of SENP2, LMP1 also decreased SENP2 activity, decreased SENP2 turnover, and altered the localization of SENP2, which led us to investigate if LMP1 regulated the biology of SENP2 by a different post-translational modification, specifically ubiquitination. Data showed that expression of LMP1 inhibited the ubiquitination of SENP2, and inhibition of ubiquitination was sufficient to mimic LMP1-induced changes in SENP2 activity and trafficking. Together, these findings suggest that LMP1 modulates different post-translational modifications of SENP2 in order to modulate its biology and identify a third member of the sumoylation machinery that is manipulated by LMP1 during latent EBV infections, which can affect oncogenesis.

Chromatin reprogramming as an adaptation mechanism in advanced prostate cancer

Tumor evolution is based on the ability to constantly mutate and activate different pathways under the selective pressure of targeted therapies. Epigenetic alterations including those of the chromatin structure are associated with tumor initiation, progression and drug resistance. Many cancers, including prostate cancer, present enlarged nuclei, and chromatin appears altered and irregular. These phenotypic changes are likely to result from epigenetic dysregulation. High-throughput sequencing applied to bulk samples and now to single cells has made it possible to study these processes in unprecedented detail. It is therefore timely to review the impact of chromatin relaxation and increased DNA accessibility on prostate cancer growth and drug resistance, and their effects on gene expression. In particular, we focus on the contribution of chromatin-associated proteins such as the bromodomain-containing proteins to chromatin relaxation. We discuss the consequence of this for androgen receptor transcriptional activity and briefly summarize wider gain-of-function effects on other oncogenic transcription factors and implications for more effective prostate cancer treatment.

Protein Inhibitor of Activated STAT (PIAS) Negatively Regulates the JAK/STAT Pathway by Inhibiting STAT Phosphorylation and Translocation

Protein inhibitor of activated STAT (PIAS) proteins are activation-suppressing proteins for signal transducer and activator of transcription (STAT), which involves gene transcriptional regulation. The inhibitory mechanism of PIAS proteins in the Janus kinase (JAK)/STAT signaling pathway has been well studied in mammals and Drosophila. However, the roles of PIAS in crustaceans are unclear. In the present study, we identified PIAS in kuruma shrimp Marsupenaeus japonicus and found that its relative expression could be induced by Vibrio anguillarum stimulation. To explore the function of PIAS in shrimp infected with V. anguillarum, we performed an RNA interference assay. After knockdown of PIAS expression in shrimp subjected to V. anguillarum infection, bacterial clearance was enhanced and the survival rate increased compared with those in the control shrimp (dsGFP injection). Simultaneously, the expression levels of antimicrobial peptides (AMPs), including anti-lipopolysaccharide factor (ALF) A1, C1, C2, and CruI-1, increased. Further study revealed that knockdown of PIAS also enhanced STAT phosphorylation and translocation. Pulldown assay indicated that PIAS interacts with activated STAT in shrimp. In conclusion, PIAS negatively regulates JAK/STAT signaling by inhibiting the phosphorylation and translocation of STAT through the interaction between PIAS and STAT, which leads to the reduction of AMP expression in shrimp. Our results revealed a new mechanism of PIAS-mediated gene regulation of the STAT signal pathway.

Embryonic hematopoiesis modulates the inflammatory response and larval hematopoiesis in Drosophila

Recent lineage tracing analyses have significantly improved our understanding of immune system development and highlighted the importance of the different hematopoietic waves. The current challenge is to understand whether these waves interact and whether this affects the function of the immune system. Here we report a molecular pathway regulating the immune response and involving the communication between embryonic and larval hematopoietic waves in Drosophila. Down-regulating the transcription factor Gcm specific to embryonic hematopoiesis enhances the larval phenotypes induced by over-expressing the pro-inflammatory Jak/Stat pathway or by wasp infestation. Gcm works by modulating the transduction of the Upd cytokines to the site of larval hematopoiesis and hence the response to chronic (Jak/Stat over-expression) and acute (wasp infestation) immune challenges. Thus, homeostatic interactions control the function of the immune system in physiology and pathology. Our data also indicate that a transiently expressed developmental pathway has a long-lasting effect on the immune response.

Nuclear Smad6 promotes gliomagenesis by negatively regulating PIAS3-mediated STAT3 inhibition

To date, the molecular mechanism underlying constitutive signal transducer and activator of transcription 3 (STAT3) activation in gliomas is largely unclear. In this study, we report that Smad6 is overexpressed in nuclei of glioma cells, which correlates with poor patient survival and regulates STAT3 activity via negatively regulating the Protein Inhibitors of Activated STAT3 (PIAS3). Mechanically, Smad6 interacts directly with PIAS3, and this interaction is mediated through the Mad homology 2 (MH2) domain of Smad6 and the Ring domain of PIAS3. Smad6 recruits Smurf1 to facilitate PIAS3 ubiquitination and degradation, which also depends on the MH2 domain and the PY motif of Smad6. Consequently, Smad6 reduces PIAS3-mediated STAT3 inhibition and promotes glioma cell growth and stem-like cell initiation. Moreover, the Smad6 MH2 transducible protein restores PIAS3 expression and subsequently reduces gliomagenesis. Collectively, we conclude that nuclear-Smad6 enhances glioma development by inducing PIAS3 degradation and subsequent STAT3 activity upregulation.

Smad4 SUMOylation is essential for memory formation through upregulation of the skeletal myopathy gene TPM2

Background

Smad4 is a critical effector of TGF-β signaling that regulates a variety of cellular functions. However, its role in the brain has rarely been studied. Here, we examined the molecular mechanisms underlying the post-translational regulation of Smad4 function by SUMOylation, and its role in spatial memory formation.

Results

In the hippocampus, Smad4 is SUMOylated by the E3 ligase PIAS1 at Lys-113 and Lys-159. Both spatial training and NMDA injection enhanced Smad4 SUMOylation. Inhibition of Smad4 SUMOylation impaired spatial learning and memory in rats by downregulating TPM2, a gene associated with skeletal myopathies. Similarly, knockdown of TPM2 expression impaired spatial learning and memory, while TPM2 mRNA and protein expression increased after spatial training. Among the TPM2 mutations associated with skeletal myopathies, the TPM2E122K mutation was found to reduce TPM2 expression and impair spatial learning and memory in rats.

Conclusions

We have identified a novel role of Smad4 SUMOylation and TPM2 in learning and memory formation. These results suggest that patients with skeletal myopathies who carry the TPM2E122K mutation may also have deficits in learning and memory functions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12915-017-0452-9) contains supplementary material, which is available to authorized users.

Functions of SUMO in the Maintenance of Genome Stability

Like in most other areas of cellular metabolism, the functions of the ubiquitin-like modifier SUMO in the maintenance of genome stability are manifold and varied. Perturbations of global sumoylation causes a wide spectrum of phenotypes associated with defects in DNA maintenance, such as hypersensitivity to DNA-damaging agents, gross chromosomal rearrangements and loss of entire chromosomes. Consistent with these observations, many key factors involved in various DNA repair pathways have been identified as SUMO substrates. However, establishing a functional connection between a given SUMO target, the cognate SUMO ligase and a relevant phenotype has remained a challenge, mainly because of the difficulties involved in identifying important modification sites and downstream effectors that specifically recognize the target in its sumoylated state. This review will give an overview over the major pathways of DNA repair and genome maintenance influenced by the SUMO system and discuss selected examples of SUMO's actions in these pathways where the biological consequences of the modification have been elucidated.

SIZ1-mediated SUMOylation during phosphate homeostasis in plants: Looking beyond the tip of the iceberg

Availability of phosphate (Pi) is often limited in rhizospheres in different agroclimatic zones and adversely affects growth and development of plants. To circumvent this impasse, there is an urgent need and global consensus to develop Pi use efficient crops. To achieve this goal, it is essential to identify the molecular entities that exert regulatory influences on the sensing and signaling cascade governing Pi homeostasis. SIZ1 encodes a small ubiquitin-like modifier (SUMO E3) ligase, and plays a pivotal role in the post-translational SUMOylation of proteins. In this review, we discuss the reverse genetics approach conventionally used for providing circumstantial evidence towards the regulatory influences of SIZ1 on several morphophysiological and molecular traits that govern Pi homeostasis in taxonomically diverse Arabidopsis thaliana (Arabidopsis) and Oryza sativa (rice) model species. However, the efforts have been rather modest in identifying SUMO protein targets that play key roles in the maintenance of Pi homeostasis in these model plants contrary to the plethora of them now known in lower organisms and animals. Therefore, to predict the SIZ1-mediated SUMOylome involved in Pi homeostasis, the state-of-the-art high-throughput technologies often used for animals thus provide an attractive paradigm towards achieving the long-term goal of developing Pi use efficient crops.

Viral manipulation of the cellular sumoylation machinery

Viruses exploit various cellular processes for their own benefit, including counteracting anti-viral responses and regulating viral replication and propagation. In the past 20 years, protein sumoylation has emerged as an important post-translational modification that is manipulated by viruses to modulate anti-viral responses, viral replication, and viral pathogenesis. The process of sumoylation is a multi-step cascade where a small ubiquitin-like modifier (SUMO) is covalently attached to a conserved ΨKxD/E motif within a target protein, altering the function of the modified protein. Here we review how viruses manipulate the cellular machinery at each step of the sumoylation process to favor viral survival and pathogenesis.

The role of JAK-STAT signaling pathway and its regulators in the fate of T helper cells

The Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway plays critical roles in orchestrating of immune system, especially cytokine receptors and they can modulate the polarization of T helper cells. This pathway is regulated by an array of regulator proteins, including Suppressors of Cytokine Signaling (SOCS), Protein Inhibitors of Activated STATs (PIAS) and Protein Tyrosine Phosphatases (PTPs) determining the initiation, duration and termination of the signaling cascades. Dysregulation of the JAK-STAT pathway in T helper cells may result in various immune disorders. In this review, we represent how the JAK-STAT pathway is generally regulated and then in Th cell subsets in more detail. Finally, we introduce novel targeted strategies as promising therapeutic approaches in the treatment of immune disorders. Studies are ongoing for identifying the other regulators of the JAK-STAT pathway and designing innovative therapeutic strategies. Therefore, further investigation is needed.

SUMO conjugation - a mechanistic view

The regulation of protein fate by modification with the small ubiquitin-related modifier (SUMO) plays an essential and crucial role in most cellular pathways. Sumoylation is highly dynamic due to the opposing activities of SUMO conjugation and SUMO deconjugation. SUMO conjugation is performed by the hierarchical action of E1, E2 and E3 enzymes, while its deconjugation involves SUMO-specific proteases. In this review, we summarize and compare the mechanistic principles of how SUMO gets conjugated to its substrate. We focus on the interplay of the E1, E2 and E3 enzymes and discuss how specificity could be achieved given the limited number of conjugating enzymes and the thousands of substrates.

SUMOylation Confers Posttranslational Stability on NPM-ALK Oncogenic Protein

Nucleophosmin-anaplastic lymphoma kinase–expressing (NPM-ALK⁺) T-cell lymphoma is an aggressive form of cancer that commonly affects children and adolescents. The expression of NPM-ALK chimeric oncogene results from the chromosomal translocation t(2;5)(p23;q35) that causes the fusion of the ALK and NPM genes. This translocation generates the NPM-ALK protein tyrosine kinase that forms the constitutively activated NPM-ALK/NPM-ALK homodimers. In addition, NPM-ALK is structurally associated with wild-type NPM to form NPM/NPM-ALK heterodimers, which can translocate to the nucleus. The mechanisms that sustain the stability of NPM-ALK are not fully understood. SUMOylation is a posttranslational modification that is characterized by the reversible conjugation of small ubiquitin-like modifiers (SUMOs) with target proteins. SUMO competes with ubiquitin for substrate binding and therefore, SUMOylation is believed to protect target proteins from proteasomal degradation. Moreover, SUMOylation contributes to the subcellular distribution of target proteins. Herein, we found that the SUMOylation pathway is deregulated in NPM-ALK⁺ T-cell lymphoma cell lines and primary lymphoma tumors from patients. We also identified Lys²⁴ and Lys³² within the NPM domain as the sites where NPM-ALK conjugates with SUMO-1 and SUMO-3. Importantly, antagonizing SUMOylation by the SENP1 protease decreased the accumulation of NPM-ALK and suppressed lymphoma cell viability, proliferation, and anchorage-independent colony formation. One possible mechanism for the SENP1-mediated decrease in NPM-ALK levels was the increase in NPM-ALK association with ubiquitin, which facilitates its degradation. Our findings propose a model in which aberrancies in SUMOylation contribute to the pathogenesis of NPM-ALK⁺ T-cell lymphoma. Unraveling such pathogenic mechanisms may lead to devising novel strategies to eliminate this aggressive neoplasm.

PIAS1 binds p300 and behaves as a coactivator or corepressor of the transcription factor c-Myb dependent on SUMO-status

The PIAS proteins (Protein Inhibitor of Activated STATs) constitute a family of multifunctional nuclear proteins operating as SUMO E3 ligases and being involved in a multitude of interactions. They participate in a range of biological processes, also beyond their well-established role in the immune system and cytokine signalling. They act both as transcriptional corepressors and coactivators depending on the context. In the present work, we investigated mechanisms by which PIAS1 causes activation or repression of c-Myb dependent target genes. Analysis of global expression data shows that c-Myb and PIAS1 knockdowns affect a subset of common targets, but with a dual outcome consistent with a role of PIAS1 as either a corepressor or coactivator. Our mechanistic studies show that PIAS1 engages in a novel interaction with the acetyltransferase and coactivator p300. Interaction and ChIP analysis suggest a bridging function where PIAS1 enhances p300 recruitment to c-Myb-bound sites through interaction with both proteins. In addition, the E3 activity of PIAS1 enhances further its coactivation. Remarkably, the SUMO status of c-Myb had a decisive role, indicating a SUMO-dependent switch in the way PIAS1 affects c-Myb, either as a coactivator or corepressor. Removal of the two major SUMO-conjugation sites in c-Myb (2KR mutant), which enhances its activity significantly, turned PIAS1 into a corepressor. Also, p300 was less efficiently recruited to chromatin by c-Myb-2KR. We propose that PIAS1 acts as a "protein inhibitor of activated c-Myb" in the absence of SUMOylation while, in its presence, PIAS behaves as a "protein activator of repressed c-Myb".

The language-related transcription factor FOXP2 is post-translationally modified with small ubiquitin-like modifiers

Mutations affecting the transcription factor FOXP2 cause a rare form of severe speech and language disorder. Although it is clear that sufficient FOXP2 expression is crucial for normal brain development, little is known about how this transcription factor is regulated. To investigate post-translational mechanisms for FOXP2 regulation, we searched for protein interaction partners of FOXP2, and identified members of the PIAS family as novel FOXP2 interactors. PIAS proteins mediate post-translational modification of a range of target proteins with small ubiquitin-like modifiers (SUMOs). We found that FOXP2 can be modified with all three human SUMO proteins and that PIAS1 promotes this process. An aetiological FOXP2 mutation found in a family with speech and language disorder markedly reduced FOXP2 SUMOylation. We demonstrate that FOXP2 is SUMOylated at a single major site, which is conserved in all FOXP2 vertebrate orthologues and in the paralogues FOXP1 and FOXP4. Abolishing this site did not lead to detectable changes in FOXP2 subcellular localization, stability, dimerization or transcriptional repression in cellular assays, but the conservation of this site suggests a potential role for SUMOylation in regulating FOXP2 activity in vivo.

SUMOylation and Potassium Channels: Links to Epilepsy and Sudden Death

Neuronal potassium ion channels play an essential role in the generation of the action potential and excitability of neurons. The dysfunction of ion channel subunits can cause channelopathies, which are associated in some cases with sudden unexplained death in epilepsy SUDEP. The physiological roles of neuronal ion channels have been largely determined, but little is known about the molecular mechanisms underlying neurological channelopathies, especially the determinants of the channels' regulation. SUMO (small ubiquitin-like modifier) proteins covalently conjugate lysine residues in a large number of target proteins and modify their functions. SUMO modification (SUMOylation) has emerged as an important regulatory mechanism for protein stability, function, subcellular localization, and protein-protein interactions. Since SUMO was discovered almost 20 years ago, the biological contribution of SUMOylation has not fully understood. It is until recently that the physiological impacts of SUMOylation on the regulation of neuronal potassium ion channels have been investigated. It is well established that SUMOylation controls many aspects of nuclear function, but it is now clear that it is also a key determinant in the function of potassium channels, and SUMOylation has also been implicated in a wide range of channelopathies, including epilepsy and sudden death.

The ubiquitin ligase Smurf2 suppresses TGFβ-induced epithelial-mesenchymal transition in a sumoylation-regulated manner

Epithelial-mesenchymal transition (EMT) is a fundamental cellular process in epithelial tissue development, and can be reactivated in cancer contributing to tumor invasiveness and metastasis. The cytokine transforming growth factor-β (TGFβ) is a key inducer of EMT, but the mechanisms that regulate TGFβ-induced EMT remain incompletely understood. Here, we report that knockdown of the ubiquitin ligase Smurf2 promotes the ability of TGFβ to induce EMT in a three-dimensional cell culture model of NMuMG mammary epithelial cells. In other studies, we identify Smurf2 as a target of the small ubiquitin like modifier (SUMO) pathway. We find that the SUMO-E2 conjugating enzyme Ubc9 and the SUMO E3 ligase PIAS3 associate with Smurf2 and promote its sumoylation at the distinct sites of Lysines 26 and 369. The sumoylation of Smurf2 enhances its ability to induce the degradation of the TGFβ receptor and thereby suppresses EMT in NMuMG cells. Collectively, our data reveal that Smurf2 acts in a sumoylation-regulated manner to suppress TGFβ-induced EMT. These findings have significant implications for our understanding of epithelial tissue development and cancer.

SUMO ligase PIAS1 functions as a target gene selective androgen receptor coregulator on prostate cancer cell chromatin

Androgen receptor (AR) is a ligand-activated transcription factor that plays a central role in the development and growth of prostate carcinoma. PIAS1 is an AR- and SUMO-interacting protein and a putative transcriptional coregulator overexpressed in prostate cancer. To study the importance of PIAS1 for the androgen-regulated transcriptome of VCaP prostate cancer cells, we silenced its expression by RNAi. Transcriptome analyses revealed that a subset of the AR-regulated genes is significantly influenced, either activated or repressed, by PIAS1 depletion. Interestingly, PIAS1 depletion also exposed a new set of genes to androgen regulation, suggesting that PIAS1 can mask distinct genomic loci from AR access. In keeping with gene expression data, silencing of PIAS1 attenuated VCaP cell proliferation. ChIP-seq analyses showed that PIAS1 interacts with AR at chromatin sites harboring also SUMO2/3 and surrounded by H3K4me2; androgen exposure increased the number of PIAS1-occupying sites, resulting in nearly complete overlap with AR chromatin binding events. PIAS1 interacted also with the pioneer factor FOXA1. Of note, PIAS1 depletion affected AR chromatin occupancy at binding sites enriched for HOXD13 and GATA motifs. Taken together, PIAS1 is a genuine chromatin-bound AR coregulator that functions in a target gene selective fashion to regulate prostate cancer cell growth.

Long-term expression of the lamin A mutant associated with dilated cardiomyopathy induces senescence

Mutation of the lamin A gene (LMNA) causes a diverse range of diseases referred to as laminopathies. Because most laminopathies have a dominant inheritance pattern and progress gradually, cultured cells stably expressing mutant lamin A at the same level as endogenous wild-type cells are required for chronological analysis. In this study, we showed that an expression system involving a lentiviral vector that carries the human metallothionein gene basal promoter ensures stable and basal-level expression of proteins and is thus suitable for investigating the properties of lamin A mutants. The small ubiquitin-related modifier (SUMO) modification (SUMOylation)-defective E203G mutant that is associated with familial dilated cardiomyopathy exhibited abnormal subnuclear distribution and inhibited normal localization of WT lamin A in a dominant-negative manner. Low-level and long-term expression of the E203G mutant resulted in multinucleated giant cells, aberrant lipid droplet accumulation in the cytoplasm and premature senescence. Expression of another SUMOylation-defective mutant (K201R) did not induce any phenotypes observed in cells expressing E203G. These results indicate that the E203G mutant may inhibit the normal functions of wild-type lamin A in a dominant-negative manner, but a defect in SUMOylation itself may not be involved in disease pathogenesis.

Identification of sumoylated proteins in the silkworm Bombyx mori

Small ubiquitin-like modifier (SUMO) modification (SUMOylation) is an important and widely used reversible modification system in eukaryotic cells. It regulates various cell processes, including protein targeting, transcriptional regulation, signal transduction, and cell division. To understand its role in the model lepidoptera insect Bombyx mori, a recombinant baculovirus was constructed to express an enhanced green fluorescent protein (eGFP)-SUMO fusion protein along with ubiquitin carrier protein 9 of Bombyx mori (BmUBC9). SUMOylation substrates from Bombyx mori cells infected with this baculovirus were isolated by immunoprecipitation and identified by LC-ESI-MS/MS. A total of 68 candidate SUMOylated proteins were identified, of which 59 proteins were functionally categorized to gene ontology (GO) terms. Analysis of kyoto encyclopedia of genes and genomes (KEGG) pathways showed that 46 of the identified proteins were involved in 76 pathways that mainly play a role in metabolism, spliceosome and ribosome functions, and in RNA transport. Furthermore, SUMOylation of four candidates (polyubiquitin-C-like isoform X1, 3-hydroxyacyl-CoA dehydrogenase, cyclin-related protein FAM58A-like and GTP-binding nuclear protein Ran) were verified by co-immunoprecipitation in Drosophila schneide 2 cells. In addition, 74% of the identified proteins were predicted to have at least one SUMOylation site. The data presented here shed light on the crucial process of protein sumoylation in Bombyx mori.