Small Ubiquitin-like Modifier Pathway Research Articles

Abstract 6605: Understanding the role of sumoylated Etv1 in mammary oncogenesis

Abstract The Small Ubiquitin-like Modifier (SUMO) pathway is a major post-translational regulatory mechanism involved in a variety of cellular functions including the DNA damage response, transcriptional regulation, and carcinogenesis. Recent discoveries by our group demonstrated that inhibiting the SUMO pathway can repress the growth of breast cancer xenografts and Neu-driven mammary oncogenesis in a genetically engineered mouse model with conditional knockout (CKO) of the SUMOylation E2 conjugating enzyme, Ube2i. However, despite the consistency of the findings, there remains considerable debate concerning the mechanisms through which SUMO inhibition represses tumorigenesis. Our downstream analysis suggested ETS Translocation Variant 1, encoded by ETV1 gene, acts as a SUMO-sensitive transcription factor that drives mammary oncogenesis and cancer growth. To examine oncogenic properties of SUMO-conjugated ETV1 in breast cancer, we cloned HA-tagged WT Etv1, SUMO-resistant Etv15xKR, or SUMO mimetic SUMO-1-Etv15xKR into a lentiviral vector with a GFP cassette. Proliferation, colony formation in soft agar, and in vivo xenograft assays were evaluated in the Ube2iF/F cell line derived from a tumor in a MMTV-c-neu/Ube2ifl/fl animal. We did ChIP-seq in Ube2iF/F cells using SUMO-1 and Etv1 antibodies to examine the effects of SUMO conjugation on Etv1 genomic occupancy. RNA-seq using siEtv1 or AdCre was also performed to compare changes in gene expression with SUMO-conjugated Etv1 genomic occupancy. Inhibition of SUMOylation via AdCre caused a significant reduction in proliferation and colony formation in vitro and completely block the formation of flank xenografts in vivo. Interestingly, expressing a SUMO-resistant ETV15xKR rescued in vitro growth effects, whereas a SUMO mimetic SUMO-1-ETV15xKR had no effect on restoring proliferation. On the contrary, in vivo xenograft assays demonstrated that the Etv15xKR-SUMO1 efficiently induced tumor formation despite the loss of Ube2i while the sumo-resistant Etv15xKR was unable to rescue tumorigenesis. Bulk RNA-seq and ChIP seq performed demonstrated different patterns of gene regulation between sumoylated and unsumoylated Etv1. Gene set enrichment analysis (GSEA) showed genes associated with cancer stemness were significantly enriched in cells expressing Etv15xKR-SUMO1. Collectively, these observations support Etv1 acting as a SUMO-sensitive transcription factor that drives a stem cell phenotype necessary for mammary oncogenesis and progression. Citation Format: Zhijie Li, Kelsey E. Koch, Dakota T. Thompson, Dana M. Van der Heide, Jeremy Chang, Christopher M. Franke, Mohammed O. Suraju, Anna C. Beck, Allison W. Lorenzen, Jeffrey R. White, Mikhail V. Kulak, David K. Meyerholz, Colin Kenny, Ronald J. Weigel. Understanding the role of sumoylated Etv1 in mammary oncogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6605.

Establishment of a SUMO pathway related gene signature for predicting prognosis, chemotherapy response and investigating the role of EGR2 in bladder cancer.

Background: Bladder cancer is a prevalent malignancy with significant clinical implications. Small Ubiquitin-like Modifier (SUMO) pathway related genes (SPRG) have been implicated in the development and progression of cancer. Methods: In this study, we conducted a comprehensive analysis of SPRG in bladder cancer. We analyzed gene expression and prognostic value of SPRG and developed a SPRG signature (SPRGS) prognostic model based on four genes (HDAC4, TRIM27, EGR2, and UBE2I) in bladder cancer. Furthermore, we investigated the relationship between SPRGS and genomic alterations, tumor microenvironment, chemotherapy response, and immunotherapy. Additionally, we identified EGR2 as a key SPRG in bladder cancer. The expression of EGR2 in bladder cancer was detected by immunohistochemistry, and the cell function experiment clarified the effect of knocking down EGR2 on the proliferation, invasion, and migration of bladder cancer cells. Results: Our findings suggest that SPRGS hold promise as prognostic markers and predictive biomarkers for chemotherapy response and immunotherapy efficacy in bladder cancer. The SPRGS prognostic model exhibited high predictive accuracy for bladder cancer patient survival. We also observed correlations between SPRG and genomic alterations, tumor microenvironment, and response to chemotherapy. Immunohistochemical results showed that EGR2 was highly expressed in bladder cancer tissues, and its overexpression was associated with poor prognosis. Knockdown of EGR2 inhibited bladder cancer cell proliferation, invasion, and migration. Conclusion: This study provides valuable insights into the landscape of SPRGS in bladder cancer and their potential implications for personalized treatment strategies. The identification of EGR2 as a key SPRG and its functional impact on bladder cancer cells further highlights its significance in bladder cancer development and progression. Overall, SPRGS may serve as important prognostic markers and predictive biomarkers for bladder cancer patients, guiding treatment decisions and improving patient outcomes.

SUMOylation indirectly suppresses activity of the HIF-1α pathway in intestinal epithelial cells

The hypoxia-inducible factor (HIF) is a master regulator of the cellular transcriptional response to hypoxia. While the oxygen-sensitive regulation of HIF-1α subunit stability via the ubiquitin-proteasome pathway has been well described, less is known about how other oxygen-independent post-translational modifications impact the HIF pathway. SUMOylation, the attachment of SUMO (small ubiquitin-like modifier) proteins to a target protein, regulates the HIF pathway, although the impact of SUMO on HIF activity remains controversial. Here, we examined the effects of SUMOylation on the expression pattern of HIF-1α in response to pan-hydroxylase inhibitor dimethyloxalylglycine (DMOG) in intestinal epithelial cells. We evaluated the effects of SUMO-1, SUMO-2, and SUMO-3 overexpression and inhibition of SUMOylation using a novel selective inhibitor of the SUMO pathway, TAK-981, on the sensitivity of HIF-1α in Caco-2 intestinal epithelial cells. Our findings demonstrate that treatment with TAK-981 decreases global SUMO-1 and SUMO-2/3 modification and enhances HIF-1α protein levels, whereas SUMO-1 and SUMO-2/3 overexpression results in decreased HIF-1α protein levels in response to DMOG. Reporter assay analysis demonstrates reduced HIF-1α transcriptional activity in cells overexpressing SUMO-1 and SUMO-2/3, whereas pretreatment with TAK-981 increased HIF-1α transcriptional activity in response to DMOG. In addition, HIF-1α nuclear accumulation was decreased in cells overexpressing SUMO-1. Importantly, we showed that HIF-1α is not directly SUMOylated, but that SUMOylation affects HIF-1α stability and activity indirectly. Taken together, our results indicate that SUMOylation indirectly suppresses HIF-1α protein stability, transcriptional activity, and nuclear accumulation in intestinal epithelial cells.

SUMOtherapeutics for Ischemic Stroke.

The small, ubiquitin-like modifier (SUMO) is a post-translational modifier with a profound influence on several key biological processes, including the mammalian stress response. Of particular interest are its neuroprotective effects, first recognized in the 13-lined ground squirrel (Ictidomys tridecemlineatus), in the context of hibernation torpor. Although the full scope of the SUMO pathway is yet to be elucidated, observations of its importance in managing neuronal responses to ischemia, maintaining ion gradients, and the preconditioning of neural stem cells make it a promising therapeutic target for acute cerebral ischemia. Recent advances in high-throughput screening have enabled the identification of small molecules that can upregulate SUMOylation, some of which have been validated in pertinent preclinical models of cerebral ischemia. Accordingly, the present review aims to summarize current knowledge and highlight the translational potential of the SUMOylation pathway in brain ischemia.

Abstract LB318: SB-4826, a first-in-class oral, covalent inhibitor of SUMO E1 that induces IFN signaling and inhibits tumor growth as monotherapy and in combination with immune checkpoint blockade

Abstract Sumoylation is a reversible post-translational modification of proteins by small ubiquitin-like modifier (SUMO) that regulates protein function and contributes to cellular response to stress. Sumoylation is an essential pathway for all cells and is involved in diverse processes such as inflammation, DNA damage response, signaling and cell survival/apoptosis. Due to its involvement in such cellular functions, sumoylation intersects with the majority of the hallmarks of cancer. Many cancers display elevated expression of SUMO pathway components, a mechanism co-opted by tumors to survive under stressful conditions. In addition to its tumor intrinsic functions, sumoylation has emerged as a novel target for activating anti-tumor immunity due to its role in regulating type I interferon (IFN) signaling. Targeting sumoylation is a compelling anti-cancer strategy due to the multiple mechanisms of action that may drive anti-tumor activity for cancer patients. We report the discovery of SB-4826, a novel, orally active, covalent small molecule inhibitor of the Sumo Activating Enzyme (SUMO E1), the initiating enzyme of the sumoylation cascade. SB-4826 selectively and irreversibly binds an allosteric pocket of SUMO E1 and drives potent biochemical and cellular activity. SB-4826 inhibits global sumoylation in cells and blocks proliferation across a broad panel (100+) of cancer cell lines. Cysteine-proteome profiling by mass spectrometry indicated that Cys-30 of SUMO E1 was the only cysteine-containing peptide (out of 14,541 measured) that met the criteria for covalent engagement indicating exquisite selectivity across the cellular proteome. In an in vivo pharmacodynamic model measuring IFN signaling SB-4826 treatment led to dose- and time-dependent induction of IFN regulated cytokines. SB-4826 treatment resulted in significant tumor growth inhibition in multiple in vivo models. In a syngeneic A20 lymphoma model SB-4826 led to tumor stasis. In a human RAJI xenograft model, SB-4826 induced near-complete inhibition of tumor growth as a single agent and resulted in tumor regression when combined with rituximab. In a mouse CT-26 colorectal tumor model which is generally refractory to anti-PD-1 treatment, SB-4826 significantly inhibited tumor growth as monotherapy and led to 60% complete tumor responses when combined with anti-PD-1. SB-4826 caused increased CD8+ T cell infiltration in CT-26 tumors supporting the role of SB-4826 in inducing IFN signaling and leading to a tumor microenvironment that is more responsive to immune checkpoint inhibition. SUMO E1 is a clinically validated cancer target as evidenced by recent data showing encouraging responses to TAK-981, an IV-administered, ATP-competitive inhibitor. SB-4826 is a differentiated and optimized SUMO E1 inhibitor that is administered orally and demonstrated improved activity in preclinical models. SB-4826 has favorable properties for development, is a new and promising cancer therapy, and is entering phase 1 clinical studies in 2023. Citation Format: Jude R. Canon, Ashley Callinan, Sarah Bradley, Laurie Wang, Mackenzie Kui, Ariel Wein, Gabriele Sulli, Peter Buchowiecki, Fang-Tsao Hong, Miles Kubota, Mary Walton, Victor J. Cee. SB-4826, a first-in-class oral, covalent inhibitor of SUMO E1 that induces IFN signaling and inhibits tumor growth as monotherapy and in combination with immune checkpoint blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB318.

Post-ovulatory aging is associated with altered patterns for small ubiquitin-like modifier (SUMO) proteins and SUMO-specific proteases.

Mammalian oocytes are ovulated arrested at metaphase of the second meiotic division. If they are not fertilized within a short period, the oocyte undergoes several progressive morphological, structural, and molecular changes during a process called oocyte aging. Herein, we focused on those functional events associated with proper cytoskeleton organization and those that correlate with spindle displacement and chromosome misalignment or scatter. Post-translational modifications by Small Ubiquitin-like Modifier (SUMO) proteins are involved in spindle organization and here we demonstrate that the SUMO pathway is involved in spindle morphology changes and chromosome movements during oocyte aging. SUMO-2/3 as well as the SUMO-specific proteases SENP-2 localization are affected by postovulatory aging in vitro. Consistent with these findings, UBC9 decreases during oocyte aging while differential ubiquitination patterns also correlate with in vitro oocyte aging. These results are consistent with postovulatory aging-related alterations in the posttranslational modifications of the spindle apparatus by SUMO and its SENP proteases. These findings are suggestive that such age-related changes in SUMOylation and the deSUMOylation of key target proteins in the spindle apparatus and kinetochore may be involved with spindle and chromosome alignment defects during mammalian oocyte postovulatory aging. Such findings may have implications for ART-related human oocyte aging in vitro regarding the activities of the SUMO pathway and fertilization success.

SUMOylation inhibition overcomes proteasome inhibitor resistance in multiple myeloma.

Proteasome inhibition is a highly effective treatment for multiple myeloma (MM). However, virtually all patients develop proteasome inhibitor resistance, which is associated with a poor prognosis. Hyperactive small ubiquitin-like modifier (SUMO) signaling is involved in both cancer pathogenesis and cancer progression. A state of increased SUMOylation has been associated with aggressive cancer biology. We found that relapsed/refractory MM is characterized by a SUMO-high state, and high expression of the SUMO E1-activating enzyme (SAE1/UBA2) is associated with poor overall survival. Consistently, continuous treatment of MM cell lines with carfilzomib (CFZ) enhanced SUMO pathway activity. Treatment of MM celllines with the SUMO E1-activating enzyme inhibitor subasumstat (TAK-981) showed synergy with CFZ in both CFZ-sensitive and CFZ-resistant MM cell lines, irrespective of the TP53 state. Combination therapy was effective in primary MM cells and in 2 murine MM xenograft models. Mechanistically, combination treatment with subasumstat and CFZ enhanced genotoxic and proteotoxic stress, and induced apoptosis was associated with activity of the prolyl isomerase PIN1. In summary, our findings reveal activated SUMOylation as a therapeutic target in MM and point to combined SUMO/proteasome inhibition as a novel and potent strategy for the treatment of proteasome inhibitor-resistant MM.

Activation of adenosine A2A receptors induces SUMOylation of HIF-1α.

Hypoxia is an established driver of numerous deleterious cell processes, including immunosuppression and tumor growth. Hypoxia-inducible factor 1α (HIF-1α) accumulates during periods of sustained hypoxia due to the action of multiple post-translational modifications, including the Small Ubiquitin-like modifier (SUMO) pathway. Although enhanced activity of the SUMO-pathway is upregulated during hypoxia, the mechanistic basis for this effect remains unclear. It has been proposed that the Gαs protein-coupled adenosine A2A receptor (A2AR), which is also activated during sustained hypoxia, mediates SUMOylation at a number of target proteins. We sought to determine if activation of A2AR by hypoxia induces SUMOylation of HIF-1α and which of three potential SUMO-sites on HIF-1α are modified by this mechanism. HEK293T cells expressing A2AR and treated with an A2AR agonist (CGS) showed significantly increased HIF-1α accumulation compared to untreated controls after exposure to hypoxia. Similarly, CGS and hypoxia enhanced SUMOylation of HIF-1α in human Jurkat T cells. Using site-directed mutagenesis and Förster resonance energy transfer (FRET), we determined that A2AR-mediated SUMOylation of HIF-1α occurs at lysine 532. Finally, we show that (1) this mechanism of regulation increases the mRNA levels of multiple HIF-1α transcriptional targets; and (2) this mechanism can be precluded by treating cells with a small molecule inhibitor of the SUMO pathway. Together, these data highlight a central role for A2AR-mediated SUMOylation of HIF-1α in mediating the effects of chronic hypoxia in Jurkat T cells.

SUMOylation regulates pre-mRNA splicing to overcome DNA damage in fungi.

Pathogenic fungi are subject to DNA damage stress derived from host immune responses during infection. Small ubiquitin-like modifier (SUMO) modification and precursor (pre)-mRNA splicing are both involved in DNA damage response (DDR). However, the mechanisms of how SUMOylation and splicing coordinated in DDR remain largely unknown. Combining with biochemical analysis, RNA-Seq method, and biological analysis, we report that SUMO pathway participates in DDR and virulence in Fusarium graminearum, a causal agent of Fusarium head blight of cereal crops world-wide. Interestingly, a key transcription factor FgSR is SUMOylated upon DNA damage stress. SUMOylation regulates FgSR nuclear-cytoplasmic partitioning and its phosphorylation by FgMec1, and promotes its interaction with chromatin remodeling complex SWI/SNF for activating the expression of DDR-related genes. Moreover, the SWI/SNF complex was found to further recruit splicing-related NineTeen Complex, subsequently modulates pre-mRNA splicing during DDR. Our findings reveal a novel function of SUMOylation in DDR by regulating a transcription factor to orchestrate gene expression and pre-mRNA splicing to overcome DNA damage during the infection of F.graminearum, which advances the understanding of the delicate regulation of DDR by SUMOylation in pathogenic fungi, and extends the knowledge of cooperation of SUMOylation and pre-mRNA splicing in DDR in eukaryotes.

Trophic factor BDNF inhibits GABAergic signaling by facilitating dendritic enrichment of SUMO E3 ligase PIAS3 and altering gephyrin scaffold

Posttranslational addition of a small ubiquitin-like modifier (SUMO) moiety (SUMOylation) has been implicated in pathologies such as brain ischemia, diabetic peripheral neuropathy, and neurodegeneration. However, nuclear enrichment of SUMO pathway proteins has made it difficult to ascertain how ion channels, proteins that are typically localized to and function at the plasma membrane, and mitochondria are SUMOylated. Here, we report that the trophic factor, brain-derived neurotrophic factor (BDNF) regulates SUMO proteins both spatially and temporally in neurons. We show that BDNF signaling via the receptor tropomyosin-related kinase B facilitates nuclear exodus of SUMO proteins and subsequent enrichment within dendrites. Of the various SUMO E3 ligases, we found that PIAS-3 dendrite enrichment in response to BDNF signaling specifically modulates subsequent ERK1/2 kinase pathway signaling. In addition, we found the PIAS-3 RING and Ser/Thr domains, albeit in opposing manners, functionally inhibit GABA-mediated inhibition. Finally, using oxygen–glucose deprivation as an in vitro model for ischemia, we show that BDNF–tropomyosin-related kinase B signaling negatively impairs clustering of the main scaffolding protein at GABAergic postsynapse, gephyrin, whereby reducing GABAergic neurotransmission postischemia. SUMOylation-defective gephyrin K148R/K724R mutant transgene expression reversed these ischemia-induced changes in gephyrin cluster density. Taken together, these data suggest that BDNF signaling facilitates the temporal relocation of nuclear-enriched SUMO proteins to dendrites to influence postsynaptic protein SUMOylation.

Targeting pancreatic cancer by TAK-981: a SUMOylation inhibitor that activates the immune system and blocks cancer cell cycle progression in a preclinical model

ObjectivePancreatic ductal adenocarcinoma (PDAC) has the characteristics of high-density desmoplastic stroma, a distinctive immunosuppressive microenvironment and is profoundly resistant to all forms of chemotherapy and immunotherapy, leading to a 5-year...

SUMO conjugating enzyme: a vital player of SUMO pathway in plants.

Plants face numerous challenges such as biotic and abiotic stresses during their whole lifecycle. As they are sessile in nature, they ought to develop multiple ways to act during stressed conditions to maintain cellular homeostasis. Among various defense mechanisms, the small ubiquitin-like modifiers (SUMO) pathway is considered as the most important because several nuclear proteins regulated by this pathway are involved in several cellular functions such as response to stress, transcription, translation, metabolism of RNA, energy metabolism, repairing damaged DNA, ensuring genome stability and nuclear trafficking. In general, the SUMO pathway has its own particular set of enzymes E1, E2, and E3. The SUMO conjugating enzyme [SCE (E2)] is a very crucial member of the pathway which can transfer SUMO to its target protein even without the involvement of E3. More than just a middle player, it has shown its involvement in effective triggered immunity in crops like tomato and various abiotic stresses like drought and salinity in maize, rice, and Arabidopsis. This review tries to explore the importance of the SUMOylation process, focusing on the E2 enzyme and its regulatory role in the abiotic stress response, plant immunity, and DNA damage repair.

Novel insights into the impact of the SUMOylation pathway in hematological malignancies (Review)

The small ubiquitin-like modifier (SUMO) system serves an important role in the regulation of protein stability and function. SUMOylation sustains the homeostatic equilibrium of protein function in normal tissues and numerous types of tumor. Accumulating evidence has revealed that SUMO enzymes participate in carcinogenesis via a series of complex cellular or extracellular processes. The present review outlines the physiological characteristics of the SUMOylation pathway and provides examples of SUMOylation participation in different cancer types, including in hematological malignancies (leukemia, lymphoma and myeloma). It has been indicated that the SUMO pathway may influence chromosomal instability, cell cycle progression, apoptosis and chemical drug resistance. The present review also discussed the possible relationship between SUMOylation and carcinogenic mechanisms, and evaluated their potential as biomarkers and therapeutic targets in the diagnosis and treatment of hematological malignancies. Developing and investigating inhibitors of SUMO conjugation in the future may offer promising potential as novel therapeutic strategies.

Viruses, SUMO, and immunity: the interplay between viruses and the host SUMOylation system.

The conjugation of small ubiquitin-like modifier (SUMO) proteins to substrates is a well-described post-translational modification that regulates protein activity, subcellular localization, and protein–protein interactions for a variety of downstream cellular activities. Several studies describe SUMOylation as an essential post-translational modification for successful viral infection across a broad range of viruses, including RNA and DNA viruses, both enveloped and un-enveloped. These viruses include but are not limited to herpes viruses, human immunodeficiency virus-1, and coronaviruses. In addition to the SUMOylation of viral proteins during infection, evidence shows that viruses manipulate the SUMO pathway for host protein SUMOylation. SUMOylation of host and viral proteins greatly impacts host innate immunity through viral manipulation of the host SUMOylation machinery to promote viral replication and pathogenesis. Other post-translational modifications like phosphorylation can also modulate SUMO function. For example, phosphorylation of COUP-TF interacting protein 2 (CTIP2) leads to its SUMOylation and subsequent proteasomal degradation. The SUMOylation of CTIP2 and subsequent degradation prevents CTIP2-mediated recruitment of a multi-enzymatic complex to the HIV-1 promoter that usually prevents the transcription of integrated viral DNA. Thus, the “SUMO switch” could have implications for CTIP2-mediated transcriptional repression of HIV-1 in latency and viral persistence. In this review, we describe the consequences of SUMO in innate immunity and then focus on the various ways that viral pathogens have evolved to hijack the conserved SUMO machinery. Increased understanding of the many roles of SUMOylation in viral infections can lead to novel insight into the regulation of viral pathogenesis with the potential to uncover new targets for antiviral therapies.

Targeting SUMOylation in cancer.

In the article, we focus on the role of SUMOylation in tumorigenesis and cancer-related processes, including Epithelial-mesenchymal transition (EMT), metastasis, resistance to cancer therapies, and antitumor immunity. Clinical perspective on small ubiquitin-like modifier (SUMO) inhibitors will be discussed. SUMOylation regulates multiple important biologic functions including gene transcription, DNA damage repair, cell cycle, and innate immunity. The SUMO pathway enzymes are usually elevated in various cancers and linked with cancer progression and poor clinical outcomes for patients. Recent studies have revealed the role of SUMOylation in EMT and metastasis through regulating E-Cadherin and Snail expression. Multiple studies demonstrate SUMOylation is involved with chemoresistance and hormone treatment resistance. Oncogene Myc and SUMOylation machinery regulation has been revealed in pancreatic cancer. SUMOylation is involved in regulating antitumor immune response through dendritic cells and T cells. A breakthrough has been made in targeting SUMOylation in cancer as first-in-class SUMO E1 inhibitor TAK-981 enters clinical trials. SUMOylation plays an important role in tumor EMT, metastasis, therapy resistance, and antitumor immune response. Pharmaceutical inhibition of SUMOylation has become promising clinical therapy to improve the outcome of the existing chemo and immune therapies.

Antagonism between SUMO1/2 and SUMO3 regulates SUMO conjugate levels and fine-tunes immunity.

The attachment of SMALL UBIQUITIN-LIKE MODIFIER (SUMO) to target proteins regulates a plethora of cellular processes across eukaryotes. In Arabidopsis thaliana, mutants with abnormal SUMO1/2 conjugate levels display a dwarf stature, autoimmunity, and altered stress responses to adverse environmental conditions. Since the SUMO pathway is known to autoregulate its biochemical activity (via allosteric interactions), we assessed whether the emergence of additional SUMO paralogs in Arabidopsis has introduced the capacity of self-regulation by means of isoform diversification in this model plant. By studying the plant defense responses elicited by the bacterial pathogen Pseudomonas syringae pv. tomato, we provide genetic evidence that SUM3, a divergent paralog, acts downstream of the two main SUMO paralogues, SUM1/2. The expression of SUM3 apparently buffers or suppresses the function of SUM1/2 by controlling the timing and amplitude of the immune response. Moreover, SUM1 and SUM2 work additively to suppress both basal and TNL-specific immunity, a specific branch of the immune network. Finally, our data reveal that SUM3 is required for the global increase in SUMO1/2 conjugates upon exposure to biotic and abiotic stresses, namely heat and pathogen exposure. We cannot exclude that this latter effect is independent of the role of SUM3 in immunity.

PIE-1 SUMOylation promotes germline fates and piRNA-dependent silencing in C. elegans.

Germlines shape and balance heredity, integrating and regulating information from both parental and foreign sources. Insights into how germlines handle information have come from the study of factors that specify or maintain the germline fate. In early Caenorhabditis elegans embryos, the CCCH zinc finger protein PIE-1 localizes to the germline where it prevents somatic differentiation programs. Here, we show that PIE-1 also functions in the meiotic ovary where it becomes SUMOylated and engages the small ubiquitin-like modifier (SUMO)-conjugating machinery. Using whole-SUMO-proteome mass spectrometry, we identify HDAC SUMOylation as a target of PIE-1. Our analyses of genetic interactions between pie-1 and SUMO pathway mutants suggest that PIE-1 engages the SUMO machinery both to preserve the germline fate in the embryo and to promote Argonaute-mediated surveillance in the adult germline.

Repression of interrupted and intact rDNA by the SUMO pathway in Drosophila melanogaster.

Ribosomal RNAs (rRNAs) are essential components of the ribosome and are among the most abundant macromolecules in the cell. To ensure high rRNA level, eukaryotic genomes contain dozens to hundreds of rDNA genes, however, only a fraction of the rRNA genes seems to be active, while others are transcriptionally silent. We found that individual rDNA genes have high level of cell-to-cell heterogeneity in their expression in Drosophila melanogaster. Insertion of heterologous sequences into rDNA leads to repression associated with reduced expression in individual cells and decreased number of cells expressing rDNA with insertions. We found that SUMO (Small Ubiquitin-like Modifier) and SUMO ligase Ubc9 are required for efficient repression of interrupted rDNA units and variable expression of intact rDNA. Disruption of the SUMO pathway abolishes discrimination of interrupted and intact rDNAs and removes cell-to-cell heterogeneity leading to uniformly high expression of individual rDNA in single cells. Our results suggest that the SUMO pathway is responsible for both repression of interrupted units and control of intact rDNA expression.

Sumoylation of sodium/calcium exchanger in brain ischemia and ischemic preconditioning

The small ubiquitin-like modifier (SUMO) conjugation (or SUMOylation) is a post-translational protein modification mechanism activated by different stress conditions that has been recently investigated in experimental models of cerebral ischemia. The expression of SUMOylation enzymes and substrates is not restricted to the nucleus, since they are present also in the cytoplasm and on plasma membrane and are involved in several physiological and pathological conditions.In the last decades, convincing evidence have supported the idea that the increased levels of SUMOylated proteins may induce tolerance to ischemic stress. In particular, it has been established that protein SUMOylation may confer neuroprotection during ischemic preconditioning.Considering the increasing evidence that SUMO can modify stability and expression of ion channels and transporters and the relevance of controlling ionic homeostasis in ischemic conditions, the present review will resume the main aspects of SUMO pathways related to the key molecules involved in maintenance of ionic homeostasis during cerebral ischemia and ischemic preconditioning, with a particular focus on the on Na+/Ca2+ exchangers.

SUMO pathway inhibition targets an aggressive pancreatic cancer subtype

ObjectivePancreatic ductal adenocarcinoma (PDAC) still carries a dismal prognosis with an overall 5-year survival rate of 9%. Conventional combination chemotherapies are a clear advance in the treatment of PDAC; however,...