Expression analysis of Ubc9, the single small ubiquitin-like modifier (SUMO) E2 conjugating enzyme, in normal and malignant tissues

SUMOylation-regulated genes in colon cancer: expression patterns and clinical implications

Colon cancer (CRC) demonstrates significant heterogeneity, and identifying effective biomarkers can advance the development of precision therapies. Emerging evidence implicates SUMOylation-regulated genes as pivotal regulators of cancer-associated pathways, yet their prognostic potential and therapeutic implications in CRC remain unexplored. A comprehensive analysis of SUMOylation-regulated gene expression, clinical and prognostic value in CRC was performed using transcriptomic data from TCGA-COAD and GEO datasets. We identified 46 differentially expressed SUMOylation-regulated genes (33 upregulated, 13 downregulated) in CRC tumors versus normal tissues. Unsupervised clustering based on 216 SUMOylation-related genes stratified CRC patients into two distinct subtypes: SUMO Cluster 1 (aggressive phenotype, poor prognosis) and SUMO Cluster 2 (favorable prognosis). Cluster 1 exhibited advanced tumor stages (N-stage, p < 0.05) and may present an immunosuppressive microenvironment marked by reduced HLA/immune checkpoint gene expression, while Cluster 2 showed enhanced anti-tumor immunity (activated dendritic cells, γδ T cells). A five-gene SUMOylation-based prognostic signature (MC1R, LRRC4C, SAGE1, GJB6, HOXC5) was developed, and patients were divided into high Riskscore and low Riskscore groups with significant survival differences (log-rank p < 0.05). The nomogram integrating risk score, age, and stage demonstrated robust predictive accuracy (C-index = 0.763, AUC = 0.728-0.785). Nomoscore-high patients exhibited resistance to AMG.706 and ABT.888, suggesting therapeutic vulnerabilities. These findings highlight SUMOylation plays a critical role in CRC heterogeneity, immune modulation, and prognosis, offering a novel biomarker system for risk stratification and personalized therapy.

The impact of dysregulation SUMOylation on prostate cancer

Prostate cancer (PCa) remains one of the most common malignancies in men, with its development and progression being governed by complex molecular pathways. SUMOylation, a post-translational modification (PTM) that involves the covalent attachment of small ubiquitin-like modifier (SUMO) proteins to target substrates, has emerged as a critical regulator of various cellular processes such as transcription, DNA repair, cell cycle progression, and apoptosis. Emerging evidence reveals that abnormal SUMOylation may contribute to PCa pathogenesis, and notably, SUMO-associated enzymes are commonly dysregulated in PCa. This review explores the mechanisms by which SUMOylation is implicated in the regulation of key pathways, and summary aberrant expression of SUMO-related enzymes or SUMOylation sites mutations of substrtes in PCa, as well as the therapeutic implications of targeting the SUMO-related enzymes in PCa treatment.

SUMOylation inhibitors activate anti-tumor immunity by reshaping the immune microenvironment in a preclinical model of hepatocellular carcinoma

PURPOSE

High levels of heterogeneity and immunosuppression characterize the HCC immune microenvironment (TME). Unfortunately, the majority of hepatocellular carcinoma (HCC) patients do not benefit from immune checkpoint inhibitors (ICIs) therapy. New small molecule therapies for the treatment of HCC are the goal of our research.

METHODS

SUMOylation inhibitors (TAK-981 and ML-792) were evaluated for the treatment of preclinical mouse HCC models (including subcutaneous and orthotopic HCC models). We profile immune cell subsets from tumor samples after SUMOylation inhibitors treatment using single-cell RNA sequencing (scRNA-seq), mass cytometry (CyTOF), flow cytometry, and multiple immunofluorescences (mIF).

RESULTS

We discover that SUMOylation is higher in HCC patient samples compared to normal liver tissue. TAK-981 and ML-792 decrease SUMOylation at nanomolar levels in HCC cells and also successfully reduced the tumor burden. Analysis combining scRNA-seq and CyTOF demonstrate that treatment with SUMOylation inhibitors reduces the exhausted CD8+T (Tex) cells while enhancing the cytotoxic NK cells, M1 macrophages and cytotoxic T lymphocytes (CTL) in preclinical mouse HCC model. Furthermore, SUMOylation inhibitors have the potential to activate innate immune signals from CD8+T, NK and macrophages while promoting TNFα and IL-17 secretion. Most notably, SUMOylation inhibitors can directly alter the TME by adjusting the abundance of intestinal microbiota, thereby restoring anti-tumor immunity in HCC models.

CONCLUSIONS

This preclinical study suggests that SUMO signaling inhibitors may be beneficial for the treatment of HCC.

The SUMOylation and ubiquitination crosstalk in cancer

BACKGROUND

The cancer occurrence and progression are largely affected by the post-translational modifications (PTMs) of proteins. Currently, it has been shown that the relationship between ubiquitination and SUMOylation is highly complex and interactive. SUMOylation affects the process of ubiquitination and degradation of substrates. Contrarily, SUMOylation-related proteins are also regulated by the ubiquitination process thus altering their protein levels or activity. Emerging evidence suggests that the abnormal regulation between this crosstalk may lead to tumorigenesis.

PURPOSE

In this review, we have discussed the study of the relationship between ubiquitination and SUMOylation, as well as the possibility of a corresponding application in tumor therapy.

METHODS

The relevant literatures from PubMed have been reviewed for this article.

CONCLUSION

The interaction between ubiquitination and SUMOylation is crucial for the occurrence and development of cancer. A greater understanding of the crosstalk of SUMOylation and ubiquitination may be more conducive to the development of more selective and effective SUMOylation inhibitors, as well as a promotion of synergy with other tumor treatment strategies.

The emerging roles of SUMOylation in pulmonary diseases

Small ubiquitin-like modifier mediated modification (SUMOylation) is a critical post-translational modification that has a broad spectrum of biological functions, including genome replication and repair, transcriptional regulation, protein stability, and cell cycle progression. Perturbation or deregulation of a SUMOylation and deSUMOylation status has emerged as a new pathophysiological feature of lung diseases. In this review, we highlighted the link between SUMO pathway and lung diseases, especially the sumoylated substrate such as C/EBPα in bronchopulmonary dysplasia (BDP), PPARγ in pneumonia, TFII-I in asthma, HDAC2 in chronic obstructive pulmonary disease (COPD), KLF15 in hypoxic pulmonary hypertension (HPH), SMAD3 in idiopathic pulmonary fibrosis (IPF), and YTHDF2 in cancer. By exploring the impact of SUMOylation in pulmonary diseases, we intend to shed light on its potential to inspire the development of innovative diagnostic and therapeutic strategies, holding promise for improving patient outcomes and overall respiratory health.

The Prognosis-Predictive and Immunoregulatory Role of SUMOylation Related Genes: Potential Novel Targets in Prostate Cancer Treatment

SUMOylation is an important part of post-translational protein modifications and regulates thousands of proteins in a dynamic manner. The dysregulation of SUMOylation is detected in many cancers. However, the comprehensive role of SUMOylation in prostate cancer (PCa) remains unclear. Using 174 SUMOylation-related genes (SRGs) from the MigDSB database and the transcript data of PCa from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO), we constructed a SUMOylation-related risk score and correlated it with prognosis, tumor mutation burden (TMB), tumor microenvironment (TME) infiltration, and response to chemotherapy and immunotherapy. Moreover, we validated two vital SRGs by RT-qPCR, western blotting, and immunohistochemistry. Two vital SRGs (DNMT3B and NUP210) were finally selected. The risk score based on these genes exhibited excellent predictive efficacy in predicting the biochemical recurrence (BCR) of PCa. A nomogram involving the risk score and T stage was established to further explore the clinical value of the risk score. We found the high-score group was correlated with worse prognosis, higher TMB, a more suppressive immune microenvironment, and a better response to Docetaxel but worse to PD-1/CTLA-4 blockade. Meanwhile, we validated the significantly higher expression level of NUP210 in PCa at mRNA and protein levels. This study elucidated the comprehensive role of SUMOylation-related genes in PCa. Importantly, we highlighted the role of an important SRG, NUP210, in PCa, which might be a promising target in PCa treatment. A better understanding of SUMOylation and utilizing the SUMOylation risk score could aid in precision medicine and improve the prognosis of PCa.

Splenic SUMO1 controls systemic inflammation in experimental sepsis

Introduction

The recent discovery of TAK981(Subasumstat), the first-in-class selective inhibitor of SUMOylation, enables new immune treatments. TAK981 is already in clinical trials to potentiate immunotherapy in metastatic tumors and hematologic malignancies. Cancer patients have more than ten times higher risk of infections, but the effects of TAK981 in sepsis are unknown and previous studies on SUMO in infections are conflicting.

Methods

We used TAK981 in two sepsis models; polymicrobial peritonitis (CLP) and LPS endotoxemia. Splenectomy was done in both models to study the role of spleen. Western blotting of SUMO-conjugated proteins in spleen lysates was done. Global SUMO1 and SUMO3 knockout mice were used to study the specific SUMO regulation of inflammation in LPS endotoxemia. Splenocytes adoptive transfer was done from SUMO knockouts to wild type mice to study the role of spleen SUMOylation in experimental sepsis.

Results and discussion

Here, we report that inhibition of SUMOylation with TAK981 improved survival in mild polymicrobial peritonitis by enhancing innate immune responses and peritoneal bacterial clearance. Thus, we focused on the effects of TAK981 on the immune responses to bacterial endotoxin, showing that TAK981 enhanced early TNFα production but did not affect the resolution of inflammation. Splenectomy decreased serum TNFα levels by nearly 60% and TAK981-induced TNFα responses. In the spleen, endotoxemia induced a distinct temporal and substrate specificity for SUMO1 and SUMO2/3, and both were inhibited by TAK981. Global genetic depletion of SUMO1, but not SUMO3, enhanced TNFα production and metabolic acidosis. The transfer of SUMO1-null, but not wild-type, splenocytes into splenectomized wild-type mice exacerbated TNFα production and metabolic acidosis in endotoxemia.

Conclusion

These results suggest that specific regulation of splenic SUMO1 can modulate immune and metabolic responses to bacterial infection.

Unconventional protein post-translational modifications: the helmsmen in breast cancer

Breast cancer is the most prevalent malignant tumor and a leading cause of mortality among females worldwide. The tumorigenesis and progression of breast cancer involve complex pathophysiological processes, which may be mediated by post-translational modifications (PTMs) of proteins, stimulated by various genes and signaling pathways. Studies into PTMs have long been dominated by the investigation of protein phosphorylation and histone epigenetic modifications. However, with great advances in proteomic techniques, several other PTMs, such as acetylation, glycosylation, sumoylation, methylation, ubiquitination, citrullination, and palmitoylation have been confirmed in breast cancer. Nevertheless, the mechanisms, effects, and inhibitors of these unconventional PTMs (particularly, the non-histone modifications other than phosphorylation) received comparatively little attention. Therefore, in this review, we illustrate the functions of these PTMs and highlight their impact on the oncogenesis and progression of breast cancer. Identification of novel potential therapeutic drugs targeting PTMs and development of biological markers for the detection of breast cancer would be significantly valuable for the efficient selection of therapeutic regimens and prediction of disease prognosis in patients with breast cancer.

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

OBJECTIVE

Pancreatic 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 survival rate of 9%. Our study aims to add novel small molecule therapeutics for the treatment of PDAC.

DESIGN

We have studied whether TAK-981, a novel highly selective and potent small molecule inhibitor of the small ubiquitin like modifier (SUMO) activating enzyme E1 could be used to treat a preclinical syngeneic PDAC mouse model and we have studied the mode of action of TAK-981.

RESULTS

We found that SUMOylation, a reversible post-translational modification required for cell cycle progression, is increased in PDAC patient samples compared with normal pancreatic tissue. TAK-981 decreased SUMOylation in PDAC cells at the nanomolar range, thereby causing a G2/M cell cycle arrest, mitotic failure and chromosomal segregation defects. TAK-981 efficiently limited tumour burden in the KPC3 syngeneic mouse model without evidence of systemic toxicity. In vivo treatment with TAK-981 enhanced the proportions of activated CD8 T cells and natural killer (NK) cells but transiently decreased B cell numbers in tumour, peripheral blood, spleen and lymph nodes. Single cell RNA sequencing revealed activation of the interferon response on TAK-981 treatment in lymphocytes including T, B and NK cells. TAK-981 treatment of CD8 T cells ex vivo induced activation of STAT1 and interferon target genes.

CONCLUSION

Our findings indicate that pharmacological inhibition of the SUMO pathway represents a potential strategy to target PDAC via a dual mechanism: inhibiting cancer cell cycle progression and activating anti-tumour immunity by inducing interferon signalling.

Combined Evaluation of mRNA and Protein Expression, Promoter Methylation, and Immune Infiltration of UBE2I in Pan-Digestive System Tumors

Background

Digestive system tumors (DSTs) have high morbidity and mortality worldwide. This study explored the potential value of ubiquitin-conjugating enzyme E2 I (UBE2I) in pan-digestive system tumors (pan-DSTs).

Methods

Differential expression, tumor stages, and survival outcomes of UBE2I in pan-DSTs were determined using the GEPIA database. The TIMER database was used to confirm the correlation of UBE2I expression with pan-DSTs and immune infiltrates. Differential analyses of UBE2I promoter methylation and protein levels were performed using the UALCAN database. The underlying mechanisms of UBE2I involvement in pan-DSTs were visualized using interaction networks. The diagnostic value of UBE2I in pan-DSTs was identified using the Oncomine database.

Results

UBE2I was differentially and highly expressed in cholangiocarcinoma (CHOL), pancreatic adenocarcinoma (PAAD), colon adenocarcinoma (COAD), rectal adenocarcinoma (READ), liver hepatocellular carcinoma (LIHC), and stomach adenocarcinoma (STAD). According to survival analysis, upregulated UBE2I was associated with adverse overall and disease-free survival in PAAD and favorable overall survival in READ. UBE2I expression was partially linked to the purity of immune infiltration in COAD, LIHC, PAAD, READ, and STAD, as indicated by the immune infiltration analysis. Promoter methylation analysis showed differential and high methylation of UBE2I in PAAD as well as stratified analysis by gender, nodal metastasis, and race. Protein expression analysis in colon cancer revealed that UBE2I had differential and high expression in tumors as well as stratified analysis by gender, tumor histology, race, and tumor stage. Mechanism explorations demonstrated that in COAD and PAAD, UBE2I was involved in spliceosomal snRNP complex, Notch signaling pathway, etc. Diagnostic analysis indicated that UBE2I had consistent diagnostic value for COAD and PAAD.

Conclusions

Upregulated UBE2I may be a diagnostic and surveillance predictive signature for PAAD and COAD. The potential significance of immune infiltrates and promoter methylation in PAAD and COAD needs further exploration.

SUMOylation Pattern Predicts Prognosis and Indicates Tumor Microenvironment Infiltration Characterization in Bladder Cancer

Background

SUMOylation is an important component of post-translational protein modifications (PTMs), and bladder cancer (BCa) is the ninth most common cancer around the world. But the comprehensive role of SUMOylation in shaping tumor microenvironment (TME) and influencing tumor clinicopathological features and also the prognosis of patients remains unclear.

Methods

Using the data downloaded from The Cancer Genome Atlas (TCGA) and the Gene Expression Omnibus (GEO), we comprehensively evaluated the SUMOylation patterns of 570 bladder cancer samples, and systematically correlated these SUMOylation patterns with TME immune cell infiltrating characteristics. The SUMO score was constructed to quantify SUMOylation patterns of individuals using principal component analysis (PCA) algorithms.

Results

Two distinct SUMOylation patterns and gene clusters were finally determined. Significant differences in the prognosis of patients were found among two different SUMOylation patterns and gene clusters, so were in the mRNA transcriptome and the landscape of TME immune cell infiltration. We also established a set of scoring system named SUMO score to quantify the SUMOylation pattern of individuals with BCa, which was discovered to be tightly connected with tumor clinicopathological characteristics and could predict the prognosis of patients with BCa. Moreover, SUMO score was a considerable predictive indicator for the survival outcome independent of tumor mutation burden (TMB) and low SUMO score was related to better response to immunotherapy using PD-1 blockade. We also found that there existed a significant relationship between sensitivity to commonly used chemotherapy drugs and SUMO score. Finally, a nomograph based on five features, namely, SUMO score, age, gender, T category, and M category was constructed to predict the survival probability of patients with BCa in 1, 3, and 5 years, respectively.

Conclusions

Our work demonstrated and overviewed the complicated regulation mechanisms of SUMOylation in bladder cancer, and better understanding and evaluating SUMOylation patterns could be helpful in guiding clinical therapeutic strategy and improving the prognosis of patients with BCa.

SUMOylation and NEDDylation in Primary and Metastatic Cancers to Bone

Post-translational modifications comprise series of enzymatically-driven chemical modifications, virtually involving the entire cell proteome, that affect the fate of a target protein and, in turn, cell activity. Different classes of modifications can be established ranging from phosphorylation, glycosylation, ubiquitination, acetylation, methylation, lipidation and their inverse reactions. Among these, SUMOylation and NEDDylation are ubiquitin-like multi-enzymatic processes that determine the bound of SUMOs and NEDD8 labels, respectively, on defined amino acidic residues of a specific protein and regulate protein function. As fate-determinants of several effectors and mediators, SUMOylation and NEDDylation play relevant roles in many aspects of tumor cell biology. Bone represents a preferential site of metastasis for solid tumors (e.g., breast and prostate cancers) and the primary site of primitive tumors (e.g., osteosarcoma, chondrosarcoma). Deregulation of SUMOylation and NEDDylation affects different aspects of neoplastic transformation and evolution such as epithelial-mesenchymal transition, adaptation to hypoxia, expression and action of tumor suppressors and oncogenic mediators, and drug resistance. Thereby, they represent potential therapeutic targets. This narrative review aims at describing the involvement and regulation of SUMOylation and NEDDylation in tumor biology, with a specific focus on primary and secondary bone tumors, and to summarize and highlight their potentiality in diagnostics and therapeutic strategies.

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

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

Identification of UBE2I as a Novel Biomarker in ccRCC Based on a Large-Scale CRISPR-Cas9 Screening Database and Immunohistochemistry

Background: The genome-wide CRISPR-cas9 dropout screening has emerged as an outstanding approach for characterization of driver genes of tumor growth. The present study aims to investigate core genes related to clear cell renal cell carcinoma (ccRCC) cell viability by analyzing the CRISPR-cas9 screening database DepMap, which may provide a novel target in ccRCC therapy. Methods: Candidate genes related to ccRCC cell viability by CRISPR-cas9 screening from DepMap and genes differentially expressed between ccRCC tissues and normal tissues from TCGA were overlapped. Weighted gene coexpression network analysis, pathway enrichment analysis, and protein-protein interaction network analysis were applied for the overlapped genes. The least absolute shrinkage and selection operator (LASSO) regression was used to construct a signature to predict the overall survival (OS) of ccRCC patients and validated in the International Cancer Genome Consortium (ICGC) and E-MTAB-1980 database. Core protein expression was determined using immunohistochemistry in 40 cases of ccRCC patients. Results: A total of 485 essential genes in the DepMap database were identified and overlapped with differentially expressed genes in the TCGA database, which were enriched in the cell cycle pathway. A total of four genes, including UBE2I, NCAPG, NUP93, and TOP2A, were included in the gene signature based on LASSO regression. The high-risk score of ccRCC patients showed worse OS compared with these low-risk patients in the ICGC and E-MTAB-1980 validation cohort. UBE2I was screened out as a key gene. The immunohistochemistry indicated UBE2I protein was highly expressed in ccRCC tissues, and a high-level nuclear translocation of UBE2I occurs in ccRCC. Based on the area under the curve (AUC) values, nuclear UBE2I had the best diagnostic power (AUC = 1). Meanwhile, the knockdown of UBE2I can inhibit the proliferation of ccRCC cells. Conclusion: UBE2I, identified by CRISPR-cas9 screening, was a core gene-regulating ccRCC cell viability, which accumulated in the nucleus and acted as a potential novel promising diagnostic biomarker for ccRCC patients. Blocking the nuclear translocation of UBE2I may have potential therapeutic value with ccRCC patients.

SUMOylation regulates Rb hyperphosphorylation and inactivation in uveal melanoma

Small ubiquitin‐like modifier (SUMO)ylation is one of the posttranslational modifications and is implicated in many tumor types. Modulation of SUMOylation can affect tumor progression, but the underlying mechanisms remain unclear. Here, we show that, for the first time, in uveal melanoma (UM), the most common intraocular malignancy in adults, global SUMOylation is upregulated and participates in tumor growth. Inhibition of SUMOylation in UM is sufficient to reduce tumor growth both in vitro and in vivo. Furthermore, we found that retinoblastoma protein (Rb) is a target protein and a critical downstream effector of the upregulated SUMOylation activity in UM. Increased SUMOylation of the Rb protein leads to its hyperphosphorylation and inactivation in UM cells, promoting UM cell proliferation. In summary, our results provide novel insight into the mechanism underlying SUMOylation‐regulated tumor growth in UM.

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.

SUMOylation Regulator-Related Molecules Can Be Used as Prognostic Biomarkers for Glioblastoma

Introduction

SUMOylation is one of the post-translational modifications. The relationship between the expression of SUMOylation regulators and the prognosis of glioblastoma is not quite clear.

Materials and Methods

The single nucleotide variant data, the transcriptome data, and survival information were acquired from The Cancer Genome Atlas, Gene Expression Omnibus, and cBioportal database. Wilcoxon test was used to analyze differentially expressed genes between glioblastoma and normal brain tissues. Gene set enrichment analysis was conducted to find the possible functions. One risk scoring model was built by the least absolute shrinkage and selection operator Cox regression. Kaplain–Meier survival curves and receiver operating characteristic curves were applied to evaluate the effectiveness of the model in predicting the prognosis of glioblastoma.

Results

Single-nucleotide variant mutations were found in SENP7, SENP3, SENP5, PIAS3, RANBP2, USPL1, SENP1, PIAS2, SENP2, and PIAS1. Moreover, UBE2I, UBA2, PIAS3, and SENP1 were highly expressed in glioblastoma, whereas PIAS1, RANBP2, SENP5, and SENP2 were downregulated in glioblastoma. Functional enrichment analysis showed that the SUMOylation regulators of glioblastoma might involve cell cycle, DNA replication, and other functions. A prognostic model of glioblastoma was constructed based on SUMOylation regulator-related molecules (ATF7IP, CCNB1IP1, and LBH). Kaplain–Meier survival curves and receiver operating characteristic curves showed that the model had a strong ability to predict the overall survival of glioblastoma.

Conclusion

This study analyzed the expression of 15 SUMOylation regulators in glioblastoma. The risk assessment model was constructed based on the SUMOylation regulator-related genes, which had a strong predictive ability for the overall survival of patients with glioblastoma. It might provide targets for the study of the relationship between SUMOylation and glioblastoma.

Sumoylation as an Emerging Target in Therapeutics against Cancer

Sumoylation is the Post-translational modification gaining most of the research interest recently. Sumoylation is involved in various crucial functions of the cell such as regulation of cell cycle, DNA damage repair, apoptosis, etc. Oncology is advancing in radiotherapy, targeted chemotherapy, various forms of immunotherapy and targeted gene therapy. Researches are being conducted to prove its connotation with a variety of cancers and inhibitors are being developed to obstruct the fatal effect caused by misbalance of the SUMO-catalytic cycle. It has been shown that up-regulation of certain enzymes of Sumoylation correlates with cancer incidence in most of the cases. However, in some cases, down-regulation also associates with cancer invasion such as underexpression of UBC9 in initial stage breast cancer. This can aid in future study, treatment, and diagnosis of a variety of cancers including breast cancer, prostate cancer, lung adenocarcinoma, melanoma, multiple myeloma, etc. Various mechanistic assays are being developed and used to identify potential inhibitors against the dysregulated proteins of Sumoylation. This review summarizes the normal roles of the enzymes involved in the SUMOcatalytic cycle, their misbalanced regulation leading to tumorigenesis and nearly all the potent inhibitors identified to date, while after detailed studied it was observed that ML-792 could be a promising inhibitor in treating cancers by inhibiting Sumoylation enzymes.

Effects of targeting sumoylation processes during latent and induced Epstein-Barr virus infections using the small molecule inhibitor ML-792

As the second leading cause of death in the United States, cancer has a considerable impact on society, and one cellular process that is commonly dysregulated in many cancers is the post-translational modification of proteins by the Small Ubiquitin-like Modifier (SUMO; sumoylation). We documented that sumoylation processes are up-regulated in lymphoma tissues in the presence of Latent Membrane Protein-1 (LMP1), the principal oncoprotein of Epstein-Barr virus (EBV). LMP1-mediated dysregulation of cellular sumoylation processes contributes to oncogenesis, modulates innate immune responses, and aids the maintenance of viral latency. Manipulation of protein sumoylation has been proposed for anti-cancer and anti-viral therapies; however, known inhibitors of sumoylation do not only target sumoylation processes. Recently, a specific and selective small-molecule inhibitor of sumoylation (ML-792) was identified; however, nothing is known about the effect of ML-792 on LMP1-mediated dysregulation of cellular sumoylation or the EBV life-cycle. We hypothesized that ML-792 modulates viral replication and the oncogenic potential of EBV LMP1 by inhibiting protein sumoylation. Results showed that ML-792 inhibited sumoylation processes in multiple EBV-positive B cell lines and EBV-positive nasopharyngeal carcinoma cell lines but not in their EBV-negative counterparts. Focusing on its effect on B cells, ML-792 inhibited B-cell growth and promoted cell death at very low doses. ML-792 also modulated LMP1-induced cell migration and cell adhesion, which suggests the abrogation of the oncogenic potential of LMP1. Finally, while higher concentrations of ML-792 were sufficient to induce low levels EBV spontaneous reactivation, they decreased the production of new infectious virus following an induced reactivation and the infection of new cells, suggesting that ML-792 has anti-viral potential. Together, these findings suggest that ML-792 may be a potential therapeutic drug to treat EBV-associated lymphoid malignancies by targeting oncogenesis and the EBV life-cycle.

The Function of SUMOylation and Its Role in the Development of Cancer Cells under Stress Conditions: A Systematic Review

Malignant tumors still pose serious threats to human health due to their high morbidity and mortality. Recurrence and metastasis are the most important factors affecting patient prognosis. Chemotherapeutic drugs and radiation used to treat these tumors mainly interfere with tumor metabolism, destroy DNA integrity, and inhibit protein synthesis. The upregulation of small ubiquitin-like modifier (SUMO) is a prevalent posttranslational modification (PTM) in various cancers and plays a critical role in tumor development. The dysregulation of SUMOylation can protect cancer cells from stresses exerted by external or internal stimuli. SUMOylation is a dynamic process finely regulated by SUMOylation enzymes and proteases to maintain a balance between SUMOylation and deSUMOylation. An increasing number of studies have reported that SUMOylation imbalance may contribute to cancer development, including metastasis, angiogenesis, invasion, and proliferation. High level of SUMOylation is required for cancer cells to survive internal or external stresses. Downregulation of SUMOylation may inhibit the development of cancer, making it an important potential clinical therapeutic target. Some studies have already begun to treat tumors by inhibiting the expression of SUMOylation family members, including SUMO E1 or E2. The tumor cells become more aggressive under internal and external stresses. The prevention of tumor development, metastasis, recurrence, and radiochemotherapy resistance by attenuating SUMOylation requires further exploration. This review focused on SUMOylation in tumor cells to discuss its effects on tumor suppressor proteins and oncoproteins as well as classical tumor pathways to identify new insights for cancer clinical therapy.

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.

An unanticipated tumor-suppressive role of the SUMO pathway in the intestine unveiled by Ubc9 haploinsufficiency

Sumoylation is an essential posttranslational modification in eukaryotes that has emerged as an important pathway in oncogenic processes. Most human cancers display hyperactivated sumoylation and many cancer cells are remarkably sensitive to its inhibition, thus supporting application of chemical sumoylation inhibitors in cancer treatment. Here we show, first, that transformed embryonic fibroblasts derived from mice haploinsufficient for Ubc9, the essential and unique gene encoding the SUMO E2 conjugating enzyme, exhibit enhanced proliferation and transformed phenotypes in vitro and as xenografts ex vivo. To then evaluate the possible impact of loss of one Ubc9 allele in vivo, we used a mouse model of intestinal tumorigenesis. We crossed Ubc9+/- mice with mice harboring a conditional ablation of Apc either all along the crypt-villus axis or only in Lgr5+ crypt-based columnar (CBC) cells, the cell compartment that includes the intestinal stem cells proposed as cells-of-origin of intestinal cancer. While Ubc9+/- mice display no overt phenotypes and no globally visible hyposumoylation in cells of the small intestine, we found, strikingly, that, upon loss of Apc in both models, Ubc9+/- mice develop more (>2-fold) intestinal adenomas and show significantly shortened survival. This is accompanied by reduced global sumoylation levels in the polyps, indicating that Ubc9 levels become critical upon oncogenic stress. Moreover, we found that, in normal conditions, Ubc9+/- mice show a moderate but robust (15%) increase in the number of Lgr5+ CBC cells when compared to their wild-type littermates, and further, that these cells display higher degree of stemness and cancer-related and inflammatory gene expression signatures that, altogether, may contribute to enhanced intestinal tumorigenesis. The phenotypes of Ubc9 haploinsufficiency discovered here indicate an unanticipated tumor-suppressive role of sumoylation, one that may have important implications for optimal use of sumoylation inhibitors in the clinic.

A Chain of Events: Regulating Target Proteins by SUMO Polymers

Small ubiquitin-like modifiers (SUMOs) regulate virtually all nuclear processes. The fate of the target protein is determined by the architecture of the attached SUMO protein, which can be of polymeric nature. Here, we highlight the multifunctional aspects of dynamic signal transduction by SUMO polymers. The SUMO-targeted ubiquitin ligases (STUbLs) RING-finger protein 4 (RNF4) and RNF111 recognize SUMO polymers in a chain-architecture-dependent manner, leading to the formation of hybrid chains, which could enable proteasomal destruction of proteins. Recent publications have highlighted essential roles for SUMO chain disassembly by the mammalian SUMO proteases SENP6 and SENP7 and the yeast SUMO protease Ulp2. SENP6 is particularly important for centromere assembly. These recent findings demonstrate the diversity of SUMO polymer signal transduction for proteolytic and nonproteolytic purposes.

SUMOylation Is Required for ERK5 Nuclear Translocation and ERK5-Mediated Cancer Cell Proliferation

The MAP kinase ERK5 contains an N-terminal kinase domain and a unique C-terminal tail including a nuclear localization signal and a transcriptional activation domain. ERK5 is activated in response to growth factors and stresses and regulates transcription at the nucleus by either phosphorylation or interaction with transcription factors. MEK5-ERK5 pathway plays an important role regulating cancer cell proliferation and survival. Therefore, it is important to define the precise molecular mechanisms implicated in ERK5 nucleo-cytoplasmic shuttling. We previously described that the molecular chaperone Hsp90 stabilizes and anchors ERK5 at the cytosol and that ERK5 nuclear shuttling requires Hsp90 dissociation. Here, we show that MEK5 or overexpression of Cdc37—mechanisms that increase nuclear ERK5—induced ERK5 Small Ubiquitin-related Modifier (SUMO)-2 modification at residues Lys6/Lys22 in cancer cells. Furthermore, mutation of these SUMO sites abolished the ability of ERK5 to translocate to the nucleus and to promote prostatic cancer PC-3 cell proliferation. We also show that overexpression of the SUMO protease SENP2 completely abolished endogenous ERK5 nuclear localization in response to epidermal growth factor (EGF) stimulation. These results allow us to propose a more precise mechanism: in response to MEK5 activation, ERK5 SUMOylation favors the dissociation of Hsp90 from the complex, allowing ERK5 nuclear shuttling and activation of the transcription.

Divergent Modulation of Proteostasis in Prostate Cancer

Proteostasis regulates key cellular processes such as cell proliferation, differentiation, transcription, and apoptosis. The mechanisms by which proteostasis is regulated are crucial and the deterioration of cellular proteostasis has been significantly associated with tumorigenesis since it specifically targets key oncoproteins and tumor suppressors. Prostate cancer (PCa) is the second most common cause of cancer death in men worldwide. Androgens mediate one of the most central signaling pathways in all stages of PCa via the androgen receptor (AR). In addition to their regulation by hormones, PCa cells are also known to be highly secretory and are particularly prone to ER stress as proper ER function is essential. Alterations in various complex signaling pathways and cellular processes including cell cycle control, transcription, DNA repair, apoptosis, cell adhesion, epithelial-mesenchymal transition (EMT), and angiogenesis are critical factors influencing PCa development through key molecular changes mainly by posttranslational modifications in PCa-related proteins, including AR, NKX3.1, PTEN, p53, cyclin D1, and p27. Several ubiquitin ligases like MDM2, Siah2, RNF6, CHIP, and substrate-binding adaptor SPOP; deubiquitinases such as USP7, USP10, USP26, and USP12 are just some of the modifiers involved in the regulation of these key proteins via ubiquitin-proteasome system (UPS). Some ubiquitin-like modifiers, especially SUMOs, have been also closely associated with PCa. On the other hand, the proteotoxicity resulting from misfolded proteins and failure of ER adaptive capacity induce unfolded protein response (UPR) that is an indispensable signaling mechanism for PCa development. Lastly, ER-associated degradation (ERAD) also plays a crucial role in prostate tumorigenesis. In this section, the relationship between prostate cancer and proteostasis will be discussed in terms of UPS, UPR, SUMOylation, ERAD, and autophagy.

A Provocative Molecular Link between Mammographic Density and BRCA1-loss associated TNBC

Triple-negative breast cancer (TNBC) is a highly aggressive form of breast cancer that has a high mortality rate and disproportionately affects young African American (AA) women who carry mutations in the BRCA1 gene. Approximately 80% of breast cancers which develop in BRCA1-mutant carriers will have TNBC and the molecular mechanism facilitating tumor development is unclear. Our earlier work suggested Ubc9 to play a critical role in BRCA1 loss mediated TNBC cell migration and metastasis. Collagen is one of the major components of the stromal extracellular matrix (ECM) network that influences tissue density. Its re-organization act as a scaffold aiding cancer cells to migrate causing metastasis. Ubc9 is known to increase the production of collagen, a key component of fibroglandular breast tissue, as well as tumorigenesis. Our work is based on the hypothesis that loss of BRCA1 in women with high breast density causes abnormal Ubc9 levels which upregulates collagen, fibronectin and inhibits SIRT1, β-catenin expression facilitating TNBC. We tested this hypothesis by studying the expression of total collagen, fibronectin, Ubc9, SIRT1, β-catenin in BRCA1 mutant TNBC cells and tumor sample derived from patient with dense breasts using immunofluorescence, immunohistochemistry, and collagen assay. Our results suggest for the first time that mutation or loss of BRCA1 function in women with fibrocystic breasts can lead to over expression of Ubc9, induction of collagen and; fibronectin, inhibition of SIRT1 and nuclear accumulation of β-catenin which could contribute to TNBC development. This network will aid not only in the identification of potential mechanism-based biomarkers that could detect disease early, but also enforce preventive measures that could reduce the risk for TNBC in women with high MD thus reducing the mortality associated with these cancers to achieve health equity.

SUMOylation in Glioblastoma: A Novel Therapeutic Target

Protein SUMOylation is a dynamic post-translational modification which is involved in a diverse set of physiologic processes throughout the cell. Of note, SUMOylation also plays a role in the pathobiology of a myriad of cancers, one of which is glioblastoma (GBM). Accordingly, herein, we review core aspects of SUMOylation as it relates to GBM and in so doing highlight putative methods/modalities capable of therapeutically engaging the pathway for treatment of this deadly neoplasm.

Hypoxia-induced Slug SUMOylation enhances lung cancer metastasis

Background

The Slug-E-cadherin axis plays a critical role in non-small-cell lung cancers (NSCLCs) where aberrant upregulation of Slug promotes cancer metastasis. Now, the post-translational modifications of Slug and their regulation mechanisms still remain unclear in lung cancer. Hence, exploring the protein linkage map of Slug is of great interest for investigating the scenario of how Slug protein is regulated in lung cancer metastasis.

Methods

The Slug associated proteins, Ubc9 and SUMO-1, were identified using yeast two-hybrid screening; and in vitro SUMOylation assays combined with immunoprecipitation and immunoblotting were performed to explore the detail events and regulations of Slug SUMOylation. The functional effects of SUMOylation on Slug proteins were examined by EMSA, reporter assay, ChIP assay, RT-PCR, migration and invasion assays in vitro, tail vein metastatic analysis in vivo, and also evaluated the association with clinical outcome of NSCLC patients.

Results

Slug protein could interact with Ubc9 and SUMO-1 and be SUMOylated in cells. Amino acids 130–212 and 33–129 of Slug are responsible for its binding to Ubc9 and protein inhibitor of activated STAT (PIAS)y, respectively. SUMOylation could enhance the transcriptional repression activity of Slug via recruiting more HDAC1, resulting in reduced expression of downstream Slug target genes and enhanced lung cancer metastasis. In addition, hypoxia could increase Slug SUMOylation through attenuating the interactions of Slug with SENP1 and SENP2. Finally, high expression Slug and Ubc9 levels were associated with poor overall survival among NSCLC patients.

Conclusions

Ubc9/PIASy-mediated Slug SUMOylation and subsequent HDAC1 recruitment may play a crucial role in hypoxia-induced lung cancer progression, and these processes may serve as therapeutic targets for NSCLC.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0996-8) contains supplementary material, which is available to authorized users.

Variation in expression of small ubiquitin-like modifiers in injured sciatic nerve of mice

Small ubiquitin-like modifiers (SUMOs) have been shown to regulate axonal regeneration, signal transduction, neuronal migration, and myelination, by covalently and reversibly attaching to the protein substrates during neuronal cell growth, development, and differentiation. It has not been reported whether SUMOs play a role in peripheral nerve injury and regeneration. To investigate any association between SUMOylation and potential neuroprotective effects during peripheral nerve injury and regeneration, C57/BL mice were randomly divided into sham and experimental groups. The sciatic nerve was exposed only in the sham group. The experimental group underwent neurotomy and epineurial neurorrhaphy. Real-time quantitative polymerase chain reaction and western blot assay results revealed different mRNA and protein expression levels of SUMO1, SUMO2, SUMO3 and UBC9 in sciatic nerve tissue (containing both 5 mm of proximal and distal stumps at the injury site) at various time points after injury. Compared with the sham group, protein levels of SUMO1 and SUMO2/3 increased in both their covalent and free states after sciatic nerve injury in the experimental group, especially in the covalent state. UBC9 protein levels showed similar changes to those of SUMO1 and SUMO2/3 in the covalent states. Immunohistochemical staining demonstrated that SUMO1 and SUMO2/3 immunopositivities were higher in the experimental group than in the sham group. Our results verified that during the repair of sciatic nerve injury, the mRNA and protein expression of SUMO1, SUMO2, SUMO3 and UBC9 in injured nerve tissues changed in varying patterns and there were clear changes in the expression of SUMO-related proteins. These findings reveal that SUMOs possibly play an important role in the repair of peripheral nerve injury. All animal protocols were approved by the Institutional Animal Care and Use Committee of Tianjin Fifth Central Hospital, China (approval No. TJWZXLL2018041) on November 8, 2018.

Developing Practical Therapeutic Strategies that Target Protein SUMOylation

Post-translational modification by small ubiquitin-like modifier (SUMO) has emerged as a global mechanism for the control and integration of a wide variety of biological processes through the regulation of protein activity, stability and intracellular localization. As SUMOylation is examined in greater detail, it has become clear that the process is at the root of several pathologies including heart, endocrine, and inflammatory disease, and various types of cancer. Moreover, it is certain that perturbation of this process, either globally or of a specific protein, accounts for many instances of congenital birth defects. In order to be successful, practical strategies to ameliorate conditions due to disruptions in this post-translational modification will need to consider the multiple components of the SUMOylation machinery and the extraordinary number of proteins that undergo this modification.

UBA2 promotes proliferation of colorectal cancer

Small ubiquitin-like modifier proteins are involved in tumorigenesis; however, the potential effects and functions of the family member ubiquitin-like modifier-activating enzyme 2 (UBA2) on colorectal cancer are not clear. The present study aimed to examine the effects of UBA2 on the proliferation of colorectal cancer cells in vitro and in vivo. The mRNA and protein expression levels of UBA2 in patients with colorectal cancer were measured by reverse transcription-quantitative polymerase chain reaction and immunohistochemistry, respectively. UBA2 expression levels in colorectal cancer tissues were significantly increased compared with the paracancerous normal tissues. The expression of UBA2 was also associated with higher stage colorectal cancer and poor prognosis. MTT and colony formation assays were used to examine proliferation in colorectal cancer cell lines. Flow cytometry was performed to examine the effects of UBA2 on the cell cycle and apoptosis of colorectal cancer cell lines and protein expression levels were examined by western blotting. Athymic nude mice were used to examine the ability of transfected colorectal cancer cells to form tumors in vivo. Downregulation of UBA2 inhibited the proliferation of colorectal cancer cell lines in vitro and in vivo through the regulation of cell cycle associated protein expression and apoptosis. Furthermore, downregulation of UBA2 decreased the expression levels of cyclin B1, B-cell lymphoma-2, phosphorylated protein kinase B and E3 ubiquitin-protein ligase MDM2 in colorectal cancer cells, whereas the expression levels of p21 and p27 were increased. UBA2 was demonstrated to serve an essential role in the proliferation of colorectal cancer and may be used as a potential biomarker to predict prognosis and as a therapeutic target in colorectal cancer.

Inhibition of the Ubc9 E2 SUMO-conjugating enzyme-CRMP2 interaction decreases NaV1.7 currents and reverses experimental neuropathic pain

We previously reported that destruction of the small ubiquitin-like modifier (SUMO) modification site in the axonal collapsin response mediator protein 2 (CRMP2) was sufficient to selectively decrease trafficking of the voltage-gated sodium channel NaV1.7 and reverse neuropathic pain. Here, we further interrogate the biophysical nature of the interaction between CRMP2 and the SUMOylation machinery, and test the hypothesis that a rationally designed CRMP2 SUMOylation motif (CSM) peptide can interrupt E2 SUMO-conjugating enzyme Ubc9-dependent modification of CRMP2 leading to a similar suppression of NaV1.7 currents. Microscale thermophoresis and amplified luminescent proximity homogeneous alpha assay revealed a low micromolar binding affinity between CRMP2 and Ubc9. A heptamer peptide harboring CRMP2's SUMO motif, also bound with similar affinity to Ubc9, disrupted the CRMP2-Ubc9 interaction in a concentration-dependent manner. Importantly, incubation of a tat-conjugated cell-penetrating peptide (t-CSM) decreased sodium currents, predominantly NaV1.7, in a model neuronal cell line. Dialysis of t-CSM peptide reduced CRMP2 SUMOylation and blocked surface trafficking of NaV1.7 in rat sensory neurons. Fluorescence dye-based imaging in rat sensory neurons demonstrated inhibition of sodium influx in the presence of t-CSM peptide; by contrast, calcium influx was unaffected. Finally, t-CSM effectively reversed persistent mechanical and thermal hypersensitivity induced by a spinal nerve injury, a model of neuropathic pain. Structural modeling has now identified a pocket-harboring CRMP2's SUMOylation motif that, when targeted through computational screening of ligands/molecules, is expected to identify small molecules that will biochemically and functionally target CRMP2's SUMOylation to reduce NaV1.7 currents and reverse neuropathic pain.

Small-Molecule Inhibitors Targeting Protein SUMOylation as Novel Anticancer Compounds

SUMOylation, one of post-translational modifications, is covalently modified on lysine residues of a target protein through an enzymatic cascade reaction similar to protein ubiquitination. Along with identification of many SUMOylated proteins, protein SUMOylation has been proven to regulate multiple biologic activities including transcription, cell cycle, DNA repair, and innate immunity. The dysregulation of protein SUMOylation and deSUMOylation modification is linked with carcinogenesis and tumor progression. The SUMOylation-associated enzymes are usually elevated in various cancers, which function as cancer biomarkers to relate to poor outcomes for patients. Considering the significance of protein SUMOylation in regulating diverse biologic functions in cancer progression, numerous small-molecule inhibitors targeting protein SUMOylation pathway are developed as potentially clinical anticancer therapeutics. Here, we systematically summarize the latest progresses of associations of small ubiquitin-like modifier (SUMO) enzymes with cancers and small-molecular inhibitors against human cancers by targeting SUMOylation enzymes. We also compared the pros and cons of several special anticancer inhibitors targeting SUMO pathway. As more efforts are invested in this field, small-molecule inhibitors targeting the SUMOylation modification pathway are promising for development into novel anticancer drugs.

Delineating the HMGB1 and HMGB2 interactome in prostate and ovary epithelial cells and its relationship with cancer

High Mobility Group B (HMGB) proteins are involved in cancer progression and in cellular responses to platinum compounds used in the chemotherapy of prostate and ovary cancer. Here we use affinity purification coupled to mass spectrometry (MS) and yeast two-hybrid (Y2H) screening to carry out an exhaustive study of HMGB1 and HMGB2 protein interactions in the context of prostate and ovary epithelia. We present a proteomic study of HMGB1 partners based on immunoprecipitation of HMGB1 from a non-cancerous prostate epithelial cell line. In addition, HMGB1 and HMGB2 were used as baits in yeast two-hybrid screening of libraries from prostate and ovary epithelial cell lines as well as from healthy ovary tissue. HMGB1 interacts with many nuclear proteins that control gene expression, but also with proteins that form part of the cytoskeleton, cell-adhesion structures and others involved in intracellular protein translocation, cellular migration, secretion, apoptosis and cell survival. HMGB2 interacts with proteins involved in apoptosis, cell motility and cellular proliferation. High confidence interactors, based on repeated identification in different cell types or in both MS and Y2H approaches, are discussed in relation to cancer. This study represents a useful resource for detailed investigation of the role of HMGB1 in cancer of epithelial origins, as well as potential alternative avenues of therapeutic intervention.

The post-translational modification, SUMOylation, and cancer (Review)

SUMOylation is a reversible post-translational modification which has emerged as a crucial molecular regulatory mechanism, involved in the regulation of DNA damage repair, immune responses, carcinogenesis, cell cycle progression and apoptosis. Four SUMO isoforms have been identified, which are SUMO1, SUMO2/3 and SUMO4. The small ubiquitin-like modifier (SUMO) pathway is conserved in all eukaryotes and plays pivotal roles in the regulation of gene expression, cellular signaling and the maintenance of genomic integrity. The SUMO catalytic cycle includes maturation, activation, conjugation, ligation and de-modification. The dysregulation of the SUMO system is associated with a number of diseases, particularly cancer. SUMOylation is widely involved in carcinogenesis, DNA damage response, cancer cell proliferation, metastasis and apoptosis. SUMO can be used as a potential therapeutic target for cancer. In this review, we briefly outline the basic concepts of the SUMO system and summarize the involvement of SUMO proteins in cancer cells in order to better understand the role of SUMO in human disease.

Probing the roles of SUMOylation in cancer cell biology by using a selective SAE inhibitor

Small ubiquitin-like modifier (SUMO) family proteins regulate target-protein functions by post-translational modification. However, a potent and selective inhibitor targeting the SUMO pathway has been lacking. Here we describe ML-792, a mechanism-based SUMO-activating enzyme (SAE) inhibitor with nanomolar potency in cellular assays. ML-792 selectively blocks SAE enzyme activity and total SUMOylation, thus decreasing cancer cell proliferation. Moreover, we found that induction of the MYC oncogene increased the ML-792-mediated viability effect in cancer cells, thus indicating a potential application of SAE inhibitors in treating MYC-amplified tumors. Using ML-792, we further explored the critical roles of SUMOylation in mitotic progression and chromosome segregation. Furthermore, expression of an SAE catalytic-subunit (UBA2) S95N M97T mutant rescued SUMOylation loss and the mitotic defect induced by ML-792, thus confirming the selectivity of ML-792. As a potent and selective SAE inhibitor, ML-792 provides rapid loss of endogenously SUMOylated proteins, thereby facilitating novel insights into SUMO biology.

Innate immune activating ligand SUMOylation affects tumor cell recognition by NK cells

Natural Killer cells are innate lymphocytes involved in tumor immunosurveillance. They express activating receptors able to recognize self-molecules poorly expressed on healthy cells but up-regulated upon stress conditions, including transformation. Regulation of ligand expression in tumor cells mainly relays on transcriptional mechanisms, while the involvement of ubiquitin or ubiquitin-like modifiers remains largely unexplored. Here, we focused on the SUMO pathway and demonstrated that the ligand of DNAM1 activating receptor, PVR, undergoes SUMOylation in multiple myeloma. Concurrently, we found that PVR is preferentially located in intracellular compartments in human multiple myeloma cell lines and malignant plasma cells and that inhibition of the SUMO pathway promotes its translocation to the cell surface, increasing tumor cell susceptibility to NK cell-mediated cytolysis. Our findings provide the first evidence of an innate immune activating ligand regulated by SUMOylation, and confer to this modification a novel role in impairing recognition and killing of tumor cells.

A novel Ubc9 -dependent pathway regulates SIRT1- ER-α Axis and BRCA1-associated TNBC lung metastasis

Triple negative breast cancer (TNBC) is a heterogeneous disease and has a higher rate of recurrence and distant metastasis. African-American (AA) women have a higher frequency of BRCA1 mutations and TNBC compared to other populations. Basal-like tumors have a higher rate of brain, lung and distant nodal metastasis more than other TNBC subtypes, contributing to higher mortality rate. Our previous work suggested Ubc9, a SUMO E2-conjugating enzyme to induce proliferation and migration of BRCA1-incompetent TNBC cells and TNBC cell lines established from the pleural effusion metastasis of a woman with TNBC. To understand the downstream signaling axis involved in distant metastasis we have used clinically relevant BRCA1 mutant and lung metastatic TNBC cell lines and our results show deregulated expression of caveolin-1, VEGF and SIRT1 in these cells compared to normal mammary epithelial cells by immunofluorescence analysis. We observed SIRT1 to be induced by wild type BRCA1a and BRCA1a I26A mutant unlike the disease associated Ubc9 binding mutants in TNBC cells. Knock down of Ubc9 induced SIRT1 expression in TNBC and ER-α expression in breast cancer cells. This is the first report demonstrating a role for Ubc9 in repressing both SIRT1 and ER-α expression in BRCA1 associated TNBC cells. It also suggests that the BARD-dependent E3 Ubiquitin ligase and HR (homologous recombination) activity of BRCA1 may not be required for inducing SIRT1 expression. Our results suggest for the first time that in BRCA1 mutant TNBC Ubc9-mediated induction of VEGF, inhibition of caveolin-1, SIRT1 and ER-α expression as a novel molecular mechanism underlying TNBC EMT (epithelial mesenchymal transition) leading to lung metastasis with pleural effusion. Drugs that target Ubc9 to both induce SIRT1 and ER-α or using SIRT1 agonists in combination with chemotherapy can be used as a promising targeted therapeutic approach for treating basal-like metastatic BRCA1-linked TNBC thus reducing the mortality in patients with TNBC.

SUMO and the robustness of cancer

Post-translational protein modification by small ubiquitin-like modifier (SUMO), termed sumoylation, is an important mechanism in cellular responses to stress and one that appears to be upregulated in many cancers. Here, we examine the role of sumoylation in tumorigenesis as a possibly necessary safeguard that protects the stability and functionality of otherwise easily misregulated gene expression programmes and signalling pathways of cancer cells.

Involvement of bleomycin hydrolase and poly(ADP-ribose) polymerase-1 in Ubc9-mediated resistance to chemotherapy agents

Ubiquitin-conjugating protein 9 (Ubc9), the sole enzyme for sumoylation, plays critical roles in many physiological functions, such as DNA damage repair and genome integrity. Its overexpression led to poor prognosis and drug resistance in tumor chemotherapy. However, the underlying mechanism by which Ubc9 promotes tumor progress and influences the susceptibility to antitumor agents remains elusive. In this study, we used nine antitumor agents with distinct actions to explore Ubc9-mediated resistance in human breast carcinoma MCF-7 cells. Increase of susceptibility, respectively, to boningmycin, hydroxycamptothecine, cis-dichlorodiamineplatinum, 5-fluorouracil, vepeside and gemcitabine, but not for doxorubicin, vincristine and norcantharidin, was observed after the knockdown of Ubc9 protein level with RNA interference. Reduction of bleomycin hydrolase and poly(ADP-ribose) polymerase-1 levels after knockdown of Ubc9 suggests their contribution to Ubc9-mediated drug resistance. This is the first report on the sensitivity to hydroxycamptothecine, cis-dichlorodiamineplatinum and gemcitabine that increased after knockdown of bleomycin hydrolase at protein level. In conclusion, Ubc9 plays different roles of action in antitumor agents in chemotherapy. The process requires bleomycin hydrolase and poly(ADP-ribose) polymerase-1. The results are beneficial to deeply understanding of Ubc9 functions and for precise prediction of chemotherapy outcomes in tumors.

Role of ATG10 expression quantitative trait loci in non-small cell lung cancer survival

The aim of this article was to evaluate whether genetic variants in autophagy-related genes affect the overall survival (OS) of non-small cell lung cancer (NSCLC) patients. We analyzed 14 single nucleotide polymorphisms (SNPs) in core autophagy-related genes for OS in 1,001 NSCLC patients. Three promising SNPs in ATG10 were subsequently annotated by the expression quantitative trait loci (eQTL) and methylation quantitative trait loci (meQTL) analyses based on Genotype-Tissue Expression (GTEx) and The Cancer Genome Atlas (TCGA) datasets. We observed that the variants of rs10514231, rs1864182 and rs1864183 were associated with poor lung cancer survival (HR = 1.33, 95% CI = 1.07-1.65; HR = 1.43, 95% CI = 1.13-1.81; HR = 1.38, 95% CI = 1.14-1.68, respectively) and positively correlated with ATG10 expression (all p < 0.05) from GTEx and TCGA datasets. The elevated expression of ATG10 may predict shorter survival time in lung cancer patients in TCGA dataset (HR = 2.10, 95% CI = 1.33-3.29). Moreover, the variants of rs10514231 and rs1864182 were associated with the increased methylation levels of cg17942617 (meQTL), which in turn contributed to the elevated ATG10 expression and decreased survival time. Further functional assays revealed that ATG10 facilitated lung cancer cell proliferation and migration. Our findings suggest that eQTL/meQTL variations of ATG10 could influence lung cancer survival through regulating ATG10 expression.

SUMO wrestling with Ras

This review discusses our current understanding of the small ubiquitin-like modifier (SUMO) pathway and how it functionally intersects with Ras signaling in cancer. The Ras family of small GTPases are frequently mutated in cancer. The role of the SUMO pathway in cancer and in Ras signaling is currently not well understood. Recent studies have shown that the SUMO pathway can both regulate Ras/MAPK pathway activity directly and support Ras-driven oncogenesis through the regulation of proteins that are not direct Ras effectors. We recently discovered that in Ras mutant cancer cells, the SUMOylation status of a subset of proteins is altered and one such protein, KAP1, is required for Ras-driven transformation. A better understanding of the functional interaction between the SUMO and Ras pathways could lead to new insights into the mechanism of Ras-driven oncogenesis.

SUMO pathway components as possible cancer biomarkers

SUMOylation is a key post-translational modification that regulates crucial cellular functions and pathological processes. Recently, Small Ubiquitin-related MOdifier (SUMO) modification has emerged as a fundamental route that may drive different steps of human tumorigenesis. Indeed, alteration in expression or activity of one of the different SUMO pathway components may completely subvert cellular properties through fine-tuning modulation of protein(s) involved in carcinogenic pathways, leading to altered cell proliferation, apoptosis resistance and metastatic potential. Here we describe some of the most interesting findings pointing to a clear link between SUMO pathway and human malignancies. Importantly, a putative role for SUMO enzymes to predict cancer behavior can be speculated, and thus the possible application of alterations in SUMO pathway components as tumor biomarkers is discussed.

Pc2-mediated SUMOylation of WWOX is essential for its suppression of DU145 prostate tumorigenesis

Tumor suppressor WW domain-containing oxidoreductase (WWOX) is depleted in various cancer types. Here we report that WWOX is modified by small ubiquitin-like modifier (SUMO) proteins and represses DU145 prostate cancer tumorigenesis in a SUMOylation-dependent manner. Ectopic WWOX was shown to associate with SUMO2/3 or E2 Ubc9. Furthermore, we revealed that WWOX SUMOylation was promoted by E3 ligase polycomb2 (Pc2), and that WWOX associated with Pc2. Meanwhile, anisomycin-induced activator protein-1 (AP-1) activity was markedly diminished by co-expression of SUMO and WWOX. Also, WWOX wild type (WT), but not WWOX SUMO mutant (K176A) markedly reduced both DU145 prostate cancer cell proliferation and xenograft tumorigenesis. Collectively, our findings demonstrate that SUMO modification of WWOX is essential for its suppressive activity for DU145 prostate cancer tumorigenesis.

SUMOylation-Mediated Regulation of Cell Cycle Progression and Cancer

Protein conjugation with Small ubiquitin-like modifier (SUMOylation) has critical roles during cell cycle progression. Many important cell cycle regulators, including many oncogenes and tumor suppressors, are functionally regulated via SUMOylation. The dynamic SUMOylation pattern observed throughout the cell cycle is ensured via distinct spatial and temporal regulation of the SUMO machinery. Additionally, SUMOylation cooperates with other post-translational modifications to mediate cell cycle progression. Deregulation of these SUMOylation and deSUMOylation enzymes causes severe defects in cell proliferation and genome stability. Different types of cancer were recently shown to be dependent on a functioning SUMOylation system, a finding that could be exploited in anticancer therapies.

Spatiotemporal distribution of SUMOylation components during mouse brain development

Posttranslational modification of proteins might play an important role in brain cellular dynamics via the rapid turnover or functional change of critical proteins controlling neuronal differentiation or synaptic transmission. Small ubiquitin-like modifier protein (SUMO) is a family of ubiquitin-like small proteins that are covalently attached to target proteins to modify their function posttranslationally. Many cellular processes, such as transcription and protein trafficking, are regulated by SUMOylation, but its functional significance in the brain remains unclear. Although developmental regulation of SUMOylation levels in rat brain was recently demonstrated, no comparative immunohistochemical analysis of the cellular distribution profiles of SUMOylation components, including SUMO1, SUMO2/3, and Ubc9, has been undertaken so far. The present study used immunohistochemical and immunoblot analysis with the different developmental stages of mice and demonstrated the developmentally regulated distribution of SUMO1, SUMO2/3, and Ubc9 in the brain. During embryonic development, SUMOylation by SUMO1 and SUMO2/3 occurred in the nucleoplasm of nestin-positive neural stem cells. Although the total amount of SUMO-modified proteins decreased during postnatal brain development, intense and persistent accumulation of SUMO2/3 was detected throughout life in neural progenitor populations in neurogenic regions, including the subventricular zone and the hippocampal subgranular zone. In contrast, many neurons in the adult brain accumulated SUMO1 rather than SUMO2/3. Heavy immunoreactivity of SUMO1 was found in large projection neurons in the brainstem, whereas SUMO2/3 was almost absent from these areas. This heterogeneous distribution implies that both proteins play a specific and unique role in the brain.

Characterization of the loss of SUMO pathway function on cancer cells and tumor proliferation

SUMOylation is a post-translational ubiquitin-like protein modification pathway that regulates important cellular processes including chromosome structure, kinetochore function, chromosome segregation, nuclear and sub-nuclear organization, transcription and DNA damage repair. There is increasing evidence that the SUMO pathway is dysregulated in cancer, raising the possibility that modulation of this pathway may have therapeutic potential. To investigate the importance of the SUMO pathway in the context of cancer cell proliferation and tumor growth, we applied lentivirus-based short hairpin RNAs (shRNA) to knockdown SUMO pathway genes in human cancer cells. shRNAs for SAE2 and UBC9 reduced SUMO conjugation activity and inhibited proliferation of human cancer cells. To expand upon these observations, we generated doxycycline inducible conditional shRNA cell lines for SAE2 to achieve acute and reversible SAE2 knockdown. Conditional SAE2 knockdown in U2OS and HCT116 cells slowed cell growth in vitro, and SAE2 knockdown induced multiple terminal outcomes including apoptosis, endoreduplication and senescence. Multinucleated cells became senescent and stained positive for the senescence marker, SA-β Gal, and displayed elevated levels of p53 and p21. In an attempt to explain these phenotypes, we confirmed that loss of SUMO pathway activity leads to a loss of SUMOylated Topoisomerase IIα and the appearance of chromatin bridges which can impair proper cytokinesis and lead to multinucleation. Furthermore, knockdown of SAE2 induces disruption of PML nuclear bodies which may further promote apoptosis or senescence. In an in vivo HCT116 xenograft tumor model, conditional SAE2 knockdown strongly impaired tumor growth. These data demonstrate that the SUMO pathway is required for cancer cell proliferation in vitro and tumor growth in vivo, implicating the SUMO pathway as a potential cancer therapeutic target.

Roles of ubiquitination and SUMOylation on prostate cancer: mechanisms and clinical implications

The initiation and progression of human prostate cancer are highly associated with aberrant dysregulations of tumor suppressors and proto-oncogenes. Despite that deletions and mutations of tumor suppressors and aberrant elevations of oncogenes at the genetic level are reported to cause cancers, emerging evidence has revealed that cancer progression is largely regulated by posttranslational modifications (PTMs) and epigenetic alterations. PTMs play critical roles in gene regulation, cellular functions, tissue development, diseases, malignant progression and drug resistance. Recent discoveries demonstrate that ubiquitination and SUMOylation are complicated but highly-regulated PTMs, and make essential contributions to diseases and cancers by regulation of key factors and signaling pathways. Ubiquitination and SUMOylation pathways can be differentially modulated under various stimuli or stresses in order to produce the sustained oncogenic potentials. In this review, we discuss some new insights about molecular mechanisms on ubiquitination and SUMOylation, their associations with diseases, oncogenic impact on prostate cancer (PCa) and clinical implications for PCa treatment.