The SUMO conjugating enzyme UBC9 as a biomarker for cervical HPV infections

Increased Small Ubiquitin-like Modifier-Activating Enzyme SAE1 Promotes Hepatocellular Carcinoma by Enhancing mTOR SUMOylation

SUMOylation, one of the most important posttranslational modifications of proteins, plays an essential role in various biological processes; however, enzymes that control SUMOylation in hepatocellular carcinoma (HCC) are still unclear. Comprehensive exploration of the expression and clinical significance of SUMO enzymes in HCC would be of great value. Here, we obtained the gene expression profile of each small ubiquitin-like modifier (SUMO) protein and the corresponding clinical information from The Cancer Genome Atlas. We found that all SUMO enzymes were significantly increased in HCC tissues compared with that in adjacent nontumorous tissues. We identified a 6-gene prognostic signature, including SAE1, PIAS2, PIAS3, SENP3, SENP5, and UBC9, that could effectively predict the overall survival in patients with HCC. Specifically, SAE1 was the most valuable prognostic indicator. In 282 clinical samples, we found that SAE1 was closely related to the clinicopathologic parameters and prognosis of patients with HCC. In vitro and in vivo studies showed that SAE1 knockdown inhibits the proliferation, migration, and invasion of HCC cells. Mechanistically, we confirmed that SAE1 plays a role in driving HCC progression, which is largely dependent on the SUMOylation of mTOR signaling. In conclusion, our study revealed that the expression of SUMO enzymes, especially SAE1, is highly associated with HCC development and acts as a promising prognostic predictor.

Human oncogenic viruses: an overview of protein biomarkers in viral cancers and their potential use in clinics

INTRODUCTION

Although the idea that carcinogenesis might be caused by viruses was first voiced about 100 years ago, today's data disappointingly show that we have not made much progress in preventing and/or treating viral cancers in a century. According to recent studies, infections are responsible for approximately 13% of cancer development in the world. Today, it is accepted and proven by many authorities that Epstein-Barr virus (EBV), Hepatitis B virus (HBV), Hepatitis C virus (HCV), Human Herpesvirus 8 (HHV8), Human T-cell Lymphotropic virus 1 (HTLV1) and highly oncogenic Human Papillomaviruses (HPVs) cause or/and contribute to cancer development in humans.

AREAS COVERED

Considering the insufficient prevention and/or treatment strategies for viral cancers, in this review we present the current knowledge on protein biomarkers of oncogenic viruses. In addition, we aimed to decipher their potential for clinical use by evaluating whether the proposed biomarkers are expressed in body fluids, are druggable, and act as tumor suppressors or oncoproteins.

EXPERT OPINION

Consequently, we believe that this review will shed light on researchers and provide a guide to find remarkable solutions for the prevention and/or treatment of viral cancers.

The UBC9/SUMO pathway affects E-cadherin cleavage in HPV-positive head and neck cancer

Functional loss of E-cadherin is frequent during tumor progression and occurs through a variety of mechanisms, including proteolytic cleavage. E-cadherin downregulation leads to the conversion of a more malignant phenotype promoting Epithelial to Mesenchymal Transition (EMT). The UBC9/SUMO pathway has been also shown to be involved in the regulation of EMT in different cancers. Here we found an increased expression of UBC9 in the progression of Head and Neck Cancer (HNC) and uncovered a role for UBC9/SUMO in hampering the HPV-mediated E-cadherin cleavage in HNC.

Detection of rapidly accumulating stress-induced SUMO in prostate cancer cells by a fluorescent SUMO biosensor

SUMO conjugates and SUMO chains form when SUMO, a small ubiquitin-like modifier protein, is covalently linked to other cellular proteins or itself. During unperturbed growth, cells maintain balanced levels of SUMO conjugates. In contrast, eukaryotic cells that are exposed to proteotoxic and genotoxic insults mount a cytoprotective SUMO stress response (SSR). One hallmark of the SSR is a rapid and massive increase of SUMO conjugates in response to oxidative, thermal, and osmotic stress. Here, we use a recombinant fluorescent SUMO biosensor, KmUTAG-fl, to investigate differences in the SSR in a normal human prostate epithelial cell line immortalized with SV40 (PNT2) and two human prostate cancer cell lines that differ in aggressiveness and response to androgen (LNCaP and PC3). In cells that grow unperturbed, SUMO is enriched in the nuclei of all three cell lines. However, upon 30 min of exposure to ultraviolet radiation or oxidative stress, we detected significant cytosolic enrichment of SUMO as measured by KmUTAG-fl staining. This rapid enrichment in cytosolic SUMO levels was on average fivefold higher in the LNCaP and PC3 prostate cancer cell lines compared to normal immortalized PNT2 cells. Additionally, this enhanced enrichment of cytosolic SUMO was reversible as cells recovered from stress exposure. Our study validates the use of the fluorescent KmUTAG-fl SUMO biosensor to detect differences of SUMO levels and localization between normal and cancer cells and provides new evidence that cancer cells may exhibit an enhanced SSR.

A cellular and bioinformatics analysis of the SENP1 SUMO isopeptidase in pancreatic cancer

Sumoylation is an important post-translational modification that involves the conjugation of the Small Ubiquitin-related Modifier (SUMO) onto target proteins. This modification is reversed through the catalytic activity of SUMO isopeptidases, known as SENPs. One of these SENPs, SENP1, was reported to be overexpressed in human pancreatic cancer cells and patient tissues. Since elevated SENP1 expression levels can be used as a prognostic marker for a subset of cancers, we set out to further explore the overexpression of SENP1 in pancreatic cancer. We found that SENP1 protein levels were not significantly different between pancreatic cancer and normal pancreas-derived cell lines. To evaluate SENP1 expression in patient samples, we analyzed large publicly available datasets and found that SENP1 mRNA levels were significantly lower in pancreatic cancer tissue as compared to normal pancreas tissue samples. Furthermore, we found that the SENP1 gene is amplified in less than 1% of sequenced pancreatic cancer patient samples and that expression levels have no association with patient survival. Based on our analysis, we conclude that SENP1 is not overexpressed in pancreatic cancer and is therefore not likely to be an effective biomarker for this disease. Through this work, we also outline a simple but powerful bioinformatics workflow for the assessment of mRNA expression levels, genomic alterations and survival analysis for putative biomarkers for common human cancers.

Association between Sumoylation-Related Gene rs77447679 Polymorphism and Risk of Gastric Cancer (GC) in a Chinese Population

Purpose: Sumoylation plays a critical role in gene regulation and tumorigenesis, and is hypothesized to correlate with the development of various cancers. So far, there has been no reported association between sumoylation-related genes and the risk of gastric cancer (GC).

Methods: A total of 17 tagging single-nucleotide polymorphisms (tag-SNPs) in 5 sumoylation-related genes were selected and genotyped by SNaPshot in a case-control study, including 1021 GC patients and 1304 controls. Odds ratio (OR) and 95% confidential interval (CI) were computed to evaluate the genetic association of the onset of GC.

Results: We demonstrated that CBX4 rs77447679 polymorphism was significantly associated with GC risk (P= 0.017; adjusted OR: 1.71; 95% CI: 1.10-2.66). The patients with CC genotype had a lower risk of GC (CC vs. CA+AA, P= 0.017; adjusted OR: 1.24; 95% CI: 1.04-1.49).

Conclusion: This study revealed that CBX4 rs77447679 polymorphism was positively associated with GC, and individuals with CC genotype had less risk of GC. The risky effects and functional effect of this polymorphism in GC require further investigation.

Viral manipulation of the cellular sumoylation machinery

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

Autophagy regulates UBC9 levels during viral-mediated tumorigenesis

UBC9, the sole E2-conjugating enzyme required for SUMOylation, is a key regulator of essential cellular functions and, as such, is frequently altered in cancers. Along these lines, we recently reported that its expression gradually increases during early stages of human papillomavirus (HPV)-mediated cervical lesions transformation. However, a better understanding of how UBC9 is exploited by transforming viral oncoproteins is still needed. In the present study, we show that in human samples HPV drives UBC9 up-regulation also in very early steps of head and neck tumorigenesis, pointing to the important role for UBC9 in the HPV-mediated carcinogenic program. Moreover, using HPV-infected pre-cancerous tissues and primary human keratinocytes as the natural host of the virus, we investigate the pathological meaning and the cellular mechanisms responsible for UBC9 de-regulation in an oncoviral context. Our results show that UBC9 overexpression is promoted by transforming viral proteins to increase host cells' resistance to apoptosis. In addition, ultrastuctural, pharmacological and genetic approaches crucially unveil that UBC9 is physiologically targeted by autophagy in human cells. However, the presence of HPV E6/E7 oncoproteins negatively impacts the autophagic process through selective inhibition of autophagosome-lysosome fusion, finally leading to p53 dependent UBC9 accumulation during viral-induced cellular transformation. Therefore, our study elucidates how UBC9 is manipulated by HPV oncoproteins, details the physiological mechanism by which UBC9 is degraded in cells, and identifies how HPV E6/E7 impact on autophagy. These findings point to UBC9 and autophagy as novel hallmarks of HPV oncogenesis, and open innovative avenues towards the treatment of HPV-related malignancies.

Targeting nuclear thymidylate biosynthesis

Thymidylate (dTMP) biosynthesis plays an essential and exclusive function in DNA synthesis and proper cell division, and therefore has been an attractive therapeutic target. Folate analogs, known as antifolates, and nucleotide analogs that inhibit the enzymatic action of the de novo thymidylate biosynthesis pathway and are commonly used in cancer treatment. In this review, we examine the mechanisms by which the antifolate 5-fluorouracil, as well as other dTMP synthesis inhibitors, function in cancer treatment in light of emerging evidence that dTMP synthesis occurs in the nucleus. Nuclear localization of the de novo dTMP synthesis pathway requires modification of the pathway enzymes by the small ubiquitin-like modifier (SUMO) protein. SUMOylation is required for nuclear localization of the de novo dTMP biosynthesis pathway, and disruption in the SUMO pathway inhibits cell proliferation in several cancer models. We summarize evidence that the nuclear localization of the dTMP biosynthesis pathway is a critical factor in the efficacy of antifolate-based therapies that target dTMP synthesis.

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.