90K Glycoprotein Promotes Degradation of Mutant β-Catenin Lacking the ISGylation or Phosphorylation Sites in the N-terminus

E3 ligase HERC5-catalyzed UGDH isgylation promotes SNAI1-mediated tumor metastasis and cisplatin resistance in oral squamous cell carcinoma

BACKGROUND

Oral squamous cell carcinoma (OSCC) is one of the leading causes of cancer-related mortality worldwide due to its high aggressive potential and drug resistance. Previous studies have revealed an important function of HECT And RLD Domain Containing E3 Ubiquitin Protein Ligase 5 (HERC5) in cancer. Six GEO gene microarrays identified HERC5 as a significant upregulated gene in OSCC tissues or cells (log2 Fold change > 1 and adj.p < 0.05). This study aimed to explore the role and underlying mechanisms of HERC5 in OSCC development.

RESULTS

High HERC5 expression in OSCC tissues was confirmed by our hospital validation cohort and positively correlated with primary tumor stages. Subsequent functional studies demonstrated that knockdown of HERC5 inhibited the migratory and invasive capabilities with decrease of Vimentin and increase of E-cadherin in OSCC cells. In cisplatin treatment, cell survival rates were significantly reduced in HERC5-silencing OSCC cells, accompanied by the increase in cytotoxicity, DNA damage and apoptosis. OSCC cell-derived tumor xenograft displayed that HERC5 depletion inhibited pulmonary metastasis as well as restored the cisplatin-induced tumor burden. In line with this, overexpression of HERC5 yielded the opposite alterations both in vivo and in vitro. Mechanistically, UDP-glucose 6-dehydrogenase (UGDH) was identified as a HERC5-binding protein. Cysteine residue at position 994 in the HECT domain of HERC5 catalyzed the conjugation of ubiquitin-like protein Interferon-induced 15 kDa protein (ISG15) to UGDH (ISGylation of UGDH) and facilitated its phosphorylation, therefore enhancing SNAI1 mRNA stability. SNAI1 depletion inhibited HERC5 overexpression-triggered invasion and cisplatin resistance of OSCC cells.

CONCLUSIONS

Our study indicates that HERC5 may be a promising therapeutic target for OSCC.

HERC5/ISG15 Enhances Glioblastoma Stemness and Tumor Progression by mediating SERBP1protein stability

Glioblastoma (GBM) is the most common malignant brain tumor, and has a low survival rate and a poor prognosis. Intensive studies of pathogenic mechanisms are essential for exploring therapeutic targets for GBM. In this study, the roles played by interferon-stimulated gene 15 (ISG15), HECT, RCC1-containing protein 5 (HERC5), and SERPINE1 mRNA binding protein 1 (SERBP1) in regulating GBM cell stemness were investigated. The real-time quantitative polymerase chain reaction (qPCR), western blotting (WB), and immunohistochemistry (IHC) were used to determine the expression levels of HERC5, ISG15, and SERBP1. Cell stemness was analyzed using a cell sphere formation assay. Colony formation and cell counting kit-8 (CCK-8) assays were performed to assess cell proliferation, Transwell assays used to evaluate cell migration and invasion, and flow cytometry was used to assess cell apoptosis after treatment with temozolomide. SERBP1 stability was assessed by a CHX chase assay. A co-immunoprecipitation (Co-IP) assay verified the binding of ISG15 and HERC5 onto SERBP1. Our results showed that HERC5 and ISG15 were highly expressed in GBM. HERC5 and ISG15 promoted the cell stemness of GBM, and increased cell proliferation, sphere formation, migration, invasion, and chemoresistance. Moreover, HERC5 and ISG15 played a synergistic role in promoting the cell stemness of GBM. We also found that HERC5/ISG15 promoted the stability of SERBP1, which also promoted the cell stemness of GBM. The tumor-promoting role of HERC5 and ISG15 was also confirmed in a subcutaneous xenograft tumor model. Collectively, HERC5/ISG15 was found to regulate GBM stemness and tumor progression by mediating SERBP1 protein stability. Our present study suggests a promising therapeutic target for GBM.

The Functional Roles of ISG15/ISGylation in Cancer

The protein ISG15 encoded by interferon-stimulated gene (ISG) 15 is the first identified member of the ubiquitin-like protein family and exists in the form of monomers and conjugated complexes. Like ubiquitin, ISG15 can mediate an ubiquitin-like modification by covalently modifying other proteins, known as ISGylation. There is growing evidence showing that both the free and conjugated ISG15 are involved in multiple key cellular processes, including autophagy, exosome secretion, DNA repair, immune regulation, and cancer occurrence and progression. In this review, we aim to further clarify the function of ISG15 and ISGylation in cancer, demonstrate the important relationship between ISG15/ISGylation and cancer, and emphasize new insights into the different roles of ISG15/ISGylation in cancer progression. This review may contribute to therapeutic intervention in cancer. However, due to the limitations of current research, the regulation of ISG15/ISGylation on cancer progression is not completely clear, thus further comprehensive and sufficient correlation studies are still needed.

Covalent conjugation of ubiquitin-like ISG15 to apoptosis inducing factor exacerbates toxic stimuli-induced apoptotic cell death

Apoptosis-inducing factor (AIF) is a mitochondrion-localized flavoprotein with NADH oxidase activity. AIF normally acts as an oxidoreductase to catalyze the transfer of electrons between molecules, but it can also kill cells when exposed to certain stimuli. For example, intact AIF is cleaved upon exposure to DNA-damaging agents such as etoposide, and truncated AIF (tAIF) is released from the mitochondria to the cytoplasm and translocated to the nucleus where it induces apoptosis. Although the serial events during tAIF-mediated apoptosis and the transition of AIF function have been widely studied from various perspectives, their underlying regulatory mechanisms and the factors involved are not fully understood. Here, we demonstrated that tAIF is a target of the covalent conjugation of the ubiquitin-like moiety ISG15 (referred to as ISGylation), which is mediated by the ISG15 E3 ligase HERC5. In addition, ISGylation increases the stability of tAIF protein as well as its K6-linked polyubiquitination. Moreover, we found that ISGylation increases the nuclear translocation of tAIF upon cytotoxic etoposide treatment, subsequently causing apoptotic cell death in human lung A549 carcinoma cells. Collectively, these results suggest that HERC5-mediated ISG15 conjugation is a key factor in the positive regulation of tAIF-mediated apoptosis, highlighting a novel role of posttranslational ISG15 modification as a switch that allows cells to live or die under the stress that triggers tAIF release.

Role of galectin 3 binding protein in cancer progression: a potential novel therapeutic target

The lectin galactoside-binding soluble 3 binding protein (LGALS3BP) is a secreted, hyperglycosylated protein expressed by the majority of human cells. It was first identified as cancer and metastasis associated protein, while its role in innate immune response upon viral infection remains still to be clarified. Since its discovery dated in early 90 s, a large body of literature has been accumulating highlighting both a prognostic and functional role for LGALS3BP in cancer. Moreover, data from our group and other have strongly suggested that this protein is enriched in cancer-associated extracellular vesicles and may be considered a promising candidate for a targeted therapy in LGALS3BP positive cancers. Here, we extensively reviewed the literature relative to LGALS3BP role in cancer and its potential value as a therapeutic target.

LGALS3BP: A Potential Plasma Biomarker Associated with Diagnosis and Prognosis in Patients with Sepsis

Purpose

This study aimed to screen differentially expressed proteins (DEPs) in plasma of patients with sepsis through data-independent acquisition (DIA) and enzyme-linked immunosorbent assays (ELISAs), and provide convenient and accurate serum markers for determining the condition of septic patients.

Methods

A total of 53 septic patients and 16 normal controls who were admitted to the Affiliated Hospital of Southwest Medical University between January 2019 and December 2020 were enrolled in this study; 6 specimens from the normal group and 15 from the sepsis group were randomly selected for DIA-based quantitative proteomic analysis. The acquired data were subjected to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, and a protein-protein interaction (PPI) network was constructed to screen potential markers. The selected proteins were further verified through ELISAs. The differences between control and sepsis groups and between survivors and non-survivors were analysed. Receiver operating characteristic (ROC) curves were drawn to explore their diagnostic value and prognostic efficacy.

Results

A total of 149 DEPs were identified by bioinformatics methods. The analyses showed that these proteins are mainly involved in biological processes such as cell movement, stress response, cell proliferation, and immune response. Functional pathway analysis showed that they are mainly involved in leukocyte transendothelial migration, protein synthesis and processing, and various bacterial infections. LGALS3BP was selected as a potential plasma biomarker and further verified through an ELISA. Its level in septic patients was significantly higher than that in normal controls, and its level in non-survivors was also higher than that in survivors. The ROC curves suggested its great diagnostic efficacy and prognostic ability in sepsis.

Conclusion

LGALS3BP levels were significantly different between the normal and sepsis groups; it has good diagnostic value in sepsis, and is related to patient prognosis; thus, it might be a biomarker for sepsis.

Same same but different - Antiviral factors interfering with the infectivity of HIV particles

Human immunodeficiency virus (HIV) is the causative agent of acquired immunodeficiency syndrome (AIDS). Novel strategies to combat this pandemic include the discovery of cellular proteins targeting distinct steps of the HIV replication cycle. Here, we summarize our current knowledge on antiviral proteins interfering with the infectivity of released HIV particles.

Glycoprotein 90K Promotes E-Cadherin Degradation in a Cell Density-Dependent Manner via Dissociation of E-Cadherin-p120-Catenin Complex

Glycoprotein 90K (also known as LGALS3BP or Mac-2BP) is a tumor-associated protein, and high 90K levels are associated with poor prognosis in some cancers. To clarify the role of 90K as an indicator for poor prognosis and metastasis in epithelial cancers, the present study investigated the effect of 90K on an adherens junctional protein, E-cadherin, which is frequently absent or downregulated in human epithelial cancers. Treatment of certain cancer cells with 90K significantly reduced E-cadherin levels in a cell-population-dependent manner, and these cells showed decreases in cell adhesion and increases in invasive cell motility. Mechanistically, 90K-induced E-cadherin downregulation occurred via ubiquitination-mediated proteasomal degradation. 90K interacted with the E-cadherin–p120-catenin complex and induced its dissociation, altering the phosphorylation status of p120-catenin, whereas it did not associate with β-catenin. In subconfluent cells, 90K decreased membrane-localized p120-catenin and the membrane fraction of the p120-catenin. Particularly, 90K-induced E-cadherin downregulation was diminished in p120-catenin knocked-down cells. Taken together, 90K upregulation promotes the dissociation of the E-cadherin–p120-catenin complex, leading to E-cadherin proteasomal degradation, and thereby destabilizing adherens junctions in less confluent tumor cells. Our results provide a potential mechanism to explain the poor prognosis of cancer patients with high serum 90K levels.