Oligosaccharyltransferase Inhibition Reduces Receptor Tyrosine Kinase Activation and Enhances Glioma Radiosensitivity

Stabilization of EREG via STT3B-mediated N-glycosylation is critical for PDL1 upregulation and immune evasion in head and neck squamous cell carcinoma

Dysregulated Epiregulin (EREG) can activate epidermal growth factor receptor (EGFR) and promote tumor progression in head and neck squamous cell carcinoma (HNSCC). However, the mechanisms underlying EREG dysregulation remain largely unknown. Here, we showed that dysregulated EREG was highly associated with enhanced PDL1 in HNSCC tissues. Treatment of HNSCC cells with EREG resulted in upregulated PDL1 via the c-myc pathway. Of note, we found that N-glycosylation of EREG was essential for its stability, membrane location, biological function, and upregulation of its downstream target PDL1 in HNSCC. EREG was glycosylated at N47 via STT3B glycosyltransferases, whereas mutations at N47 site abrogated N-glycosylation and destabilized EREG. Consistently, knockdown of STT3B suppressed glycosylated EREG and inhibited PDL1 in HNSCC cells. Moreover, treatment of HNSCC cells with NGI-1, an inhibitor of STT3B, blocked STT3B-mediated glycosylation of EREG, leading to its degradation and suppression of PDL1. Finally, combination of NGI-1 treatment with anti-PDLl therapy synergistically enhanced the efficacy of immunotherapy of HNSCC in vivo. Taken together, STT3B-mediated N-glycosylation is essential for stabilization of EREG, which mediates PDL1 upregulation and immune evasion in HNSCC.

Pharmacological suppression of HHLA2 glycosylation restores anti-tumor immunity in colorectal cancer

Immunotherapy aimed at inhibiting the negative co-stimulatory molecule programmed cell death-ligand 1 (PD-L1) has limited effectiveness, with clinical response rates remaining below 10%-15%. Therefore, new immune checkpoints need to be explored. Our study focused on human endogenous retrovirus H long terminal repeat-associating protein 2 (HHLA2), a highly glycosylated member of the B7 family that is widely expressed in colorectal cancer. HHLA2 expression negatively correlates with the prognosis of colorectal cancer. Glycosylation of HHLA2, which is regulated by the glycosyltransferase STT3 oligosaccharyltransferase complex catalytic subunit A (STT3A), is crucial for protein stability and expression in cell membranes. Additionally, the binding of HHLA2 to the receptors killer cell immunoglobulin-like receptor, three immunoglobulin domains and long cytoplasmic tail 3 (KIR3DL3) and transmembrane and immunoglobulin (Ig) domain containing 2 (TMIGD2) is dependent on N-glycosylation. Moreover, N-glycosylation of HHLA2 promotes immune evasion in colorectal cancer by suppressing the immune response of NK cells. Notably, the STT3A inhibitor NGI-1 enhances the anti-tumor immune response of NK cells. Our findings provide new insights and a molecular basis for targeting HHLA2 in immunotherapy for colorectal cancer.

Positive selection CRISPR screens reveal a druggable pocket in an oligosaccharyltransferase required for inflammatory signaling to NF-κB

Nuclear factor κB (NF-κB) plays roles in various diseases. Many inflammatory signals, such as circulating lipopolysaccharides (LPSs), activate NF-κB via specific receptors. Using whole-genome CRISPR-Cas9 screens of LPS-treated cells that express an NF-κB-driven suicide gene, we discovered that the LPS receptor Toll-like receptor 4 (TLR4) is specifically dependent on the oligosaccharyltransferase complex OST-A for N-glycosylation and cell-surface localization. The tool compound NGI-1 inhibits OST complexes in vivo, but the underlying molecular mechanism remained unknown. We did a CRISPR base-editor screen for NGI-1-resistant variants of STT3A, the catalytic subunit of OST-A. These variants, in conjunction with cryoelectron microscopy studies, revealed that NGI-1 binds the catalytic site of STT3A, where it traps a molecule of the donor substrate dolichyl-PP-GlcNAc2-Man9-Glc3, suggesting an uncompetitive inhibition mechanism. Our results provide a rationale for and an initial step toward the development of STT3A-specific inhibitors and illustrate the power of contemporaneous base-editor and structural studies to define drug mechanism of action.

Predictive potentials of glycosylation-related genes in glioma prognosis and their correlation with immune infiltration

Glycosylation is currently considered to be an important hallmark of cancer. However, the characterization of glycosylation-related gene sets has not been comprehensively analyzed in glioma, and the relationship between glycosylation-related genes and glioma prognosis has not been elucidated. Here, we firstly found that the glycosylation-related differentially expressed genes in glioma patients were engaged in biological functions related to glioma progression revealed by enrichment analysis. Then seven glycosylation genes (BGN, C1GALT1C1L, GALNT13, SDC1, SERPINA1, SPTBN5 and TUBA1C) associated with glioma prognosis were screened out by consensus clustering, principal component analysis, Lasso regression, and univariate and multivariate Cox regression analysis using the TCGA-GTEx database. A glycosylation-related prognostic signature was developed and validated using CGGA database data with significantly accurate prediction on glioma prognosis, which showed better capacity to predict the prognosis of glioma patients than clinicopathological factors do. GSEA enrichment analysis based on the risk score further revealed that patients in the high-risk group were involved in immune-related pathways such as cytokine signaling, inflammatory responses, and immune regulation, as well as glycan synthesis and metabolic function. Immuno-correlation analysis revealed that a variety of immune cell infiltrations, such as Macrophage, activated dendritic cell, Regulatory T cell (Treg), and Natural killer cell, were increased in the high-risk group. Moreover, functional experiments were performed to evaluate the roles of risk genes in the cell viability and cell number of glioma U87 and U251 cells, which demonstrated that silencing BGN, SDC1, SERPINA1, TUBA1C, C1GALT1C1L and SPTBN5 could inhibit the growth and viability of glioma cells. These findings strengthened the prognostic potentials of our predictive signature in glioma. In conclusion, this prognostic model composed of 7 glycosylation-related genes distinguishes well the high-risk glioma patients, which might potentially serve as caner biomarkers for disease diagnosis and treatment.

Abnormal glycosylation in glioma: related changes in biology, biomarkers and targeted therapy

Glioma is a rapidly growing and aggressive primary malignant tumor of the central nervous system that can diffusely invade the brain tissue around, and the prognosis of patients is not significantly improved by traditional treatments. One of the most general posttranslational modifications of proteins is glycosylation, and the abnormal distribution of this modification in gliomas may shed light on how it affects biological behaviors of glioma cells, including proliferation, migration, and invasion, which may be produced by regulating protein function, cell-matrix and cell‒cell interactions, and affecting receptor downstream pathways. In this paper, from the perspective of regulating protein glycosylation changes and abnormal expression of glycosylation-related proteins (such as glycosyltransferases in gliomas), we summarize how glycosylation may play a crucial role in the discovery of novel biomarkers and new targeted treatment options for gliomas. Overall, the mechanistic basis of abnormal glycosylation affecting glioma progression remains to be more widely and deeply explored, which not only helps to inspire researchers to further explore related diagnostic and prognostic markers but also provides ideas for discovering effective treatment strategies and improving glioma patient survival and prognosis.

FOXK1 regulates malignant progression and radiosensitivity through direct transcriptional activation of CDC25A and CDK4 in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is a serious malignancy with poor prognosis, necessitating identification of oncogenic mechanisms for novel therapeutic strategies. Recent studies have highlighted the significance of the transcription factor forkhead box K1 (FOXK1) in diverse biological processes and carcinogenesis of multiple malignancies, including ESCC. However, the molecular pathways underlying FOXK1's role in ESCC progression are not fully understood, and its potential role in radiosensitivity remains unclear. Here, we aimed to elucidate the function of FOXK1 in ESCC and explore the underlying mechanisms. Elevated FOXK1 expression levels were found in ESCC cells and tissues, positively correlated with TNM stage, invasion depth, and lymph node metastasis. FOXK1 markedly enhanced the proliferative, migratory and invasive capacities of ESCC cells. Furthermore, silencing FOXK1 resulted in heightened radiosensitivity by impeding DNA damage repair, inducing G1 arrest, and promoting apoptosis. Subsequent studies demonstrated that FOXK1 directly bound to the promoter regions of CDC25A and CDK4, thereby activating their transcription in ESCC cells. Moreover, the biological effects mediated by FOXK1 overexpression could be reversed by knockdown of either CDC25A or CDK4. Collectively, FOXK1, along with its downstream target genes CDC25A and CDK4, may serve as a promising set of therapeutic and radiosensitizing targets for ESCC.

Mining glycosylation-related prognostic lncRNAs and constructing a prognostic model for overall survival prediction in glioma: A study based on bioinformatics analysis

Dysregulation of protein glycosylation plays a crucial role in the development of glioma. Long noncoding RNA (lncRNAs), functional RNA molecules without protein-coding ability, regulate gene expression and participate in malignant glioma progression. However, it remains unclear how lncRNAs are involved in glycosylation glioma malignancy. Identification of prognostic glycosylation-related lncRNAs in gliomas is necessary. We collected RNA-seq data and clinicopathological information of glioma patients from the cancer genome atlas and Chinese glioma genome atlas. We used the "limma" package to explore glycosylation-related gene and screened related lncRNAs from abnormally glycosylated genes. Using univariate Cox analyses Regression and least absolute shrinkage and selection operator analyses, we constructed a risk signature with 7 glycosylation-related lncRNAs. Based on the median risk score (RS), patients with gliomas were divided into low- and high-risk subgroups with different overall survival rates. Univariate and multivariate Cox analyses regression analyses were performed to assess the independent prognostic ability of the RS. Twenty glycosylation-related lncRNAs were identified by univariate Cox regression analyses. Two glioma subgroups were identified using consistent protein clustering, with the prognosis of the former being better than that of the latter. Least absolute shrinkage and selection operator analysis identified 7 survival RSs for glycosylation-related lncRNAs, which were identified as independent prognostic markers and predictors of glioma clinicopathological features. Glycosylation-related lncRNAs play an important role in the malignant development of gliomas and may help guide treatment options.

Molecular basis for glycan recognition and reaction priming of eukaryotic oligosaccharyltransferase

Oligosaccharyltransferase (OST) is the central enzyme of N-linked protein glycosylation. It catalyzes the transfer of a pre-assembled glycan, GlcNAc₂Man₉Glc₃, from a dolichyl-pyrophosphate donor to acceptor sites in secretory proteins in the lumen of the endoplasmic reticulum. Precise recognition of the fully assembled glycan by OST is essential for the subsequent quality control steps of glycoprotein biosynthesis. However, the molecular basis of the OST-donor glycan interaction is unknown. Here we present cryo-EM structures of S. cerevisiae OST in distinct functional states. Our findings reveal that the terminal glucoses (Glc₃) of a chemo-enzymatically generated donor glycan analog bind to a pocket formed by the non-catalytic subunits WBP1 and OST2. We further find that binding either donor or acceptor substrate leads to distinct primed states of OST, where subsequent binding of the other substrate triggers conformational changes required for catalysis. This alternate priming allows OST to efficiently process closely spaced N-glycosylation sites.

Highly expressed genes in multiple myeloma cells - what can they tell us about the disease?

Cancer cells can convert proto‐oncoproteins into oncoproteins by increasing the expression of genes that are oncogenic when expressed at high levels. Such genes can promote oncogenesis without being mutated. To find overexpressed genes in cancer cells from patients with multiple myeloma, we retrieved mRNA expression data from the CoMMpass database and ranked genes by their expression levels. We grouped the most highly expressed genes based on a set of criteria and we discuss the role a selection of them can play in the disease pathophysiology. The list was highly concordant with a similar list based on mRNA expression data from the PADIMAC study. Many well‐known “myeloma genes” such as MCL1, CXCR4, TNFRSF17, SDC1, SLAMF7, PTP4A3, and XBP1 were identified as highly expressed, and we believe that hitherto unrecognized key players in myeloma pathogenesis are also enriched on the list. Highly expressed genes in malignant plasma cells that were absent or expressed at only a low level in healthy plasma cells included IFI6, IFITM1, PTP4A3, SIK1, ALDOA, ATP5MF, ATP5ME, and PSMB4. The ambition of this article is not to validate the role of each gene but to serve as a guide for studies aiming at identifying promising treatment targets.

Glycosylation and its research progress in endometrial cancer

Endometrial cancer (EC) is one of the most common tumors in the female reproductive system, which seriously threatens women's health, particularly in developed countries. 13% of the patients with EC have a poor prognosis due to recurrence and metastasis. Therefore, identifying good predictive biomarkers and therapeutic targets is critical to enable the early detection of metastasis and improve the prognosis. For decades, extensive studies had focused on glycans and glycoproteins in the progression of cancer. The types of glycans that are covalently attached to the polypeptide backbone, usually via nitrogen or oxygen linkages, are known as N‑glycans or O‑glycans, respectively. The degree of protein glycosylation and the aberrant changes in the carbohydrate structures have been implicated in the extent of tumorigenesis and reported to play a critical role in regulating tumor invasion, metabolism, and immunity. This review summarizes the essential biological role of glycosylation in EC, with a focus on the recent advances in glycomics and glycosylation markers, highlighting their implications in the diagnosis and treatment of EC.

Nascent Glycoproteome Reveals That N-Linked Glycosylation Inhibitor-1 Suppresses Expression of Glycosylated Lysosome-Associated Membrane Protein-2

Glycosylation inhibition has great potential in cancer treatment. However, the corresponding cellular response, protein expression and glycosylation changes remain unclear. As a cell-permeable small-molecule inhibitor with reduced cellular toxicity, N-linked glycosylation inhibitor-1 (NGI-1) has become a great approach to regulate glycosylation in mammalian cells. Here for the first time, we applied a nascent proteomic method to investigate the effect of NGI-1 in hepatocellular carcinoma (HCC) cell line. Besides, hydrophilic interaction liquid chromatography (HILIC) was adopted for the enrichment of glycosylated peptides. Glycoproteomic analysis revealed the abundance of glycopeptides from LAMP2, NICA, and CEIP2 was significantly changed during NGI-1 treatment. Moreover, the alterations of LAMP2 site-specific intact N-glycopeptides were comprehensively assessed. NGI-1 treatment also led to the inhibition of Cathepsin D maturation and the induction of autophagy. In summary, we provided evidence that NGI-1 repressed the expression of glycosylated LAMP2 accompanied with the occurrence of lysosomal defects and autophagy.

Aberrant Cellular Glycosylation May Increase the Ability of Influenza Viruses to Escape Host Immune Responses through Modification of the Viral Glycome

Individuals with metabolic dysregulation of cellular glycosylation often experience severe influenza disease, with a poor immune response to the virus and low vaccine efficacy. Here, we investigate the consequences of aberrant cellular glycosylation for the glycome and the biology of influenza virus. We transiently induced aberrant N-linked glycosylation in cultured cells with an oligosaccharyltransferase inhibitor, NGI-1. Cells treated with NGI-1 produced morphologically unaltered viable influenza virus with sequence-neutral glycosylation changes (primarily reduced site occupancy) in the hemagglutinin and neuraminidase proteins. Hemagglutinin with reduced glycan occupancy required a higher concentration of surfactant protein D (an important innate immunity respiratory tract collectin) for inhibition compared to that with normal glycan occupancy. Immunization of mice with NGI-1-treated virus significantly reduced antihemagglutinin and antineuraminidase titers of total serum antibody and reduced hemagglutinin protective antibody responses. Our data suggest that aberrant cellular glycosylation may increase the risk of severe influenza as a result of the increased ability of glycome-modified influenza viruses to evade the immune response.

Glycomaterials to Investigate the Functional Role of Aberrant Glycosylation in Glioblastoma

Glioblastoma (GBM) is a stage IV astrocytoma that carries a dismal survival rate of ≈10 months postdiagnosis and treatment. The highly invasive capacity of GBM and its ability to escape therapeutic challenges are key factors contributing to the poor overall survival rate. While current treatments aim to target the cancer cell itself, they fail to consider the significant role that the GBM tumor microenvironment (TME) plays in promoting tumor progression and therapeutic resistance. The GBM tumor glycocalyx and glycan-rich extracellular matrix (ECM), which are important constituents of the TME have received little attention as therapeutic targets. A wide array of aberrantly modified glycans in the GBM TME mediate tumor growth, invasion, therapeutic resistance, and immunosuppression. Here, an overview of the landscape of aberrant glycan modifications in GBM is provided, and the design and utility of 3D glycomaterials are discussed as a tool to evaluate glycan-mediated GBM progression and therapeutic efficacy. The development of alternative strategies to target glycans in the TME can potentially unveil broader mechanisms of restricting tumor growth and enhancing the efficacy of tumor-targeting therapeutics.

Receptor tyrosine kinases and cancer: oncogenic mechanisms and therapeutic approaches

Receptor tyrosine kinases (RTKs) are transmembrane receptors of great clinical interest due to their role in disease, notably cancer. Since their discovery, several mechanisms of RTK dysregulation have been identified, resulting in multiple cancer types displaying 'oncogenic addiction' to RTKs. As a result, RTKs have represented a major class for targeted therapeutics over the past two decades, with numerous small molecule-based tyrosine kinase inhibitor (TKI) therapeutics having been developed and clinically approved for several cancers. However, many of the current RTK inhibitor treatments eventually result in the rapid development of acquired resistance and subsequent tumor relapse. Recent technological advances and tools are being generated for the identification of novel RTK small molecule therapeutics. These newer technologies will be important for the identification of diverse types of RTK inhibitors, targeting both the receptors themselves as well as key cellular factors that play important roles in the RTK signaling cascade.

Ganoderic acid T improves the radiosensitivity of HeLa cells via converting apoptosis to necroptosis

The use of natural substances derived from traditional Chinese medicine and natural plants as safe radiosensitizing adjuvants is a new trend for cancer radiotherapy. Ganoderma lucidum has been used as a traditional Chinese medicine with a history of more than 2000 years. Ganoderic acid T (GAT) is a typical triterpene of G. lucidum, which has strong cytotoxicity to cancer cells, but whether it has radiation sensitization effect has not been explored. In this work, we treated the HeLa cells with different concentrations of GAT before exposure to gamma-ray radiation and investigated its influence on the radiosensitivity. The cell viability, apoptosis rate, necoptosis rate, intracellular ATP level, cell cycle, the amount of H2AX and 53BP1, reactive oxygen species, and mitochondrial membrane potential were examined. Apoptotic, necroptotic, and autophagic biomarker proteins, including caspase 8, cytochrome c, caspase 3, RIPK, MLKL, P62, and LC3, were analyzed. As a result, we confirmed that with treatment of GAT, the gamma-ray radiation induced both apoptosis and necroptosis in HeLa cells, and with increase of GAT, the percentage ratio of necroptosis was increased. The involved pathways and mechanisms were also explored and discussed.

LINCS gene expression signature analysis revealed bosutinib as a radiosensitizer of breast cancer cells by targeting eIF4G1

Radioresistance is the predominant cause for radiotherapy failure and disease progression, resulting in increased breast cancer‑associated mortality. Using gene expression signature analysis of the Library of Integrated Network‑Based Cellular Signatures (LINCS) and Gene Expression Omnibus (GEO), the aim of the present study was to systematically identify potential candidate radiosensitizers from known drugs. The similarity of integrated gene expression signatures between irradiated eukaryotic translation initiation factor 4 γ 1 (eIF4G1)‑silenced breast cancer cells and known drugs was measured using enrichment scores (ES). Drugs with positive ES were selected as potential radiosensitizers. The radiosensitizing effects of the candidate drugs were analyzed in breast cancer cell lines (MCF‑7, MX‑1 and MDA‑MB‑231) using CCK‑8 and colony formation assays following exposure to ionizing radiation. Cell apoptosis was measured using flow cytometry. The expression levels of eIF4G1 and DNA damage response (DDR) proteins were analyzed by western blotting. Bosutinib was identified as a promising radiosensitizer, as its administration markedly reduced the dosage required both for the drug and for ionizing radiation, which may be associated with fewer treatment‑associated adverse reactions. Moreover, combined treatment of ionizing radiation and bosutinib significantly increased cell killing in all three cell lines, compared with ionizing radiation or bosutinib alone. Among the three cell lines, MX‑1 cells were identified as the most sensitive to both ionizing radiation and bosutinib. Bosutinib markedly downregulated the expression of eIF4G1 in a dose‑dependent manner and also reduced the expression of DDR proteins (including ATM, XRCC4, ATRIP, and GADD45A). Moreover, eIF4G1 was identified as a key target of bosutinib that may regulate DNA damage induced by ionizing radiation. Thus, bosutinib may serve as a potential candidate radiosensitizer for breast cancer therapy.

STING enhances cell death through regulation of reactive oxygen species and DNA damage

Resistance to DNA-damaging agents is a significant cause of treatment failure and poor outcomes in oncology. To identify unrecognized regulators of cell survival we performed a whole-genome CRISPR-Cas9 screen using treatment with ionizing radiation as a selective pressure, and identified STING (stimulator of interferon genes) as an intrinsic regulator of tumor cell survival. We show that STING regulates a transcriptional program that controls the generation of reactive oxygen species (ROS), and that STING loss alters ROS homeostasis to reduce DNA damage and to cause therapeutic resistance. In agreement with these data, analysis of tumors from head and neck squamous cell carcinoma patient specimens show that low STING expression is associated with worse outcomes. We also demonstrate that pharmacologic activation of STING enhances the effects of ionizing radiation in vivo, providing a rationale for therapeutic combinations of STING agonists and DNA-damaging agents. These results highlight a role for STING that is beyond its canonical function in cyclic dinucleotide and DNA damage sensing, and identify STING as a regulator of cellular ROS homeostasis and tumor cell susceptibility to reactive oxygen dependent, DNA damaging agents.

UAP1L1 plays an oncogene-like role in glioma through promoting proliferation and inhibiting apoptosis

BACKGROUND

Uridine diphosphate-N-acetylglucosamine pyrophosphorylase-1-like-1 (UAP1L1) is involved in protein glycosylation and promotes proliferation in some tumors. By analyzing the publicly available Gene Expression Omnibus (GEO) database, we found that UAP1L1 displayed a significant change between paired glioma and normal brain tissues. The purpose of this study was to investigate the expression and functional role of UAP1L1 in glioma.

METHODS

To determine the expression level of UAP1L1 in glioma, immunohistochemistry (IHC) staining was performed in tissue microarrays of 160 gliomas and 24 normal brain tissues. The correlation between UAP1L1 expression and the outcomes of glioma patients was analyzed. Human glioblastoma cell lines, U251 and U87, were employed in this study. Endogenous UAP1L1 expression in U251 and U87 cells was detected by quantitative real-time polymerase chain reaction (qRT-PCR). A lentiviral short hairpin RNA (shRNA) vector (shUAP1L1) was constructed and used to infect U251 and U87 cells to knock down the expression of UAP1L1. We performed 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, colony formation assay, flow cytometry, human apoptosis antibody array, and in vivo subcutaneous xenograft model to investigate the biological functions of UAP1L1.

RESULTS

We revealed that UAP1L1 expression was obviously upregulated in the glioma tissues. The increased UAP1L1 expression level was clinically associated with higher tumor grades and poorer patient prognoses. Moreover, we demonstrated that UAP1L1 knockdown suppressed proliferation and increased apoptosis of glioma cells in vitro. In the xenograft mouse model, we further verified that UAP1L1 knockdown could attenuate the growth of glioma cells in vivo.

CONCLUSIONS

These results indicated that UAP1L1 may play an oncogene-like role in glioma, especially in high grade glioma, and thus may be of clinical importance as a future therapeutic target.

The translocon-associated protein (TRAP) complex regulates quality control of N-linked glycosylation during ER stress

Asparagine (N)-linked glycosylation is required for endoplasmic reticulum (ER) homeostasis, but how this co- and posttranslational modification is maintained during ER stress is unknown. Here, we introduce a fluorescence-based strategy to detect aberrant N-glycosylation in individual cells and identify a regulatory role for the heterotetrameric translocon-associated protein (TRAP) complex. Unexpectedly, cells with knockout of SSR3 or SSR4 subunits restore N-glycosylation over time concurrent with a diminished ER stress transcriptional signature. Activation of ER stress or silencing of the ER chaperone BiP exacerbates or rescues the glycosylation defects, respectively, indicating that SSR3 and SSR4 enable N-glycosylation during ER stress. Protein levels of the SSR3 subunit are ER stress and UBE2J1 dependent, revealing a mechanism that coordinates upstream N-glycosylation proficiency with downstream ER-associated degradation and proteostasis. The fidelity of N-glycosylation is not static in both nontransformed and tumor cells, and the TRAP complex regulates ER glycoprotein quality control under conditions of stress.

Identification of proteins associated with development of metastasis from cutaneous squamous cell carcinomas (cSCCs) via proteomic analysis of primary cSCCs

BACKGROUND

Cutaneous squamous cell carcinoma (cSCC) is one of the most common cancers capable of metastasizing. Proteomic analysis of cSCCs can provide insight into the biological processes responsible for metastasis, as well as future therapeutic targets and prognostic biomarkers.

OBJECTIVES

To identify proteins associated with development of metastasis in cSCC.

METHODS

A proteomic-based approach was employed on 105 completely excised, primary cSCCs, comprising 52 that had metastasized (P-M) and 53 that had not metastasized at 5 years post-surgery (P-NM). Formalin-fixed, paraffin-embedded cSCCs were microdissected and subjected to proteomic profiling after one-dimensional (1D), and separately two-dimensional (2D), liquid chromatography fractionation.

RESULTS

A discovery set of 24 P-Ms and 24 P-NMs showed 144 significantly differentially expressed proteins, including 33 proteins identified via both 1D and 2D separation, between P-Ms and P-NMs. Several differentially expressed proteins were also associated with survival in SCCs of other organs. The findings were verified by multiple reaction monitoring on six peptides from two proteins, annexin A5 (ANXA5) and dolichyl-diphosphooligosaccharide-protein glycosyltransferase noncatalytic subunit (DDOST), in the discovery group and validated on a separate cohort (n = 57). Increased expression of ANXA5 and DDOST was associated with reduced time to metastasis in cSCC and decreased survival in cervical and oropharyngeal cancer. A prediction model using ANXA5 and DDOST had an area under the curve of 0·93 (confidence interval 0·83-1·00), an accuracy of 91·2% and higher sensitivity and specificity than cSCC staging systems currently in clinical use.

CONCLUSIONS

This study highlights that increased expression of two proteins, ANXA5 and DDOST, is significantly associated with poorer clinical outcomes in cSCC.

Pharmacologic Suppression of B7-H4 Glycosylation Restores Antitumor Immunity in Immune-Cold Breast Cancers

Despite widespread utilization of immunotherapy, treating immune-cold tumors has proved to be a challenge. Here, we report that expression of the immune checkpoint molecule B7-H4 is prevalent among immune-cold triple-negative breast cancers (TNBC), where its expression inversely correlates with that of PD-L1. Glycosylation of B7-H4 interferes with its interaction/ubiquitination by AMFR, resulting in B7-H4 stabilization. B7-H4 expression inhibits doxorubicin-induced cell death through the suppression of eIF2α phosphorylation required for calreticulin exposure vis-à-vis the cancer cells. NGI-1, which inhibits B7-H4 glycosylation causing its ubiquitination and subsequent degradation, improves the immunogenic properties of cancer cells treated with doxorubicin, enhancing their phagocytosis by dendritic cells and their capacity to elicit CD8⁺ IFNγ-producing T-cell responses. In preclinical models of TNBC, a triple combination of NGI-1, camsirubicin (a noncardiotoxic doxorubicin analogue) and PD-L1 blockade was effective in reducing tumor growth. Collectively, our findings uncover a strategy for targeting the immunosuppressive molecule B7-H4. SIGNIFICANCE: This work unravels the regulation of B7-H4 stability by ubiquitination and glycosylation, which affects tumor immunogenicity, particularly regarding immune-cold breast cancers. The inhibition of B7-H4 glycosylation can be favorably combined with immunogenic chemotherapy and PD-L1 blockade to achieve superior immuno-infiltration of cold tumors, as well as improved tumor growth control.See related commentary by Pearce and Läubli, p. 1789.This article is highlighted in the In This Issue feature, p. 1775.

UAE1 inhibition mediates the unfolded protein response, DNA damage and caspase-dependent cell death in pancreatic cancer

The Unfolded Protein Response (UPR) plays a key role in the adaptive response to loss of protein homeostasis within the endoplasmic reticulum (ER). The UPR has an adaptive function in protein homeostasis, however, sustained activation of the UPR due to hypoxia, nutrient deprivation, and increased demand for protein synthesis, alters the UPR program such that additional perturbation of ER homeostasis activates a pro-apoptotic program. Since ubiquitination followed by proteasomal degradation of misfolded proteins within the ER is a central mechanism for restoration of ER homeostasis, inhibitors of this pathway have proven to be valuable anti-cancer therapeutics. Ubiquitin activating enzyme 1(UAE1), activates ubiquitin for transfer to target proteins for proteasomal degradation in conjunction with E2 and E3 enzymes. Inhibition of UAE1 activity in response to TAK-243, leads to an accumulation of misfolded proteins within the ER, thereby aggravating ER stress, leading to DNA damage and arrest of cells in the G2/M phase of the cell cycle. Persistent drug treatment mediates a robust induction of apoptosis following a transient cell cycle arrest. These biological effects of TAK-243 were recapitulated in mouse models of PDAC demonstrating antitumor activity at a dose and schedule that did not exhibit obvious normal tissue toxicity. In vitro as well as studies in mouse models failed to show enhanced efficacy when TAK-243 was combined with ionizing radiation or gemcitabine, providing an impetus for future studies to identify agents that synergize with this class of agents for improved tumor control in PDAC.

Significance

The UAE1 inhibitor TAK-243, mediates activation of the unfolded protein response, accumulation of DNA breaks and apoptosis, providing a rationale for the use as a safe and efficacious anti-cancer therapeutic for PDAC.

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Inhibition of Ubiquitin activating enzyme 1(UAE1) leads to an accumulation of misfolded proteins within the ER.

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Persistent drug treatment mediates a robust induction of apoptosis in mouse models of Pancreatic Cancer demonstrating antitumor activity at a dose and schedule that did not exhibit obvious normal tissue toxicity.

The impact of PD-L1 N-linked glycosylation on cancer therapy and clinical diagnosis

N-linked glycosylation is one of the most abundant posttranslational modifications of membrane-bound proteins in eukaryotes and affects a number of biological activities, including protein biosynthesis, protein stability, intracellular trafficking, subcellular localization, and ligand-receptor interaction. Accumulating evidence indicates that cell membrane immune checkpoint proteins, such as programmed death-ligand 1 (PD-L1), are glycosylated with heavy N-linked glycan moieties in human cancers. N-linked glycosylation of PD-L1 maintains its protein stability and interaction with its cognate receptor, programmed cell death protein 1 (PD-1), and this in turn promotes evasion of T-cell immunity. Studies have suggested targeting PD-L1 glycosylation as a therapeutic option by rational combination of cancer immunotherapies. Interestingly, structural hindrance by N-glycan on PD-L1 in fixed samples impedes its recognition by PD-L1 diagnostic antibodies. Notably, the removal of N-linked glycosylation enhances PD-L1 detection in a variety of bioassays and more accurately predicts the therapeutic efficacy of PD-1/PD-L1 inhibitors, suggesting an important clinical implication of PD-L1 N-linked glycosylation. A detailed understanding of the regulatory mechanisms, cellular functions, and diagnostic limits underlying PD-L1 N-linked glycosylation could shed new light on the clinical development of immune checkpoint inhibitors for cancer treatment and deepen our knowledge of biomarkers to identify patients who would benefit the most from immunotherapy. In this review, we highlight the effects of protein glycosylation on cancer immunotherapy using N-linked glycosylation of PD-L1 as an example. In addition, we consider the potential impacts of PD-L1 N-linked glycosylation on clinical diagnosis. The notion of utilizing the deglycosylated form of PD-L1 as a predictive biomarker to guide anti-PD-1/PD-L1 immunotherapy is also discussed.

Glycomics and glycoproteomics of viruses: Mass spectrometry applications and insights toward structure-function relationships

The advancement of viral glycomics has paralleled that of the mass spectrometry glycomics toolbox. In some regard the glycoproteins studied have provided the impetus for this advancement. Viral proteins are often highly glycosylated, especially those targeted by the host immune system. Glycosylation tends to be dynamic over time as viruses propagate in host populations leading to increased number of and/or "movement" of glycosylation sites in response to the immune system and other pressures. This relationship can lead to highly glycosylated, difficult to analyze glycoproteins that challenge the capabilities of modern mass spectrometry. In this review, we briefly discuss five general areas where glycosylation is important in the viral niche and how mass spectrometry has been used to reveal key information regarding structure-function relationships between viral glycoproteins and host cells. We describe the recent past and current glycomics toolbox used in these analyses and give examples of how the requirement to analyze these complex glycoproteins has provided the incentive for some advances seen in glycomics mass spectrometry. A general overview of viral glycomics, special cases, mass spectrometry methods and work-flows, informatics and complementary chemical techniques currently used are discussed. © 2020 The Authors. Mass Spectrometry Reviews published by John Wiley & Sons Ltd. Mass Spec Rev.

A lectin-based glycomic approach identifies FUT8 as a driver of radioresistance in oesophageal squamous cell carcinoma

PURPOSE

Radio-resistance is recognized as a main factor in the failure of radiotherapy in oesophageal squamous cell carcinoma (ESCC). Aberrant cell surface glycosylation has been reported to correlate with radio-resistance in different kinds of tumours. However, glycomic alterations and the corresponding enzymes associated with ESCC radio-resistance have not yet been defined.

METHODS

Two radioresistant cell lines, EC109R and TE-1R, were established from parental ESCC cell lines EC109 and TE-1 by fractionated irradiation. A lectin microarray was used to screen for altered glycan patterns. RNA-sequencing (RNA-seq) was employed to identify differentially expressed glycosyltransferases. Cell Counting Kit-8, colony formation and flow cytometry assays were used to measure cell viability and radiosensitivity. Expression of glycosyltransferase in ESCC tissues was assessed by immunohistochemistry. In vivo radiosensitivity was analysed using a nude mouse xenograft model. Downstream effectors of the enzyme were verified using a lectin-based pull-down assay combined with mass spectrometry.

RESULTS

We found that EC109R and TE-1R cells were more resistant to irradiation than the parental EC109 and TE-1 cells. Using lectin microarrays combined with RNA sequencing, we found that α1, 6-fucosyltransferase (FUT8) was overexpressed in the radioresistant ESCC cell lines. Both gain- and loss-of-function studies confirmed that FUT8 regulates the sensitivity of ESCC cells to irradiation. Importantly, we found that high FUT8 expression was positively linked to radio-resistance and a poor prognosis in ESCC patients who received radiation therapy. Moreover, FUT8 inhibition suppressed the growth and formation of xenograft tumours in nude mice after irradiation. Using a lectin-based pull-down assay and mass spectrometry, we found that CD147 could be glycosylated by FUT8. As expected, inhibition of CD147 partly reversed FUT8-induced radio-resistance in ESCC cells.

CONCLUSIONS

Our results indicate that FUT8 functions as a driver of radio-resistance in ESCC by targeting CD147. Therefore, FUT8 may serve as a marker for predicting the response to radiation therapy in patients with ESCC.

Glycosylation in the Tumor Microenvironment: Implications for Tumor Angiogenesis and Metastasis

Just as oncogene activation and tumor suppressor loss are hallmarks of tumor development, emerging evidence indicates that tumor microenvironment-mediated changes in glycosylation play a crucial functional role in tumor progression and metastasis. Hypoxia and inflammatory events regulate protein glycosylation in tumor cells and associated stromal cells in the tumor microenvironment, which facilitates tumor progression and also modulates a patient's response to anti-cancer therapeutics. In this review, we highlight the impact of altered glycosylation on angiogenic signaling and endothelial cell adhesion, and the critical consequences of these changes in tumor behavior.

Selective inhibition of N-linked glycosylation impairs receptor tyrosine kinase processing

Global inhibition of N-linked glycosylation broadly reduces glycan occupancy on glycoproteins, but identifying how this inhibition functionally impacts specific glycoproteins is challenging. This limits our understanding of pathogenesis in the congenital disorders of glycosylation (CDG). We used selective exo-enzymatic labeling of cells deficient in the two catalytic subunits of oligosaccharyltransferase - STT3A and STT3B - to monitor the presence and glycosylation status of cell surface glycoproteins. We show reduced abundance of two canonical tyrosine receptor kinases - the insulin receptor and insulin-like growth factor 1 receptor (IGF-1R) - at the cell surface in STT3A-null cells, due to decreased N-linked glycan site occupancy and proteolytic processing in combination with increased endoplasmic reticulum localization. Providing cDNA for Golgi-resident proprotein convertase subtilisin/kexin type 5a (PCSK5a) and furin cDNA to wild-type and mutant cells produced under-glycosylated forms of PCSK5a, but not furin, in cells lacking STT3A. Reduced glycosylation of PCSK5a in STT3A-null cells or cells treated with the oligosaccharyltransferase inhibitor NGI-1 corresponded with failure to rescue receptor processing, implying that alterations in the glycosylation of this convertase have functional consequences. Collectively, our findings show that STT3A-dependent inhibition of N-linked glycosylation on receptor tyrosine kinases and their convertases combines to impair receptor processing and surface localization. These results provide new insight into CDG pathogenesis and highlight how the surface abundance of some glycoproteins can be dually impacted by abnormal glycosylation.

No Sugar Added: A New Strategy to Inhibit Glioblastoma Receptor Tyrosine Kinases

A novel inhibitor of N-linked glycosylation (NGI-1) inhibits the glycosylation and phosphorylation of multiple receptor tyrosine kinases in glioblastoma (GBM). NGI-1 sensitizes multiple models of GBM to chemotherapy and radiation in vitro and in vivo and may be especially effective in GBMs that retain active PTEN.See related article by Baro et al., p. 784.