Exosomal lncRNA DUXAP8 affecting CHPF2 in the pathogenesis of intracranial aneurysms

OBJECTIVE

This study endeavored to explore the relationship between exosome-derived lncRNA Double Homeobox A Pseudogene 8 (DUXAP8) and Chondroitin Polymerizing Factor 2 (CHPF2), and their roles in the pathogenesis of intracranial aneurysm (IA).

METHODS

The shared targeted molecules (DUXAP8 and CHPF2) were detected via GSE122897 and GSE75436 datasets. A total of 312 patients with IAs were incorporated into this study. Exosomes were isolated from serum samples, and their identity was confirmed using Western blotting for exosomal markers (CD9, CD63 and ALIX). Inflammatory responses in IA tissues were evaluated using Hematoxylin-Eosin staining. CHPF2 protein concentration and the expression levels of DUXAP8 and CHPF2 mRNA in exosomal samples were assessed using Immunochemistry (IHC), Western Blotting, and qRT-PCR, respectively. Cell-based assays involving Human Umbilical Vein Endothelial Cells (HuvECs), including transfection with exosomal DUXAP8, Western Blotting, qRT-PCR, and Cell Counting Kit-8, were conducted. Receiver Operating Characteristic (ROC) curves were derived using SPSS.

RESULTS

DUXAP8 level affects the level of CHPF2. DUXAP8 expression within exosomes was associated with increased CD9, CD63, ALIX and CHPF2 levels during IA development and inflammatory stress. In HuvECs, transfection with exosomes carrying DUXAP8 siRNA resulted in reduced CHPF2 expression, whereas DUXAP8 mimic increased CHPF2 concentrations. The Area Under the ROC Curve (AUC) for exosomal DUXAP8 expression and CHPF2 levels, and aneurysm size was 0.768 (95% CI, 0.613 to 0.924), 0.937 (95% CI, 0.853 to 1.000), and 0.943 (95% CI, 0.860, 1.000), respectively.

CONCLUSION

Exosome-derived DUXAP8 promotes IA progression by affecting CHPF2 expression.

Deficiency of polypeptide N-acetylgalactosamine transferase 9 contributes to a risk for Parkinson's disease via mitochondrial dysfunctions

Polypeptide N-acetylgalactosamine transferase 9 (GALNT9) catalyzes the initial step of mucin-type O-glycosylation via linking N-acetylgalactosamine (GalNAc) to serine/threonine in a protein. To unravel the association of GALNT9 with Parkinson's disease (PD), a progressive neurodegenerative disorder, GALNT9 levels were evaluated in the patients with PD and mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and statistically analyzed based on the GEO datasets of GSE114918 and GSE216281. Glycoproteins with exposing GalNAc were purified using lectin affinity chromatography and identified by LC-MS/MS. The influence of GALNT9 on cells was evaluated via introducing a GALNT9-specific siRNA into SH-SY5Y cells. Consequently, GALNT9 deficiency was found to occur under PD conditions. GALNT9 silencing contributed to a causative factor in PD pathogenesis via reducing the levels of intracellular dopamine, tyrosine hydroxylase and soluble α-synuclein, and promoting α-synuclein aggregates. MS identification revealed 14 glycoproteins. 5 glycoproteins, including ACO2, ATP5B, CKB, CKMT1A, ALDOC, were associated with energy metabolism. GALNT9 silencing resulted in mitochondrial dysfunctions via increasing ROS accumulation, mitochondrial membrane depolarization, mPTPs opening, Ca2+ releasing and activation of the CytC-related apoptotic pathway. The dysfunctional mitochondria then triggered mitophagy, possibly intermediated by adenine nucleotide translocase 1. Our study suggests that GALNT9 is potentially developed into an auxiliary diagnostic index and therapeutic target of PD.

An unusual dual sugar-binding lectin domain controls the substrate specificity of a mucin-type O-glycosyltransferase

N-acetylgalactosaminyl-transferases (GalNAc-Ts) initiate mucin-type O-glycosylation, an abundant and complex posttranslational modification that regulates host-microbe interactions, tissue development, and metabolism. GalNAc-Ts contain a lectin domain consisting of three homologous repeats (α, β, and γ), where α and β can potentially interact with O-GalNAc on substrates to enhance activity toward a nearby acceptor Thr/Ser. The ubiquitous isoenzyme GalNAc-T1 modulates heart development, immunity, and SARS-CoV-2 infectivity, but its substrates are largely unknown. Here, we show that both α and β in GalNAc-T1 uniquely orchestrate the O-glycosylation of various glycopeptide substrates. The α repeat directs O-glycosylation to acceptor sites carboxyl-terminal to an existing GalNAc, while the β repeat directs O-glycosylation to amino-terminal sites. In addition, GalNAc-T1 incorporates α and β into various substrate binding modes to cooperatively increase the specificity toward an acceptor site located between two existing O-glycans. Our studies highlight a unique mechanism by which dual lectin repeats expand substrate specificity and provide crucial information for identifying the biological substrates of GalNAc-T1.

Runx2 Regulates Galnt3 and Fgf23 Expressions and Galnt3 Decelerates Osteoid Mineralization by Stabilizing Fgf23

Runx2 (runt related transcription factor 2) is an essential transcription factor for osteoblast proliferation and differentiation. Uridine diphosphate (UDP)-N-acetylgalactosamine (GalNAc): polypeptide GalNAc-transferase 3 (Galnt3) prevents proteolytic processing of fibroblast growth factor 23 (Fgf23), which is a hormone that regulates the serum level of phosphorus. Runx2 and Galnt3 were expressed in osteoblasts and osteocytes, and Fgf23 expression was restricted to osteocytes in bone. Overexpression and knock-down of Runx2 upregulated and downregulated, respectively, the expressions of Galnt3 and Fgf23, and Runx2 directly regulated the transcriptional activity of Galnt3 in reporter assays. The expressions of Galnt3 and Fgf23 in osteoblast-specific Runx2 knockout (Runx2fl/flCre) mice were about half those in Runx2fl/fl mice. However, the serum levels of phosphorus and intact Fgf23 in Runx2fl/flCre mice were similar to those in Runx2fl/fl mice. The trabecular bone volume was increased during aging in both male and female Galnt3-/- mice, but the osteoid was reduced. The markers for bone formation and resorption in Galnt3-/- mice were similar to the control in both sexes. Galnt3-/- mice exhibited hyperphosphatemia and hypercalcemia, and the intact Fgf23 was about 40% that of wild-type mice. These findings indicated that Runx2 regulates the expressions of Galnt3 and Fgf23 and that Galnt3 decelerates the mineralization of osteoid by stabilizing Fgf23.

GALNT12 suppresses the bone-specific prostate cancer metastasis by activating BMP pathway via the O-glycosylation of BMPR1A

Bone metastasis caused the majority death of prostate cancer (PCa) but the mechanism remains poorly understood. In this present study, we show that polypeptide N-acetylgalactosaminyltransferase 12 (GALNT12) suppresses bone-specific metastasis of PCa. GALNT12 suppresses proliferation, migration, invasion and cell division ability of PCa cells by activating the BMP pathway. Mechanistic investigations showed that GALNT12 augments the O-glycosylation of BMPR1A then actives the BMP pathway. Activated BMP signaling inhibits the expression of integrin αVβ3 to reduce the bone-specific seeding of PCa cells. Furthermore, activated BMP signaling remolds the immune microenvironment by suppressing the STAT3 pathway. Our results of this study illustrate the role and mechanism of GALNT12 in the process of bone metastasis of PCa and identify GALNT12 as a potential therapeutic target for metastatic PCa.

ISOGlyP: O-Glycosylation Site Prediction Using Peptide Sequences and GALNTs

Mucin-type O-glycosylation is one of the most common posttranslational modifications of proteins. The abnormal expression of various polypeptide GalNAc-transferases (GALNTs) which initiate and define sites of O-glycosylation is linked to many cancers and other diseases. Many current O-glycosylation prediction programs utilize O-glycoproteomics data obtained without using the transferase isoform(s) responsible for the glycosylation. With 20 different GALNTs in humans, having the ability to predict and interpret O-glycosylation sites in terms of specific GALNT isoforms is invaluable.To fill this gap, ISOGlyP (isoform-specific O-glycosylation prediction) has been developed. Using position-specific enhancement values generated based on GalNAc-T isoform-specific amino acid preferences, ISOGlyP predicts the propensity that a site would be glycosylated by a specific transferase. ISOGlyP gave an overall prediction accuracy of 70% against in vivo data, which is comparable to that of the NetOGlyc4.0 predictor. Additionally, ISOGlyP can identify the known effects of long- and short-range prior glycosylation and can generate potential peptide sequences selectively glycosylated by specific isoforms. ISOGlyP is freely available for use at https://ISOGlyP.utep.edu . The code is also available on GitHub ( https://github.com/jonmohl/ISOGlyP ).

Polypeptide N-acetylgalactosaminyltransferase (GalNAc-T) isozyme surface charge governs charge substrate preferences to modulate mucin type O-glycosylation

A large family of polypeptide N-acetylgalactosaminyltransferases (GalNAc-Ts) initiate mucin type O-glycosylation transferring α-GalNAc from a UDP-GalNAc donor to the hydroxyl groups of Ser and Thr residues of peptides and proteins, thereby defining sites of O-glycosylation. Mutations and differential expression of several GalNAc-Ts are associated with many disease states including cancers. The mechanisms by which these isozymes choose their targets and their roles in disease are not fully understood. We previously showed that the GalNAc-Ts possess common and unique specificities for acceptor type, peptide sequence and prior neighboring, and/or remote substrate GalNAc glycosylation. In the present study, the role of flanking charged residues was investigated using a library of charged peptide substrates containing the central -YAVTPGP- acceptor sequence. Eleven human and one bird GalNAc-T were initially characterized revealing a range of preferences for net positive, net negative, or unique combinations of flanking N- and/or C-terminal charge, correlating to each isozyme's different electrostatic surface potential. It was further found that isoforms with high sequence identity (>70%) within a subfamily can possess vastly different charge specificities. Enzyme kinetics, activities obtained at elevated ionic strength, and molecular dynamics simulations confirm that the GalNAc-Ts differently recognize substrate charge outside the common +/-3 residue binding site. These electrostatic interactions impact how charged peptide substrates bind/orient on the transferase surface, thus modulating their activities. In summary, we show the GalNAc-Ts utilize more extended surfaces than initially thought for binding substrates based on electrostatic, and likely other hydrophobic/hydrophilic interactions, furthering our understanding of how these transferases select their target.

Bump-and-hole engineering of human polypeptide N-acetylgalactosamine transferases to dissect their protein substrates and glycosylation sites in cells

Despite the known disease relevance of glycans, the biological function and substrate specificities of individual glycosyltransferases are often ill-defined. Here, we describe a protocol to develop chemical, bioorthogonal reporters for the activity of the GalNAc-T family of glycosyltransferases using a tactic termed bump-and-hole engineering. This allows identification of the protein substrates and glycosylation sites of single GalNAc-Ts. Despite requiring transfection of cells with the engineered transferases and enzymes for biosynthesis of bioorthogonal substrates, the tactic complements methods in molecular biology. For complete details on the use and execution of this protocol, please refer to Schumann et al. (2020)1, Cioce et al. (2021)2, and Cioce et al. (2022)3.

Ganglioside Microdomains on Cellular and Intracellular Membranes Regulate Neuronal Cell Fate Determination

Gangliosides are sialylated glycosphingolipids (GSLs) with essential but enigmatic functions in brain activities and neural stem cell (NSC) maintenance. Our group has pioneered research on the importance of gangliosides for growth factor receptor signaling and epigenetic regulation of NSC activity and differentiation. The primary localization of gangliosides is on cell-surface microdomains and the drastic dose and composition changes during neural differentiation strongly suggest that they are not only important as biomarkers, but also are involved in modulating NSC fate determination. Ganglioside GD3 is the predominant species in NSCs and GD3-synthase knockout (GD3S-KO) revealed reduction of postnatal NSC pools with severe behavioral deficits. Exogenous administration of GD3 significantly restored the NSC pools and enhanced the stemness of NSCs with multipotency and self-renewal. Since morphological changes during neurogenesis require a huge amount of energy, mitochondrial functions are vital for neurogenesis. We discovered that a mitochondrial fission protein, the dynamin-related protein-1 (Drp1), as a novel GD3-binding protein, and GD3 regulates mitochondrial dynamics. Furthermore, we discovered that GM1 ganglioside promotes neuronal differentiation by an epigenetic regulatory mechanism. Nuclear GM1 binds with acetylated histones on the promoters of N-acetylgalactosaminyltransferase (GalNAcT; GM2 synthase) as well as on the NeuroD1 genes in differentiated neurons. In addition, epigenetic activation of the GalNAcT gene was detected as accompanied by an apparent induction of neuronal differentiation in NSCs responding to an exogenous supplement of GM1. GM1 is indeed localized in the nucleus where it can interact with transcriptionally active histones. Interestingly, GM1 could induce epigenetic activation of the tyrosine hydroxylase (TH) gene, with recruitment of nuclear receptor related 1 (Nurr1, also known as NR4A2), a dopaminergic neuron-associated transcription factor, to the TH promoter region. In this way, GM1 epigenetically regulates dopaminergic neuron specific gene expression. GM1 interacts with active chromatin via acetylated histones to recruit transcription factors at the nuclear periphery, resulting in changes in gene expression for neuronal differentiation. The significance is that multifunctional gangliosides modulate lipid microdomains to regulate functions of important molecules on multiple sites: the plasma membrane, mitochondrial membrane, and nuclear membrane. Versatile gangliosides could regulate functional neurons as well as sustain NSC functions via modulating protein and gene activities on ganglioside microdomains.

GALNT3 protects against phosphate-induced calcification in vascular smooth muscle cells by enhancing active FGF23 and inhibiting the wnt/β-catenin signaling pathway

Vascular calcification (VC) acts as a notable risk factor in the cardiovascular system. Disorder of phosphorus (Pi) metabolism promotes VC. Recent findings show that polypeptide N-acetylgalactosaminyltransferase 3(GALNT3) is Pi responsive and with potent effects on Pi homeostasis. However, whether GALNT3 is involved in high Pi-induced VC remains unclear. The present study investigated the potential role of GALNT3 as a novel regulator of VC. In vitro, human aortic smooth muscle cells (HASMCs) calcification was induced by inorganic Pi, while in vivo, C57BL/6 J mice were used to determine the effects of GALNT3 on Vitamin D3-induced medial arterial calcification. Alizarin red staining, Von Kossa staining, calcium and alkaline phosphatase (ALP) activity were performed to test VC. We showed that expression of GALNT3 was increased in the calcified HASMCs and aortas of the calcified mice.In vitro, overexpression of GALNT3 increased the levels of active full-length FGF23, accompanied by suppression of the osteoblast-related factors (Runx2 and BMP2), and further inhibited the formation of calcified nodules. Moreover, the protein levels of Wnt3a and active β-catenin were determined and it was found that GALNT3 significantly inhibited their expression. LiCl, a Wnt/β-catenin signaling activator, was observed to reverse the protective effect of GALNT3 overexpression. The opposite results were observed in the GALNT3 knockdown cells. In vivo, overexpression of GALNT3 by adeno-associated virus decreased the serum Pi and slowed the formation of aortic calcification in the calcified mice. In conclusion, our results indicate that GALNT3 counteracts high Pi-induced osteoblastic differentiation of VSMCs and protects against the initiation and progression of VC by inhibiting the Wnt/β-catenin signaling pathway.

Sensory Nerve Maintains Intervertebral Disc Extracellular Matrix Homeostasis Via CGRP/CHSY1 Axis

Sensory nerves are long being recognized as collecting units of various outer stimuli; recent advances indicate that the sensory nerve also plays pivotal roles in maintaining organ homeostasis. Here, this study shows that sensory nerve orchestrates intervertebral disc (IVD) homeostasis by regulating its extracellular matrix (ECM) metabolism. Specifically, genetical sensory denervation of IVD results in loss of IVD water preserve molecule chondroitin sulfate (CS), the reduction of CS bio-synthesis gene chondroitin sulfate synthase 1 (CHSY1) expression, and dysregulated ECM homeostasis of IVD. Particularly, knockdown of sensory neuros calcitonin gene-related peptide (CGRP) expression induces similar ECM metabolic disorder compared to sensory nerve denervation model, and this effect is abolished in CHSY1 knockout mice. Furthermore, in vitro evidence shows that CGRP regulates nucleus pulposus cell CHSY1 expression and CS synthesis via CGRP receptor component receptor activity-modifying protein 1 (RAMP1) and cyclic AMP response element-binding protein (CREB) signaling. Therapeutically, local injection of forskolin significantly attenuates IVD degeneration progression in mouse annulus fibrosus puncture model. Overall, these results indicate that sensory nerve maintains IVD ECM homeostasis via CGRP/CHSY1 axis and promotes IVD repair, and this expands the understanding concerning how IVD links to sensory nerve system, thus shedding light on future development of novel therapeutical strategy to IVD degeneration.

Galnt17 loss-of-function leads to developmental delay and abnormal coordination, activity, and social interactions with cerebellar vermis pathology

GALNT17 encodes a N-acetylgalactosaminyltransferase (GalNAc-T) protein specifically involved in mucin-type O-linked glycosylation of target proteins, a process important for cell adhesion, cell signaling, neurotransmitter activity, neurite outgrowth, and neurite sensing. GALNT17, also known as WBSCR17, is located at the edge of the Williams-Beuren Syndrome (WBS) critical region and adjacent to the AUTS2 locus, genomic regions associated with neurodevelopmental phenotypes that are thought to be co-regulated. Although previous data have implicated Galnt17 in neurodevelopment, the in vivo functions of this gene have not been investigated. In this study, we have analyzed behavioral, brain pathology, and molecular phenotypes exhibited by Galnt17 knockout (Galnt17-/-) mice. We show that Galnt17-/- mutants exhibit developmental neuropathology within the cerebellar vermis, along with abnormal activity, coordination, and social interaction deficits. Transcriptomic and protein analysis revealed reductions in both mucin type O-glycosylation and heparan sulfate synthesis in the developing mutant cerebellum along with disruption of pathways central to neuron differentiation, axon pathfinding, and synaptic signaling, consistent with the mutant neuropathology. These brain and behavioral phenotypes and molecular data confirm a specific role for Galnt17 in brain development and suggest new clues to factors that could contribute to phenotypes in certain WBS and AUTS2 syndrome patients.

Development of a GalNAc-Tyrosine-Specific Monoclonal Antibody and Detection of Tyrosine O-GalNAcylation in Numerous Human Tissues and Cell Lines

Glycosylation is a vital post-translational modification involved in a range of biological processes including protein folding, signaling, and cell-cell interactions. In 2011, a new type of O-linked glycosylation was discovered, wherein the side-chain oxygen of tyrosine is modified with a GalNAc residue (GalNAc-Tyr). At present, very little is known about GalNAc-Tyr prevalence, function, or biosynthesis. Herein, we describe the design and synthesis of a GalNAc-Tyr-derived hapten and its use in generating a GalNAc-Tyr selective monoclonal antibody. The antibody, G10C, has an unusually high affinity (app KD = 100 pM) and excellent selectivity for GalNAc-Tyr. We also obtained a crystal structure of the G10C Fab region in complex with 4-nitrophenyl-N-acetyl-α-d-galactosaminide (a small molecule mimic of GalNAc-Tyr) providing insights into the structural basis for high affinity and selectivity. Using this antibody, we discovered that GalNAc-Tyr is widely expressed in most human tissues, indicating that it is a ubiquitous and underappreciated post-translational modification. Localization to specific cell types and organ substructures within those tissues indicates that GalNAc-Tyr is likely regulated in a cell-specific manner. GalNAc-Tyr was also observed in a variety of cell lines and primary cells but was only present on the external cell surface in certain cancer cell lines, suggesting that GalNAc-Tyr localization may be altered in cancer cells. Collectively, the results shed new light on this under-studied form of glycosylation and provide access to new tools that will enable expanded biochemical and clinical investigations.

GALNT8 suppresses breast cancer cell metastasis potential by regulating EGFR O-GalNAcylation

Breast cancer represents the most lethal malignancy that threatens the health of females. Metastasis is the fatal hallmark of breast cancer, and current effective therapeutic targets of metastasis are still lacking. Aberrant O-GalNAcylation, which is attributed to alteration of polypeptide N-acetylgalactosaminyl transferases (GALNTs), has been implicated in cancer metastasis. However, GALNTs that drive metastasis in breast cancer and their underlying mechanisms are largely unclear. In the present study, a negative correlation between GALNT8 and the prognosis of breast cancer patients was observed in multiple groups of Gene Expression Omnibus (GEO) datasets. We then constructed a stable GALNT8 knockdown MCF7 cell line and performed transcriptome analysis using RNA sequencing, which revealed that the expression of multiple migration-related genes was changed. GALNT8 was identified as a regulator of epithelial-mesenchymal transition (EMT) markers, including E-cadherin, N-cadherin, ZO-1 and vimentin. Moreover, loss- and gain-of-function GALNT8 assays demonstrated that this glycosyltransferase inhibited the metastatic potential of breast cancer cells. Interestingly, the O-GalNAcylation of EGFR, which is the key factor related to the metastasis cascade, was impacted by GALNT8. Furthermore, our results suggested that the GALNT8-mediated O-GalNAcylation led to the suppression of the EGFR signaling pathway and metastatic potential in breast cancer cells. These results suggested that GALNT8 acts as a tumor suppressor, represses tumor metastasis and inhibits the EMT process through the EGFR signaling pathway. This finding may provide insight into the mechanism by which aberrant O-glycosylation modulates breast cancer metastasis.

Glycoproteomic and Phenotypic Elucidation of B4GALNT2 Expression Variants in the SID Histo-Blood Group System

The Sda histo-blood group antigen (GalNAcβ1-4(NeuAcα2-3)Galβ-R) is implicated in various infections and constitutes a potential biomarker for colon cancer. Sd(a−) individuals (2−4% of Europeans) may produce anti-Sda, which can lead to incompatible blood transfusions, especially if donors with the high-expressing Sd(a++)/Cad phenotype are involved. We previously reported the association of B4GALNT2 mutations with Sd(a−), which established the SID blood-group system. The present study provides causal proof underpinning this correlation. Sd(a−) HEK293 cells were transfected with different B4GALNT2 constructs and evaluated by immunostaining and glycoproteomics. The predominant SIDnull candidate allele with rs7224888:T>C (p.Cys406Arg) abolished Sda synthesis, while this antigen was detectable as N- or O-glycans on glycoproteins following transfection of wildtype B4GALNT2. Surprisingly, two rare missense variants, rs148441237:A>G and rs61743617:C>T, found in a Sd(a−) compound heterozygote, gave results similar to wildtype. To elucidate on whether Sd(a++)/Cad also depends on B4GALNT2 alterations, this gene was sequenced in five individuals. No Cad-specific changes were identified, but a detailed erythroid Cad glycoprotein profile was obtained, especially for glycophorin-A (GLPA) O-glycosylation, equilibrative nucleoside transporter 1 (S29A1) O-glycosylation, and band 3 anion transport protein (B3AT) N-glycosylation. In conclusion, the p.Cys406Arg β4GalNAc-T2 variant causes Sda-deficiency in humans, while the enigmatic Cad phenotype remains unresolved, albeit further characterized.

N-terminome analyses underscore the prevalence of SPPL3-mediated intramembrane proteolysis among Golgi-resident enzymes and its role in Golgi enzyme secretion

Golgi membrane proteins such as glycosyltransferases and other glycan-modifying enzymes are key to glycosylation of proteins and lipids. Secretion of soluble Golgi enzymes that are released from their membrane anchor by endoprotease activity is a wide-spread yet largely unexplored phenomenon. The intramembrane protease SPPL3 can specifically cleave select Golgi enzymes, enabling their secretion and concomitantly altering global cellular glycosylation, yet the entire range of Golgi enzymes cleaved by SPPL3 under physiological conditions remains to be defined. Here, we established isogenic SPPL3-deficient HEK293 and HeLa cell lines and applied N-terminomics to identify substrates cleaved by SPPL3 and released into cell culture supernatants. With high confidence, our study identifies more than 20 substrates of SPPL3, including entirely novel substrates. Notably, our N-terminome analyses provide a comprehensive list of SPPL3 cleavage sites demonstrating that SPPL3-mediated shedding of Golgi enzymes occurs through intramembrane proteolysis. Through the use of chimeric glycosyltransferase constructs we show that transmembrane domains can determine cleavage by SPPL3. Using our cleavage site data, we surveyed public proteome data and found that SPPL3 cleavage products are present in human blood. We also generated HEK293 knock-in cells expressing the active site mutant D271A from the endogenous SPPL3 locus. Immunoblot analyses revealed that secretion of select novel substrates such as the key mucin-type O-glycosylation enzyme GALNT2 is dependent on endogenous SPPL3 protease activity. In sum, our study expands the spectrum of known physiological substrates of SPPL3 corroborating its significant role in Golgi enzyme turnover and secretion as well as in the regulation of global glycosylation pathways.

Novel Quinic Acid Glycerates from Tussilago farfara Inhibit Polypeptide GalNAc-Transferase

The discovery of a bioactive inhibitor tool for human polypeptide N-acetylgalactosaminyl transferases (GalNAc-Ts), the initiating enzyme for mucin-type O-glycosylation, remains challenging. In the present study, we identified an array of quinic acid derivatives, including four new glycerates (1-4) from Tussilago farfara, a traditional Chinese medicinal plant, as active inhibitors of GalNAc-T2 using a combined screening approach with a cell-based T2-specific sensor and purified enzyme assay. These inhibitors dose-dependently inhibited human GalNAc-T2 but did not affect O-linked N-acetylglucosamine transferase (OGT), the other type of glycosyltransferase. Importantly, they are not cytotoxic and retain inhibitory activity in cells lacking elongated O-glycans, which are eliminated by the CRISPR/Cas9 gene editing tool. A structure-activity relationship study unveiled a novel quinic acid-caffeic acid conjugate pharmacophore that directs inhibition. Overall, these new natural product inhibitors could serve as a basis for developing an inhibitor tool for GalNAc-T2.

Biosynthesis and Biological Significances of LacdiNAc Group on N- and O-Glycans in Human Cancer Cells

An increasing number of studies have shown that the disaccharide GalNAcβ1→4GlcNAc (LacdiNAc) group bound to N- and O-glycans in glycoproteins is expressed in a variety of mammalian cells. Biosynthesis of the LacdiNAc group was well studied, and two β4-N-acetylgalactosaminyltransferases, β4GalNAcT3 and β4GalNAcT4, have been shown to transfer N-acetylgalactosamine (GalNAc) to N-acetylglucosamine (GlcNAc) of N- and O-glycans in a β-1,4-linkage. The LacdiNAc group is often sialylated, sulfated, and/or fucosylated, and the LacdiNAc group, with or without these modifications, is recognized by receptors and lectins and is thus involved in the regulation of several biological phenomena, such as cell differentiation. The occurrences of the LacdiNAc group and the β4GalNAcTs appear to be tissue specific and are closely associated with the tumor progression or regression, indicating that they will be potent diagnostic markers of particular cancers, such as prostate cancer. It has been demonstrated that the expression of the LacdiNAc group on N-glycans of cell surface glycoproteins including β1-integrin is involved in the modulation of their protein functions, thus affecting cellular invasion and other malignant properties of cancer cells. The biological roles of the LacdiNAc group in cancer cells have not been fully understood. However, the re-expression of the LacdiNAc group on N-glycans, which is lost in breast cancer cells by transfection of the β4GalNAcT4 gene, brings about the partial restoration of normal properties and subsequent suppression of malignant phenotypes of the cells. Therefore, elucidation of the biological roles of the LacdiNAc group in glycoproteins will lead to the suppression of breast cancers.

Role of GALNT2 on Insulin Sensitivity, Lipid Metabolism and Fat Homeostasis

O-linked glycosylation, the greatest form of post-translational modifications, plays a key role in regulating the majority of physiological processes. It is, therefore, not surprising that abnormal O-linked glycosylation has been related to several human diseases. Recently, GALNT2, which encodes the GalNAc-transferase 2 involved in the first step of O-linked glycosylation, has attracted great attention as a possible player in many highly prevalent human metabolic diseases, including atherogenic dyslipidemia, type 2 diabetes and obesity, all clustered on the common ground of insulin resistance. Data available both in human and animal models point to GALNT2 as a molecule that shapes the risk of the aforementioned abnormalities affecting diverse protein functions, which eventually cause clinically distinct phenotypes (a typical example of pleiotropism). Pathways linking GALNT2 to dyslipidemia and insulin resistance have been partly identified, while those for type 2 diabetes and obesity are yet to be understood. Here, we will provide a brief overview on the present knowledge on GALNT2 function and dysfunction and propose novel insights on the complex pathogenesis of the aforementioned metabolic diseases, which all impose a heavy burden for patients, their families and the entire society.

Expression of GALNT8 and O-glycosylation of BMP receptor 1A suppress breast cancer cell proliferation by upregulating ERα levels

BACKGROUND

Mucin-type O-glycosylation is one of the most abundant types of O-glycosylation and plays important roles in various human carcinomas, including breast cancer. A large family of polypeptide N-acetyl-α-galactosaminyltransferases (GALNTs) initiate and define sites of mucin-type O-glycosylation. However, the specific mechanisms underlying GALNT8 expression and its roles in tumorigenesis remain poorly characterized.

METHODS

GALNT8 expression was assessed in 140 breast cancer patients. Immunofluorescence, immunoprecipitation, lectin blot and quantitative real-time PCR were used to investigate the expression of GALNT8 and its role in regulating estrogen receptor α (ERα) via bone morphogenetic protein (BMP) signaling.

RESULTS

The expression of GALNT8 was associated with breast cancer patient survival. GALNT8 downregulation was associated with a reduction in ERα levels, while GALNT8 overexpression elevated the transcription and protein levels of ERα and suppressed colony formation, suggesting an important role of GALNT8 in cancer cell proliferation. Conversely, GALNT8 knockdown led to the inhibition of BMP/SMAD/RUNX2 axis, which decreased ERα transcription. Further analysis suggested that BMP receptor 1A (BMPR1A) was O-GalNAcylated. Sites mutation of BMPR1A indicated that Thr137 and Ser37/Ser39/Ser44/Thr49 of BMPR1A were the main O-glycosylation sites. Although we cannot exclude the indirect effect of GALNT8, our results demonstrated that the expression of GALNT8 and O-glycosylation of BMPR1A play key roles in regulating the activity of BMP/SMAD/RUNX2 signaling and ERα expression.

CONCLUSION

These findings suggest that GALNT8 expression and abnormal O-GalNAcylation of BMPR1A increase ERα expression and suppress breast cancer cell proliferation by modulating the BMP signaling pathway.

GENERAL SIGNIFICANCE

Our results identify the involvement of GALNT8 in regulating ERα expression.

LncRNA LINC01094 contributes to glioma progression by modulating miR-224-5p/CHSY1 axis

Glioma serves as the most common malignancy influencing modern people and is associated with severe morbidity and high mortality. Long non-coding RNAs (lncRNAs) as crucial regulators participate in multiple cancer progression. However, the role of lncRNA LINC01094 in the development of glioma remains unclear. Here, we aimed to explore the effect of lncRNA LINC01094 on the glioma progression and the underlying mechanism. Significantly, we revealed that the expression levels of LINC01094 were elevated in the glioma patient tissues compared to adjacent normal tissues. The LINC01094 expression was enhanced in the glioma cell lines. The depletion of LINC01094 inhibited cell viability and colony formation in the glioma cells. Meanwhile, the migration and invasion of glioma cells were impaired by the depletion of LINC01094. Mechanically, we identified that LINC01094 was able to sponge the miR-224-5p in the glioma cells and miR-224-5p inhibitor could reverse the effect of LINC01094 on glioma progression. In addition, miR-224-5p targeted CHSY1 and LINC01094 up-regulated CHSY1 by targeting miR-224-5p in the glioma cells. LINC01094 promoted glioma progression by the positive regulation of CHSY1. Moreover, tumorigenicity analysis showed that LINC01094 enhanced tumor growth of glioma in vivo. Thus, we conclude that lncRNA LINC01094 promotes glioma progression by modulating miR-224-5p/CHSY1 axis. Our finding provides new insights into the mechanism by which lncRNA LINC01094 contributes to the development of glioma, improving the understanding of lncRNA LINC01094 and glioma. LncRNA LINC01094, miR-224-5p, and CHSY1 may serve as potential targets for glioma.

Targeting Chondroitin Sulfate Reduces Invasiveness of Glioma Cells by Suppressing CD44 and Integrin β1 Expression

Chondroitin sulfate (CS) is a major component of the extracellular matrix found to be abnormally accumulated in several types of cancer tissues. Previous studies have indicated that CS synthases and modification enzymes are frequently elevated in human gliomas and are associated with poor prognosis. However, the underlying mechanisms of CS in cancer progression and approaches for interrupting its functions in cancer cells remain largely unexplored. Here, we have found that CS was significantly enriched surrounding the vasculature in a subset of glioma tissues, which was akin to the perivascular niche for cancer-initiating cells. Silencing or overexpression of the major CS synthase, chondroitin sulfate synthase 1 (CHSY1), significantly regulated the glioma cell invasive phenotypes and modulated integrin expression. Furthermore, we identified CD44 as a crucial chondroitin sulfate proteoglycan (CSPG) that was modified by CHSY1 on glioma cells, and the suppression of CS formation on CD44 by silencing the CHSY1-inhibited interaction between CD44 and integrin β1 on the adhesion complex. Moreover, we tested the CS-specific binding peptide, resulting in the suppression of glioma cell mobility in a fashion similar to that observed upon the silencing of CHSY1. In addition, the peptide demonstrated significant affinity to CD44, promoted CD44 degradation, and suppressed integrin β1 expression in glioma cells. Overall, this study proposes a potential regulatory loop between CS, CD44, and integrin β1 in glioma cells, and highlights the importance of CS in CD44 stability. Furthermore, the targeting of CS by specific binding peptides has potential as a novel therapeutic strategy for glioma.

Furin cleavage of the SARS-CoV-2 spike is modulated by O-glycosylation

The SARS-CoV-2 coronavirus responsible for the global pandemic contains a novel furin cleavage site in the spike protein (S) that increases viral infectivity and syncytia formation in cells. Here, we show that O-glycosylation near the furin cleavage site is mediated by members of the GALNT enzyme family, resulting in decreased furin cleavage and decreased syncytia formation. Moreover, we show that O-glycosylation is dependent on the novel proline at position 681 (P681). Mutations of P681 seen in the highly transmissible alpha and delta variants abrogate O-glycosylation, increase furin cleavage, and increase syncytia formation. Finally, we show that GALNT family members capable of glycosylating S are expressed in human respiratory cells that are targets for SARS-CoV-2 infection. Our results suggest that host O-glycosylation may influence viral infectivity/tropism by modulating furin cleavage of S and provide mechanistic insight into the role of the P681 mutations found in the highly transmissible alpha and delta variants.

Analysis of the proximal promoter of the human colon-specific B4GALNT2 (Sda synthase) gene: B4GALNT2 is transcriptionally regulated by ETS1

BACKGROUND

The Sda antigen and corresponding biosynthetic enzyme B4GALNT2 are primarily expressed in normal colonic mucosa and are down-regulated to a variable degree in colon cancer tissues. Although their expression profile is well studied, little is known about the underlying regulatory mechanisms.

METHODS

To clarify the molecular basis of Sda expression in the human gastrointestinal tract, we investigated the transcriptional regulation of the human B4GALNT2 gene. The proximal promoter region was delineated using luciferase assays and essential trans-acting factors were identified through transient overexpression and silencing of several transcription factors.

RESULTS

A short cis-regulatory region restricted to the -72 to +12 area upstream of the B4GALNT2 short-type transcript variant contained the essential promoter activity that drives the expression of the human B4GALNT2 regardless of the cell type. We further showed that B4GALNT2 transcriptional activation mostly requires ETS1 and to a lesser extent SP1.

CONCLUSIONS

Results presented herein are expected to provide clues to better understand B4GALNT2 regulatory mechanisms.

Role of GALNT4 in protecting against cardiac hypertrophy through ASK1 signaling pathway

Pathological myocardial hypertrophy is regulated by multiple pathways. However, its underlying pathogenesis has not been fully explored. The goal of this work was to elucidate the function of polypeptide N-acetylgalactosaminyltransferase 4 (GALNT4) in myocardial hypertrophy and its underlying mechanism of action. We illustrated that GALNT4 was upregulated in the models of hypertrophy. Two cardiac hypertrophy models were established through partial transection of the aorta in GALNT4-knockout (GALNT4-KO) mice and adeno-associated virus 9-GALNT4 (AAV9-GALNT4) mice. The GALNT4-KO mice demonstrated accelerated cardiac hypertrophy, dysfunction, and fibrosis, whereas the opposite phenotype was observed in AAV9-GALNT4 mice. Similarly, GALNT4 overexpression mitigated the degree of phenylephrine-induced cardiomyocyte hypertrophy in vitro whereas GALNT4 knockdown aggravated the hypertrophy. In terms of mechanism, GALNT4 deficiency increased the phosphorylation and activation of ASK1 and its downstream targets (JNK and p38), whereas GALNT4 overexpression inhibited activation of the ASK1 pathway. Furthermore, we demonstrated that GALNT4 can directly bind to ASK1 inhibiting its N-terminally mediated dimerization and the subsequent phosphorylation of ASK1. Finally, an ASK1 inhibitor (iASK1) was able to reverse the effects of GALNT4 in vitro. In summary, GALNT4 may serve as a new regulatory factor and therapeutic target by blocking the activation of the ASK1 signaling cascade.

Investigation of sequon engineering for improved O-glycosylation by the human polypeptide N-acetylgalactosaminyl transferase T2 isozyme and two orthologues

We have been developing bacterial expression systems for human mucin-type O-glycosylation on therapeutic proteins, which is initiated by the addition of α-linked GalNAc to serine or threonine residues by enzymes in the GT-27 family of glycosyltransferases. Substrate preference across different isoforms of this enzyme is influenced by isoform-specific amino acid sequences at the site of glycosylation, which we have exploited to engineer production of Core 1 glycan structures in bacteria on human therapeutic proteins. Using RP-HPLC with a novel phenyl bonded phase to resolve intact protein glycoforms, the effect of sequon mutation on O-glycosylation initiation was examined through in vitro modification of the naturally O-glycosylated human interferon α-2b, and a sequon engineered human growth hormone. As part of the development of our glycan engineering in the bacterial expression system we are surveying various orthologues of critical enzymes to ensure complete glycosylation. Here we present an in vitro enzyme kinetic profile of three related GT-27 orthologues on natural and engineered sequons in recombinant human interferon α2b and human growth hormone where we show a significant change in kinetic properties with the amino acid changes. It was found that optimizing the protein substrate amino acid sequence using Isoform Specific O-Glycosylation Prediction (ISOGlyP, http://isoglyp.utep.edu/index.php) resulted in a measurable increase in kcat/KM, thus improving glycosylation efficiency. We showed that the Drosophila orthologue showed superior activity with our human growth hormone designed sequons compared with the human enzyme.

CHPF promotes gastric cancer tumorigenesis through the activation of E2F1

Chondroitin polymerizing factor (CHPF) is an important glycosyltransferase involved in the biosynthesis of chondroitin sulfate. However, the relationship between CHPF and gastric cancer has not been fully investigated. CHPF expression in gastric cancer tissues was detected by immunohistochemistry and correlated with gastric cancer patient prognosis. Cultured gastric cancer cells and human gastric epithelial cell line GES1 were used to investigate the effects of shCHPF and shE2F1 on the development and progression of gastric cancer by MTT, western blotting, flow cytometry analysis of cell apoptosis, colony formation, transwell and gastric cancer xenograft mouse models, in vitro and in vivo. In gastric cancer tissues, CHPF was found to be significantly upregulated, and its expression correlated with tumor infiltration and advanced tumor stage and shorter patient survival in gastric cancer. CHPF may promote gastric cancer development by regulating cell proliferation, colony formation, cell apoptosis and cell migration, while knockdown induced the opposite effects. Moreover, the results from in vivo experiments demonstrated that tumor growth was suppressed by CHPF knockdown. Additionally, E2F1 was identified as a potential downstream target of CHPF in the regulation of gastric cancer, and its knockdown decreased the CHPF-induced promotion of gastric cancer. Mechanistic study revealed that CHPF may regulate E2F1 through affecting UBE2T-mediated E2F1 ubiquitination. This study showed, for the first time, that CHPF is a potential prognostic indicator and tumor promoter in gastric cancer whose function is likely carried out through the regulation of E2F1.

Polypeptide N-acetylgalactosaminyltransferase-Associated Phenotypes in Mammals

Mucin-type O-glycosylation involves the attachment of glycans to an initial O-linked N-acetylgalactosamine (GalNAc) on serine and threonine residues on proteins. This process in mammals is initiated and regulated by a large family of 20 UDP-GalNAc: polypeptide N-acetylgalactosaminyltransferases (GalNAc-Ts) (EC 2.4.1.41). The enzymes are encoded by a large gene family (GALNTs). Two of these genes, GALNT2 and GALNT3, are known as monogenic autosomal recessive inherited disease genes with well characterized phenotypes, whereas a broad spectrum of phenotypes is associated with the remaining 18 genes. Until recently, the overlapping functionality of the 20 members of the enzyme family has hindered characterizing the specific biological roles of individual enzymes. However, recent evidence suggests that these enzymes do not have full functional redundancy and may serve specific purposes that are found in the different phenotypes described. Here, we summarize the current knowledge of GALNT and associated phenotypes.

Endothelial ganglioside GM3 regulates angiogenesis in solid tumors

Cancer cells require oxygen and nutrients for growth, making angiogenesis one of the essential components of tumor growth. Gangliosides, constituting membrane lipid rafts, regulate intracellular signal transduction and are involved in the malignancy of cancer cells. While endothelial cells, as well as cancer cells, express vast amounts of gangliosides, the precise function of endothelial gangliosides in angiogenesis remains unclear. In this study, we focused on gangliosides of vascular endothelial cells and analyzed their functions on tumor angiogenesis. In human breast cancer, GM3 synthase was highly expressed in vascular endothelial cells as well as immune cells. Angiogenesis increased in GM3S-KO mice. In BAEC, RNA interference of GM3S showed increased cellular invasion and oxidative stress tolerance through activation of ERK. In the breast cancer model, GM3-KO mice showed an increase in tumor growth and angiogenesis. These results suggest that the endothelial ganglioside GM3 regulates tumor angiogenesis by suppressing cellular invasion and oxidative stress tolerance in endothelial cells.

Polypeptide N-acetylgalactosaminyltransferase 18 retains in endoplasmic reticulum depending on its luminal regions interacting with ER resident UGGT1, PLOD3 and LPCAT1

Mucin-type O-glycosylation is initiated by the polypeptide: N-acetylgalactosaminyltransferase (ppGalNAc-T) family of enzymes, which consists of 20 members in humans. Among them, unlike other ppGalNAc-Ts located in Golgi apparatus, ppGalNAc-T18 distributes primarily in the endoplasmic reticulum (ER) and non-catalytically regulates ER homeostasis and O-glycosylation. Here, we report the mechanism for ppGalNAc-T18 ER localization and the function of each structural domain of ppGalNAc-T18. By using ppGalNAc-T18 truncation mutants, we revealed that the luminal stem region and catalytic domain of ppGalNAc-T18 are essential for ER localization, whereas the lectin domain and N-glycosylation of ppGalNAc-T18 are not required. In the absence of the luminal region (i.e., stem region, catalytic and lectin domains), the conserved Golgi retention motif RKTK within the cytoplasmic tail combined with the transmembrane domain ensure ER export and Golgi retention, as observed for other Golgi resident ppGalNAc-Ts. Results from coimmunoprecipitation assays showed that the luminal region interacts with ER resident proteins UGGT1, PLOD3 and LPCAT1. Furthermore, flow cytometry analysis showed that the entire luminal region is required for the non-catalytic O-GalNAc glycosylation activity of ppGalNAc-T18. The findings reveal a novel subcellular localization mechanism of ppGalNAc-Ts and provide a foundation to further characterize the function of ppGalNAc-T18 in the ER.

BAG3 epigenetically regulates GALNT10 expression via WDR5 and facilitates the stem cell-like properties of platin-resistant ovarian cancer cells

Ovarian cancer is the most lethal gynecologic malignant cancer, frequently due to its late diagnosis and high recurrence. Cancer stem cells (CSCs) from different malignancies including ovarian cancer have been linked to chemotherapy resistance and poor prognosis. Therefore, identifying the molecular mechanisms mediating therapy resistance is urgent to finding novel targets for therapy-resistant tumors. Aberrant O-glycosylation ascribed to subtle alteration of GALNT family members during malignant transformation facilitate metastasis in various cancers. The current study demonstrated that BAG3 was upregulated in platin-resistant ovarian cancer tissues and cells, and high BAG3 predicted dismal disease-free survival of patients with ovarian cancer. In addition, the current study showed that BAG3 facilitated CSC-like properties of ovarian cancer cells via regulation of GALTN10. In a term of mechanism, BAG3 epigenetically regulated GALNT10 transactivation via histone H3 lysine 4 (H3K4) presenter WDR5. We demonstrated that WDR5 increased H3K4 trimethylation (H3K4me3) modification at the promoter regions of GALNT10, facilitating recruitment of transcription factor ZBTB2 to the GALNT10 promoter. Collectively, our study uncovers an epigenetic upregulation of GALNT10 by BAG3 via WDR5 to facilitate CSCs of platin-resistant ovarian cancers, providing additional information for further identification of attractive targets with therapeutic significance in platin-resistant ovarian cancer.

GALNT2 promotes cell proliferation, migration, and invasion by activating the Notch/Hes1-PTEN-PI3K/Akt signaling pathway in lung adenocarcinoma

AIMS

Our study aimed to investigate the function of GALNT2 in lung adenocarcinoma (LUAD).

MAIN METHODS

We used network tools and tissue microarray immunohistochemistry to measure the expression levels of GALNT2 in LUAD. Kaplan-Meier curves and Cox regression methods were used in survival analysis. We detected the role of GALNT2 in cell lines by Cell Counting Kit-8, colony formation, transwell, and wound healing assays. We performed Western blotting to evaluate downstream protein levels.

KEY FINDINGS

GALNT2 was highly expressed in LUAD samples and indicated a poor prognosis. Knockdown of GALNT2 suppressed cell line proliferation, migration, and invasion abilities, while overexpression of GALNT2 enhanced those phenotypes. Moreover, GALNT2 activated Notch/Hes1-PTEN-PI3K/Akt signaling axis.

SIGNIFICANCE

Our data confirmed the cancer-promoting effect of GALNT2, and might provide a new approach for LUAD therapy.

Morphological and molecular characterization of GALNT2-mediated adipogenesis

3T3L1 mouse pre-adipocytes develop into adipocytes differently in response to GALNT2 overexpression or to stimulation with rosiglitazone, a reference inducer of adipogenesis. To investigate the biology of alternative pathways of adipogenesis, we studied lipid droplets (LD) morphology, chromatin organization, and gene expression in GALNT2- versus rosiglitazone-induced 3T3L1 adipogenesis. 3T3L1 overexpressing either GALNT2 (GALNT2) or GFP and treated with rosiglitazone (GFPR) were differentiated into adipocytes. LD and nuclei were profiled measuring their morphological features. The expression of adipogenesis-related genes was measured by RT-PCR. As compared to GFPR, GALNT2 showed smaller and more clustered LD, more nuclei with condensed chromatin and several gene expression changes (P < 0.001 for all). As compared to those stimulated by rosiglitazone, GALNT2 overexpressing cells show differences in the most established readouts of adipogenesis. Characterizing alternative pathways of adipogenesis may help tackle those diseases which are secondary to increased dysfunctional mass of adipose tissue.

High Expression of N-Acetylgalactosaminyl-transferase 1 (GALNT1) Associated with Invasion, Metastasis, and Proliferation in Osteosarcoma

BACKGROUND Osteosarcoma (OS) is very common worldwide, and the mechanisms underlying its development remain unclear. This study aims to identify key genes promoting the reproduction, invasion, and transfer of osteosarcoma cells. MATERIAL AND METHODS Gene expression profile data (GSE42352 and GSE42572) were downloaded from the Gene Expression Omnibus database. Differentially expressed genes were calculated using R software. Gene ontology and enriched pathway analysis of mRNAs were analyzed by using FunRich. Verification of the genes was conducted by using quantitative real-time polymerase chain reaction and western blot analyses to measure gene expression. Transwell and wound-healing assays were performed on osteosarcoma cells after knockdown to detect whether the genes enhanced the aggressiveness of osteosarcoma. RESULTS In total, 34 genes were selected after filtering. Kyoto Encyclopedia of Genes and Genomes enrichment analysis demonstrated that the genes were enriched in multiple tumor pathways. N-acetylgalactosaminyltransferase 1 (GALNT1) was identified for further study, and its expression was higher in osteosarcoma cells than in human osteoblasts. The invasion ability of cells was significantly decreased after gene knockdown. CONCLUSIONS Through the use of microarray and bioinformatics analysis, differentially expressed genes were selected and a complete gene network was constructed. Our findings provide new biomarkers for the treatment and prognosis of osteosarcoma. These biomarkers may contribute to the discovery of new therapeutic targets for clinical application.

Selective pharmacological inhibition of the sodium-dependent phosphate cotransporter NPT2a promotes phosphate excretion

The sodium-phosphate cotransporter NPT2a plays a key role in the reabsorption of filtered phosphate in proximal renal tubules, thereby critically contributing to phosphate homeostasis. Inadequate urinary phosphate excretion can lead to severe hyperphosphatemia as in tumoral calcinosis and chronic kidney disease (CKD). Pharmacological inhibition of NPT2a may therefore represent an attractive approach for treating hyperphosphatemic conditions. The NPT2a-selective small-molecule inhibitor PF-06869206 was previously shown to reduce phosphate uptake in human proximal tubular cells in vitro. Here, we investigated the acute and chronic effects of the inhibitor in rodents and report that administration of PF-06869206 was well tolerated and elicited a dose-dependent increase in fractional phosphate excretion. This phosphaturic effect lowered plasma phosphate levels in WT mice and in rats with CKD due to subtotal nephrectomy. PF-06869206 had no effect on Npt2a-null mice, but promoted phosphate excretion and reduced phosphate levels in normophophatemic mice lacking Npt2c and in hyperphosphatemic mice lacking Fgf23 or Galnt3. In CKD rats, once-daily administration of PF-06869206 for 8 weeks induced an unabated acute phosphaturic and hypophosphatemic effect, but had no statistically significant effect on FGF23 or PTH levels. Selective pharmacological inhibition of NPT2a thus holds promise as a therapeutic option for genetic and acquired hyperphosphatemic disorders.

miR-885-5p inhibits proliferation and metastasis by targeting IGF2BP1 and GALNT3 in human intrahepatic cholangiocarcinoma

The incidence of intrahepatic cholangiocarcinoma (iCCA) continues to increase worldwide, however its molecular pathogenesis remains poorly understood. Recent studies have implicated microRNAs in iCCA progression. In this study, we demonstrated that miR-885-5p was significantly decreased in iCCA tissues. Downregulation of miR-885-5p was correlated with vascular invasion, lymph node metastasis, unfavorable overall survival, and shorter disease-free survival. Silencing or overexpressing miR-885-5p by lentiviral approaches significantly influenced iCCA cell proliferation and metastasis in vitro and in vivo. Mechanistically, overexpression of miR-885-5p inhibited iCCA metastasis and proliferation by directly inhibiting GALNT3 as well as by indirectly promoting the downregulation of insulin-like growth factor-2 mRNA-binding protein 1 (IGF2BP1). Furthermore, miR-885-5p inhibited iCCA metastasis by downregulating the PI3K/AKT/MMPs signaling pathway via targeting GALNT3. Collectively, we demonstrated that miR-885-5p was an important mediator of iCCA proliferation and metastasis by regulating GALNT3 and IGF2BP1, thus offering a potential target for iCCA treatment.

GALNT10 promotes the proliferation and metastatic ability of gastric cancer and reduces 5-fluorouracil sensitivity by activating HOXD13

OBJECTIVE

To investigate the expression and potential mechanism of GALNT10 in gastric cancer (GC).

PATIENTS AND METHODS

A total of 60 cases of GC tissues, as well as normal tissues were collected. The total RNA of GC specimens and cells were extracted by TRIzol method and the level of GALNT10 was examined by quantitative real-time polymerase chain reaction (qRT-PCR). In addition, the relationship between GALNT10 and clinical parameters and prognosis of GC patients was analyzed. Subsequently, Lentivirus was used to construct GALNT10 knockdown GC cell lines, and cell counting kit-8 (CCK-8) and transwell assays were applied to analyze the influence of GALNT10 on GC cell function. Bioinformatics and Luciferase assay was used to evaluate the relationship between GALNT10 and HOXD13. Furthermore, 5-fluorouracil (5-Fu)-resistant cells were used to detect the relationship between GALNT10 and 5-Fu sensitivity of GC cells.

RESULTS

qRT-PCR results revealed that GALNT10 level was markedly increased in tissues, as well as cell lines of GC. Statistical analysis suggested that GALNT10 expression was in close relation with the incidence of lymph node and distant metastasis along with poor prognosis in GC patients, but not with other indicators. CCK-8 and transwell migration experiment results indicated that GALNT10 silencing can inhibit the proliferative and migration ability of GC cells. Western blot results displayed that the HOXD13 level was remarkably decreased after GALNT10 knocking down. In addition, Luciferase gene assay indicated that GALNT10 could bind to HOXD13. Further rescue experiments showed that HOXD13overexpression can synergistically reverse the inhibitory effect of GALNT10 knockdown on GC cell proliferative and migration ability, which further demonstrated that GALNT10 could promote GC cell metastasis ability and reduce the sensitivity to 5-Fu by regulating HOXD13.

CONCLUSIONS

GALNT10 could regulate the proliferative and migration ability of GC cells and reduce the sensitivity to 5-Fu by enhancing the expression of HOXD13. Therefore, GALNT10 was expected to be a new therapeutic target for diagnosis of 5-fluorouracil resistance in GC.

Type 2 diabetes mellitus facilitates endometrial hyperplasia progression by activating the proliferative function of mucin O-glycosylating enzyme GALNT2

OBJECTIVE

Type 2 diabetes mellitus (T2DM) is thought to be a risk factor for endometrial hyperplasia, but potential links between the two diseases are unknown. This study aims to evaluate the role of T2DM in the progression of endometrial hyperplasia.

METHODS

Female Sprague-Dawley rats were randomly divided into normal (N) group, endometrial hyperplasia (NH) group, T2DM (T) group, and endometrial hyperplasia with T2DM (TH) group. Proteomics analysis was performed to determine the protein profile of endometrial tissues. Proliferation, migration, and invasion of cells with/without GLANT2-knockdown were assessed. Immunohistochemical staining and ELISA were used to examine the expression of GALNT2 in endometrial tissues and serum of clinical samples.

RESULTS

The highest uterus index and endometrial thickness were observed in TH group, with the expression of proliferation marker PCNA increased significantly, indicating that T2DM facilitates the progress of endometrial hyperplasia. Proteomics analysis showed that there were significant differences in protein profiles among groups and differential proteins were mainly enriched in metabolic pathways. Further verification by molecular biology analysis indicated that GALNT2 is the key target for T2DM facilitating endometrial hyperplasia. The expression of GALNT2 was significantly decreased in high glucose environment. T2DM could synergize the proliferative function of GALNT2 aberration by activating EGFR/AKT/ERK pathway. The decreased expressions of GALNT2 in clinical samples were associated with worse subtypes of endometrial hyperplasia.

CONCLUSION

T2DM promoted the progression of endometrial hyperplasia by regulating the GALNT2-mediated phosphorylation of EGFR and enhancing cell proliferation. GALNT2 has the potential to be a novel biomarker in the treatment of endometrial hyperplasia.

Ser and Thr acceptor preferences of the GalNAc-Ts vary among isoenzymes to modulate mucin-type O-glycosylation

A family of polypeptide GalNAc-transferases (GalNAc-Ts) initiates mucin-type O-glycosylation, transferring GalNAc onto hydroxyl groups of Ser and Thr residues of target substrates. The 20 GalNAc-T isoenzymes in humans are classified into nine subfamilies according to sequence similarity. GalNAc-Ts select their sites of glycosylation based on weak and overlapping peptide sequence motifs, as well prior substrate O-GalNAc glycosylation at sites both remote (long-range) and neighboring (short-range) the acceptor. Together, these preferences vary among GalNAc-Ts imparting each isoenzyme with its own unique specificity. Studies on the first identified GalNAc-Ts showed Thr acceptors were preferred over Ser acceptors; however studies comparing Thr vs. Ser glycosylation across the GalNAc-T family are lacking. Using a series of identical random peptide substrates, with single Thr or Ser acceptor sites, we determined the rate differences (Thr/Ser rate ratio) between Thr and Ser substrate glycosylation for 12 isoenzymes (representing 7 GalNAc-T subfamilies). These Thr/Ser rate ratios varied across subfamilies, ranging from ~2 to ~18 (for GalNAc-T4/GalNAc-T12 and GalNAc-T3/GalNAc-T6, respectively), while nearly identical Thr/Ser rate ratios were observed for isoenzymes within subfamilies. Furthermore, the Thr/Ser rate ratios did not appreciably vary over a series of fixed sequence substrates of different relative activities, suggesting the ratio is a constant for each isoenzyme against single acceptor substrates. Finally, based on GalNAc-T structures, the different Thr/Ser rate ratios likely reflect differences in the strengths of the Thr acceptor methyl group binding to the active site pocket. With this work, another activity that further differentiates substrate specificity among the GalNAc-Ts has been identified.

Circ_WBSCR17 aggravates inflammatory responses and fibrosis by targeting miR-185-5p/SOX6 regulatory axis in high glucose-induced human kidney tubular cells

BACKGROUND

Diabetic nephropathy (DN), a severe microvascular complication of diabetes, has complex pathogenesis. Circular RNAs (circRNAs) exert broad biological functions on human diseases. This study intended to explore the role and mechanism of circ_WBSCR17 in DN.

METHODS

DN mice models were constructed using streptozotocin injection, and DN cell models were assembled using high glucose (HG) treatment in human kidney 2 cells (HK-2). The expression of circ_WBSCR17, miR-185-5p and SRY-Box Transcription Factor 6 (SOX6) was detected by quantitative real-time polymerase chain reaction (qRT-PCR). The protein levels of SOX6 and fibrosis markers were examined by western blot. The release of inflammatory cytokines, cell proliferation and apoptosis, were assessed by enzyme-linked immunosorbent assay (ELISA), cell counting kit-8 (CCK-8) assay and flow cytometry assay, respectively. The predicted interaction between miR-185-5p and circ_WBSCR17 or SOX6 was verified by dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay.

RESULT

Circ_WBSCR17 was highly expressed in DN mice models and HG-induced HK-2 cells. Circ_WBSCR17 knockdown or SOX6 knockdown promoted cell proliferation and blocked cell apoptosis, inflammatory responses and fibrosis, while circ_WBSCR17 overexpression or SOX6 overexpression conveyed the opposite effects. MiR-185-5p was a target of circ_WBSCR17 and directly bound to SOX6. MiR-185-5p could reverse the role of circ_WBSCR17 or SOX6. Moreover, the expression of SOX6 was modulated by circ_WBSCR17 through intermediating miR-185-5p.

CONCLUSION

Circ_WBSCR17 triggered the dysfunction of HG-induced HK-2 cells, including inflammatory responses and fibrosis, which was accomplished via the miR-185-5p/SOX6 regulatory axis.

GALNT2 regulates ANGPTL3 cleavage in cells and in vivo of mice

Angiopoietin-like protein 3 (ANGPTL3) is an important inhibitor of lipoprotein lipase and endothelial lipase that plays critical roles in lipoprotein metabolism. It specifically expresses in the liver and undergoes proprotein convertase-mediated cleavage during secretion, which generates an N-terminal coiled-coil domain and C-terminal fibrinogen-like domain that has been considered as the activation step for its function. Previous studies have reported that the polypeptide GalNAc-transferase GALNT2 mediates the O-glycosylation of the ANGPTL3 near the cleavage site, which inhibits the proprotein convertase (PC)-mediated cleavage in vitro and in cultured cells. However, loss-of-function mutation for GALNT2 has no effect on ANGPTL3 cleavage in human. Thus whether GALNT2 regulates the cleavage of ANGPTL3 in vivo is unclear. In present study, we systematically characterized the cleavage of Angptl3 in cultured cells and in vivo of mice. We found that endogenous Angptl3 is cleaved in primary hepatocytes and in vivo of mice, and this cleavage can be blocked by Galnt2 overexpression or PC inhibition. Moreover, suppressing galnt2 expression increases the cleavage of Angptl3 in mice dramatically. Thus, our results support the conclusion that Galnt2 is a key endogenous regulator for Angptl3 cleavage both in vitro and in vivo.

The Sda Synthase B4GALNT2 Reduces Malignancy and Stemness in Colon Cancer Cell Lines Independently of Sialyl Lewis X Inhibition

Background: The Sd^a antigen and its biosynthetic enzyme B4GALNT2 are highly expressed in healthy colon but undergo a variable down-regulation in colon cancer. The biosynthesis of the malignancy-associated sialyl Lewis x (sLe^x) antigen in normal and cancerous colon is mediated by fucosyltransferase 6 (FUT6) and is mutually exclusive from that of Sd^a. It is thought that the reduced malignancy associated with high B4GALNT2 was due to sLe^x inhibition. Methods: We transfected the cell lines SW480 and SW620, derived respectively from a primary tumor and a metastasis of the same patient, with the cDNAs of FUT6 or B4GALNT2, generating cell variants expressing either the sLe^x or the Sd^a antigens. Transfectants were analyzed for growth in poor adherence, wound healing, stemness and gene expression profile. Results: B4GALNT2/Sd^a expression down-regulated all malignancy-associated phenotypes in SW620 but only those associated with stemness in SW480. FUT6/sLe^x enhanced some malignancy-associated phenotypes in SW620, but had little effect in SW480. The impact on the transcriptome was stronger for FUT6 than for B4GALNT2 and only partially overlapping between SW480 and SW620. Conclusions: B4GALNT2/Sd^a inhibits the stemness-associated malignant phenotype, independently of sLe^x inhibition. The impact of glycosyltransferases on the phenotype and the transcriptome is highly cell-line specific.

Ultrasensitive Detection of Enzymatic Activity Using Single Molecule Arrays

Enzyme assays are important for many applications including clinical diagnostics, functional proteomics, and drug discovery. Current methods for enzymatic activity measurement often suffer from low analytical sensitivity. We developed an ultrasensitive method for the detection of enzymatic activity using Single Molecule Arrays (eSimoa). The eSimoa assay is accomplished by conjugating substrates to paramagnetic beads and measuring the conversion of substrates to products using single molecule analysis. We demonstrated the eSimoa method for the detection of protein kinases, telomerase, histone H3 methyltransferase SET7/9, and polypeptide N-acetylgalactosaminyltransferase with unprecedented sensitivity. In addition, we tested enzyme inhibition and performed theoretical calculations for the binding of inhibitor to its target enzyme and show the need for an ultrasensitive enzymatic assay to evaluate the potency of tight binding inhibitors. The eSimoa assay was successfully used to determine inhibition constants of both bosutinib and dasatinib. Due to the ultrasensitivity of this method, we also were able to measure the kinase activities at the single cell level. We show that the eSimoa assay is a simple, fast, and highly sensitive approach, which can be easily extended to detect a variety of other enzymes, providing a promising platform for enzyme-related fundamental research and inhibitor screening.

Long non-coding RNA TP73-AS1 contributes to glioma tumorigenesis by sponging the miR-103a/GALNT7 pathway

Glioma is the most aggressive, commonly occurring brain tumor in adults. Long non-coding RNAs (lncRNAs) are among the gene expression regulators in cancer development. Previous research posited that the up-regulation of LncRNA TP73-AS1 (TP73-AS1) in glioma is linked to low survival rates. However, the precise LncRNA TP73-AS1 mechanism in glioma remains unknown. Herein, we found that TP73-AS1 was up-regulated in glioma and was associated with a dismal prognosis. The silencing of TP73-AS1 repressed the multiplication of glioma cells and caused cell death. Mechanistically, we identified that TP73-AS1 in glioma acts as a ceRNA by sequestering miR-103a from GALNT7. Further, the results of this study revealed a reciprocal expression between TP73-AS1 and miR-103a, and a positive regulation between TP73-AS1 and GALNT7, validating the identified mechanism. Besides, luciferase reporter assay identified miR-103a as the direct binding site of both TP73-AS1 and GALNT7. Moreover, the findings of CCK-8 and colony-formation assays indicated that exogenous expression of GALNT7 reversed TP73-AS1-induced division inhibition of glioma cells. Altogether, our results established that TP73-AS1 facilitates the progression of glioma through competing for endogenous RNA (ceRNA) in a TP73-AS1/miR-103a/GALNT7 loop.

A simple bacterial expression system for human ppGalNAc-T and used for the synthesis of O-GalNAc glycosylated interleukin 2

Mucin-type O-glycosylation (hereafter referred to as O-GalNAc glycosylation) is one of the most abundant glycosylation on proteins. It is initiated by the members of polypeptide N-acetyl-α-galactosaminyltransferases (ppGalNAc-Ts) family. The ppGalNAc-Ts could be used as tool enzymes to modify target proteins including therapeutic glycoprotein drugs with O-GalNAc glycosylation at specific glycosylated sites in vitro. Obtaining a large amount of ppGalNAc-T can greatly increase the yield of therapeutic O-glycoprotein and reduce the culture costs. In this study, we reported a simple Escherichia coli (E. coli) expression system capable of producing human ppGalNAc-Ts. By co-expressing human PDI, we could simply obtain active ppGalNAc-Ts with high efficiency. Using the E. coli expressed ppGalNAc-T2, we site-specifically synthesized O-glycosylated IL-2 at the native glycosylated site Thr23 residue. These results reveal the E. coli system we constructed is suitable to produce active ppGalNAc-Ts and thus has the potential value for basic research and production of therapeutic O-glycoproteins in vitro.

Phosphate-sensing and regulatory mechanism of FGF23 production

BACKGROUND

Inorganic phosphate (Pi) is an essential mineral for human. Hypophosphatemia and hyperphosphatemia cause rickets/osteomalacia and ectopic calcification, respectively, indicating that serum Pi level needs to be regulated. Fibroblast growth factor (FGF) 23 is a principal hormone to regulate serum Pi level. FGF23 is produced by the bone, especially by the osteoblasts and osteocytes, and works by binding to FGF receptor (FGFR) 1c and α-Klotho complex in the kidney. FGF23 reduces serum Pi level by inhibiting both renal phosphate reabsorption and intestinal phosphate absorption via reduction of serum 1,25-dihydroxyvitamin D level. It has been unclear how the bone senses changes of serum Pi level and how the bone regulates the production of FGF23.

RECENT FINDINGS

Our recent results indicate that the post-translational modification of FGF23 protein through a gene product of GALNT3 is the main regulatory mechanism of enhanced FGF23 production by high dietary Pi. Furthermore, high extracellular Pi directly activates FGFR1 and its downstream intracellular signaling pathway regulates the expression level of GALNT3.

CONCLUSIONS

We propose that FGFR1 works as a Pi-sensing receptor in the regulation of FGF23 production and serum Pi level. There is a negative feedback system, which is a basic mechanism of endocrine regulation, in the regulation of serum Pi involving FGFR1, and FGF23. These findings may lead to the development of new therapeutic methods to treat diseases caused by abnormal Pi level.

Fibroblast growth factor receptor as a potential candidate for phosphate sensing

PURPOSE OF REVIEW

Phosphate plays essential roles in many biological processes. Serum phosphate level needs to be regulated because hypophosphatemia and hyperphosphatemia cause rickets/osteomalacia and ectopic calcification, respectively. Fibroblast growth factor (FGF) 23 is the principal hormone to regulate serum phosphate level. FGF23 is produced by the bone and works to reduce serum phosphate level by binding to FGF receptor (FGFR) 1c and α-Klotho complex in the kidney. It has been unclear how the bone senses the changes of serum phosphate level and how the bone regulates the production of FGF23.

RECENT FINDINGS

Our recent results indicate that high extracellular phosphate activates FGFR1c. Its downstream intracellular signalling pathway regulates the expression of GALNT3 encoding a protein involved in the regulation of the posttranslational modification of FGF23 protein. This FGFR1c-GALNT3 axis is considered to be the main regulatory mechanism of enhanced FGF23 production in response to high phosphate.

SUMMARY

We propose that FGFR1c works as a phosphate-sensing molecule in the regulation of FGF23 production and serum phosphate level. Feedback system is present in the regulation of serum phosphate involving FGFR1c and FGF23. These findings uncover so far unrecognized function of FGFR and molecular basis of phosphate sensing.