Aberrant O-glycosylation inhibits stable expression of dysadherin, a carcinoma-associated antigen, and facilitates cell-cell adhesion

Glycan Metabolic Fluorine Labeling for In Vivo Visualization of Tumor Cells and In Situ Assessment of Glycosylation Variations

The abnormality in the glycosylation of surface proteins is critical for the growth and metastasis of tumors and their capacity for immunosuppression and drug resistance. This anomaly offers an entry point for real-time analysis on glycosylation fluctuations. In this study, we report a strategy, glycan metabolic fluorine labeling (MEFLA), for selectively tagging glycans of tumor cells. As a proof of concept, we synthesized two fluorinated unnatural monosaccharides with distinctive 19 F chemical shifts (Ac4 ManNTfe and Ac4 GalNTfa). These two probes could undergo selective uptake by tumor cells and subsequent incorporation into surface glycans. This approach enables efficient and specific 19 F labeling of tumor cells, which permits in vivo tracking of tumor cells and in situ assessment of glycosylation changes by 19 F MRI. The efficiency and specificity of our probes for labeling tumor cells were verified in vitro with A549 cells. The feasibility of our method was further validated with in vivo experiments on A549 tumor-bearing mice. Moreover, the capacity of our approach for assessing glycosylation changes of tumor cells was illustrated both in vitro and in vivo. Our studies provide a promising means for visualizing tumor cells in vivo and assessing their glycosylation variations in situ through targeted multiplexed 19 F MRI.

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.

High-Intensity Training Represses FXYD5 and Glycosylates Na,K-ATPase in Type II Muscle Fibres, Which Are Linked with Improved Muscle K+ Handling and Performance

Na+/K+ ATPase (NKA) comprises several subunits to provide isozyme heterogeneity in a tissue-specific manner. An abundance of NKA α, β, and FXYD1 subunits is well-described in human skeletal muscle, but not much is known about FXYD5 (dysadherin), a regulator of NKA and β1 subunit glycosylation, especially with regard to fibre-type specificity and influence of sex and exercise training. Here, we investigated muscle fibre-type specific adaptations in FXYD5 and glycosylated NKAβ1 to high-intensity interval training (HIIT), as well as sex differences in FXYD5 abundance. In nine young males (23.8 ± 2.5 years of age) (mean ± SD), 3 weekly sessions of HIIT for 6 weeks enhanced muscle endurance (220 ± 102 vs. 119 ± 99 s, p < 0.01) and lowered leg K+ release during intense knee-extensor exercise (0.5 ± 0.8 vs. 1.0 ± 0.8 mmol·min–1, p < 0.01) while also increasing cumulated leg K+ reuptake 0–3 min into recovery (2.1 ± 1.5 vs. 0.3 ± 0.9 mmol, p < 0.01). In type IIa muscle fibres, HIIT lowered FXYD5 abundance (p < 0.01) and increased the relative distribution of glycosylated NKAβ1 (p < 0.05). FXYD5 abundance in type IIa muscle fibres correlated inversely with the maximal oxygen consumption (r = –0.53, p < 0.05). NKAα2 and β1 subunit abundances did not change with HIIT. In muscle fibres from 30 trained males and females, we observed no sex (p = 0.87) or fibre type differences (p = 0.44) in FXYD5 abundance. Thus, HIIT downregulates FXYD5 and increases the distribution of glycosylated NKAβ1 in type IIa muscle fibres, which is likely independent of a change in the number of NKA complexes. These adaptations may contribute to counter exercise-related K+ shifts and enhance muscle performance during intense exercise.

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.

Efficient inhibition of O-glycan biosynthesis using the hexosamine analog Ac5GalNTGc

There is a critical need to develop small-molecule inhibitors of mucin-type O-linked glycosylation. The best-known reagent currently is benzyl-GalNAc, but it is effective only at millimolar concentrations. This article demonstrates that Ac₅GalNTGc, a peracetylated C-2 sulfhydryl-substituted GalNAc, fulfills this unmet need. When added to cultured leukocytes, breast cells, and prostate cells, Ac₅GalNTGc increased cell-surface VVA binding by ∼10-fold, indicating truncation of O-glycan biosynthesis. Cytometry, mass spectrometry, and western blot analysis of HL-60 promyelocytes demonstrated that 50-80 μM Ac₅GalNTGc prevented elaboration of 30%-60% of the O-glycans beyond the Tn-antigen (GalNAcα1-Ser/Thr) stage. The effect of the compound on N-glycans and glycosphingolipids was small. Glycan inhibition induced by Ac₅GalNTGc resulted in 50%-80% reduction in leukocyte sialyl-Lewis X expression and L-/P-selectin-mediated rolling under flow conditions. Ac₅GalNTGc was pharmacologically active in mouse. It reduced neutrophil infiltration to sites of inflammation by ∼60%. Overall, Ac₅GalNTGc may find diverse applications as a potent inhibitor of O-glycosylation.

Low expression of FXYD5 reverses the cisplatin resistance of epithelial ovarian cancer cells

OBJECTIVE

To investigate the effect of the downregulation of FXYD domain-containing ion transport regulator 5 (FXYD5) on the cisplatin resistance (CisR) of epithelial ovarian cancer (EOC) cells.

METHODS

A2780-CisR and SKOV3-CisR cells were obtained through repeated administrations of different cisplatin concentrations, and the half-maximal inhibition concentration (IC50) was calculated by MTT assays. After transfection with FXYD5 siRNA-1 and FXYD5 siRNA-2, the IC50 values of the A2780-CisR and SKOV3-CisR cells were also detected by the MTT method. Cell proliferation, migration, invasion and apoptosis were evaluated through 5-ethynyl-2'-deoxyuridine (EdU) DNA synthesis, wound healing, Transwell invasion and Annexin-V-FITC/PI dual-staining assays, respectively. qRT-PCR and Western blotting were conducted to detect mRNA and protein expression.

RESULTS

Compared with the sensitive parental cells, the A2780-CisR and SKOV3-CisR cells had increased IC50 and FXYD5 expression. FXYD5 siRNA reduced the IC50 value of cisplatin in the A2780-CisR and SKOV3-CisR cells and decreased the expression of ABCG2 (BCRP) and ABCB1 (MDR1). In addition, FXYD5 inhibition reduced the invasion and migration of the A2780-CisR and SKOV3-CisR cells, with upregulation of E-cadherin and downregulation of Snail and Vimentin. Both FXYD5 siRNA-1 and FXYD5 siRNA-2 inhibited the proliferation and promoted the apoptosis of the A2780-CisR and SKOV3-CisR cells with reduced Ki-67 and increased caspase-3.

CONCLUSION

FXYD5 downregulation may reduce the invasion, migration and EMT formation of EOC cells to increase their sensitivity to cisplatin chemotherapy by inhibiting cell proliferation and promoting cell apoptosis.

Advances in molecular mechanisms of drugs affecting abnormal glycosylation and metastasis of breast cancer

Breast cancer remains the leading cause of cancer-related death among women worldwide, and its incidence is also increasing. High recurrence rate and metastasis rate are the key causes of poor prognosis and death. It is suggested that abnormal glycosylation plays an important role in the growth, invasion, metastasis and resistance to therapy of breast cancer cells. Meanwhile, it can be used as the biomarkers for the early detection and prognosis of breast cancer and the potential attractive targets for drug treatment. However, only a few attentions have been paid to the molecular mechanism of abnormal glycosylation in the epithelial-mesenchymal transition (EMT) of breast cancer cells and the related intervention of drugs. This manuscript thus investigated the relationship between abnormal glycosylation, the EMT, and breast cancer metastasis. Then, the process of abnormal glycosylation, the classification and their molecular regulatory mechanisms of breast cancer were analyzed in detail. Last, potential drugs are introduced in different categories, which are expected to reverse or intervene the abnormal glycosylation of breast cancer. This review is conducive to an in-depth understanding of the metastasis and drug resistance of breast cancer cells, which will provide new ideas for the clinical regulation of glycosylation and related drug treatments in breast cancer.

Deep Structural Analysis and Quantitation of O-Linked Glycans on Cell Membrane Reveal High Abundances and Distinct Glycomic Profiles Associated with Cell Type and Stages of Differentiation

Proteins on cell membrane are modified by N- and O-glycans. N-Glycans have been extensively characterized using advanced separation and mass spectrometry techniques. However, O-glycans remain a challenge, because of the lack of universal enzymes to release them and the large background abundances of N-glycans. Here, we report a method for in-depth structural analysis and quantitation of O-glycans derived from human cell membrane. O-Glycans were chemically released from isolated cell membrane glycoproteins following N-glycan and lipid/glycolipid removal by PNGase F digestion and Folch extraction, respectively. Released O-glycans were purified by an optimized protocol to eliminate interference from small molecules and degraded proteins. Cell surface O-glycans were then analyzed using a nanoLC-chip-QTOF mass spectrometer with a porous graphitized carbon (PGC) column, while the N-glycans and glycolipids isolated from the same cell membrane fractions were analyzed in parallel using previously reported methods. The monosaccharide compositions and linkages of the detected O-glycans were identified by exoglycosidase digestion facilitated with tandem mass spectrometry (MS/MS). Using this method, we identified 44 cell membrane O-glycan isomers with MS/MS, and, among them, we unambiguously characterized 25 O-glycan structures with exoglycosidase digestion to create a library with their complete structures, accurate masses, and retention times. In this process, we identified and characterized unexpected mannose oligomers that are α(1-2/3) linked. This library enabled the identification and quantification of unique cell surface O-glycans from different cell lines and the study of specific O-glycan changes during cell differentiation.

A strategy for generating cancer-specific monoclonal antibodies to aberrant O-glycoproteins: identification of a novel dysadherin-Tn antibody

Successful application of potent antibody-based T-cell engaging immunotherapeutic strategies is currently limited mainly to hematological cancers. One major reason is the lack of well-characterized antigens on solid tumors with sufficient cancer specific expression. Aberrantly O-glycosylated proteins contain promising cancer-specific O-glycopeptide epitopes suitable for immunotherapeutic applications, but currently only few examples of such antibody epitopes have been identified. We previously showed that chimeric antigen receptor T-cells directed towards aberrantly O-glycosylated MUC1 can control malignant growth in a mouse model. Here, we present a discovery platform for the generation of cancer-specific monoclonal antibodies targeting aberrant O-glycoproteins. The strategy is based on cancer cell lines engineered to homogeneously express the truncated Tn O-glycoform, the so-called SimpleCells. We used SimpleCells of different cancer origin to elicit monoclonal antibodies with selectivity for aberrant O-glycoproteins. For validation we selected and characterized one monoclonal antibody (6C5) directed to a Tn-glycopeptide in dysadherin (FXYD5), known to be upregulated in cancer and promote metastasis. While dysadherin is widely expressed also in normal cells, we demonstrated that the 6C5 epitope is specifically expressed in cancer.

Thioglycosides Are Efficient Metabolic Decoys of Glycosylation that Reduce Selectin Dependent Leukocyte Adhesion

Metabolic decoys are synthetic analogs of naturally occurring biosynthetic acceptors. These compounds divert cellular biosynthetic pathways by acting as artificial substrates that usurp the activity of natural enzymes. While O-linked glycosides are common, they are only partially effective even at millimolar concentrations. In contrast, we report that N-acetylglucosamine (GlcNAc) incorporated into various thioglycosides robustly truncate cell surface N- and O-linked glycan biosynthesis at 10-100 μM concentrations. The >10-fold greater inhibition is in part due to the resistance of thioglycosides to hydrolysis by intracellular hexosaminidases. The thioglycosides reduce β-galactose incorporation into lactosamine chains, cell surface sialyl Lewis-X expression, and leukocyte rolling on selectin substrates including inflamed endothelial cells under fluid shear. Treatment of granulocytes with thioglycosides prior to infusion into mouse inhibited neutrophil homing to sites of acute inflammation and bone marrow by ∼80%-90%. Overall, thioglycosides represent an easy to synthesize class of efficient metabolic inhibitors or decoys. They reduce N-/O-linked glycan biosynthesis and inflammatory leukocyte accumulation.

Effect of rosuvastatin on the expression of candidate gene GALNT3 in atherosclerosis

The effect of rosuvastatin on the expression of candidate gene polypeptide N-acetylgalactosaminyltrans ferase 3 (GALNT3) in atherosclerosis was studied. Sixty Wistar rats were randomly divided into the control (n=20), model (atherosclerosis group, n=20) and administration (rosuvastatin group, n=20) groups. The atherosclerosis model was established via injecting D3.6 million units of vitamin per kilogram of body weight and then the rats were fed with high-fat diet for 6 weeks. The total cholesterol, serum triglyceride and nitric oxide contents were detected using the kits, the morphological changes in thoracic aorta were observed via hematoxylin and eosin (H&E) staining, the mRNA expression of candidate gene GALNT3 was detected via reverse transcription-polymerase chain reaction (RT-PCR), and the protein expression of candidate gene GALNT3 was detected via western blot analysis. Compared with those in the control group, the contents of serum triglyceride and total cholesterol in the model group were significantly increased, and then significantly decreased after drug administration. Morphological observation showed that the surface of thoracic aorta was not smooth with endothelial shedding, and the smooth muscle cells were arranged irregularly and their number was obviously increased. Moreover, RT-PCR and western blot analysis revealed that the mRNA and protein expressions of GALNT3 were significantly increased in the administration group. Rosuvastatin can therefore significantly upregulate the expression of candidate gene GALNT3 in atherosclerosis, thereby reducing the incidence of atherosclerosis.

Simultaneous analyses of N-linked and O-linked glycans of ovarian cancer cells using solid-phase chemoenzymatic method

BACKGROUND

Glycans play critical roles in a number of biological activities. Two common types of glycans, N-linked and O-linked, have been extensively analyzed in the last decades. N-glycans are typically released from glycoproteins by enzymes, while O-glycans are released from glycoproteins by chemical methods. It is important to identify and quantify both N- and O-linked glycans of glycoproteins to determine the changes of glycans.

METHODS

The effort has been dedicated to study glycans from ovarian cancer cells treated with O-linked glycosylation inhibitor qualitatively and quantitatively. We used a solid-phase chemoenzymatic approach to systematically identify and quantify N-glycans and O-glycans in the ovarian cancer cells. It consists of three steps: (1) immobilization of proteins from cells and derivatization of glycans to protect sialic acids; (2) release of N-glycans by PNGase F and quantification of N-glycans by isobaric tags; (3) release and quantification of O-glycans by β-elimination in the presence of 1-phenyl-3-methyl-5-pyrazolone (PMP).

RESULTS

We used ovarian cancer cell lines to study effect of O-linked glycosylation inhibitor on protein glycosylation. Results suggested that the inhibition of O-linked glycosylation reduced the levels of O-glycans. Interestingly, it appeared to increase N-glycan level in a lower dose of the O-linked glycosylation inhibitor. The sequential release and analyses of N-linked and O-linked glycans using chemoenzymatic approach are a platform for studying N-glycans and O-glycans in complex biological samples.

CONCLUSION

The solid-phase chemoenzymatic method was used to analyze both N-linked and O-linked glycans sequentially released from the ovarian cancer cells. The biological studies on O-linked glycosylation inhibition indicate the effects of O-glycosylation inhibition to glycan changes in both O-linked and N-linked glycan expression.

The O-glycosylated ectodomain of FXYD5 impairs adhesion by disrupting cell-cell trans-dimerization of Na,K-ATPase β1 subunits

FXYD5 (also known as dysadherin), a regulatory subunit of the Na,K-ATPase, impairs intercellular adhesion by a poorly understood mechanism. Here, we determined whether FXYD5 disrupts the trans-dimerization of Na,K-ATPase molecules located in neighboring cells. Mutagenesis of the Na,K-ATPase β1 subunit identified four conserved residues, including Y199, that are crucial for the intercellular Na,K-ATPase trans-dimerization and adhesion. Modulation of expression of FXYD5 or of the β1 subunit with intact or mutated β1-β1 binding sites demonstrated that the anti-adhesive effect of FXYD5 depends on the presence of Y199 in the β1 subunit. Immunodetection of the plasma membrane FXYD5 was prevented by the presence of O-glycans. Partial FXYD5 deglycosylation enabled antibody binding and showed that the protein level and the degree of O-glycosylation were greater in cancer than in normal cells. FXYD5-induced impairment of adhesion was abolished by both genetic and pharmacological inhibition of FXYD5 O-glycosylation. Therefore, the extracellular O-glycosylated domain of FXYD5 impairs adhesion by interfering with intercellular β1-β1 interactions, suggesting that the ratio between FXYD5 and α1-β1 heterodimer determines whether the Na,K-ATPase acts as a positive or negative regulator of intercellular adhesion.

FXYD5: Na(+)/K(+)-ATPase Regulator in Health and Disease

FXYD5 (Dysadherin, RIC) is a single span type I membrane protein that plays multiple roles in regulation of cellular functions. It is expressed in a variety of epithelial tissues and acts as an auxiliary subunit of the Na⁺/K⁺-ATPase. During the past decade, a correlation between enhanced expression of FXYD5 and tumor progression has been established for various tumor types. In this review, current knowledge on FXYD5 is discussed, including experimental data on the functional effects of FXYD5 on the Na⁺/K⁺-ATPase. FXYD5 modulates cellular junctions, influences chemokine production, and affects cell adhesion. The accumulated data may provide a basis for understanding the molecular mechanisms underlying FXYD5 mediated phenotypes.

FXYD5 Protein Has a Pro-inflammatory Role in Epithelial Cells

The FXYD proteins are a family of small membrane proteins that share an invariant four amino acid signature motif F-X-Y-D and act as tissue-specific regulatory subunits of the Na,K-ATPase. FXYD5 (also termed dysadherin or RIC) is a structurally and functionally unique member of the FXYD family. As other FXYD proteins, FXYD5 specifically interacts with the Na,K-ATPase and alters its kinetics by increasing Vmax However, unlike other family members FXYD5 appears to have additional functions, which cannot be readily explained by modulation of transport kinetics. Knockdown of FXYD5 in MDA-MB-231 breast cancer cells largely decreases expression and secretion of the chemokine CCL2 (MCP-1). A related effect has also been observed in renal cell carcinoma cells. The current study aims to further characterize the relationship between the expression of FXYD5 and CCL2 secretion. We demonstrate that transfection of M1 epithelial cell line with FXYD5 largely increases lipopolysaccharide (LPS) stimulated CCL2 mRNA and secretion of the translated protein. We have completed a detailed analysis of the molecular events leading to the above response. Our key findings indicate that FXYD5 generates a late response by increasing the surface expression of the TNFα receptor, without affecting its total protein level, or mRNA transcription. LPS administration to mice demonstrates induced secretion of CCL2 and TNFα in FXYD5-expressing lung peripheral tissue, which suggests a possible role for FXYD5 in normal epithelia during inflammation.

Short O-GalNAc glycans: regulation and role in tumor development and clinical perspectives

BACKGROUND

While the underlying causes of cancer are genetic modifications, changes in cellular states mediate cancer development. Tumor cells display markedly changed glycosylation states, of which the O-GalNAc glycans called the Tn and TF antigens are particularly common. How these antigens get over-expressed is not clear. The expression levels of glycosylation enzymes fail to explain it.

SCOPE OF REVIEW

We describe the regulation of O-GalNAc glycosylation initiation and extension with emphasis on the initiating enzymes ppGalNAcTs (GALNTs), and introduce the GALA pathway--a change in GALNTs compartmentation within the secretory pathway that regulates Tn levels. We discuss the roles of O-GalNAc glycans and GALNTs in tumorigenic processes and finally consider diagnostic and therapeutic perspectives.

MAJOR CONCLUSIONS

Contrary to a common hypothesis, short O-glycans in tumors are not the result of an incomplete glycosylation process but rather reveal the activation of regulatory pathways. Surprisingly, high Tn levels reveal a major shift in the O-glycoproteome rather than a shortening of O-glycans. These changes are driven by membrane trafficking events.

GENERAL SIGNIFICANCE

Many attempts to use O-glycans for biomarker, antibody and therapeutic vaccine development have been made, but suffer limitations including poor sensitivity and/or specificity that may in part derive from lack of a mechanistic understanding. Deciphering how short O-GalNAc glycans are regulated would open new perspectives to exploit this biology for therapeutic usage. This article is part of a Special Issue entitled "Glycans in personalised medicine" Guest Editor: Professor Gordan Lauc.

Beneficial Renal and Pancreatic Phenotypes in a Mouse Deficient in FXYD2 Regulatory Subunit of Na,K-ATPase

The fundamental role of Na,K-ATPase in eukaryotic cells calls for complex and efficient regulation of its activity. Besides alterations in gene expression and trafficking, kinetic properties of the pump are modulated by reversible association with single span membrane proteins, the FXYDs. Seven members of the family are expressed in a tissue-specific manner, affecting pump kinetics in all possible permutations. This mini-review focuses on functional properties of FXYD2 studied in transfected cells, and on noteworthy and unexpected phenotypes discovered in a Fxyd2^−∕− mouse. FXYD2, the gamma subunit, reduces activity of Na,K-ATPase either by decreasing affinity for Na⁺, or reducing V_max. FXYD2 mRNA splicing and editing provide another layer for regulation of Na,K-ATPase. In kidney of knockouts, there was elevated activity for Na,K-ATPase and for NCC and NKCC2 apical sodium transporters. That should lead to sodium retention and hypertension, however, the mice were in sodium balance and normotensive. Adult Fxyd2^−∕− mice also exhibited a mild pancreatic phenotype with enhanced glucose tolerance, elevation of circulating insulin, but no insulin resistance. There was an increase in beta cell proliferation and beta cell mass that correlated with activation of the PI3K-Akt pathway. The Fxyd2^−∕− mice are thus in a highly desirable state: the animals are resistant to Na⁺ retention, and showed improved glucose control, i.e., they display favorable metabolic adaptations to protect against development of salt-sensitive hypertension and diabetes. Investigation of the mechanisms of these adaptations in the mouse has the potential to unveil a novel therapeutic FXYD2-dependent strategy.

Modulation of cell polarization by the Na+-K+-ATPase-associated protein FXYD5 (dysadherin)

FXYD5 (dysadherin or also called a related to ion channel, RIC) is a transmembrane auxiliary subunit of the Na(+)-K(+)-ATPase shown to increase its maximal velocity (Vmax). FXYD5 has also been identified as a cancer-associated protein whose expression in tumor-derived cell lines impairs cytoskeletal organization and increases cell motility. Previously, we have demonstrated that the expression of FXYD5 in M1 cells derived from mouse kidney collecting duct impairs the formation of tight and adherence junctions. The current study aimed to further explore effects of FXYD5 at a single cell level. It was found that in M1, as well as three other cell lines, FXYD5 inhibits transformation of adhered single cells from the initial radial shape to a flattened, elongated shape in the first stage of monolayer formation. This is also correlated to less ordered actin cables and fewer focal points. Structure-function analysis has demonstrated that the transmembrane domain of FXYD5, and not its unique extracellular segment, mediates the inhibition of change in cell shape. This domain has been shown before to be involved in the association of FXYD5 with the Na(+)-K(+)-ATPase, which leads to the increase in Vmax. Furthermore, specific transmembrane point mutations in FXYD5 that either increase or decrease its effect on cell elongation had a corresponding effect on the coimmunoprecipitation of FXYD5 with α Na(+)-K(+)-ATPase. These findings lend support to the possibility that FXYD5 affects cell polarization through its transmembrane domain interaction with the Na(+)-K(+)-ATPase. Yet interaction of FXYD5 with other proteins cannot be excluded.

Dysadherin expression promotes the motility and survival of human breast cancer cells by AKT activation

High dysadherin expression has been recognized as a biological predictor of metastasis and poor prognosis for many different cancer types; however, the molecular mechanisms of how dysadherin affects cancer progression are still poorly understood. In this study, we examined whether AKT signaling could link dysadherin expression with downstream events that promote the metastatic potential of human breast cancer cells. Immunohistochemical analysis of breast cancer tissues showed that dysadherin expression was highly associated with elevated expression of phospho-AKT. The introduction of dysadherin cDNA into BT-474, MCF-7 and T-47D breast cancer cell lines enhanced their levels of AKT phosphorylation, while knockdown of dysadherin in MDA-MB-231 and Hs578T breast cancer cell lines suppressed AKT phosphorylation. Treatment with the AKT inhibitor triciribine suppressed dysadherin-mediated pro-metastatic effects, including epithelial-mesenchymal transition, cell motility and drug resistance. These findings suggest that dysadherin might contribute to breast cancer progression through AKT activation.

p120RasGAP-mediated activation of c-Src is critical for oncogenic Ras to induce tumor invasion

Ras genes are the most common targets for somatic gain-of-function mutations in human cancers. In this study, we found a high incidence of correlation between Ras oncogenic mutations and c-Src activation in human cancer cells. We showed that oncogenic Ras induces c-Src activation mainly on the Golgi complex and endoplasmic reticulum. Moreover, we identified p120RasGAP as an effector for oncogenic Ras to activate c-Src. The recruitment of p120RasGAP to the Golgi complex by oncogenic Ras facilitated its interaction with c-Src, thereby leading to c-Src activation, and this p120RasGAP-mediated activation of c-Src was important for tumor invasion induced by oncogenic Ras. Collectively, our findings unveil a relationship between oncogenic Ras, p120RasGAP, and c-Src, suggesting a critical role for c-Src in cancers evoked by oncogenic mutations in Ras genes.

Role of the recently identified dysadherin in E-cadherin adhesion molecule downregulation in head and neck cancer

Dysadherin is a cancer-related cell membrane glycoprotein, recently identified, playing an important role in tumor progression and metastasis. In the present minireview article, we are focusing on the role of dysadherin in E-cadherin downregulation, the various expression patterns of the molecule in head and neck cancer as well as its potential role as a molecular target for future applications in diagnosis, clinical routine and prognosis of the disease.

FXYD5 (dysadherin) regulates the paracellular permeability in cultured kidney collecting duct cells

FXYD5 (dysadherin or RIC) is a member of the FXYD family of single-span transmembrane proteins associated with the Na(+)-K(+)-ATPase. Several studies have demonstrated enhanced expression of FXYD5 during metastasis and effects on cell adhesion and motility. The current study examines effects of FXYD5 on the paracellular permeability in the mouse kidney collecting duct cell line M1. Expressing FXYD5 in these cells leads to a large decrease in amiloride-insensitive transepithelial electrical resistance as well as increased permeability to 4-kDa dextran. Impairment of cell-cell contact was also demonstrated by staining cells for the tight and adherence junction markers zonula occludens-1 and β-catenin, respectively. This is further supported by large expansions of the interstitial spaces, visualized in electron microscope images. Expressing FXYD5 in M1 cells resulted in a decrease in N-glycosylation of β1 Na(+)-K(+)-ATPase, while silencing it in H1299 cells had an opposite effect. This may provide a mechanism for the above effects, since normal glycosylation of β1 plays an important role in cell-cell contact formation (Vagin O, Tokhtaeva E, Sachs G. J Biol Chem 281: 39573-39587, 2006).

Expression of dysadherin in the human male reproductive tract and in spermatozoa

OBJECTIVE

To study expression of dysadherin in human testis, epididymis, and spermatozoa.

DESIGN

Prospective study.

SETTING

Basic research laboratory.

PATIENT(S)

Testis, epididymis, and testicular spermatozoa from patients under treatment and semen from volunteer donors.

INTERVENTION(S)

Reverse transcription-polymerase chain reaction, immunohistochemistry, immunocytochemistry, and Western immunoblotting.

MAIN OUTCOME MEASURE(S)

Dysadherin messenger RNA (mRNA) analysis in testis, epididymis, and ejaculated spermatozoa, immunohistochemistry of both tissues, Western immunoblotting of tissue/cell extracts, and immunocytochemistry of spermatozoa.

RESULT(S)

Dysadherin mRNA was found in testis, epididymis, and ejaculated spermatozoa. Whereas testis and spermatozoa exhibited a distinctive 91-kDa protein form, the epididymis showed a 50-kDa moiety, also found in MDA-MB-231 breast cancer cells. Nucleotide sequence analysis revealed >99% homology between testicular and somatic cell mRNA, suggesting differential protein glycosylation. Dysadherin was immunodetected in round spermatids and testicular/ejaculated spermatozoa. It localizes to the acrosomal region and flagellum and colocalized with E-cadherin in the head and with the Na(+),K(+)-ATPase α4 subunit in the flagellum.

CONCLUSION(S)

This is the first report on expression of dysadherin in the male gonad and in spermatozoa. Its colocalization with E-cadherin and Na(+),K(+)-ATPase leads us to postulate a role for dysadherin as a modulator of sperm function.

Core2 O-glycan structure is essential for the cell surface expression of sucrase isomaltase and dipeptidyl peptidase-IV during intestinal cell differentiation

Alterations in glycosylation play an important role during intestinal cell differentiation. Here, we compared expression of mucin-type O-glycan synthases from proliferating and differentiated HT-29 and Caco-2 cells. Mucin-type O-glycan structures were analyzed at both stages by mass spectrometry. Core2 β1,6-N-acetylglucosaminyltransferase-2 (C2GnT-2) was markedly increased in differentiated HT-29 and Caco-2 cells, but the core3 structure was hardly detectable. To determine whether such differential expression of mucin-type O-glycan structures has physiological significance in intestinal cell differentiation, expression of sucrase isomaltase (SI) and dipeptidyl-peptidase IV (DPP-IV), two well known intestinal differentiation markers, was examined. Interestingly, the fully glycosylated mature form of SI was decreased in C2GnT-2 knock-out mice but not in core2 N-acetylglucosaminyltransferase-3 (C2GnT-3) nulls. In addition, expression of SI and DPP-IV was dramatically reduced in C2GnT-1-3 triple knock-out mice. These patterns were confirmed by RNAi analysis; C2GnT-2 knockdown significantly reduced cell surface expression of SI and DPP-IV in Caco-2 cells. Similarly, overexpression of the core3 structure in HT-29 cells attenuated cell surface expression of both enzymes. These findings indicate that core3 O-glycan structure regulates cell surface expression of SI and DPP-IV and that core2 O-glycan is presumably an essential mucin-type O-glycan structure found in both molecules in vivo. Finally, goblet cells in the upper part of the crypt showed impaired maturation in the core2 O-glycan-deficient mice. These studies are the first to clearly identify functional mucin-type O-glycan structures modulating cell surface expression of SI and DPP-IV during the intestinal cell differentiation.

Role of EBAG9 protein in coat protein complex I-dependent glycoprotein maturation and secretion processes in tumor cells

Many proteins mature within the secretory pathway by the acquisition of glycans. Failure to maintain the proper distribution of the glycosylation machinery might lead to disease. High expression levels of the ubiquitous Golgi protein estrogen receptor-binding fragment-associated gene 9 (EBAG9) in human tumors correlate with poor clinical prognosis, and EBAG9 overexpression in epithelial cell lines induces truncated glycans, typical of many carcinomas. Here, we addressed the pathogenetic link between EBAG9 expression and the alteration of the cellular glycome. We applied confocal microscopy, live imaging, pulse-chase labeling in conjunction with immunoprecipitation, and enzymatic activity assays in a variety of EBAG9-overexpressing or depleted epithelial tumor cell lines. EBAG9 shuttles between the ER-Golgi intermediate compartment and the cis-Golgi, and we demonstrate association of EBAG9 with coat protein complex I (COPI)-coated transport vesicles. EBAG9 overexpression imposes delay of endoplasmic reticulum-to-Golgi transport and mislocalizes components of the ER quality control and glycosylation machinery. Conversely, EBAG9 down-regulation accelerates glycoprotein transport through the Golgi and enhances mannosidase activity. Thus, EBAG9 acts as a negative regulator of a COPI-dependent ER-to-Golgi transport pathway in epithelial cells and represents a novel pathogenetic principle in which interference with intracellular membrane trafficking results in the emergence of a tumor-associated glycome.

Cell surface O-glycans limit Staphylococcus aureus adherence to corneal epithelial cells

The mucin-rich environment of the intact corneal epithelium is thought to contribute to the prevention of Staphylococcus aureus infection. This study examined whether O-glycans, which constitute the majority of the mucin mass of epithelial cell glycocalyces, prevented bacterial adhesion and growth. Abrogation of mucin O glycosylation using the chemical primer benzyl-alpha-GalNAc resulted in increased adherence of parental strain RN6390 to apical human corneal-limbal epithelial (HCLE) cells and to biotinylated cell surface protein in static and liquid phase adhesion assays, consistent with a role of mucin O-glycans in preventing bacterial adhesion. Comparable results were found with ALC135, an isogenic mutant strain defective in the accessory gene regulators agr and sar, indicating that the agr- and/or sar-regulated virulence factors did not play a major role in mediating adhesion to the corneal cell surface after mucin O-glycan truncation. In exoglycosidase digestion studies, treatment with sialidase from Arthrobacter ureafaciens--which hydrolyzed mucin-associated O-acetyl sialic acid--but not from Clostridium perfringens resulted in an increase in RN6390 and ALC135 adhesion. Abrogation of mucin O glycosylation in HCLE cell cultures did not affect bacterial growth. Overall, these data indicate that mucin O-glycans contribute to the prevention of bacterial adherence to the apical surface of corneal epithelial cells and suggest that alteration of cell surface glycosylation from disease or trauma, including that stemming from contact lens wear, could contribute to a higher risk of infection.

FXYD5 modulates Na+ absorption and is increased in cystic fibrosis airway epithelia

FXYD5, also known as dysadherin, belongs to a family of tissue-specific regulators of the Na(+)-K(+)-ATPase. We determined the kinetic effects of FXYD5 on Na(+)-K(+)-ATPase pump activity in stably transfected Madin-Darby canine kidney cells. FXYD5 significantly increased the apparent affinity for Na(+) twofold and decreased the apparent affinity for K(+) by 60% with a twofold increase in V(max) of K(+), a pattern that would increase activity and Na(+) removal from the cell. To test the effect of increased Na(+) uptake on FXYD5 expression, we analyzed Madin-Darby canine kidney cells stably transfected with an inducible vector expressing all three subunits of the epithelial Na(+) channel (ENaC). Na(+)-K(+)-ATPase activity increased sixfold after 48-h ENaC induction, but FXYD5 expression decreased 75%. FXYD5 expression was also decreased in lung epithelia from mice that overexpress ENaC, suggesting that chronic Na(+) absorption by itself downregulates epithelial FXYD5 expression. Patients with cystic fibrosis (CF) display ENaC-mediated hyperabsorption of Na(+) in the airways, accompanied by increased Na(+)-K(+)-ATPase activity. However, FXYD5 was significantly increased in the lungs and nasal epithelium of CF mice as assessed by RT-PCR, immunohistochemistry, and immunoblot analysis (P < 0.001). FXYD5 was also upregulated in nasal scrapings from human CF patients compared with controls (P < 0.02). Treatment of human tracheal epithelial cells with a CFTR inhibitor (I-172) confirmed that loss of CFTR function correlated with increased FXYD5 expression (P < 0.001), which was abrogated by an inhibitor of NF-kappaB. Thus FXYD5 is upregulated in CF epithelia, and this change may exacerbate the Na(+) hyperabsorption and surface liquid dehydration observed in CF airway epithelia.

Antiadhesive character of mucin O-glycans at the apical surface of corneal epithelial cells

PURPOSE

Prolonged contact of opposite mucosal surfaces, which occurs on the ocular surface, oral cavity, reproductive tract, and gut, requires a specialized apical cell surface that prevents adhesion. The purpose of this study was to evaluate the contribution of mucin O-glycans to the antiadhesive character of human corneal-limbal epithelial (HCLE) cells.

METHODS

Mucin O-glycan biosynthesis in HCLE cells was disrupted by metabolic interference with benzyl-alpha-GalNAc. The cell surface mucin MUC16 and its carbohydrate epitope H185 were detected by immunofluorescence and Western blot. HCLE cell surface features were assessed by field emission scanning electron microscopy. Cell-cell adhesion assays were performed under static conditions and in a parallel plate laminar flow chamber.

RESULTS

Benzyl-alpha-GalNAc disrupted the biosynthesis of O-glycans without affecting apomucin biosynthesis or cell surface morphology. Static adhesion assays showed that the apical surface of differentiated HCLE cells expressing MUC16 and H185 was more antiadhesive than undifferentiated HCLE cells, which lacked MUC16. Abrogation of mucin O-glycosylation in differentiated cultures with benzyl-alpha-GalNAc resulted in increased adhesion of applied corneal epithelial cells and corneal fibroblasts. The antiadhesive effect of mucin O-glycans was further demonstrated by fluorescence video microscopy in dynamic flow adhesion assays. Cationized ferritin labeling of the cell surface indicated that anionic repulsion did not contribute to the antiadhesive character of the apical surface.

CONCLUSIONS

These results indicate that epithelial O-glycans contribute to the antiadhesive properties of cell surface-associated mucins in corneal epithelial cells and suggest that alterations in mucin O-glycosylation are involved in the pathology of drying mucosal diseases (e.g., dry eye).

Post-translational modifications of Epstein Barr virus BARF1 oncogene-encoded polypeptide

Epstein-Barr virus is associated with several human lymphomas and carcinomas, and its BARF1 oncogene encodes a protein that is thought to play an important role in carcinogenesis. A BARF1 recombinant adenovirus expression system, which led us to discover the macromolecular size of the cleaved and secreted form of the BARF1 protein in the native state and its mitogenic capacity on various cell lines in culture, was used further to investigate the structure and maturation of the BARF1 protein. We recently reported biophysical studies that showed dimer-based oligomerization of the BARF1 polypeptide. Here, new data are presented that confirm post-translational modifications predicted from the BARF1 sequence: phosphorylation on serine and threonine, and N- and O-glycosylation. The N- and O-glycans were partially characterized and it was demonstrated that both modifications are required for active secretion of the BARF1 protein via the classical pathway.

Structural and functional interactions between FXYD5 and the Na+-K+-ATPase

FXYD5 is a member of a family of tissue-specific regulators of the Na(+)-K(+)-ATPase expressed in kidney tubules. Previously, we have shown that FXYD5 interacts with the alphabeta-subunits of the Na(+)-K(+)-ATPase and increases its V(max) (Lubarski I, Pihakaski-Maunsbach K, Karlish SJ, Maunsbach AB, Garty H. J Biol Chem 280: 37717-37724, 2005). The current study further characterizes structural interaction and structure-function relationships of FXYD5. FXYD5/FXYD4 chimeras expressed in Xenopus laevis oocytes have been used to demonstrate that both the high-affinity association with the pump and the increase in V(max) are mediated by the transmembrane domain of FXYD5. Several amino acids that participate in the high-affinity interaction between FXYD5 and the alpha-subunit of the Na(+)-K(+)-ATPase have been identified. The data suggest that different FXYD proteins interact similarly with the Na(+)-K(+)-ATPase and their transmembrane domains play a key role in both the structural interactions and functional effects. Other experiments have identified at least one splice variant of FXYD5 with 10 additional amino acids at the COOH terminus, suggesting the possibility of other functional effects not mediated by the transmembrane domain. FXYD5 could be specifically bound to wheat germ agglutinin beads, indicating that it is glycosylated. However, unlike previous findings in metastatic cells, such glycosylation does not evoke a large increase in the size of the protein expressed in native epithelia and X. laevis oocytes.

Dysadherin: a new player in cancer progression

Dysadherin is a cancer-associated cell membrane glycoprotein that promotes experimental cancer metastasis. Here we review recent work that has provided insights into possible mechanisms of action of this newly recognized player in the cancer progression process. Dysadherin modulates cell phenotype in a number of ways, including down-regulation of E-cadherin-mediated cell adhesion, and up-regulation of chemokine production. In this way, expression of dysadherin in a tumor can influence both the tumor cell itself and the stromal compartment, so as to create conditions that are more permissive for metastatic spread. Dysadherin expression is also an independent prognostic indicator of metastasis and survival for many different types of human cancer. Thus, dysadherin may represent a new molecular target for the visualization, prevention or treatment of advanced cancer.

In breast carcinoma dysadherin expression is correlated with invasiveness but not with E-cadherin

Reduction/loss of E-cadherin is associated with the development and progression of many epithelial tumours. Dysadherin, recently characterised by members of our research team, has an anti-cell–cell adhesion function and downregulates E-cadherin in a post-transcriptional manner. The aim of the present study was to study the role of dysadherin in breast cancer progression, in association with the E-cadherin expression and the histological type. We have selected ductal carcinoma, which is by far the most common type and lobular carcinoma, which has a distinctive microscopic appearance. Dysadherin and E-cadherin expression was examined immunohistochemically in 70 invasive ductal carcinomas, no special type (NST), and 30 invasive lobular carcinomas, with their adjacent in situ components. In ductal as well as in lobular carcinoma dysadherin was expressed only in the invasive and not in the in situ component, and this expression was independent of the E-cadherin expression. Specifically, all 10 (100%) Grade 1, 37out of 45(82.2%) Grade 2 and six out of 15 (40%) Grade 3 invasive ductal carcinomas showed preserved E-cadherin expression, while ‘positive dysadherin expression’ was found in six out of 10 (60%) Grade 1, 34 out of 45(75.5%) Grade 2 and all 15 (100%) Grade 3 neoplasms. None of the 30 infiltrating lobular carcinomas showed preserved E-cadherin expression, while all the 30 infiltrating lobular carcinomas exhibited ‘positive dysadherin expression’. Dysadherin may play an important role in breast cancer progression by promoting invasion and, particularly in lobular carcinomas, it might also be used as a marker of invasion.

Mucin-type O-glycans in human colon and breast cancer: glycodynamics and functions

The glycoproteins of tumour cells are often abnormal, both in structure and in quantity. In particular, the mucin-type O-glycans have several cancer-associated structures, including the T and Tn antigens, and certain Lewis antigens. These structural changes can alter the function of the cell, and its antigenic and adhesive properties, as well as its potential to invade and metastasize. Cancer-associated mucin antigens can be exploited in diagnosis and prognosis, and in the development of cancer vaccines. The activities and Golgi localization of glycosyltransferases are the basis for the glycodynamics of cancer cells, and determine the ranges and amounts of specific O-glycans produced. This review focuses on the glycosyltransferases of colon and breast cancer cells that determine the pathways of mucin-type O-glycosylation, and the proposed functional and pathological consequences of altered O-glycans.

Multiplicity of expression of FXYD proteins in mammalian cells: dynamic exchange of phospholemman and gamma-subunit in response to stress

Functional properties of Na-K-ATPase can be modified by association with FXYD proteins, expressed in a tissue-specific manner. Here we show that expression of FXYDs in cell lines does not necessarily parallel the expression pattern of FXYDs in the tissue(s) from which the cells originate. While being expressed only in lacis cells in the juxtaglomerular apparatus and in blood vessels in kidney, FXYD1 was abundant in renal cell lines of proximal tubule origin (NRK-52E, LLC-PK1, and OK cells). Authenticity of FXYD1 as a part of Na-K-ATPase in NRK-52E cells was demonstrated by co-purification, co-immunoprecipitation, and co-localization. Induction of FXYD2 by hypertonicity (500 mosmol/kgH(2)O with NaCl for 48 h or adaptation to 700 mosmol/kgH(2)O) correlated with downregulation of FXYD1 at mRNA and protein levels. The response to hypertonicity was influenced by serum factors and entailed, first, dephosphorylation of FXYD1 at Ser(68) (1-5 h) and, second, induction of FXYD2a and a decrease in FXYD1 with longer exposure. FXYD1 was completely replaced with FXYD2a in cells adapted to 700 mosmol/kgH(2)O and showed a significantly decreased sodium affinity. Thus dephosphorylation of FXYD1 followed by exchange of regulatory subunits is utilized to make a smooth transition of properties of Na-K-ATPase. We also observed expression of mRNA for multiple FXYDs in various cell lines. The expression was dynamic and responsive to physiological stimuli. Moreover, we demonstrated expression of FXYD5 protein in HEK-293 and HeLa cells. The data imply that FXYDs are obligatory rather than auxiliary components of Na-K-ATPase, and their interchangeability underlies responses of Na-K-ATPase to cellular stress.

Expression patterns of dysadherin and E-cadherin in lymph node metastases of colorectal carcinoma

Reduction/loss of E-cadherin is associated with the development and progression of many epithelial tumors, while in a limited number of neoplasms, E-cadherin is re-expressed in metastases. Dysadherin, recently characterized by members of our research team, has an anti-cell-cell adhesion function and downregulates E-cadherin in a posttranscriptional manner. Colorectal cancer (CRC) is one of the most common tumors in the developed world, and lymph node metastases are harbingers of aggressive behavior. The aim of the present study was to examine the dysadherin and E-cadherin expression patterns in lymph node metastases vs primary CRC. Dysadherin and E-cadherin expression was examined immunohistochemically in 78 patients with CRC, Dukes' stage C in the primary tumor and in one lymph node metastasis. Dysadherin was expressed in 42% while E-cadherin immunoreactivity was reduced in 45% of primary tumors. In lymph nodes, 33 and 81% of metastatic tumors were positive for dysadherin and E-cadherin, respectively. Dysadherin expression was not correlated with E-cadherin expression in the primary tumor with a reverse correlation evident in the lymph node metastases. Our results suggest that different mechanisms govern E-cadherin expression in the primary tumor and the corresponding lymph node metastases.

FXYD proteins: new regulators of Na-K-ATPase

FXYD proteins belong to a family of small-membrane proteins. Recent experimental evidence suggests that at least five of the seven members of this family, FXYD1 (phospholemman), FXYD2 (gamma-subunit of Na-K-ATPase), FXYD3 (Mat-8), FXYD4 (CHIF), and FXYD7, are auxiliary subunits of Na-K-ATPase and regulate Na-K-ATPase activity in a tissue- and isoform-specific way. These results highlight the complexity of the regulation of Na+ and K+ handling by Na-K-ATPase, which is necessary to ensure appropriate tissue functions such as renal Na+ reabsorption, muscle contractility, and neuronal excitability. Moreover, a mutation in FXYD2 has been linked to cases of human hypomagnesemia, indicating that perturbations in the regulation of Na-K-ATPase by FXYD proteins may be critically involved in pathophysiological states. A better understanding of this novel regulatory mechanism of Na-K-ATPase should help in learning more about its role in pathophysiological states. This review summarizes the present knowledge of the role of FXYD proteins in the modulation of Na-K-ATPase as well as of other proteins, their regulation, and their structure-function relationship.

Involvement of dysadherin and E-cadherin in the development of testicular tumours

Testicular neoplasms are comprised of a variety of histologically different forms, and their pathogenesis has not been elucidated. Dysadherin is a recently described cell membrane glycoprotein, which has an anticell–cell adhesion function and downregulates E-cadherin. In this study, we examined immunohistochemically the expression of E-cadherin and dysadherin in 120 testicular neoplasms (37 seminomas-26 classic, five spermatocytic and six anaplastic-, 45 embryonal carcinomas, 10 mixed germ cell tumours, two yolk sac tumours, 10 mature and eight immature teratomas and eight non-Hodgkin B-cell lymphomas), clinical stage I. The intensity, the expression pattern and the percentage of neoplastic cell staining was recorded and correlated with the histologic type and vascular/lymphatic invasion. Dysadherin was not expressed in non-neoplastic germ cells, neither in CIS/ITGCNU, but it was highly expressed in all types of germ cell tumours, that demonstrated either embryonic phenotype or somatic differentiation, in most terminally differentiated neoplasms, and in all lymphomas. Dysadherin expression did not correlate with vascular invasion. Increased dysadherin expression was correlated with aberrant E-cadherin expression in most tumours. In 17% of embryonal carcinomas colocalisation of dysadherin and membranous E-cadherin staining was noted. This is the first report on dysadherin expression and its association with E-cadherin in testicular tumours. Since dysadherin is not normally expressed in non-neoplastic testis, it is conceivable that it plays a role in the neoplastic transformation of germ cells. In testicular tumours, as in other neoplasms, dysadherin downregulates E-cadherin expression, at least in part.

Interaction with the Na,K-ATPase and Tissue Distribution of FXYD5 (Related to Ion Channel)

FXYD5 (related to ion channel, dysadherin) is a member of the FXYD family of single span type I membrane proteins. Five members of this group have been shown to interact with the Na,K-ATPase and to modulate its properties. However, FXYD5 is structurally different from other family members and has been suggested to play a role in regulating E-cadherin and promoting metastasis (Ino, Y., Gotoh, M., Sakamoto, M., Tsukagoshi, K., and Hirohashi, S. (2002) Proc. Natl. Acad. Sci. U. S. A. 99, 365-370). The goal of this study was to determine whether FXYD5 can modulate the Na,K-ATPase activity, establish its cellular and tissue distribution, and characterize its biochemical properties. Anti-FXYD5 antibodies detected a 24-kDa polypeptide that was preferentially expressed in kidney, intestine, spleen, and lung. In kidney, FXYD5 resides in the basolateral membrane of the connecting tubule, the collecting tubule, and the intercalated cells of the collecting duct. However, there is also labeling of the apical membrane in long thin limb of Henle's loop. FXYD5 was effectively immunoprecipitated by antibodies to the alpha subunit of Na,K-ATPase and the anti-FXYD5 antibody immunoprecipitates alpha. Co-expressing FXYD5 with the alpha1 and beta1 subunits of the Na,K-ATPase in Xenopus oocytes elicited a more than 2-fold increase in pump activity, measured either as ouabain-blockable outward current or as ouabain-sensitive (86)Rb(+) uptake. Thus, as found with other FXYD proteins, FXYD5 interacts with the Na,K-ATPase and modulates its properties.

Fine carbohydrate recognition of Euphorbia milii lectin

Glycans are key structures involved in biological processes such as cell attachment, migration, and invasion. Information coded on cell-surface glycans is frequently deciphered by proteins, as lectins, that recognize specific carbohydrate topology. Here, we describe the fine carbohydrate specificity of Euphorbia milii lectin (EML). Competitive assays using various sugars showed that GalNAc was the strongest inhibitor, and that the hydroxyl axial position of C4 and acetamido on C2 of GalNAc are critical points of EML recognition. A hydrophobic locus adjacent to GalNAc is also an important region for EML binding. Direct binding assays of EML revealed a stereochemical requirement for a structure adjacent to terminal GalNAc, showing that GalNAc residue is a necessary but not sufficient condition for EML interaction. The capacity of EML to bind epithelial tumor cells makes it a potentially useful tool for study of some over-expressed GalNAc glycoconjugates.

Prognostic significance of dysadherin expression in cervical squamous cell carcinoma

The protein and mRNA expression of dysadherin was studied in a series of squamous cell cervical carcinomas, and their clinicopathological associations and prognostic value were explored. Immunohistochemistry was used to assess protein expression of dysadherin in 206 patients with squamous cell cervical carcinoma, FIGO stage Ia-IVb. Frozen tissues from 20 cases in which the tumors showed variable dysadherin protein expression were used for laser capture microdissection (LCM) and processed for RTPCR detection of dysadherin mRNA. Immunohistochemically, all the dysadherin-positive staining was membranous. Positive cell membranous dysadherinpositive staining was often observed at the edge of tumor nests, although strong immunoreactivity throughout whole tumor nests was also seen in some tumors. Basal cells of the normal cervical epithelia were positive for dysadherin while its expression in the squamous cell cervical carcinomas was variable. Among the 206 tumors, 23 (11.2%) were negative, 53 (25.7%) were scored 1+, 54 (26.2%) were scored 2+ and 76 (36.9%) were scored 3+. In the 20 tumors analyzed, mRNA expression of dysadherin basically corresponded to its protein expression. No significant correlation between expression of dysadherin and age, FIGO stage or lymph node status was observed. Higher level of dysadherin expression, however, was significantly associated with shorter overall survival (p=0.04). We conclude that there is dysadherin protein expression in basal and parabasal cells of normal cervical epithelia, and higher level of dysadherin protein expression in squamous cell cervical carcinoma is predictive of a shorter overall survival, indicating that dysadherin may be a valuable prognostic marker in cervical carcinoma.

Dysadherin expression facilitates cell motility and metastatic potential of human pancreatic cancer cells

Dysadherin is a membrane glycoprotein expressed strongly in several human cancers. Overexpression of dysadherin in tumor cells is closely associated with malignant phenotype (e.g., metastasis) and poor prognosis. In our analysis, six pancreatic cancer cell lines showed a positive correlation between dysadherin expression and cell motility. Introduction of small interfering RNA (siRNA) against dysadherin into the Panc-1 cell line caused reduction of dysadherin expression and suppression of cell motility. In contrast, stable transfection of a dysadherin expression vector into the Capan-1 cell line increased cell motility. In vivo, the metastatic potential of orthotopically transplanted Capan-1 tumor cells in severe combined immunodeficient mice was increased by dysadherin overexpression. Cell morphology and actin organization were also influenced by modulation of dysadherin expression. Cells transfected with dysadherin siRNA tended to have a relatively larger, more spread shape and increased transverse actin stress fibers compared with parent cells and cells transfected with control siRNA. Our study suggests that dysadherin is able to modulate actin structures, stimulate cell motility, and contribute directly to the metastatic potential of human pancreatic cancer cells.

Role of Peptide Sequence and Neighboring Residue Glycosylation on the Substrate Specificity of the Uridine 5'-Diphosphate−α-N-acetylgalactosamine:PolypeptideN-acetylgalactosaminyl Transferases T1 and T2: Kinetic Modeling of the Porcine and Canine Submaxillary Gland Mucin Tandem Repeats†

A large family of uridine 5'-diphosphate (UDP)-alpha-N-acetylgalactosamine (GalNAc):polypeptide N-acetylgalactosaminyl transferases (ppGalNAc Ts) initiates mucin-type O-glycan biosynthesis at serine and threonine. The peptide substrate specificities of individual family members are not well characterized or understood, leaving an inability to rationally predict or comprehend sites of O-glycosylation. Recently, a kinetic modeling approach demonstrated neighboring residue glycosylation as a major factor modulating the O-glycosylation of the porcine submaxillary gland mucin 81 residue tandem repeat by ppGalNAc T1 and T2 [Gerken et al. (2002) J. Biol. Chem. 277, 49850-49862]. To confirm the general applicability of this model and its parameters, the ppGalNAc T1 and T2 glycosylation kinetics of the 80+ residue tandem repeat from the canine submaxillary gland mucin was obtained and characterized. To reproduce the glycosylation patterns of both mucins (comprising 50+ serine/threonine residues), specific effects of neighboring peptide sequence, in addition to the previously described effects of neighboring residue glycosylation, were required of the model. Differences in specificity of the two transferases were defined by their sensitivities to neighboring proline and nonglycosylated hydroxyamino acid residues, from which a ppGalNAc T2 motif was identified. Importantly, the model can approximate the previously reported ppGalNAc T2 glycosylation kinetics of the IgA1 hinge domain peptide [Iwasaki, et al. (2003) J. Biol. Chem. 278, 5613-5621], further validating both the approach and the ppGalNAc T2 positional weighting parameters. The characterization of ppGalNAc transferase specificity by this approach may prove useful for the search for isoform-specific substrates, the creation of isoform-specific inhibitors, and the prediction of mucin-type O-glycosylation sites.

Kinetic modeling confirms the biosynthesis of mucin core 1 (beta-Gal(1-3) alpha-GalNAc-O-Ser/Thr) O-glycan structures are modulated by neighboring glycosylation effects

Glycoproteins containing heavily O-glycosylated, mucin-like domains serve important biological functions in which the O-linked glycans play a major role. Although not well understood, O-glycan structures are known to vary reproducibly as a function of their position in the peptide sequence. Toward understanding such behavior, an analysis of the in vivo Core 1 (beta-Gal(1-3) alpha-GalNAc-O-Ser/Thr) site-specific glycosylation pattern of the porcine salivary gland mucin 81 residue tandem repeat has been undertaken. When a kinetic modeling approach is utilized, the in vivo Core 1 glycosylation pattern could be reproduced by incorporation of the inhibitory effects of neighboring residue glycosylation plus and minus three residues of the site of glycosylation. The obtained positional weighing parameters suggest that the porcine salivary gland Core 1 transferase (UDP-galactose:glycoprotein-alpha-GalNAc beta3-galactosyltransferase) is most sensitive to the presence of glycans C terminal to the site of glycosylation. The analysis further suggests that neighboring peptide core alpha-GalNAc residues are primarily responsible for the effect. These findings further support the notion that the formation of the Core 1 structure, an important initial step in O-glycan biosynthesis, may be regulated to a large extent by neighboring residue glycosylation. As a result, the development of approaches for predicting O-glycan core structures in a site-specific manner may now appear a distinct possibility.