Cell surface beta 1,4-galactosyltransferase functions during neural crest cell migration and neurulation in vivo

β1,4-galactosyltransferase-I protects chondrocytes against TNF-induced apoptosis by blocking the TLR4 signaling pathway

Osteoarthritis (OA) is the most common degenerative disease of the cartilage and is characterized by inflammation of the synovial membrane and subchondral osteosclerosis. β1,4-galactosyltransferase-I (β1,4-GalT-I) is a crucial regulator of inflammation based on its role in the stimulation and sustenance of inflammation in OA. In the present study, we aimed at elucidating the expression pattern and potential biological activity of β1,4-GalT-I in chondrocytes isolated from OA patients. Chondrocytes were isolated from the cartilage and cultured. Western blotting and quantitative real-time polymerase chain reaction (qRT-PCR) were used to analyze β1,4-GalT-I expression. Isolated chondrocytes were stimulated with tumor necrosis factor (TNF). Our results indicate significantly enhanced expression of β1,4-GalT-I in cultivated chondrocytes upon stimulation with TNF. β1,4-GalT-I inhibited the inflammation and cell death triggered by TNF. In addition, β1,4-GalT-Iinhibited the expression of Toll-like receptor 4 (TLR4) and phosphorylation of p65 and IKK. In conclusion, our findings suggest the protective effect of β1,4-GalT-I in chondrocytes against OA induced by TNF based on its ability to block the TLR4 signaling pathway. Our results also indicate significant contribution of β1,4-GalT-I towards the anti-inflammation in the cartilage of patients suffering from OA.

Extrinsic sialylation is dynamically regulated by systemic triggers in vivo

Recent reports have documented that extracellular sialyltransferases can remodel both cell-surface and secreted glycans by a process other than the canonical cell-autonomous glycosylation that occurs within the intracellular secretory apparatus. Despite association of the abundance of these extracellular sialyltransferases, particularly ST6Gal-1, with disease states such as cancer and a variety of inflammatory conditions, the prevalence of this extrinsic glycosylation pathway in vivo remains unknown. Here we observed no significant extrinsic sialylation in resting mice, suggesting that extrinsic sialylation is not a constitutive process. However, extrinsic sialylation in the periphery could be triggered by inflammatory challenges, such as exposure to ionizing radiation or to bacterial lipopolysaccharides. Sialic acids from circulating platelets were used in vivo to remodel target cell surfaces. Platelet activation was minimally sufficient to elicit extrinsic sialylation, as demonstrated with the FeCl₃ model of mesenteric artery thrombosis. Although extracellular ST6Gal-1 supports extrinsic sialylation, other sialyltransferases are present in systemic circulation. We also observed in vivo extrinsic sialylation in animals deficient in ST6Gal-1, demonstrating that extrinsic sialylation is not mediated exclusively by ST6Gal-1. Together, these observations form an emerging picture of glycans biosynthesized by the canonical cell-autonomous glycosylation pathway, but subjected to remodeling by extracellular glycan-modifying enzymes.

Identification of Mutations in Myocilin and Beta-1,4-galactosyltransferase 3 Genes in a Chinese Family with Primary Open-angle Glaucoma

BACKGROUND

Glaucoma is a major cause of irreversible blindness worldwide. There is evidence showing that a subset of the disease is genetically determined. In this study, we screened for mutations in chromosome 1q-linked open-angle glaucoma (GLC1A) in a Chinese family with primary open-angle glaucoma (POAG).

METHODS

A total of 23 members from five generations of a family were enrolled and underwent thorough ophthalmologic examinations. In addition, 200 unrelated healthy Chinese controls were also recruited as normal control. GLC1A gene was amplified by polymerase chain reaction, and DNA sequencing was performed to screen for mutations.

RESULTS

Six members were diagnosed as POAG, with severe clinical manifestations, and history of high intraocular pressures. The mean age of disease onset was 26.3 years. However, the others were asymptomatic. In six affected and three asymptomatic members, gene sequencing revealed a mutation c.C1456T in exon 3 of myocilin gene (MYOC). Furthermore, we also identified a novel mutation c.G322A in beta-1,4-galactosyltransferase 3 (B4GALT3) gene in all six affected and three asymptomatic members, which was not reported previously in POAG patients. The two newly identified variants were absent in other family members as well as controls.

CONCLUSION

The mutations c.1456C < T (p.L486F) in MYOC and c.322G < A (p.V108I) in B4GALT3 are likely responsible for the pathogenesis of POAG in this family.

HCG induces β1,4-GalT I expression and promotes embryo implantation

Embryo implantation is regarded as a critical physiological process for the success of pregnancy. There are so many reports on the research of human chorionic gonadotropin (HCG) in artificial insemination, but the impact of HCG on endometrial receptivity has not been elucidated. Beta1, 4-Galactosyltransferase-I (β1,4-GalT-I) is ubiquitously expresses in human tissues with the exception of the brain. It not only transfers galactose from UDP-galactoside to GlcNAc to form Galβl,4-GlcNAc, but plays crucial role as cell adhesion molecule by recognizing and adhering other extracellular matrix and galactose of cell surface glycoprotein and glycolipid in cancer cells invasion and migration. The process of the embryos implantation is very similar to tumor invasion, so many biological factors participate in the tumor invasion also play a role in embryo implantation. We hypothesize that β1,4-GalT-I may take part in embryo implantation. In this study, we demonstrated that the over expression of β1,4-GalT-I was induced by HCG in RL95-2 cells. Moreover, the expression of some molecules, such as TIMP-1, LN and MMPs could be regulated by engineered expression of β1,4-GalT-I and therefore lead to the significantly alteration of adhesion capability of RL95-2 cells, even result in reduced adhesive ability between JAR cells and RL95-2 cells. Furthermore, our results indicated that HCG can obviously increase the EGFR signaling pathways-dependent molecular expression through β1,4-GalT-I, HCG also improved the adhesive ability between JAR cells and RL95-2 cells (P<0.01). Taken together, our data suggested that HCG provides a mechanism to bridge embryo to endometrium through β1,4-GalT.

The functional interaction between CDK11p58 and β-1,4-galactosyltransferase I involved in astrocyte activation caused by lipopolysaccharide

Glial cells are mediating the main activation of the central nervous system (CNS), being astrocytes the mayor glial cells in the brain. Glial activation may result beneficial since it could promote tissue repair and pathogen elimination. However, excessive glial activation mechanism can also have do harm to the tissue. β-1,4-Galactosyltransferase I (β-1,4-GalT-I) is a key inflammatory mediator that participates in the initiation and maintenance of inflammatory reaction in some diseases. Moreover, CDK11(p58) has been reported to be associated with β-1,4-GalT-I. We have found that CDK11(p58) and β-1,4-GalT-I are induced in lipopolysaccharide (LPS)-challenged rat primary astrocytes in a affinis dose- and time-dependent manner. CDK11(p58) regulates the expression of β-1,4-GalT-I by interacting with it. After the knockdown of CDK11(p58) expression, the expression of β-1,4-GalT-I decreases, and astrocyte activation downregulates. Inversely, the expression of β-1,4-GalT-I increases, and astrocyte activation enhances due to the overexpression of CDK11(p58). Knockdown of β-1,4-GalT-I reduces the activation potentiation caused by the overexpression of CDK11(p58), illustrating the function of CDK11(p58) to promote astrocyte activation depends on β-1,4-GalT-I. The interaction between CDK11(p58) and β-1,4-GalT-I to upregulate astrocyte activation is related to activating p38 and JNK pathways. These findings indicated that the functional interaction between CDK11(p58) and β-1,4-GalT-I may play an important role during astrocyte activation after LPS administration.

Elevated expression of β1,4-galactosyltransferase-I in cartilage and synovial tissue of patients with osteoarthritis

Osteoarthritis (OA) is considered a complex illness, characterized by cartilage degeneration, secondary synovial membrane inflammation, and subchondral bone sclerosis. Previous studies have shown β1,4-galactosylransferase-I (β1,4-GalT-I) to be a key inflammatory mediator that participates in the initiation and maintenance of inflammatory reaction in diseases. In the present study, we investigated the expression and possible biological function of β1,4-GalT-I in the cartilage and synovial tissue of OA patients. Cartilage and synovial tissue samples from OA patients and healthy controls were stained for β1,4-GalT-I. Reverse transcription-polymerase chain reaction was used to observe the expression of β1,4-GalT-I, and western blot was carried out for E-selectin. The interaction between β1,4-GalT-I and E-selectin was analyzed by double labeling immunohistochemistry and immunoprecipitation. The expression of β1,4-GalT-I increased in the cartilage and synovial tissue of OA patients compared with healthy controls. E-selectin was overexpressed and was correlated with β1,4-GalT-I in OA cartilage and synovial tissue. These data suggest that β1,4-GalT-I may play an important role in the inflammatory processes in cartilage and synovial tissue of patients with OA.

Osteopontin increases the expression of β1, 4-galactosyltransferase-I and promotes adhesion in human RL95-2 cells

Beta1, 4-Galactosyltransferase-I (β1, 4-GalT-I), which transfers galactose from UDP-Gal to N-acetylglucosamine and N-acetylglucosamine-terminated oligosaccharides of N- and O-linked glycans in a β(1-4) linkage, plays a critical role in cell adhesion, sperm-egg recognition, neurite growth, and tumor cell migration and invasion. Our previously experiments also show that β1, 4-GalT-I was up-regulated by estrogens and some important cytokines of embryo implantation especially Interleukin-1 (IL-1), TGF-α and Leukemia Inhibitory Factor (LIF) in endometrial cells. In the receptive phase human uterus, osteopontin (OPN) is the most highly up-regulated extracellular matrix/adhesion molecule/cytokine. In this study, we demonstrated the correlated expression of OPN and β1, 4-GalT-I in endometrium during early pregnancy, and recombinant human OPN (rhOPN) protein induced the β1, 4-GalT-I up-regulation in RL95-2 cells. Inhibition of MEK/ERK, PI3K/AKT and NF-κB suppressed rhOPN-induced β1, 4-GalT-I expression. In addition, rhOPN promoted the adhesion of blastocysts cells in vitro in β1, 4-GalT-I-dependent manner. Moreover, the adhesion is greatly inhibited when β1, 4-GalT-I was blocked with the specific antibody. Taken together, our data suggest that β1, 4-GalT-I provides a mechanism to bridge embryo to endometrium during implantation.

Tumor necrosis factor-α up-regulates the expression of β1,4-galactosyltransferase-I in human fibroblast-like synoviocytes

β1,4-Galactosyltransferase-I (β1,4-GalT-I), which transfers galactose to the terminal N-acetylglucosamine of N- and O-linked glycans in a β1,4-linkage, is considered to be the major galactosyltransferase among the seven members of the subfamily responsible for β4 galactosylation. We previously reported, for the first time, that β1,4-GalT-I may play an important role in the inflammatory processes in synovial tissue of patients with rheumatoid arthritis (RA). In this study, we analyzed whether β1,4-GalT-I expression correlates with the expression of tumor necrosis factor-α (TNF-α) in RA. We show firstly the overexpression and co-localization of β1,4-GalT-I and TNF-α in synovial tissue of RA patients. Then, lipopolysaccharide (LPS) induces β1,4-GalT-I mRNA up-regulation in fibroblast-like synoviocytes (FLSs) through endogenous TNF-α overexpression. In addition, we observed that not only endogenous TNF-α but also exogenous TNF-α induced β1,4-GalT-I mRNA production in FLSs, and TNF-α-knockdown reverses the up-regulation of β1,4-GalT-I in FLSs induced by LPS or TNF-α. These results suggest that TNF-α contributes to the up-regulation of β1,4-GalT-I mRNA in human FLSs.

β1,4-Galactosyltransferase-I contributes to the inflammatory processes in synovial tissue of patients with rheumatoid arthritis

OBJECTIVE AND DESIGN

The aim of the study is to examine the expression and possible biological function of β1,4-galactosyltransferase-I (β1,4-GalT-I) in synovial tissue from rheumatoid arthritis (RA) patients.

METHODS

Synovial tissue samples from twelve RA patients were stained for β1,4-GalT-I. Samples from seven patients with osteoarthritis (OA) and eight healthy people were obtained as controls. Real-time PCR or western blot analysis was used to observe the expression of β1,4-GalT-I and E-selectin. Cellular colocalization of β1,4-GalT-I, galactose-containing glycans and other molecules was analyzed by double immunofluorescence.

RESULTS

Expression of β1,4-GalT-I and galactose-containing glycans increased in synovial tissue of RA patients compared with OA patients and healthy controls. Most galactose-containing glycans and β1,4-GalT-I were expressed in inflammatory cells. E-selectin overexpressed and was correlated with galactose-containing glycans in RA synovial tissue.

CONCLUSION

These results suggested that β1,4-GalT-I may play an important role in the inflammatory processes in synovial tissue of patients with rheumatoid arthritis.

Lipopolysaccharide induced upregulation of beta-1,4-galactosyltransferase-I in Schwann cell

beta4 Galactosylation of glycoproteins is one of the most important post-translational modifications. Recent studies have demonstrated that aberrant galactosylation associates with some inflammation diseases. beta-1,4-galactosyltransferase-I (beta-1,4-GalT-I), which transfers galactose to the terminal N-acetylglucosamine of N- and O-linked glycans in a beta-1,4- linkage, considered to be the major galactosyltransferse among the seven members of the subfamily responsible for beta4 galactosylation. In the present study, we investigated the expression of beta-1,4-GalT-I in Schwann cells under Lipopolysaccharide (LPS) treatment. RT-PCR revealed that the beta-1,4-GalT-I mRNA was significant increased as early as 2 h after LPS stimulation. Immunofluorescence showed that beta-1,4-GalT-I was located in Golgi apparatus and membrane of Schwann cells. With the 1 microg/ml LPS treatment, expression levels of beta-1,4-GalT-I was much higher compared with control group. In addition, lectin blot indicated that the beta4 galactosylation of glycoproteins such as integrin alpha5 was enhanced, which may due to the induced beta-1,4-GalT-I expression. These results suggested that beta-1,4-GalT-I may play an important role in adhesion and migration of Schwann cells during inflammation.

Expression of beta-1,4-galactosyltransferase-I affects cellular adhesion in human peripheral blood CD4+ T cells

beta-1,4-galactosyltransferase-I (beta-1,4-GalT-I) has two isoforms that differ only in the length of their cytoplasmic domains. In this study, we found that both the long and short isoforms of beta-1,4-GalT-I were expressed in human CD4(+) T lymphocytes, and localized in the cytoplasm and on the plasma membrane. The expression level of beta-1,4-GalT-I was increased in CD4(+) T cells after stimulation with interleukin (IL)-2, and was further increased after stimulation with IL-2+IL-12, but decreased after stimulation with IL-2+IL-4 when compared to stimulation with IL-2 alone. We also demonstrated that the cellular adhesion of CD4(+) T cells was significantly increased upon cytokine stimulation, and was inhibited by alpha-lactalbumin, indicating that the increase in adhesion was positively correlated with the expression and activity of long beta-1,4-GalT-I. Collectively, the data suggest that beta-1,4-GalT-I plays a role in the cellular adhesion of CD4(+) T cells.

beta-1,4-Galactosyltransferase-I participates in lipopolysaccharide induced reactive microgliosis

beta-1,4-Galactosyltransferase-I (beta-1,4-GalT-I) is one of the best studied glycosyltransferases. Previous studies demonstrated that beta-1,4-GalT-I was a major galactosyltransferase responsible for selectin-ligand biosynthesis and that inflammatory responses of beta-1,4-GalT-I deficient mice were impaired. Our previous study suggest that beta-1,4-GalT-I may play an important role in regulating immune cell migration into the inflammatory site. In this study, we investigate beta-1,4-GalT-I may play an important role in mediating microgliosis. The results of this study demonstrated that beta-1,4-GalT-I was strongly induced in the ventral midbrain by intranigral injection of LPS. Most galactose-containing glycans and beta-1,4-GalT-I were expressed in microglia. Moreover, an Ab against beta-1,4-GalT-I attenuated both LPS-induced microglial activation and phagocytosis. We therefore suggest that beta-1,4-GalT-I may play an important role in regulating immune cell migration into the inflammatory site and mediating microgliosis.

The role of beta-1,4-galactosyltransferase-I in the skin wound-healing process

Cell-surface carbohydrate chains are known to contribute to cell migration, interaction, and proliferation. beta-1,4-galactosyltransferase-I (beta-1,4-GalT-I), which is one of the best-studied glycosyltransferases, plays a key role in the synthesis of type 2 chains in N-glycans and the core 2 branch in O-glycans. Recently, it has been reported that skin wound healing is significantly delayed in beta-1,4-GalT-I mice. However, the expression of beta-1,4-GalT-I and its biological function in the skin wound-healing process remain to be elucidated. We used real-time polymerase chain reaction to demonstrate that the expression of beta-1,4-GalT-I mRNA reached plateau values at 12 hours after skin was injured and remained elevated until 11 days after the injury. Furthermore, lectin blotting showed that beta-1,4-galactosylated carbohydrate chains were also increased after skin injury. A double-staining method combining lectin-fluorescent staining with RCA-I and immunofluorescence was first used to determine the cellular localization of beta-1,4-galactosylated carbohydrate chains. Morphological analysis showed that the chains were primarily expressed in neutrophils and partially expressed in macrophages, endothelial cells, and collagen. Our results suggest that beta-1,4-GalT-I and beta-1,4-galactosylated carbohydrate chains participate in leukocyte recruitment, angiogenesis, and collagen deposition in the skin wound-healing process.

Expression of beta-1,4-galactosyltransferase-I in rat during inflammation

beta-1,4-Galactosyltransferase-I (beta-1,4-GalT-I) which is one of the best-studied glycosyltransferases, plays a key role in the synthesis of selectin ligands such as sialy Lewis (sLe( x )) and sulfated sLe( x ). Previous studies showed that inflammatory responses of beta-1,4-GalT-I-deficient mice were impaired because of the defect in selectin-ligand biosynthesis. However, the expression of beta-1,4-GalT-I during inflammation and its biological function remains to be elucidated. Real-time PCR showed that intraperitoneal administration of LPS strongly induced beta-1,4-GalT-I mRNA expression in the lung, heart, liver, spleen, kidney, lymph node, hippocampus, and testis, as well as in the cerebral cortex. In the rat lung, liver and testis, LPS stimulation of beta-1,4-GalT-I mRNA expression is time-dependent and biphasic. Lectin-fluorescent staining with RCA-I showed that LPS induced expression of galactose-containing glycans in rat lung and liver to the higher lever. Morphology analysis observed that galactose-containing glycans and beta-1,4-GalT-I mRNA was mostly expressed in neutrophils, macrophages and endothelial cells. These findings indicated that beta-1,4-GalT-I may play an important role in the inflammation reaction.

Apoptosis and involution in the mammary gland are altered in mice lacking a novel receptor, beta1,4-Galactosyltransferase I

Receptor-mediated cell-extracellular matrix (ECM) interactions are critical regulators of cell survival, and perturbing these signaling pathways can disrupt cellular differentiation and function in a variety of tissues, including the mammary gland. One such receptor is the cell surface-associated, long isoform of beta1,4-galactosyltransferase I (GalT I). Deletion of long GalT I leads to increased mammary ductal branching morphogenesis [Dev. Biol., 244 (2002) 114]. Here, we show that this expansion in the mammary epithelial (ME) cell compartment is accomplished through decreased apoptosis during pregnancy and involution. Decreased apoptosis during involution is concomitant with delayed alveolar collapse, persistent expression of the milk protein gene alpha-lactalbumin and delayed expression of genes associated with the tissue-remodeling phase of involution. Using 3-dimensional in vitro cultures, we show that the decrease in apoptosis is dependent on laminin 1, a ligand for surface GalT I, suggesting that surface GalT I negatively influences ECM-dependent cell survival, a novel function for an ECM receptor. In the best-studied examples, ECM promotes survival through integrin receptor-mediated activation of focal adhesion kinase (FAK). Aggregation of surface GalT I also activates FAK, therefore, we asked if FAK activation was altered in ME from long GalT I null mice. Activated FAK was appropriately localized to focal adhesions in long GalT I null ME. However, FAK activation was constitutively reduced 4.5-fold in long GalT I nulls relative to wild type. Expression of the integrin beta1 subunit was not affected by loss of long GalT I. Collectively, these results suggest that surface GalT I might negatively regulate ME cell survival by linking integrin-independent FAK activation to apoptotic rather than survival signaling events.

Primordial germ cell migration in the rat: preliminary evidence for a role of galactosyltransferase

The precise cellular mechanism of primordial germ cell (PGC) migration remains unknown. Cell surface galactosyltransferase (GalTase) is known to play unique roles in the process of locomotion of many migratory cells. With an objective to seek evidence for possible involvement of GalTase in the migratory process of PGC, we evaluated germ cell migration in the rat following experimental modulation of embryonic GalTase activity. Pregnant rats were laparotomized under anesthesia on Day 10 of pregnancy. While embryos of one uterine horn received lysozyme (100 microg/fetus), those of the other received alpha-lactalbumin (LA; 100 microg/fetus), N-acetylglucosamine (GlcNAc; 250 nmole/fetus), uridine 5'-monophosphate (UMP; 2.5 micromole/fetus), uridine diphosphate-galactose (UDP-gal; 250 nmole/fetus), or a combination of 250 nmole of UDP-gal and 2.5 micromole of UMP/fetus. Between gestation Days 12 and 14, embryos were dissected out and processed for histochemical localization of PGC on the basis of binding of Dolichos biflorus agglutinin on the surface glycoconjugate of the germ cells. The number of PGC in each embryo was counted. There was a daywise increase in the number of PGC in all groups. As compared with lysozyme-exposed controls, the numbers of PGCs at the day-specific sites on all days of examination were significantly lower in the LA- as well as GlcNAc-exposed groups. UMP or UDP-gal individually exerted little or no influence, while the total PGC count rose significantly over the respective control values under simultaneous exposure to UMP and UDP-gal. The present findings suggest a likely catalytic role of GalTase in the process of germ cell migration.

Differential expression of two cell adhesion molecules, Ephrin-A5 and Integrin alpha6, during cranial neurulation in the chick embryo

The formation of the neural tube (neurulation) depends on the physical properties of the cells and tissues both inside and outside the neural plate. One such important physical property is cell adhesion. Theoretical and biological evidence support a role for cell adhesion in neurulation, but few specific cell adhesion molecules have been identified during this process. Ephrin-A5 and Integrin alpha6 are two of the known genes encoding cell adhesion molecules that are likely to be directly involved in neurulation because neural tube defects result when they are knocked out in mice. Yet it remains unclear how they can act on the cell and tissue behaviors of neurulation, because their domains of expression in neurulating tissues have not been reported. We report here the detailed pattern of expression of these two cell adhesion molecules in the chick embryo throughout the stages of neurulation at the mRNA and protein level. We show that Ephrin-A5 and Integrin alpha6 are differentially expressed in the ectoderm, outside and inside the neural plate, respectively, and that they are both restricted to neurulation at cranial (brain) levels. We discuss the potential contribution of this differential expression to the cell adhesion mechanisms involved in cranial neurulation and anencephaly.

Cell surface beta1,4-galactosyltransferase function in mammary gland morphogenesis: insights from transgenic and knockout mouse models

Development and morphogenesis are profoundly influenced by cell-cell and cell-extracellular matrix (ECM) interactions that are governed by cell surface receptor association with specific ligands. One such receptor is the long isoform of beta1,4-galactosyltransferase I (GalT I), a small proportion of which is targeted to the plasma membrane. Surface-expressed GalT I binds to specific glycoside residues on multiple extracellular ligands, and GalT I binding to specific ligands mediates cell-cell as well as cell-matrix interactions for a variety of cells, including mammary epithelia. Significant insight into surface GalT I function in mammary gland development and morphogenesis has been gained through the analysis of mouse transgenic and knockout models of surface GalT I misexpression. Overexpression of cell surface GalT I leads to impaired lactation as a result of reduced branching and differentiation and elevated apoptosis, while deleting surface GalT I enhances branching and differentiation and reduces apoptosis. These phenotypes can be attributed in large part to altered cell-ECM interactions. The current and future challenges are to use these mouse models to dissect the molecular mechanisms that govern surface GalT I function as a receptor in the normal mammary gland, as well as to assess the potential for surface GalT I misexpression to contribute to disease.

An immunohistochemical study of beta1,4-galactosyltransferase in human skin tissue

An immunohistochemical investigation of beta1,4-galactosyltransferase (beta1,4-GalT) on human skin tissue was performed on formalin-fixed paraffin-embedded sections using a monoclonal antibody, MAb8628, which specifically recognizes a protein moiety of human beta1,4-GalT. Distribution of the galactose beta1,4-N-acetylglucosamine (Gal beta1,4GlcNAc)-R epitope was also detected by staining with Ricinus communis agglutinin (RCA) 120. The beta1,4-GalT was observed to be localized at the perinuclear region of epidermal keratinocytes. The fine localization was also observed at the supranuclear region in the cells of apocrine glands, eccrine ducts and glands. The positive staining with RCA 120 was well colocalized with the cells expressing the beta1,4-GalT. An electron microscopic study revealed that positive signals of beta1,4-GalT definitely reside in the Golgi apparatus. No immunoreactivity was observed in any other intracellular structure or on the cell surface. These findings strongly indicated that the beta1,4-GalT is the major enzyme responsible for the Gal beta1,4GlcNAc-R epitope synthesis in human skin tissue.

TGFbeta2 and TGFbeta3 have separate and sequential activities during epithelial-mesenchymal cell transformation in the embryonic heart

Heart valve formation is initiated by an epithelial-mesenchymal cell transformation (EMT) of endothelial cells in the atrioventricular (AV) canal. Mesenchymal cells formed from cardiac EMTs are the initial cellular components of the cardiac cushions and progenitors of valvular and septal fibroblasts. It has been shown that transforming growth factor beta (TGFbeta) mediates EMT in the AV canal, and TGFbeta1 and 2 isoforms are expressed in the mouse heart while TGFbeta 2 and 3 are expressed in the avian heart. Depletion of TGFbeta3 in avian or TGFbeta2 in mouse leads to developmental defects of heart tissue. These observations raise questions as to whether multiple TGFbeta isoforms participate in valve formation. In this study, we examined the localization and function of TGFbeta2 and TGFbeta3 in the chick heart during EMT. TGFbeta2 was present in both endothelium and myocardium before and after EMT. TGFbeta2 antibody inhibited endothelial cell-cell separation. In contrast, TGFbeta3 was present only in the myocardium before EMT and was in the endothelium at the initiation of EMT. TGFbeta3 antibodies inhibited mesenchymal cell formation and migration into the underlying matrix. Both TGFbeta2 and 3 increased fibrillin 2 expression. However, only TGFbeta2 treatment increased cell surface beta-1,4-galactosyltransferase expression. These data suggest that TGFbeta2 and TGFbeta3 are sequentially and separately involved in the process of EMT. TGFbeta2 mediates initial endothelial cell-cell separation while TGFbeta3 is required for the cell morphological change that enables the migration of cells into the underlying ECM.

Epithelial-mesenchymal transformation in the embryonic heart is mediated through distinct pertussis toxin-sensitive and TGFbeta signal transduction mechanisms

During early development, progenitors of the heart valves and septa are formed by epithelial-mesenchymal transformation (EMT) of endothelial cells in the atrioventricular (AV) canal. Previously, we showed that pertussis toxin, a specific inhibitor of a subset of G proteins, inhibited EMT in chick AV canal cultures. This study examines in detail the effects of pertussis toxin on the process of EMT. One of the major mediators of EMT is Transforming Growth Factor beta 3 (TGFbeta3) which acts through the TGFbeta Type II receptor. To determine whether pertussis toxin affects EMT via the TGFbeta Type II receptor pathway, we compared AV cultures treated with pertussis toxin and TGFbeta Type II receptor blocking antibody. Pertussis toxin inhibited several elements of EMT. At all stages tested, pertussis toxin blocked endothelial cell-cell separation, cell hypertrophy, and the cellular polarization associated with endothelial activation. These activities were unaffected by TGFbeta Type II receptor antibodies. Pertussis toxin also reduced transformed mesenchymal cell migration by 61%. The expression patterns of several proteins (as markers of EMT) were analyzed in untreated, pertussis toxin-treated, and TGFbeta Type II receptor blocking antibody-treated cultures. These markers were alpha-smooth muscle actin, Mox-1, fibrillin 2, tenascin, cell surface beta 1,4 galactosyltransferase (GalTase), and integrin alpha6. Clear differences in marker expression were found between the two inhibitors. For example, in all cells, pertussis toxin inhibited expression of alpha-smooth muscle actin and GalTase while TGFbeta Type II receptor antibody treatment increased expression of these two proteins. These data suggest that G protein-mediated signaling is required for several elements of EMT. Furthermore, distinct G protein and TGFbeta signal transduction pathways mediate discrete components of EMT.

The chicken genome contains two functional nonallelic beta1,4-galactosyltransferase genes. Chromosomal assignment to syntenic regions tracks fate of the two gene lineages in the human genome

Two distinct but related groups of cDNA clones, CKbeta4GT-I and CKbeta4GT-II, have been isolated by screening a chicken hepatoma cDNA library with a bovine beta1,4-galactosyltransferase (beta4GT) cDNA clone. CKbeta4GT-I is predicted to encode a type II transmembrane glycoprotein of 41 kDa with one consensus site for N-linked glycosylation. CKbeta4GT-II is predicted to encode a type II transmembrane glycoprotein of 43 kDa with five potential N-linked glycosylation sites. At the amino acid level, the coding regions of CKbeta4GT-I and CKbeta4GT-II are 52% identical to each other and 62 and 49% identical, respectively, to bovine beta4GT. Despite this divergence in amino acid sequence, high levels of expression of each cDNA in Trichoplusia ni insect cells demonstrate that both CKbeta4GT-I and CKbeta4GT-II encode an alpha-lactalbumin-responsive, UDP-galactose:N-acetylglucosamine beta4-galactosyltransferase. An analysis of CKbeta4GT-I and CKbeta4GT-II genomic clones established that the intron positions within the coding region are conserved when compared with each other, and these positions are identical to the mouse and human beta4GT genes. Thus CKbeta4GT-I and CKbeta4GT-II are the result of the duplication of an ancestral gene and subsequent divergence. CKbeta4GT-I maps to chicken chromosome Z in a region of conserved synteny with the centromeric region of mouse chromosome 4 and human chromosome 9p, where beta4-galactosyltransferase (EC 2.4.1.38) had previously been mapped. Consequently, during the evolution of mammals, it is the CKbeta4GT-I gene lineage that has been recruited for the biosynthesis of lactose. CKbeta4GT-II maps to a region of chicken chromosome 8 that exhibits conserved synteny with human chromosome 1p. An inspection of the current human gene map of expressed sequence tags reveals that there is a gene noted to be highly similar to beta4GT located in this syntenic region on human chromosome 1p. Because both the CKbeta4GT-I and CKbeta4GT-II gene lineages are detectable in mammals, duplication of the ancestral beta4-galactosyltransferase gene occurred over 250 million years ago in an ancestral species common to both mammals and birds.

Mammary gland morphogenesis is inhibited in transgenic mice that overexpress cell surface beta1,4-galactosyltransferase

Mammary gland morphogenesis is facilitated by a precise sequence of cell-cell and cell-matrix interactions, which are mediated in part through a variety of cell surface receptors and their ligands (Boudreau, N., Myers, C. and Bissell, M. J. (1995). Trends in Cell Biology 5, 1–4). Cell surface beta1,4-galactosyltransferase (GalTase) is one receptor that participates in a variety of cell-cell and cell-matrix interactions during fertilization and development, including mammary epithelial cell-matrix interactions (Barcellos-Hoff, M. H. (1992). Exp. Cell Res. 201, 225–234). To analyze GalTase function during mammary gland morphogenesis in vivo, we created transgenic animals that overexpress the long isoform of GalTase under the control of a heterologous promoter. As expected, mammary epithelial cells from transgenic animals had 2.3 times more GalTase activity on their cell surface than did wild-type cells. Homozygous transgenic females from multiple independent lines failed to lactate, whereas transgenic mice overexpressing the Golgi-localized short isoform of GalTase lactated normally. Glands from transgenic females overexpressing surface GalTase were characterized by abnormal and reduced ductal development with a concomitant reduction in alveolar expansion during pregnancy. The phenotype was not due to a defect in proliferation, since the mitotic index for transgenic and wild-type glands was similar. Morphological changes were accompanied by a dramatic reduction in the expression of milk-specific proteins. Immunohistochemical markers for epithelia and myoepithelia demonstrated that both cell types were present. To better understand how overexpression of surface GalTase impairs ductal morphogenesis, primary mammary epithelial cultures were established on basement membranes. Cultures derived from transgenic mammary glands were unable to form anastomosing networks of epithelial cells and failed to express milk-specific proteins, unlike wild-type mammary cultures that formed epithelial tubules and expressed milk proteins. Our results suggest that cell surface GalTase is an important mediator of mammary cell interaction with the extracellular matrix. Furthermore, perturbing surface GalTase levels inhibits the expression of mammary-specific gene products, implicating GalTase as a component of a receptor-mediated signal transduction pathway required for normal mammary gland differentiation.

Immunocytochemical localization of the protein reactive to human beta-1, 4-galactosyltransferase antibodies during chick embryonic skin differentiation

BACKGROUND

beta-1, 4-Galactosyltransferase (GalTase) transfers galactose from UDP-galactose to terminal N-acetylglucosamine in glycoconjugates and is located both in the Golgi apparatus and in the plasma membrane. The cell surface GalTase is thought to be involved in cell-to-cell recognition and cell-to-extracellular matrix interaction.

METHODS

By the use of specific monoclonal antibodies against human GalTase, changes in cell surface localization of the protein reactive to the antibodies in chick embryonic skin during its differentiation in vivo and in vitro were detected immunohistochemically at both light- and electron microscopic levels. The distribution of glycoconjugates having terminal N-acetylglucosamine residues was detected by staining with succinylated wheat germ agglutinin (s-WGA).

RESULTS

Under the light microscope, intense immunostaining was observed in the keratinized epidermis, particularly in the intermediate layer. Marked changes in the localization of the staining were observed in vitamin A-induced mucus-secreting skin, in which keratinization was suppressed. The localization of the immunostaining was in parallel with that of glycoconjugates having terminal N-acetylglucosamine residues. Immunoelectron microscopically the immunostaining was located on the cell surface and in the intercellular space of the desmosomes in the intermediate cells of the keratinized epidermis. However, the staining was not present on the cell surface but was detected on the limiting membrane of the mucous granules, in the mucous metaplastic epidermis. In contrast, the staining was always found in the Golgi apparatus in all of the cells.

CONCLUSIONS

These results suggest that the protein reactive to human GalTase antibody may be involved in chick epidermal differentiation.

Overexpressing sperm surface beta 1,4-galactosyltransferase in transgenic mice affects multiple aspects of sperm-egg interactions

Sperm surface beta 1,4-galactosyltransferase (GalTase) mediates fertilization in mice by binding to specific O-linked oligosaccharide ligands on the egg coat glycoprotein ZP3. Before binding the egg, sperm GalTase is masked by epididymally derived glycosides that are shed from the sperm surface during capacitation. After binding the egg, sperm-bound oligosaccharides on ZP3 induce the acrosome reaction by receptor aggregation, presumably involving GalTase. In this study, we asked how increasing the levels of sperm surface GalTase would affect sperm-egg interactions using transgenic mice that overexpress GalTase under the control of a heterologous promoter. GalTase expression was elevated in many tissues in adult transgenic animals, including testis. Sperm from transgenic males had approximately six times the wild-type level of surface GalTase protein, which was localized appropriately on the sperm head as revealed by indirect immunofluorescence. As expected, sperm from transgenic mice bound more radiolabeled ZP3 than did wild-type sperm. However, sperm from transgenic animals were relatively unable to bind eggs, as compared to sperm from wild-type animals. The mechanistic basis for the reduced egg-binding ability of transgenic sperm was attributed to alterations in two GalTase-dependent events. First, transgenic sperm that overexpress surface GalTase bound more epididymal glycoside substrates than did sperm from wild-type mice, thus masking GalTase and preventing it from interacting with its zona pellucida ligand. Second, those sperm from transgenic mice that were able to bind the zona pellucida were hypersensitive to ZP3, such that they underwent precocious acrosome reactions and bound to eggs more tenuously than did wild-type sperm. These results demonstrate that sperm-egg binding requires an optimal, rather than maximal, level of surface GalTase expression, since increasing this level decreases sperm reproductive efficiency both before and after egg binding. Although sperm GalTase is required for fertilization by serving as a receptor for the egg zona pellucida, excess surface GalTase is counterproductive to successful sperm-egg binding.

Dual function of macrophage galactose/N-acetylgalactosamine-specific lectins: glycoprotein uptake and tumoricidal cellular recognition

We investigated whether the interaction of peritoneal macrophages with extracellular ligands is mediated by C-type lectins specific for galactose and N-acetylgalactosamine. The carbohydrate-binding domain of mouse galactose/N-acetylgalactosamine-specific lectin was prepared in a recombinant form. The purified recombinant lectins were tested for competitive inhibition against glycoprotein uptake and against tumoricidal effect. Thioglycolate-elicited macrophages internalized galactosylated bovine serum albumin in vitro. The internalization was blocked by recombinant macrophage lectins. Activated macrophages obtained after intraperitoneal injection of a nonspecific immune potentiator, OK432, did not internalize galactosylated bovine serum albumin. These cells elicited a cytotoxic effect against P815 murine mastocytoma cells, and the effect was blocked by recombinant macrophage lectins. These results indicated that galactose/N-acetylgalactosamine-specific C-type lectins expressed on the surface of inflammatory macrophages and on activated tumoricidal macrophages mediate two distinct functions, i.e. glycoprotein uptake and tumoricidal effector mechanisms.

Rat olfactory neurons can utilize the endogenous lectin, L-14, in a novel adhesion mechanism

L-14 is a divalent, lactosamine-binding lectin expressed in many vertebrate tissues. In the rat nervous system, L-14 expression has been observed previously in restricted neuronal subsets within the dorsal root ganglia and spinal cord. In this study we report that L-14 is expressed by nonneuronal cells in the rat olfactory nerve. We demonstrate that L-14 binds and co-localizes with two ligands in the rat olfactory system: a beta-lactosamine-containing glycolipid, and a putative member of the laminin family. The former is expressed on the surfaces of nascent olfactory axons originating from neuron cell bodies in the olfactory epithelium. The latter is present in the extracellular matrix of the axonal path leading to synaptic targets in the olfactory bulb. In vitro, we find that recombinant L-14 promotes primary olfactory neuron adhesion to two laminin family members, and promotes intercellular adhesion. Both activities are dose-dependent, and are independent of integrin-mediated mechanisms. We have thus found that L-14 can serve two distinct adhesive functions in vitro, and propose that L-14 in vivo can promote olfactory axon fasciculation by crosslinking adjacent axons and promote axonal adhesion to the extracellular matrix.

Adhesion molecules in neural crest development

Peripheral nerve cells, various endocrine and pigment cells and cranial connective tissue cells of vertebrates stem mainly from the embryonic neural crest. This originates with the central nervous system, but the crest cells detach from this tissue, via a decrease of cell-cell adhesion involving, particularly, a reduction of the adherens junction cell adhesive molecule A-CAM. This epithelio-mesenchymal transformation allows crest cells to migrate along pathways that are defined partly by the distribution of substrate adhesion molecules, the archetype being fibronectin, an extracellular matrix molecule recognized by integrin receptors on crest cells. Many other molecules, however, may act in the same way. In contrast, some molecules may define migration pathways by reducing adhesion; chondroitin sulfate proteoglycan is a candidate for this role. Pathway selection is most likely achieved by balanced combinations of molecules that promote and reduce adhesion. Cessation of migration, in the case of the nervous ganglia, correlated with re-expression of cell-cell adhesion molecules like A-CAM and others, consistent with an adhesive basis, although functional tests have not yet been performed. The development of the neural crest system provides a useful model that emphasizes the role of adhesion in morphogenesis.

Adhesion molecules of the nervous system

The structural and functional characterization of neural cell-cell adhesion molecules continues to progress at a rapid rate, exposing the complex nature of these large multidomain receptors and their intricate relationship with the cell. Over the past year, significant progress has been made in the description of multiple binding activities, signaling potentials, and cytoplasmic associations of cell-cell adhesion molecules. In addition, new modes for developmental regulation of adhesion molecule function have been identified.

Mechanisms of neural crest cell migration

Neural crest cells are remarkable in their extensive and stereotypic patterns of migration. The pathways of neural crest migration have been documented by cell marking techniques, including interspecific neural tube grafts, immunocytochemistry and DiI-labelling. In the trunk, neural crest cells migrate dorsally under the skin or ventrally through the somites, where they move in a segmental fashion through the rostral half of each sclerotome. The segmental migration of neural crest cells appears to be prescribed by the somites, perhaps by an inhibitory cue from the caudal half. Within the rostral sclerotome, neural crest cells fill the available space except for a region around the notochord, suggesting the notochord may inhibit neural crest cells in its vicinity. In the cranial region, antibody perturbation experiments suggest that multiple cell-matrix interactions are required for proper in vivo migration of neural crest cells. Neural crest cells utilize integrin receptors to bind to a number of extracellular matrix molecules. Substrate selective inhibition of neural crest cell attachment in vitro by integrin antibodies and antisense oligonucleotides has demonstrated that they possess at least three integrins, one being an alpha 1 beta 1 integrin which functions in the absence of divalent cations. Thus, neural crest cells utilize complex sets of interactions which may differ at different axial levels.

Dominant negative mutation in cell surface beta 1,4-galactosyltransferase inhibits cell-cell and cell-matrix interactions

In addition to its traditional location within the Golgi complex, beta 1,4-galactosyltransferase (GalTase) is also present on the cell surface, where it is thought to function as a cell adhesion molecule by binding to extracellular oligosaccharide ligands. Recent studies suggest that cells contain two forms of GalTase with distinct cytoplasmic domains. The longer form of GalTase contains a 13-amino acid cytoplasmic extension and is preferentially targeted to the plasma membrane, relative to the shorter GalTase protein that is confined primarily to the Golgi compartment. In this study, we created a dominant negative mutation that interferes with the function of cell surface GalTase by transfecting into cells cDNAs encoding truncated versions of the long form of GalTase containing the complete cytoplasmic and transmembrane domains, but devoid of the catalytic domain. In both F9 embryonal carcinoma cells and Swiss 3T3 fibroblasts, overexpressing the truncated long GalTase (TLGT) protein displaced the endogenous cell surface GalTase from its association with the cytoskeleton, resulting in a loss of intercellular adhesion and cell spreading specifically on matrices that use GalTase as a cell surface receptor. In contrast, overexpressing the analogous truncated short GalTase (TSGT) protein did not affect cell morphology or GalTase activity. In control assays, inducing the TLGT protein had no effect on cell interactions with fibronectin (which is independent of GalTase), or on the cytoskeleton attachment of another matrix receptor (beta 1 integrin), or on overall glycoprotein synthesis, thus eliminating nonspecific effects of the TLGT protein on cellular adhesion and metabolism. These results represent the first molecular manipulation of cell surface GalTase expression and confirm its function as a cell adhesion molecule. These studies further suggest that the cytoskeleton contains a defined, saturable number of binding sites for GalTase, which enables it to function as an adhesion molecule.