Characterization of the 5'-flanking fragment of the human GM3-synthase gene

Magnetic Particles: Their Applications from Sample Preparations to Biosensing Platforms

The growing interest in magnetic materials as a universal tool has been shown by an increasing number of scientific publications regarding magnetic materials and its various applications. Substantial progress has been recently made on the synthesis of magnetic iron oxide particles in terms of size, chemical composition, and surface chemistry. In addition, surface layers of polymers, silica, biomolecules, etc., on magnetic particles, can be modified to obtain affinity to target molecules. The developed magnetic iron oxide particles have been significantly utilized for diagnostic applications, such as sample preparations and biosensing platforms, leading to the selectivity and sensitivity against target molecules and the ease of use in the sensing systems. For the process of sample preparations, the magnetic particles do assist in target isolation from biological environments, having non-specific molecules and undesired molecules. Moreover, the magnetic particles can be easily applied for various methods of biosensing devices, such as optical, electrochemical, and magnetic phenomena-based methods, and also any methods combined with microfluidic systems. Here we review the utilization of magnetic materials in the isolation/preconcentration of various molecules and cells, and their use in various techniques for diagnostic biosensors that may greatly contribute to future innovation in point-of-care and high-throughput automation systems.

Identification and Functional Characterization of ST3GAL5 and ST8SIA1 Variants in Patients with Thyroid-Associated Ophthalmopathy

PURPOSE

This study was conducted to identify and to functionally characterize genetic variants in ST3GAL5 and ST8SIA1 in Korean patients with thyroid-associated ophthalmopathy (TAO).

MATERIALS AND METHODS

Genetic analyses were conducted using DNA samples from TAO patients (n=50) and healthy subjects (n=48) to identify TAO-specific genetic variants of ST3GAL5 or ST8SIA1. The effect of each genetic variant on the transcription or expression of these genes was examined. Additionally, correlations between functional haplotypes of ST3GAL5 or ST8SIA1 and clinical characteristics of the patients were investigated.

RESULTS

Six promoter variants and one nonsynonymous variant of ST3GAL5 were identified, and four major promoter haplotypes were assembled. Additionally, three promoter variants and two major haplotypes of ST8SIA1 were identified. All ST3GAL5 and ST8SIA1 variants identified in TAO patients were also found in healthy controls. Promoter activity was significantly decreased in three promoter haplotypes of ST3GAL5 and increased in one promoter haplotype of ST8SIA1. Transcription factors activating protein-1, NKX3.1, and specificity protein 1 were revealed as having roles in transcriptional regulation of these haplotypes. The nonsynonymous variant of ST3GAL5, H104R, did not alter the expression of ST3GAL5. While no differences in clinical characteristics were detected in patients possessing the functional promoter haplotypes of ST3GAL5, exophthalmic values were significantly lower in patients with the ST8SIA1 haplotype, which showed a significant increase in promoter activity.

CONCLUSION

These results from genotype-phenotype analysis might suggest a possible link between the ST8SIA1 functional promoter haplotype and the clinical severity of TAO. However, further studies with larger sample sizes are warranted.

PUGNAc treatment provokes globotetraosylceramide accumulation in human umbilical vein endothelial cells

PUGNAc is a well-investigated inhibitor for protein-O-GlcNAcase, whereas recent investigations showed that PUGNAc had a broad range as inhibitor for cellular β-hexosaminidases. Here we report that PUGNAc treatment provokes globotetraosylceramide (Gb4Cer) accumulation in human umbilical vein endothelial cells (HUVEC). HPLC analysis and a quantitative ELISA using newly developed anti-Gb4Cer monoclonal antibody revealed that PUGNAc treatment specifically increased the expression of Gb4Cer among glycosphingolipids expressed in HUVEC. Although the effect was weaker than PUGNAc, an O-GlcNAcase selective inhibitor (Thiamet-G) treatment also increased Gb4Cer levels in HUVEC. Furthermore, both of PUGNAc and Thiamet-G treatment up-regulated the expression levels of α-1,4-galactosyltransferase/Gb3Cer synthase gene which encodes a key enzyme in Gb4Cer synthesis. These results indicate that protein-O-GlcNAcylation can regulate the expression levels of cellular Gb4Cer.

Functional roles of gangliosides in neurodevelopment: an overview of recent advances

Gangliosides are sialic acid-containing glycosphingolipids that are most abundant in the nervous system. They are localized primarily in the outer leaflets of plasma membranes and participated in cell-cell recognition, adhesion, and signal transduction and are integral components of cell surface microdomains or lipid rafts along with proteins, sphingomyelin and cholesterol. Ganglioside-rich lipid rafts play an important role in signaling events affecting neural development and the pathogenesis of certain diseases. Disruption of gangloside synthase genes in mice induces developmental defects and neural degeneration. Targeting ganglioside metabolism may represent a novel therapeutic strategy for intervention in certain diseases. In this review, we focus on recent advances on metabolic and functional studies of gangliosides in normal brain development and in certain neurological disorders.

Ganglioside GM3 and its biological functions

Metabolism, topology, and possible mechanisms for regulation of the ganglioside GM3 content in the cell are reviewed. Under consideration are biological functions of GM3, such as involvement in cell differentiation, proliferation, oncogenesis, and apoptosis.

The cytoplasmic tail of GM3 synthase defines its subcellular localization, stability, and in vivo activity

GM3 synthase (SAT-I) is the primary glycosyltransferase responsible for the biosynthesis of ganglio-series gangliosides. In this study, we identify three isoforms of mouse SAT-I proteins, named M1-SAT-I, M2-SAT-I, and M3-SAT-I, which possess distinct lengths in their NH(2)-terminal cytoplasmic tails. These isoforms are produced by leaky scanning from mRNA variants of mSAT-Ia and mSAT-Ib. M2-SAT-I and M3-SAT-I were found to be localized in the Golgi apparatus, as expected, whereas M1-SAT-I was exclusively found in the endoplasmic reticulum (ER). Specific multiple arginines (R) arranged in an R-based motif, RRXXXXR necessary for ER targeting, were found in the cytoplasmic tail of M1-SAT-I, and in vivo GM3 biosynthesis by M1-SAT-I was very low because of restricted transport to the Golgi apparatus. In addition, M1-SAT-I and M3-SAT-I had a long half-life relative to M2-SAT-I. This is the first report demonstrating the presence of an ER-targeting R-based motif in the cytoplasmic tail of a protein in the mammalian glycosyltransferase family of enzymes. The system, which produces SAT-I isoforms having distinct characteristics, is likely to be of critical importance for the regulation of GM3 biosynthesis under various pathological and physiological conditions.

Identification and characterization of the human Gb3/CD77 synthase gene promoter

Hemolytic uremic syndrome (HUS) is triggered by verotoxin (VT) produced by the Escherichia coli O157 strain. Several studies have demonstrated that VT induces endothelial cell (EC) death via the VT receptor globotriaosylceramide (Gb3/CD77) leading to this symptom. Inflammatory mediators which are produced as a result of E. coli O157 infection, increase the expression level of Gb3 in EC. Therefore increased expression of Gb3 is considered as a progression step for HUS. The increased expression of Gb3 is due to the transcriptional upregulation of Gb3/CD77 synthase gene (Gb3S, also known as alpha1,4-galactosyltransferase gene), the mechanism of which still remains unknown. To understand the transcriptional machinery and to elucidate the onset mechanism of HUS, we cloned and characterized the human Gb3S promoter. A modified 5'-RACE was used to determine the transcriptional initiation site, which revealed the presence of a TATA-less GC-rich sequence in the proximal region. Promoter activity measured using a luciferase assay demonstrated that the GC-rich sequence is necessary for the basal transcriptional activity, and two silencer elements located 5'-upstream of this GC-rich region regulated the transcriptional level. Furthermore, we found that the GC-rich sequence contained three potential Sp1 binding sites and that all three Sp1 binding elements acted as positive regulators. Since Sp1 is an inducer of several genes in the presence of the inflammatory cytokines in EC, our results suggest that the transcriptional regulation of the Gb3S gene by Sp1 might affect the VT sensitivity of EC and HUS progression.

Cloning and transcriptional regulation of genes responsible for synthesis of gangliosides

Ganglioside synthases are glycosyltransferases involved in the biosynthesis of glycoconjugates. A number of ganglioside synthase genes have been cloned and characterized. They are classified into different families of glycosyltransferases based on similarities of their amino acid sequences. Tissue-specific expression of these genes has been analyzed by hybridization using cDNA fragments. Enzymatic characterization with the expressed recombinant enzymes showed these enzymes differ in their donor and acceptor substrate specificities and other biochemical parameters. In vitro enzymatic analysis also showed that one linkage can be synthesized by multiple enzymes and one enzyme may be responsible for synthesis of multiple gangliosides. Following the cloning of the ganglioside synthase genes, the promoters of the key synthase genes in the ganglioside biosynthetic pathway have been cloned and analyzed. All of the promoters are TATA-less, lacking a CCAAT box but containing GC-rich boxes, characteristic of the house-keeping genes, although transcription of ganglioside synthase genes is subject to complex developmental and tissue-specific regulation. A set of cis-acting elements and transcription factors, including Sp1, AP2, and CREB, function in the proximal promoters. Negative-regulatory regions have also been defined in most of the promoters. We present here an overview of these genes and their transcriptional regulation.

Bcl-2 overexpression in PhIP-induced colon tumors: cloning of the rat Bcl-2 promoter and characterization of a pathway involving beta-catenin, c-Myc and E2F1

Beta-catenin/T-cell factor (Tcf) signaling is constitutively active in the majority of human colorectal cancers, and there are accompanying changes in Bcl-2 expression. Similarly, 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP)-induced colon tumors in the rat have increased beta-catenin and elevated Bcl-2. To examine the possible direct transcriptional regulation of rat Bcl-2 by beta-catenin/Tcf, we cloned and characterized the corresponding promoter region and found 70.1% similarity with its human counterpart, BCL2. Bcl-2 promoter activity was increased in response to LiCl and exogenous beta-catenin, including oncogenic mutants of beta-catenin found in PhIP-induced colon tumors. Protein/DNA arrays identified E2F1, but not beta-catenin/Tcf, as interacting most strongly with the rat Bcl-2 promoter. Exogenous E2F1 increased the promoter activity of rat Bcl-2, except in mutants lacking the E2F1 sites. As expected, beta-catenin induced its downstream target c-Myc, as well as E2F1 and Bcl-2, and this was blocked by siRNA to c-Myc or E2F1. These findings suggest an indirect pathway for Bcl-2 over-expression in PhIP-induced colon tumors involving beta-catenin, c-Myc and E2F1.

Selective alterations of transcription factors in MPP+-induced neurotoxicity in PC12 cells

MPP(+) (1-methyl-4-phenylpyridinium; the active metabolite of the neurotoxin MPTP (1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine)) depletes dopamine (DA) content and elicits cell death in PC12 cells. However, the mechanism of MPP(+)-induced neurotoxicity is still unclear. In this study, the dose response and time-course of MPP(+)-induced DA depletion and decreased cell viability were determined in nerve growth factor (NGF)-differentiated PC12 cells. The alteration of transcription factors (TFs) induced by MPP(+) from a selected dose level and time point was then evaluated using protein/DNA-binding arrays. K-means clustering analysis identified four patterns of protein/DNA-binding changes. Three of the 28 TFs identified in PC12 cells increased by 100% (p53, PRE, Smad SBE) and 2 decreased by 50% (HSE, RXR(DR1)) of control with MPP(+) treatment. In addition, three TFs decreased within the range of 33-50% (TFIID, E2F1, CREB) and two TFs increased within the range of 50-100% (PAX-5, Stat4). An electrophoretic mobility shift assay (EMSA) was used to confirm the changes of p53 and HSE. The observed changes in TFs correlated with the alterations of DA and cell viability. The data indicates that selective transcription factors are involved in MPP(+)-induced neurotoxicity and it provides mechanistic information that may be applicable to animal studies with MPTP and clinical studies of Parkinson's disease.

Sp1 and AP2 enhance promoter activity of the mouse GM3-synthase gene

Promoters of the glycosyltransferase genes for ganglioside synthesis are TATA-less and often have multiple binding sites for transcription factors Sp1 and AP2 in their proximal regions. However, the function of Sp1 and AP2 in the promoters has not yet been defined. Here, we cloned 5'-flanking fragments of the mouse GM3-synthase gene and assessed the promoter activity of these fragments in mouse Neuro-2a cells. This promoter is TATA-less and contains a number of potential transcription factor-binding sites. Multiple putative transcriptional initiation sites for this gene were identified, including several downstream initiation sites. We then set out to dissect the regulatory elements important for GM3-synthase promoter function. We found that a 5'-flanking 254-bp DNA fragment of the gene contained regulatory elements including two Sp1-binding and six AP2-binding sites that were essential for the basal activity of the promoter in mouse Neuro-2a cells. The effects of the individual Sp1- and AP2-binding sites on basal activity of the GM3-synthase gene were investigated. Mutations in the juxtaposed Sp1/AP2-binding site and in an AP2-binding site decreased the activity of the proximal promoter to approximately 50%. In vitro and in vivo interactions between transcription factors Sp1 and AP2 and these regulatory elements were confirmed by EMSA and the chromatin immunoprecipitation approach, respectively. Therefore, our results demonstrate that Sp1 and AP2 enhance the basal activity of the TATA-less mouse GM3-synthase promoter.

Regulation of ganglioside biosynthesis in the nervous system

Ganglioside biosynthesis is strictly regulated by the activities of glycosyltransferases and is necessarily controlled at the levels of gene transcription and posttranslational modification. Cells can switch between expressing simple and complex gangliosides or between different series within these two groups during brain development. The sequential biosynthesis of gangliosides in parallel enzymatic pathways, however, requires fine-tuned subcellular sequestration and orchestration of glycosyltransferases. A popular model predicts that this regulation is achieved by the vectorial organization of ganglioside biosynthesis: sequential biosynthetic steps occur with the traffic of ganglioside intermediates through subsequent subcellular compartments. Here, we review current models for the subcellular distribution of glycosyltransferases and discuss results that suggest a critical role of N-glycosylation for the processing, transport, and complex formation of these enzymes. In this context, we attempt to illustrate the regulation of ganglioside biosynthesis as well as the biological significance of N-glycosylation as a posttranslational regulatory mechanism. We also review the results of analyses of the 5' regulatory sequences of several glycosyltransferases in ganglioside biosynthesis and provide insights into how their synthesis can be regulated at the level of transcription.

Involvement of gangliosides in glucosamine-induced proliferation decrease of retinal pericytes

The hexosamine pathway (HP) is a biochemical hypothesis recently proposed explaining cellular alterations occurring during diabetic microvascular complications. Diabetic retinopathy is a common microvascular complication of diabetes, and it is known that cell proliferation is severely affected during the development of the disease. Particularly, early stages are characterized by death of the retinal microvascular cells, pericytes. Gangliosides have often been described to regulate cell growth; however, very few studies focused on the potential role of gangliosides in diabetic microvascular alterations. The aim of this article was to investigate the effect of the HP activation on pericyte proliferation and determine the potential implication of gangliosides in this process. Results indicate first that HP activation, mimicked by glucosamine treatment, decreased pericyte proliferation. Second, glucosamine treatment induced a modification of gangliosides pattern, particularly GM1 and GD3 were significantly increased. Next, results showed that exogenous addition of a-series gangliosides (GM3, GM2, GM1, GD1a) and b-series ganglioside (GD3) caused a decrease of pericyte proliferation, whereas nonsialylated precursors glucosylceramide and lactosylceramide were without effect. Furthermore, when ganglioside biosynthesis was blocked using PPMP, a glucosylceramide synthase inhibitor, the effects of glucosamine on pericyte proliferation were partially reversed. Our results suggest that in retinal pericytes, gangliosides and particularly GM1 and GD3 that are increased in response to glucosamine, are involved in the antiproliferative effect of glucosamine. These observations also underlie the potential involvement of gangliosides in a pathological context, such as diabetic microvascular complications.

CD44 modulates Smad1 activation in the BMP-7 signaling pathway

Bone morphogenetic protein 7 (BMP-7) regulates cellular metabolism in embryonic and adult tissues. Signal transduction occurs through the activation of intracellular Smad proteins. In this paper, using a yeast two-hybrid screen, Smad1 was found to interact with the cytoplasmic domain of CD44, a receptor for the extracellular matrix macromolecule hyaluronan. Coimmunoprecipitation experiments confirmed the interaction of Smad1 with full-length CD44—interactions that did not occur when CD44 receptors truncated within the cytoplasmic domain were tested. Chondrocytes overexpressing a truncated CD44 on a background of endogenous full-length CD44 no longer exhibited Smad1 nuclear translocation upon BMP-7 stimulation. Further, pretreatment of chondrocytes with Streptomyces hyaluronidase to disrupt extracellular hyaluronan–cell interactions inhibited BMP-7–mediated Smad1 phosphorylation, nuclear translocation of Smad1 or Smad4, and SBE4–luciferase reporter activation. These results support a functional link between the BMP signaling cascade and CD44. Thus, changes in hyaluronan–cell interactions may serve as a means to modulate cellular responsiveness to BMP.

Magnetic techniques for the isolation and purification of proteins and peptides

Isolation and separation of specific molecules is used in almost all areas of biosciences and biotechnology. Diverse procedures can be used to achieve this goal. Recently, increased attention has been paid to the development and application of magnetic separation techniques, which employ small magnetic particles. The purpose of this review paper is to summarize various methodologies, strategies and materials which can be used for the isolation and purification of target proteins and peptides with the help of magnetic field. An extensive list of realised purification procedures documents the efficiency of magnetic separation techniques.

Cloning of the rat beta-catenin gene (Ctnnb1) promoter and its functional analysis compared with the Catnb and CTNNB1 promoters

Considerable recent interest has focused on the stabilization and accumulation of beta-catenin protein in human and animal tumors and the corresponding activation of downstream beta-catenin/TCF/LEF target genes. However, there is only sparse information on the regulation of beta-catenin expression at the transcriptional level and its possible involvement in physiological and pathophysiological processes. We report here the cloning and characterization of a 3.6-kb promoter fragment from the rat beta-catenin gene, Ctnnb1, and its comparison with corresponding promoters from the mouse and human genes, Catnb and CTNNB1. Several AP1 binding sites were confirmed in the promoters of all three species using mobility shift and reporter assays, and one putative TCF/LEF site also was observed in the promoter of CTNNB1. Subsequently, protein/DNA array analyses identified numerous other transcription factors through their high-affinity binding to the Ctnnb1 promoter, including E2F1, NFkappaB, MEF1, Pax5, ISRE2, Smad3/4, GATA, and ZIC. The strong binding of E2F1 and NFkappaB is especially noteworthy, because the former transcription factor is regulated by cyclin D1, a downstream target of beta-catenin/TCF/LEF signaling, whereas the latter transcription factor has been implicated in "cross talk" between the Wnt and the NFkappaB signaling pathways. These results are discussed in terms of their implications for human cancer development and specifically the various tumors in which beta-catenin mRNA is overexpressed, as well as for embryonic development, when reversible changes in beta-catenin expression occur in response to secreted Wnt ligands. The findings reported here should provide important avenues for further research focused on the regulation of Ctnnb1 activity, including the ability of beta-catenin/Tcf downstream targets to modulate beta-catenin expression at the transcriptional level.

Transcriptional regulation of the human GM3 synthase (hST3Gal V) gene during monocytic differentiation of HL-60 cells

We studied the transcriptional regulation of human GM3 synthase (hST3Gal V) during monocytic differentiation of HL-60 cells induced by 12-O-tetradecanoylphorbol-13-acetate (TPA). Northern blot and reverse transcription polymerase chain reaction indicated that the induction of hST3Gal V by TPA is regulated at the transcriptional level. To elucidate the mechanism underlying the regulation of hST3Gal V gene expression during the differentiation of HL-60 cells induced by TPA, we characterized the promoter region of the hST3Gal V gene. Functional analysis of the 5'-flanking region of the hST3Gal V gene by the transient expression method showed that the -177 to -83 region, which contains a cAMP responsive element binding protein (CREB) binding site at -143, functions as the TPA-inducible promoter in HL-60 cells. In addition, gel shift assays and site-directed mutagenesis indicated that the CREB binding site at -143 is crucial for the TPA-induced expression of the hST3Gal V in HL-60 cells.

Involvement of CREB in the transcriptional regulation of the human GM3 synthase (hST3Gal V) gene during megakaryocytoid differentiation of human leukemia K562 cells

We studied the transcriptional regulation of human GM3 synthase (hST3Gal V) during megakaryocytic differentiation of K562 cells induced by PMA. Northern blot and reverse transcription polymerase chain reaction (RT-PCR) indicated that the induction of hST3Gal V by phorbol 12-myristate 13-acetate (PMA) is regulated at transcriptional level. To elucidate the mechanism underlying the regulation of the hST3Gal V gene expression during the differentiation of K562 cells induced by PMA, we characterized the promoter region of the hST3Gal V gene. Functional analysis of the 5(')-flanking region of the hST3Gal V gene by transient expression method showed that the -177 to -83 region, which contains a CREB binding site at -143, functions as the PMA-inducible promoter in K562 cells. In addition, gel shift assay and site-directed mutagenesis indicated that the CREB binding site at -143 is crucial for the PMA-induced expression of the hST3Gal V in K562 cells.