A combined NMR, MD and DFT conformational analysis of 9-O-acetyl sialic acid-containing GM3 ganglioside glycan and its 9-N-acetyl mimic.

O-Acetylation of carbohydrates such as sialic acids is common in nature, but its role is not clearly understood due to the lability of O-acetyl groups. We demonstrated previously that 9-acetamido-9-deoxy-N-acetylneuraminic acid (Neu5Ac9NAc) is a chemically and biologically stable mimic of the 9-O-acetyl-N-acetylneuraminic acid (Neu5,9Ac2) of the corresponding sialoglycans. Here, a systematic nuclear magnetic resonance (NMR) spectroscopic and molecular dynamics (MD) simulation study was undertaken for Neu5,9Ac2-containing GM3 ganglioside glycan (GM3-glycan) and its Neu5Ac9NAc analog. GM3-glycan with Neu5Ac as the non-O-acetyl form of Neu5,9Ac2 was used as a control. Complete 1H and 13C NMR chemical shift assignments, three-bond 1H-13C trans-glycosidic coupling constants (3JCH), accurate 1H-1H coupling constants (3JHH), nuclear Overhauser effects and hydrogen bonding detection were carried out. Results show that structural modification (O- or N-acetylation) on the C-9 of Neu5Ac in GM3 glycan does not cause significant conformational changes on either its glycosidic dihedral angles or its secondary structure. All structural differences are confined to the Neu5Ac glycerol chain, and minor temperature-dependent changes are seen in the aglycone portion. We also used Density Functional Theory (DFT) quantum mechanical calculations to improve currently used 3JHH Karplus relations. Furthermore, OH chemical shifts were assigned at -10°C and no evidence of an intramolecular hydrogen bond was observed. The results provide additional evidence regarding structural similarities between sialosides containing 9-N-acetylated and 9-O-acetylated Neu5Ac and support the opportunity of using 9-N-acetylated Neu5Ac as a stable mimic to study the biochemical role of 9-O-acetylated Neu5Ac.

Assay Development and Screening for the Identification of Ganglioside GM3 Synthase Inhibitors.

Ganglioside GM3 is a sialylated membrane-based glycosphingolipid that regulates insulin receptor signaling via direct association with the receptor. The level of expression of GM3 synthase (GM3S) and GM3 is increased in tissues of patients with diabetes and murine models of diabetes, and obesity-induced insulin resistance is attenuated in GM3S-deficient mice. Therefore, GM3S has been considered a therapeutic target for type II diabetes; however, no GM3S inhibitors have been reported to date. In this study, we established a high-throughput scintillation proximity assay that can detect GM3S activity to screen GM3S inhibitors from our original chemical library. We also established methods for detecting the activity of GM3S and another sialyltransferase, ST3Gal3, through direct measurement of the enzyme products using an automatic rapid solid-phase extraction system directly coupled to a mass spectrometer. Consequently, we successfully identified two different chemotypes of GM3S-selective inhibitors with a mixed mode of inhibition. We believe that these compounds can be further developed into drugs to treat or prevent diabetes as well as contribute to the development of the ganglioside research field.

Deficient ganglioside synthesis restores responsiveness to leptin and melanocortin signaling in obese KKAy mice.

GM3, a precursor for synthesis of a- and b-series gangliosides, is elevated in adipocytes of obese model animals and in sera of obese human patients with type 2 diabetes and/or dyslipidemia. GM3 synthase (GM3S)-KO C57BL/6 mice display enhanced insulin sensitivity and reduced development of high-fat diet-induced insulin resistance. However, the pathophysiological roles of GM3 and related gangliosides in the central control of feeding and metabolism remain unclear. We found that a mouse model (KKAy GM3S KO) generated by KO of the GM3S gene in the yellow obese strain, KKAy, displayed significant amelioration of obese phenotype. Whereas KKAy mice were hyperphagic and developed severe obesity, KKAy GM3S KO mice had significantly lower body weight and food intake, and greater glucose and insulin tolerance. The hypothalamic response to intraperitoneal administration of leptin was greatly reduced in KKAy mice, but was retained in KKAy GM3S KO mice. In studies of a cultured mouse hypothalamic neuronal cell line, enhanced leptin-dependent phosphorylation of ERK was observed in GM3S-deficient cells. Furthermore, KKAy GM3S KO mice did show altered coat color, suggesting that GM3S is also involved in melanocortin signaling. Our findings, taken together, indicate that GM3-related gangliosides play key roles in leptin and melanocortin signaling.

Identification of a new liver-specific c-type mRNA transcriptional variant for mouse ST3GAL5 (GM3/GM4 synthase).

GM3, a major lipid component of the plasma membrane outer leaflet in mammalian cells, is synthesized in the luminal side of Golgi by ST3GAL5 protein (ST3G5), a type II membrane protein. Two strains of St3Gal5 knockout mice have been established for studies of GM3 physiological function: St3Gal5-Ex5-KO (lacking exon 5, which contains the catalytic domain of ST3G5), and St3Gal5-Ex3-KO (lacking exon 3, which contains the initiation codons). Results of the present study demonstrate that GM3 synthesis is still present, at a low level, in liver of St3Gal5-Ex3-KO mice. St3Gal5 has two mRNA transcriptional variants: a-type and b-type. When exon 3 is deleted, ST3G5 is not translated from a-type or b-type, as a result of initiation codon deletion or frame shift. Through NCBI database search and real-time PCR analyses of various mouse tissues, we identified a liver-specific St3Gal5 transcriptional variant (c-type) capable of producing artificial ST3G5 (M*-ST3G5) having GM3 synthase activity in the absence of exon 3. St3Gal5-Ex3-KO mice expressed c-type mRNA without exon 3 (c-type-/-) in liver. The transmembrane and catalytic domains of M*-ST3G5 translated from c-type-/- were identical to those from wild-type, although the cytoplasmic regions differed. Expression of M*-ST3G5 in embryonic fibroblasts derived from St3Gal5-Ex3-KO mice led to GM3 synthesis; M*-ST3G5 thus displayed enzyme activity in vivo. Taken together, our findings indicate that expression of liver-specific c-type variant accounts for the residual GM3 synthase activity observed in liver of St3Gal5-Ex3-KO mice.

Induction of Glycosphingolipid GM3 Expression by Valproic Acid Suppresses Cancer Cell Growth.

Glycosphingolipid GM3, a known suppressor of epidermal growth factor receptor (EGFR) phosphorylation, inhibits cell proliferation. Valproic acid, conversely, is known as an up-regulator of GM3 synthase gene (ST3GAL5). To test the possibility that valproic acid could inhibit EGFR phosphorylation by increasing the level of GM3 in cells, we treated A431 epidermoid carcinoma cells with valproic acid and found that valproic acid treatment caused an about 6-fold increase in the GM3 level but only a marginal increase in the GM2 level in these cells and that the observed increase in GM3 level was valproic acid dose-dependent. Consistent with this observation, valproic acid treatment induced GM3 synthase gene expression by about 8-fold. Furthermore, phosphorylation of EGFR was reduced, and cell proliferation was inhibited following valproic acid treatment. Consistent with these results, transient expression of GM3 synthase gene in A431 cells also increased cellular level of GM3, reduced phosphorylation of EGFR, and inhibited cell proliferation. Treatment with l-phenyl-2-decanoylamino-3-morpholino-l-propanol, an inhibitor of glucosylceramide synthesis, decreased the cellular level of GM3 and reduced the inhibitory effects of valproic acid on EGFR phosphorylation and cell proliferation. These results suggested that induction of GM3 synthesis was enough to inhibit proliferation of cancer cells by suppressing EGFR activity. Valproic acid treatment similarly increased the GM3 level and reduced phosphorylation of EGFR in U87MG glioma cells and inhibited their proliferation. These results suggested that up-regulators of GM3 synthase gene, such as valproic acid, are potential suppressors of cancer cell proliferation.

Frequent co-expression of EGFR and NeuGcGM3 ganglioside in cancer: it's potential therapeutic implications.

Interaction between epidermal growth factor receptor (EGFR) signaling with GM3 ganglioside expression has been previously described. However, little is known about EGFR and NeuGcGM3 co-expression in cancer patients and their therapeutic implications. In this paper, we evaluate the co-expression of EGFR and NeuGcGM3 ganglioside in tumors from 92 patients and in two spontaneous lung metastasis models of mice (Lewis lung carcinoma (3LL-D122) in C57BL/6 and mammary carcinoma (4T1) in BALB/c). As results, co-expression of EGFR and NeuGcGM3 ganglioside was frequently observed in 63 of 92 patients (68 %), independently of histological subtype. Moreover, EGFR is co-expressed with NeuGcGM3 ganglioside in the metastasis of 3LL-D122 and 4T1 murine models. Such dual expression appears to be therapeutically relevant, since combined therapy with mAbs against these two molecules synergistically increase the survival of mice treated. Overall, our results suggest that NeuGcGM3 and EGFR may coordinately contribute to the tumor cell biology and that therapeutic combinations against these two targets might be a valid strategy to explore.

Ganglioside GM3 as a gatekeeper of obesity-associated insulin resistance: Evidence and mechanisms.

Gangliosides constitute a large family of sialic acid-containing glycosphingolipids which play a key regulatory role in a diverse array of cellular processes, including receptor-associated signalling. Accordingly, the aberrant production of the ganglioside GM3 has been linked to pathophysiological changes associated with obesity, which in turn can lead to metabolic disorders such as insulin resistance and type 2 diabetes mellitus. This review examines the role of GM3 in mediating obesity-induced perturbations in metabolic function, including impaired insulin action. By doing so, we highlight the potential use of therapies targeting GM3 biosynthesis in order to counteract obesity-related metabolic disorders.

Ganglioside GM3 exerts opposite effects on motility via epidermal growth factor receptor and hepatocyte growth factor receptor-mediated migration signaling.

The ganglioside GM3 exerts its different effects via various growth factor receptors. The present study investigated and comparatively analyzed the opposing effects exerted by GM3 on the migration of mouse hepatocellular carcinoma Hepa1­6 cells via epidermal growth factor receptor (EGFR) and hepatocyte growth factor receptor (HGFR/cMet). The results demonstrated that GM3 inhibited EGF­stimulated motility, but promoted HGF­stimulated motility of the Hepa1­6 cells via phosphatidylinositol 3­kinase/Akt­mediated migration signaling. It is well established that the main cytokines modulating cell proliferation, invasion and metastasis are different in different types of tumor. This difference may, at least in part, explain why GM3 exerted its actions in a tumor­type specific manner.

A mutation in a ganglioside biosynthetic enzyme, ST3GAL5, results in salt & pepper syndrome, a neurocutaneous disorder with altered glycolipid and glycoprotein glycosylation.

'Salt & Pepper' syndrome is an autosomal recessive condition characterized by severe intellectual disability, epilepsy, scoliosis, choreoathetosis, dysmorphic facial features and altered dermal pigmentation. High-density SNP array analysis performed on siblings first described with this syndrome detected four shared regions of loss of heterozygosity (LOH). Whole-exome sequencing narrowed the candidate region to chromosome 2p11.2. Sanger sequencing confirmed a homozygous c.994G>A transition (p.E332K) in the ST3GAL5 gene, which encodes for a sialyltransferase also known as GM3 synthase. A different homozygous mutation of this gene has been previously associated with infantile-onset epilepsy syndromes in two other cohorts. The ST3GAL5 enzyme synthesizes ganglioside GM3, a glycosophingolipid enriched in neural tissue, by adding sialic acid to lactosylceramide. Unlike disorders of glycosphingolipid (GSL) degradation, very little is known regarding the molecular and pathophysiologic consequences of altered GSL biosynthesis. Glycolipid analysis confirmed a complete lack of GM3 ganglioside in patient fibroblasts, while microarray analysis of glycosyltransferase mRNAs detected modestly increased expression of ST3GAL5 and greater changes in transcripts encoding enzymes that lie downstream of ST3GAL5 and in other GSL biosynthetic pathways. Comprehensive glycomic analysis of N-linked, O-linked and GSL glycans revealed collateral alterations in response to loss of complex gangliosides in patient fibroblasts and in zebrafish embryos injected with antisense morpholinos that targeted zebrafish st3gal5 expression. Morphant zebrafish embryos also exhibited increased apoptotic cell death in multiple brain regions, emphasizing the importance of GSL expression in normal neural development and function.

Renal distribution of ganglioside GM3 in rat models of types 1 and 2 diabetes.

Ganglioside GM3 is particularly abundant in the kidney tissue and is thought to play an important role in the maintenance of the charge-selective filtration barrier of glomeruli. Altered expression of ganglioside GM3 was pathologically related with glomerular hypertrophy occurring in diabetic human and rat kidneys. Considering the role of GM3 ganglioside in kidney function, the aim of this study was to determine the difference in expression of GM3 ganglioside in glomeruli and tubules using immunofluorescence microscopy both in rat models of types 1 and 2 diabetes mellitus. Diabetes was induced with streptozotocin (55 mg/kg for type 1 diabetes and 35 mg/kg for type 2 diabetes) injection to male Sprague-Dawley rats which were fed with normal pellet diet (type 1 diabetes) or high-fat diet (type 2 diabetes). Rats were sacrificed 2 weeks after diabetes induction, frozen renal sections were stained with primary antibody GM3(Neu5Ac) and visualized by secondary antibody coupled with Texas red. In addition, renal gangliosides GM3 were analyzed by high-performance thin-layer chromatography followed by GM3 immunostaining. Immunofluorescent microscopy detected 1.7-fold higher GM3 expression in tubules and 1.25-fold higher GM3 in glomeruli of type 1 diabetes mellitus compared with control group. Type 2 diabetes mellitus rats showed slight GM3 increase in whole kidney, unchanged GM3 in glomeruli, but significant higher GM3 expression in tubules, compared with control animals. Taking into consideration increased tubular GM3 content in both types of diabetes, we could hypothesize the role of GM3 in early pathogenesis of diabetic nephropathy.

[Activation of ganglioside GM3 biosynthesis in human blood mononuclear cells in atherosclerosis].

Using blood monocytes and lymphocytes from atherosclerotic patients and healthy subjects we have investigated activity of GM3 synthase, cellular levels of ganglioside GM3 and its role in monocyte adhesion to cultured human umbilical vein endothelial cells (HUVEC). The results showed that activity of GM3 synthase and cellular levels of ganglioside GM3 in blood mononuclear cells from atherosclerotic patients were several-fold higher than those from healthy subjects. In monocytes the activity of GM3 synthase was one an order of magnitude higher than in lymphocytes from both groups studied; this suggests the major contribution of monocytes to enhanced biosynthesis and levels of GM3 in mononuclear cells in atherosclerosis. Enrichment of monocytes from healthy subjects with ganglioside GM3 by incubation in medium containing this ganglioside increased adherence of these monocytes to HUVEC up to the values typical for monocytes from atherosclerotic patients. In addition, an increase in CD1 1b integrin expression was observed that was comparable to that seen in lipopolysaccharide-activated monocytes. It is suggested that in atherosclerosis the enhanced cellular levels of GM3 in monocytes and lymphocytes may be an important element of cell activation that facilitates their adhesion to endothelial cells and penetration into intima.

[The regulation of ganglioside GM3 synthesis].

Glycosphingolipids (GSLs) exist in the outer leaflet of the plasma membrane, where they form lipid microdomains that function as platforms for the regulation of trans-membrane signal transduction. In mammals, complex GSLs differing in the number and/or type of sugar species are produced in a cell-type specific manner, and the variety of glycan structures in GSLs are believed to determine specific cell functions. The glycan moieties of GSLs are synthesized at the luminal side of the Golgi apparatus by multiple Golgi-resident glycosyltransferases. Since the expression levels of most endogenous glycosyltransferases are relatively low, their detection is generally difficult. Nevertheless, we have succeeded in detecting endogenous mouse GM3 synthase (GM3S), the primary glycosyltransferase responsible for the biosynthesis of ganglio-series gangliosides. Mouse GM3S (mGM3S) has three isoforms (M1-GM3S, M2-GM3S, and M3-GM3S), each with a distinct length in its NH2-terminal cytoplasmic tail. These isoforms are produced by leaky scanning from two mRNA variants, mGM3Sa and mGM3Sb. M1-GM3S is stably localized in the endoplasmic reticulum (ER), as a result of retrograde transport signals (arginine [R]-based motifs); consequently, its in vivo GM3 synthesis activity is very low compared with that of other isoforms. In contrast, both M2-GM3S and M3-GM3S are localized in the Golgi apparatus, yet each exhibits a distinct intracellular fate. M2-GM3S is rapidly degraded in the lysosomes, whereas M3-GM3S is retained in the Golgi apparatus. A system that produces GM3S isoforms having such distinct characteristics is likely to be of critical importance in the regulation of GM3 biosynthesis under various pathological and physiological conditions.

Glycosphingolipids regulate ameloblastin expression in dental epithelial cells.

Neurotrophin 4 (NT-4) and its receptors regulate the differentiation of ameloblasts in tooth development. Gangliosides, sialic acids that contain glycosphingolipids (GSLs), are involved in a variety of membrane-associated cell physiological functions such as ligand-receptor signal transmission. However, the expression patterns and functions of GSLs during tooth development remain unclear. In this study, we identified strong expressions of GM3 and LacCer in dental epithelium, which give rise to differentiation into enamel-secreting ameloblasts. Exogenous GM3 and LacCer in dental epithelial cells induced the expression of ameloblastin (Ambn), while it was also interesting that GM3 synergistically exerted enhancement of NT-4-mediated Ambn expression. In addition, consistently exogenous GM3 and LacCer in dental epithelial cells induced distinct activation of extracellular signal-regulated kinase 1/2 (ERK1/2), an event upstream of the expression of Ambn. Furthermore, depletion of GSLs from dental epithelial cells by D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP) inhibited Ambn expression as well as phosphorylation of ERK1/2. In contrast, exogenous addition of GM3 or LacCer rescued the phosphorylation of ERK1/2 repressed by pre-treatment with D-PDMP. Taken together, these results suggest that GM3 and LacCer are essential for NT-4-mediated Ambn expression, and contribute to dental epithelial cell differentiation into ameloblasts.

Defective GM3 synthesis in Cog2 null mutant CHO cells associates to mislocalization of lactosylceramide sialyltransferase in the Golgi complex.

The conserved oligomeric Golgi (COG) complex is a eight subunit (COG1 to 8) tethering complex involved in the retrograde trafficking of multiple Golgi processing proteins. Here we studied the glycolipid synthesis status in ldlC cells, a Cog2 null mutant CHO cell line. Biochemical studies revealed a block in the coupling between LacCer and GM3 synthesis, resulting in decreased levels of GM3 in these cells. Uncoupling was not attributable to decreased activity of the glycosyltransferase that uses LacCer as acceptor substrate (SialT1). Rather, immunocytochemical experiments evidenced a mislocalization of SialT1 as consequence of the lack of Cog2 in these cells. Co-immunoprecipitation experiments disclose a Cog2 mediated interaction of SialT1 with the COG complex member Cog1. Results indicate that cycling of some Golgi glycolipid glycosyltransferases depends on the participation of the COG complex and that deficiencies in COG complex subunits, by altering their traffic and localization, affect glycolipid composition.

Ganglioside GM3 levels are altered in a mouse model of HIBM: GM3 as a cellular marker of the disease.

OBJECTIVE: HIBM (Hereditary Inclusion Body Myopathy) is a recessive hereditary disease characterized by adult-onset, slowly progressive muscle weakness sparing the quadriceps. It is caused by a single missense mutation of each allele of the UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE) gene, a bifunctional enzyme catalyzing the first two steps of sialic acid synthesis in mammals. However, the mechanisms and cellular pathways affected by the GNE mutation and causing the muscle weakness could not be identified so far. Based on recent evidence in literature, we investigated a new hypothesis, i.e. the involvement in the disease of the GM3 ganglioside, a specific glycolipid implicated in muscle cell proliferation and differentiation. METHODS: qRT-PCR analysis of St3gal5 (GM3 synthase) gene expression and HPLC quantification of GM3 ganglioside were conducted on muscle tissue from a mouse model of HIBM harboring the M712T mutation of GNE (Gne(M712T/M712T) mouse) vs control mice (Gne(+/+) mouse). RESULTS: St3gal5 mRNA levels were significantly lower in Gne(M712T/M712T) mouse muscles vs Gne(+/+) mouse muscles (64.41%+/-10% of Gne(+/+) levels). GM3 ganglioside levels showed also a significant decrease in Gne(M712T/M712T) mouse muscle compared to Gne(+/+) mouse muscle (18.09%+/-5.33% of Gne(+/+) levels). Although these Gne(M712T/M712T) mice were described to suffer severe glomerular proteinuria, no GM3 alterations were noted in kidneys, highlighting a tissue specific alteration of gangliosides. CONCLUSION: The M712T mutation of GNE hampers the muscle ability to synthesize normal levels of GM3. This is the first time that a mutation of GNE can be related to the molecular pathological mechanism of HIBM.

Tissue micro array analysis of ganglioside N-glycolyl GM3 expression and signal transducer and activator of transcription (STAT)-3 activation in relation to dendritic cell infiltration and microvessel density in non-small cell lung cancer.

BACKGROUND: Tumor immune escape and angiogenesis contribute to tumor progression, and gangliosides and activation of signal transducer and activator of transcription (STAT)-3 are implicated in these processes. As both are considered as novel therapeutic targets, we assessed the possible association of ganglioside GM3 expression and STAT3 activation with suppression of dendritic cell (DC) activation and angiogenesis in non-small cell lung cancer (NSCLC). METHODS: Immunohistochemistry was performed on a tissue array to determine N-glycolyl GM3 (GM3) and phosphorylated STAT3 (pSTAT3) expression in 176 primary NSCLC resections. Median values of GM3 and pSTAT3 expression were used as cut off. Microvessel density (MVD) was determined by CD34 staining and morphology. CD1a and CD83 were used to determine infiltrating immature and mature dendritic cells, respectively. RESULTS: 94% and 71% of the NSCLC samples expressed GM3 and nuclear pSTAT3, respectively. Median overall survival was 40.0 months. Both low GM3 expression and high pSTAT3 expression were associated with a worse survival, which reached near significance for GM3 (P = 0.08). Microvessel density (MVD), determined by CD34 staining and morphology, was lower in NSCLC samples with high GM3 expression. CD1a+ cells (immature DCs) were more frequent in NSCLC tissues as compared to peritumoral lung tissue, while CD83+ cells (mature DCs) were more frequent in peritumoral lung tissue. CD83+ DCs were less frequent in NSCLC tissues with high GM3 expression. CONCLUSION: GM3 and pSTAT3 are widely expressed in NSCLC. Based on CD83 expression, GM3, but not pSTAT3, appeared to be involved in tumor-induced DC suppression. pSTAT3 expression was not associated with MVD, while GM3 might play an anti-angiogenic role.

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.

Characterization of the antibody response against NeuGcGM3 ganglioside elicited in non-small cell lung cancer patients immunized with an anti-idiotype antibody.

1E10 mAb is an anti-Id murine mAb (Ab2 mAb) specific for an Ab1 mAb that reacts with NeuGc-containing gangliosides, sulfatides, and Ags expressed in some human tumors. In preclinical studies, this Ab2 Ab was able to mimic NeuGc-containing gangliosides only in animals lacking expression of these Ags in normal tissues. In this study, we report on the immune responses elicited in 20 non-small cell lung cancer patients treated with 1 mg of aluminum hydroxide-precipitated 1E10 mAb. In the hyperimmune sera from 16 of 20 patients, a strong specific Ab response of both IgM and IgG isotypes against NeuGcGM3 ganglioside was observed. Patient immune sera were able to induce complement-independent cell death of NeuGcGM3-expressing X63 murine myeloma target cells. Significant immunoreactivity to NeuGcGM3 was still detected after the complete abrogation of the reactivity against 1E10 mAb by the adsorption of patient sera with this Ab. We hypothesize that Id(-)Ag(+) Abs could reflect the activation of an autologous idiotypic cascade into the patients. Both Id(+)Ag(+) and Id(-)Ag(+) fractions were separated by affinity chromatography and characterized. Although IgG isotype Abs were found in both fractions, IgM isotype Abs were found only in the Id(-)Ag(+) fraction. Both Id(+)Ag(+) and Id(-)Ag(+) Abs were able to specifically recognize and induce cell death in NeuGcGM3-expressing X63 myeloma target cells. Patients that developed IgG and/or IgM Abs against NeuGcGM3 showed longer median survival times.

Valproic acid-mediated transcriptional regulation of human GM3 synthase (hST3Gal V) in SK-N-BE(2)-C human neuroblastoma cells.

AIM: To investigate whether valproic acid (VPA) modulates human GM3 synthase (hST3Gal V) mRNA expression, as a part of ganglioside GM3 biosynthesis, in human neuroblastoma cells. METHODS: Using RT-PCR and immunofluorescent confocal microscopy, we examined hST3Gal V mRNA and GM3 levels during VPA-induced differentiation of human neuroblastoma SK-N-BE(2)-C cells. We characterized the VPA-inducible promoter region within the hST3- Gal V gene using luciferase constructs carrying 5'-deletions of the hST3Gal V promoter. RESULTS: RT-PCR indicated that VPA-mediated hST3Gal V induction is transcriptionally regulated. Functional analysis of the 5'-flanking region of the hST3Gal V gene demonstrated that the -177 to -83 region, which contains a cAMP-responsive element (CRE) at -143, functions as the VPA-inducible promoter by actively binding CRE binding protein (CREB). In addition, sitedirected mutagenesis and electrophoretic mobility shift assay indicated that the CRE at -143 is crucial for the VPA-induced expression of hST3Gal V in SK-NBE( 2)-C cells. CONCLUSION: Our results isolated the core promoter region in the hST3Gal V promoter, a CRE at -143, and demonstrated that it is essential for transcriptional activation of hST3Gal V in VPA-induced SK-N-BE(2)-C cells. Subsequent CREB binding to this CRE mediates VPA-dependent upregulation of hST3Gal V gene expression.