Organization of the beta-galactoside alpha 2,6-sialyltransferase gene. Evidence for the transcriptional regulation of terminal glycosylation

Expression of mouse Gal beta 1,4GlcNAc alpha 2,6-sialyltransferase in an insoluble form in Escherichia coli and partial renaturation

Mouse Gal beta 1,4GlcNAc alpha 2,6-sialyltransferase was produced in an insoluble form in Escherichia coli cells harboring expression plasmids. The insoluble protein was solubilized with 8 M urea and diluted for renaturation of the enzyme. The substrate specificity and kinetic parameters, except for the specific activity, of the renatured enzyme were similar to those of the enzyme obtained from rat liver. These results suggest that a bacterial expression system is a potentially powerful tool for the large scale production of sialyltransferases and for elucidating the molecular mechanisms of sialyltransferases.

Two step single primer mediated polymerase chain reaction. Application to cloning of putative mouse, beta-galactoside alpha 2,6-sialyltransferase cDNA

Using the 2 step single primer mediated polymerase chain reaction(PCR), mouse beta-galactoside alpha 2,6-sialyltransferase cDNA was cloned. Single primer mediated PCR is a method to amplify a particular DNA fragment beyond its known sequence region. It employs only one primer for the reaction. Compared to other PCR methods to amplify an adjacent sequence of known DNA fragment, this method requires no enzymatic manipulation on template DNA and is applicable to a template on long DNA fragment. First, a short DNA fragment of the enzyme was obtained from mouse cDNA by the usual PCR method using degenerate primers synthesized according to a relatively conserved region in rat and human beta-galactoside alpha 2,6-sialyltransferase. Four primers were synthesized based on this sequence, then 2 step single primer mediated PCR were performed to obtain 5' and 3' flanking sequences of this short fragment resulting in 1.0 kb and 1.3 kb fragments being amplified respectively. The integrity of the two fragments was confirmed by an additional PCR using primers synthesized according to the joined sequence, which contained 1.2kb complete putative mouse beta-galactoside alpha 2,6-sialyltransferase coding region. The result showed that the specificity and consequently applicability of the single primer mediated PCR for amplifying a particular DNA fragment beyond known sequence region was remarkably improved by the successive 2nd reaction.

CDw75 antigen expression in breast lesions

Alterations on the cell surface of the oligosaccharide portion of glycoproteins and glycolipids are thought to play a role in tumorigenesis. Sialyltransferase catalyzes the incorporation of sialic acid to the carbohydrate group of glycoconjugates. Sialyltransferase has been found elevated in different tumour tissues and in the serum of cancer patients. In the present study we have examined the expression of the beta-galactosyl alpha 2,6-sialyltransferase requiring epitope CDw75, with the monoclonal antibody HH2. 142 breast lesions were included. 21% of the carcinomas in situ and 35% of the invasive carcinomas showed a diffuse cytoplasmic staining. Seven cases of invasive carcinomas also showed a distinct membrane immunoreactivity. We found no correlation between reactivity for CDw75 in malignant lesions and their metastatic potential. Only five out of 11 primary tumours with metastases expressed CDw75 in the primary tumour. In the benign lesions, there was a positive reaction in proliferating lesions, e.g. intraductal papillomas (2 out of 3 cases) and in epithelial proliferations in fibrocystic disease (10 out of 14 cases). None of the four fibroadenomas and phyllodes tumours and only one out of 22 cases of normal breast tissues showed immunoreactivity for HH2. In the malignant lesions, CDw75 was more frequently expressed in the carcinomas of high malignancy grade. The high frequency of immunoreactivity among the benign breast lesions can be indicative of activation of the epithelial cells.

Cell-specific expression of human beta-galactoside alpha 2,6-sialyltransferase transcripts differing in the 5' untranslated region

In humans, two cDNAs have been isolated encoding beta-galactoside alpha 2,6-sialyltransferase, differing only in part of the 5' untranslated region. Primer extension data show that the two cDNAs are near full-length clones. RNase protection analysis of different cell types showed that the transcript corresponding to the alpha 2,6-sialyltransferase cDNA isolated from a B-cell library resided only in mature B cells. In contrast, the transcript corresponding to the alpha 2,6-sialyltransferase cDNA isolated from a placenta library was found in all cells tested. Our results also indicate the existence of a third alpha 2,6-sialyltransferase transcript in the hepatoma cell line HepG2. Mature B cells were found to express high amounts of alpha 2,6-sialyltransferase mRNA, compared to other cell types tested, as shown by Northern blot analysis. Moreover there was an increased expression of beta-galactoside alpha 2,6-sialyltransferase mRNA in activated B cells compared to resting B cells. In vitro transcription and translation of the cDNAs resulted in a protein of 45 kDa, but the transcripts were translated with different efficiency, suggesting a role for the 5' untranslated region in regulation of translation. We have also made an alpha 2,6-sialyltransferase construct lacking the specific 5' regions of the two cDNAs. A transcript generated from this construct was translated more efficiently in vitro than the two alpha 2,6-sialyltransferase cDNAs.

Regulation of expression of beta-galactoside alpha 2,6-sialyltransferase in a rat tumor, Zajdela ascitic hepatoma

Tumor cell surface sialic acid levels determine a number of important properties governing cellular interactions and cell-cell communication. Towards understanding the mechanism of regulation of sialic acid levels upon cellular transformation, we have studied the regulation of expression of beta-galactoside alpha 2,6-sialyltransferase in a rat tumor, the Zajdela ascitic hepatoma. We demonstrate distinct differences in the regulation of expression of the enzyme in the tumor cells as compared to normal liver cells. The expression of sialyltransferase is regulated both at the transcriptional and post-transcriptional level in a tissue-specific manner.

Enzymatic characterization of CMP-NeuAc:Gal beta 1-4GlcNAc-R alpha(2-3)-sialyltransferase from human placenta

In this report we present the enzymatic characterization of CMP-NeuAc:Gal beta 1-4GlcNAc-R alpha(2-3)-sialyltransferase from human placenta using placenta membranes as an enzyme preparation. This sialyltransferase is highly sensitive to detergents and prefers type 2 chain (Gal beta 1-4GlcNAc) over type 1 chain (Gal beta 1-3GlcNAc) acceptors. Oligosaccharides and glycopeptides were better acceptor substrates than glycoproteins. Of the branched oligosaccharides, those with a bisected N-acetylglucosamine (GlcNAc) structure appeared to be poorer substrates, while triantennary structures containing a Gal beta 1-4GlcNAc beta 1-4Man alpha 1-3Man branch were preferred. Product characterization, using 400 MHz 1H-NMR spectroscopy, confirmed that sialic acid was introduced into the Gal beta 1-4GlcNAc-R units of the acceptor substrates in an alpha (2-3) linkage, and revealed that this sialyltransferase does not prefer either of the two branches of a complex type di-antennary glycopeptide acceptor for sialic acid attachment. These properties distinguish this enzyme from all other sialyltransferases characterized to date.

Clinical aspects of glycoprotein biosynthesis

Glycoproteins are widely distributed among species in soluble and membrane-bound forms, associated with many different functions. The heterogenous sugar moieties of glycoproteins are assembled in the endoplasmic reticulum and in the Golgi and are implicated in many roles that require further elucidation. Glycoprotein-bound oligosaccharides show significant changes in their structures and relative occurrences during growth, development, and differentiation. Diverse alterations of these carbohydrate chains occur in diseases such as cancer, metastasis, leukemia, inflammatory, and other diseases. Structural alterations may correlate with activities of glycosyltransferases that assemble glycans, but often the biochemical origin of these changes remains unclear. This suggests a multitude of biosynthetic control mechanisms that are functional in vivo but have not yet been unraveled by in vitro studies. The multitude of carbohydrate alterations observed in disease states may not be the primary cause but may reflect the growth and biochemical activity of the affected cell. However, knowledge of the control mechanisms in the biosynthesis of glycoprotein glycans may be helpful in understanding, diagnosing, and treating disease.

Organization and localization to chromosome 5 of the human UDP-N-acetylglucosamine:alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I gene

UDP-N-acetylglucosamine:alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I (GlcNAc-T I; EC 2.4.1.101) is a medial-Golgi enzyme essential for the synthesis of hybrid and complex N-glycans. We have isolated two overlapping genomic DNA clones which span 18 kilobases (kb) containing a single 2.5 kb exon for GlcNAc-T I. The exon includes most of the 5'-untranslated region, the complete coding sequence (1335 bases) for GlcNAc-T I (445 amino acids) and the complete 3'-untranslated region. The remaining exon (or exons) is at least 2.0 kb upstream of the intron-exon junction. Transient transfection of either clone into Lec 1 Chinese hamster ovary cell mutants (which lack GlcNAc-T I) indicates the presence of a promoter responsible for expression of a truncated transcript. Southern blot analysis indicates that the gene exists in single copy in the human genome and is located on chromosome 5. The human and rabbit enzymes are 85% similar at the nucleotide sequence level and 92% similar at the amino acid sequence level.