Molecular characterization and expression analyses of ST8Sia II and IV in piglets during postnatal development: lack of correlation between transcription and posttranslational levels

The NMR studies of CMP inhibition of polysialylation

The overexpression of polysialic acid (polySia) on neural cell adhesion molecules (NCAM) promotes hypersialylation, and thus benefits cancer cell migration and invasion. It has been proposed that the binding between the polysialyltransferase domain (PSTD) and CMP-Sia needs to be inhibited in order to block the effects of hypersialylation. In this study, CMP was confirmed to be a competitive inhibitor of polysialyltransferases (polySTs) in the presence of CMP-Sia and triSia (oligosialic acid trimer) based on the interactional features between molecules. The further NMR analysis suggested that polysialylation could be partially inhibited when CMP-Sia and polySia co-exist in solution. In addition, an unexpecting finding is that CMP-Sia plays a role in reducing the gathering extent of polySia chains on the PSTD, and may benefit for the inhibition of polysialylation. The findings in this study may provide new insight into the optimal design of the drug and inhibitor for cancer treatment.

The Graphical Studies of the Major Molecular Interactions for Neural Cell Adhesion Molecule (NCAM) Polysialylation by Incorporating Wenxiang Diagram into NMR Spectroscopy

Polysialylation is a process of polysialic acid (polySia) addition to neural cell adhesion molecule (NCAM), which is associated with tumor cell migration and progression in many metastatic cancers and neurocognition. Polysialylation can be catalyzed by two highly homologous mammalian polysialyltransferases (polySTs), ST8Sia II (STX) and ST8Sia IV (PST). It has been proposed that two polybasic domains, polybasic region (PBR) and polysialyltransferase domain (PSTD) in polySTs, are possible binding sites for the intermolecular interactions of polyST-NCAM and polyST-polySia, respectively, as well as the intramolecular interaction of PSTD-PBR. In this study, Chou's wenxiang diagrams of the PSTD and PBR are used to determine the key amino acids of these intermolecular and intramolecular interactions, and thus it may be helpful for the identification of the crucial amino acids in the polyST and for the understanding of the molecular mechanism of NCAM polysialylation by incorporating the wenxiang diagram and molecular modeling into NMR spectroscopy.

Molecular Mechanisms Underlying How Sialyllactose Intervention Promotes Intestinal Maturity by Upregulating GDNF Through a CREB-Dependent Pathway in Neonatal Piglets

Sialylated milk oligosaccharides (SMOs) have a multifunctional health benefit, yet the molecular details underlying their potential role in modulating intestinal maturation remains unknown. To test the hypothesis that sialyllactose (SL) may mediate intestinal maturation and function through controlling neuronal function, studies were carried out where the diet of postnatal piglets was supplemented with a mixture of 3'- and 6'-sialyllactose from postnatal day 3 to 38. Gene transcription pathways regulating enteric nervous system function, polysialic acid (polySia) synthesis, and cell proliferation were quantified. Our new findings show that SL intervention: (1) upregulated the level of gene and protein expression of the glial-derived neurotrophic factor (GDNF) in the ileum; (2) upregulated phosphorylation of the cAMP responsive element-binding protein (CREB), the downstream target of GDNF signaling pathway; (3) promoted cell proliferation based on an increase in the number and density of Ki-67 positive cells in the crypts; (4) increased the crypt width in the ileum by 10%, while gene markers for the functional cells were not affected; (5) upregulated mRNA expression level of ST8Sia IV, a key polysialyltransferase responsible for synthesis of polySia-NCAM; (6) reduced the incidence and severity of diarrhea. These results show that SL promotes intestinal maturation in neonatal piglets by upregulating GDNF, synthesis of polySia and CREB-interactive pathway.

Biochemical Characterization and Analyses of Polysialic-Acid-Associated Carrier Proteins and Genes in Piglets during Neonatal Development

Polysialic acid plays a key role in cancer metastasis and neurodevelopment. Our aim was to determine the developmental gene-expression profiles for the two polysialyltransferases ST8Sia II and ST8Sia IV, neural cell-adhesion molecules (NCAMs), SynCAM 1, neuropilin-2 (NRP2) and their polysialylated cognate glycans in different regions of the piglet brain during postnatal development. Our findings show that: 1) the cellular levels of mRNA coding for ST8Sia II and ST8Sia IV, NCAMs, SynCAM 1, NRP2 and polySia are age-dependent and cell-type-specific during neonatal brain development, 2) there was a lack of correlation between abundance level of mRNA coding for ST8Sia II and ST8Sia IV and the abundance level of the post-translation expression of polySia in all nine brain regions, 3) expression levels of polySia did not correlate with the levels of the carrier proteins NCAM-140, SynCAM 1 and NRP2 in nine brain regions, and 4) the cellular abundance of ST8Sia II and ST8Sia IV in nine subregions of piglet brain is regulated at the level of translation/post-translation, and not at the level of transcription. Collectively, our findings suggest that neuronal and glial cells within different regions of the brain have different transcriptional programs that can direct cell division at different rates based on the activity levels of ST8Sia II and ST8Sia IV and the level of their carrier proteins during neurodevelopment.

Metabolic Glycoengineering with N-Acyl Side Chain Modified Mannosamines

In metabolic glycoengineering (MGE), cells or animals are treated with unnatural derivatives of monosaccharides. After entering the cytosol, these sugar analogues are metabolized and subsequently expressed on newly synthesized glycoconjugates. The feasibility of MGE was first discovered for sialylated glycans, by using N-acyl-modified mannosamines as precursor molecules for unnatural sialic acids. Prerequisite is the promiscuity of the enzymes of the Roseman-Warren biosynthetic pathway. These enzymes were shown to tolerate specific modifications of the N-acyl side chain of mannosamine analogues, for example, elongation by one or more methylene groups (aliphatic modifications) or by insertion of reactive groups (bioorthogonal modifications). Unnatural sialic acids are incorporated into glycoconjugates of cells and organs. MGE has intriguing biological consequences for treated cells (aliphatic MGE) and offers the opportunity to visualize the topography and dynamics of sialylated glycans in vitro, ex vivo, and in vivo (bioorthogonal MGE).