The homozygous M712T mutation of UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase results in reduced enzyme activities but not in altered overall cellular sialylation in hereditary inclusion body myopathy

AbstractHereditary inclusion body myopathy (HIBM) is a neuromuscular disorder, caused by mutations in UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase, the key enzyme of sialic acid biosynthesis. In Middle Eastern patients a single homozygous mutation occurs, converting methionine-712 to threonine. Recombinant expression of the mutated enzyme revealed slightly reduced N-acetylmannosamine kinase activity, in agreement with the localization of the mutation within the kinase domain. B lymphoblastoid cell lines derived from patients expressing the mutated enzyme also display reduced UDP-N-acetylglucosamine 2-epimerase activity. Nevertheless, no reduced cellular sialylation was found in those cells by colorimetric assays and lectin analysis, indicating that HIBM is not directly caused by an altered overall expression of sialic acids

Glycation Interferes with the expression of sialyltransferases in meningiomas

Meningiomas are the most common non-malignant intracranial tumors and prefer, like most tumors, anaerobic glycolysis for energy production (Warburg effect). This anaerobic glycolysis leads to an increased synthesis of the metabolite methylglyoxal (MGO) or glyoxal (GO), which is known to react with amino groups of proteins. This reaction is called glycation, thereby building advanced glycation end products (AGEs). In this study, we investigated the influence of glycation on sialylation in two meningioma cell lines, representing the WHO grade I (BEN-MEN-1) and the WHO grade III (IOMM-Lee). In the benign meningioma cell line, glycation led to differences in expression of sialyltransferases (ST3GAL1/2/3/5/6, ST6GAL1/2, ST6GALNAC2/6, and ST8SIA1/2), which are known to play a role in tumor progression. We could show that glycation of BEN-MEN-1 cells led to decreased expression of ST3Gal5. This resulted in decreased synthesis of the ganglioside GM3, the product of ST3Gal5. In the malignant meningioma cell line, we observed changes in expression of sialyltransferases (ST3GAL1/2/3, ST6GALNAC5, and ST8SIA1) after glycation, which correlates with less aggressive behavior.Proteomic

Interactome Analyses Identify Ties of PrPC and Its Mammalian Paralogs to Oligomannosidic N-Glycans and Endoplasmic Reticulum-Derived Chaperones

The physiological environment which hosts the conformational conversion of the cellular prion protein (PrPC) to disease-associated isoforms has remained enigmatic. A quantitative investigation of the PrPC interactome was conducted in a cell culture model permissive to prion replication. To facilitate recognition of relevant interactors, the study was extended to Doppel (Prnd) and Shadoo (Sprn), two mammalian PrPC paralogs. Interestingly, this work not only established a similar physiological environment for the three prion protein family members in neuroblastoma cells, but also suggested direct interactions amongst them. Furthermore, multiple interactions between PrPC and the neural cell adhesion molecule, the laminin receptor precursor, Na/K ATPases and protein disulfide isomerases (PDI) were confirmed, thereby reconciling previously separate findings. Subsequent validation experiments established that interactions of PrPC with PDIs may extend beyond the endoplasmic reticulum and may play a hitherto unrecognized role in the accumulation of PrPSc. A simple hypothesis is presented which accounts for the majority of interactions observed in uninfected cells and suggests that PrPC organizes its molecular environment on account of its ability to bind to adhesion molecules harboring immunoglobulin-like domains, which in turn recognize oligomannose-bearing membrane proteins

Highlight: Dolce vita - a sample from European glycobiology

Proteomic

Biochemical engineering of neural cell surfaces by the synthetic N-Propanoyl-substituted neuraminic acid precursor

Sialylation of glycoproteins and glycolipids plays an important role during development, regeneration, and pathogenesis of diseases. During times of intense plasticity within the nervous system, such as development and regeneration, sialylation of neural cells is distinct from the time of its maintenance. In this study, a synthetic precursor of neuraminic acid, N-propanoylmannosamine (N-propanoyl neuraminic acid precursor (P-NAP)), is applied to the culture medium of oligodendrocyte progenitor cells, microglia, astrocytes, and neurons from neonatal rat brains to alter sialylation of glycoconjugates within these cells. P-NAP is metabolized and incorporated as N-propanoyl neuraminic acid into glycoproteins of the cell membrane. P-NAP stimulates the proliferation of astrocytes and microglia but not of oligodendrocyte progenitor in vitro. However, P-NAP increases the number of oligodendrocyte progenitor cells expressing the early oligodendroglial surface marker A2B5 epitope. In the presence of P-NAP, cerebellar neurons (but not astrocytes) in microexplant cultures start to express the oligodendroglial progenitor marker A2B5 epitope, which is normally undetectable on these cells. The controls, which were performed in the absence of any additive or in the presence of the physiological precursor of neuraminic acid, N-acetylmannosamine, did not show any increase in A2B5 expression

Expression of Ndufb11 encoding the neuronal protein 15.6 during neurite outgrowth and development.

Neurite outgrowth (e.g. axonal or dendrite outgrowth) of neurons is necessary for the development and functioning of the central nervous system. It is well accepted that the differentiation of neurons and neurite outgrowth involve alterations in gene expression. Furthermore, mitochondria play a role in different aspects of neurite outgrowth. Here we show that the expression of Ndufb11, a gene encoding the mitochondrial protein NP15.6 is decreased in the course of neuronal differentiation. NP15.6 is homologous to the bovine protein ESSS, a component of the mitochondrial complex 1. The homologous human NDUFB11 gene is localized to Xp11.3–Xp11.23, a region associated with neurogenetic disorders. The down-regulation of NP15.6 correlates with neurite outgrowth of PC12 cells induced by nerve growth factor. Furthermore, we analyzed the expression of Ndufb11 in the embryonic and adult mouse