Incorporation of 9-amino-[3H]acetylneuraminate and 9-[14C]acetamidoacetylneuraminate into glycoconjugates of rat hepatoma cells (H35) and hepatocytes <i>in vitro</i> and rat liver <i>in vivo</i>

Ferwerda, W; Blok, Corrie M.; Groß, Hans‐Jürgen; Rijcken, W R Pels; Rose, Ursula M.; Brossmer, Reinhard

doi:10.1042/bst0170744

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“…in fibroblasts [19] and Ferwerda et al . in hepatocytes [21]. 9‐[ 3 H]NeuAc uptake in our study was temperature‐dependent, nonsaturable up to at least 10 m m , and was unaffected by different agents interfering with endocytotic pathways.…”

Section: Discussionmentioning

confidence: 70%

“…The rather low plasma concentration makes it unlikely that the uptake of free sialic acid is a major contributor to cells' sialic acid pool, although higher local concentrations in specific tissue compartments are conceivable. Cellular uptake of sialic acid might contribute to the regulation of the sialic acid plasma level, which appears to be regulated mainly by urinary excretion [21,54].…”

Section: Discussionmentioning

confidence: 99%

“…Cellular uptake from the extracellular space by eukaryotic cells has been well documented for a variety of hexoses: except for d ‐fucose [14], d ‐mannose [15], and d ‐glucose [16], for which specific transporters have been characterized, little is known about the exact mechanisms governing their plasma membrane transfer. In mammalian cells no biologically significant uptake of free sialic acid has been demonstrated although the uptake of very small amounts of radioactively labeled NeuAc has been suggested [17–21]. However, this has led to the widely accepted view that free sialic acids cannot be efficiently taken up and incorportated in cellular glycoconjugates in eukaryotic cells.…”

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Evidence for efficient uptake and incorporation of sialic acid by eukaryotic cells

Oetke

Hinderlich

Brossmer

et al. 2001

European Journal of Biochemistry

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Sialic acids are the most abundant terminal carbohydrate moiety on cell surface glycoconjugates in eukaryotic cells and are of functional importance for many biological ligand-receptor interactions. It is a widely accepted view that sialic acids cannot be efficiently taken up from the extracellular space by eukaryotic cells. To test this assumption, we cultivated two recently identified human hematopoetic cell lines which are hyposialylated due to a deficiency in de novo sialic acid biosynthesis in the presence of N-acetylneuraminic acid (NeuAc), the most frequently found sialic acid. Surprisingly, NeuAc medium supplementation rapidly and potently compensated for the endogenous hyposialylation in a concentration-dependent manner, resulting in the presentation of cell surface sialoglycans involved in cell adhesion, virus infection and signal transduction. We provide several lines of experimental evidence that all suggest that NeuAc was neither extracellularly incorporated nor degraded to a less complex sugar before uptake. Importantly, NeuAc induced a marked increase in intracellular CMP-NeuAc levels in both human cell lines and in primary cells regardless of the prior sialylation status of the cells. Studies employing 9-[ 3 H]NeuAc revealed an uptake consistent with the observed incorporation of unlabeled NeuAc. We propose the existence of an efficient uptake mechanism for NeuAc in eukaryotic cells.

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Section: Discussionmentioning

confidence: 70%

Section: Discussionmentioning

confidence: 99%

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confidence: 99%

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