Occurrence of α1‐2‐fucosylation in membrane glycoproteins of Morris hepatoma 7777 but not in liver

Abstract

A comparative study was undertaken to characterize the linkages of L-fucose in N-glycans of plasma membrane glycoproteins from Morris hepatoma 7777, host liver and kidney cortex, as well as from rat serum.After in-vivo radiolabelling of rats with ~-[6-~H]fucose, the asparagine-linked carbohydrate chains were released from delipidated plasma membrane glycoproteins, as well as from serum glycoproteins, by enzymic digestion with peptide-N4-(N-acetyl-~-glucosaminyl)asparagine amidase from Flavobacterium meningosepticum. They were then converted to their corresponding oligosaccharide alditols by reduction with sodium borohydride.Two specific a-L-fucosidases from almond emulsin and from Aspergillus niger, combined with affinity HPLC on immobilized Aleuria aurantia lectin were used to study the linkage of L-fucose in the oligosaccharide chains.Fucose a1-2 linked to galactose, was present only in the plasma membrane of hepatoma 7777 (18% of total ~-[~H]fucose in N-glycans), but was not expressed in host liver, kidney cortex and serum. None of the investigated sources contained an appreciable amount of fucose al-3/4 linked to N-acetyl-D-glucosamine. All the radioactively labelled oligosaccharides from host liver, kidney cortex and serum, but only 82% of these oligosaccharides from hepatoma, contained a-fucosyl residues linked at the C6 position of the proximal N-acetyl-D-glucosamine.Several differences have been found in the structure of sugar chains of glycoconjugates produced in normal and malignant cells [l -31. One of the most frequently found phenomena in malignant cells is an increased degree of branching and quite often, due to repeating units, an elongation of the outer chains of N-linked oligosaccharides in glycoproteins, paralleled by an increased activity of p-N-acetylglucosaminyltransferase V [4]. A bisecting N-acetyl-D-glucosamine residue, pl-4 linked to the mannosyl-chitobiose core, is also possibly the result of an altered, tumour-associated glycosylation [S].Furthermore, malignant transformation has been reported to be accompanied by alterations in the content and linkage of the terminal sugar residues, L-fucose and sialic acid [2, 6, 71, which play an important role in blood-group antigens [8].

Glycosylation and Liver Cancer

“…Initial work showed that AFP with an attached α-1,6 core fucosylated monosaccharide was a better marker of HCC than AFP alone(Aoyagi, 1994; Aoyagi et al, 1998; Aoyagi et al, 2002; Aoyagi et al, 1993a; Aoyagi et al, 1993b; Aoyagi et al, 1988; Buamah et al, 1986; Yamashita et al, 1993). Subsequently, other highly abundant serum proteins such as transferrin and alpha-1-anti-trypsin (A1AT) were found to contain increased levels of fucosylation with HCC(Aoyagi et al, 1993a; Callewaert et al, 2003; Comunale et al, 2006; Goodarzi and Turner, 1995; Miyoshi et al, 1999; Morelle et al, 2006; Naitoh et al, 1999b; Noda et al, 1998; Nuck et al, 1992; Ryden et al, 1999; Thompson et al, 1988; Turner, 1995). Core fucosylated AFP is the success story in the field of glycomics as it has shown great clinical value and is currently the only test approved by the United States Food and Drug Administration (USFDA) for the detection of HCC.…”