Glycoprotein metabolism in inflammatory and neoplastic diseases of the human colon

Abstract

Carbohydrate compositions of the membrane and cytoplasmic fractions of human normal and cancerous colonic mucosa were compared in patients with blood groups O and B. The total sugar content in both fractions was reduced in the cancer tissues to about one-third of that in the normal colonic mucosa. The sugars that are associated with mucinous glycoproteins such as fucose and N-acetylgalactosamine were reduced significantly, while sugars that are primarily associated with "serum-type" glycoproteins were relatively unchanged or reduced to a lesser extent. The activities of glycoprotein:glycosyltransferases were variable, some showing so significant change, others beinb significnatly reduced in cancerous tissues. A polypeptidyl:N-acetylgalactosaminyltransferase (an enzyme that catalyzes the transfer of the first sugar to hydroxyamino acids of the protein core of mucinous glycoproteins), a sialyltransferase (involved in the addition of sialic acid to mucinous glycoproteins), and a galactoxyltransferase (thought to be responsible for blood group B antigenicity) were reduced in the cancerous colonic tissue. In contrast, the activities of these glycosyltransferases were unchanged in the colonic mucosa of patients with granulomatosis or ulcerative colitis. Glycosidase activities in the normal, cancerous, and inflammatory tissues were the same. These results suggest that in colonic cancer tissues the synthesis of one type of oligosaccharide chain may be greatly affected, while another family of oligosaccharides may remain relatively unaffected.