Expression of UDP-GalNAc:NeuAc alpha 2,3Gal beta-R beta 1,4(GalNAc to Gal) N-acetylgalactosaminyltransferase involved in the synthesis of Sda antigen in human large intestine and colorectal carcinomas.
N-Acetylgalactosamine beta 1,4-linked to a galactose residue substituted in O-3 with one N-acetylneuraminic acid residue is the immunodominant sugar of the human blood group Sda antigen which is also largely present in the kidney medulla and colon mucosa. A beta 1,4-N-acetylgalactosaminyltransferase very similar to that previously described in urine of Sd(a+) individuals (F. Serafini-Cessi, N. Malagolini, and F. Dall'Olio. Arch. Biochem. Biophys., 266: 573-582, 1988) has been identified in cells released from human large intestine. The higher values of beta 1,4-N-acetylgalactosaminyltransferase activity were detected in proximal and medial segments of the large intestine, suggesting a proximal-distal gradient of the enzyme expression. When the beta 1,4-N-acetylgalactosaminyltranferase activity of colorectal carcinoma specimens from 18 patients was compared with that of the normal mucosa surrounding the tumor, a constant and in several cases drastic reduction of the activity was detected in tumor cells. Three human colorectal adenocarcinoma cell lines (Colo-205, SW-48, and SW-948) have been found to lack the beta 1,4-N-acetylgalactosaminyltransferase activity. Altogether, these results support the notion that the malignant transformation drastically affects the expression of this glycosyltransferase in large bowel cells.