Thomsen-Friedenreich (TF)-related
blood group antigens, such as TF, Tn, and their sialylated variants, belong to a family of
tumor-associated
carbohydrates. The aim of the present study was to examine
tumor-associated alterations of
glycosyltransferases involved in the biosynthesis of the TF glycotope in
colorectal carcinomas. To this end,
glycosyltransferase expression was examined in 40 cases of
colorectal carcinoma specimens classified according to the WHO/Union International Contre
Cancer guidelines and in "normal" mucosa of the same patients. Occurrence of TF glycotope was examined by immunohistochemistry with the
monoclonal antibody A78-G/A7. Expression of
sialyltransferases CMP-sialic acid:Galbeta1,3GalNAc-R alpha3-sialyltransferase I and II (ST3Gal-I and ST3Gal-II) and
CMP-sialic acid:Galbeta1,3GalNAc-R
alpha6-sialyltransferase (ST6GalNAc-II) and of core 2 beta1,6-N-acetylglucosaminyltransferase was determined by reverse transcription-PCR in the same cryostat sections used for immunohistochemistry. Additionally, alpha2,3-sialyltransferase
enzyme activity was studied in each of these tissues. The TF glycotope was detected in 7% of the normal mucosa, but in 57% of the
carcinoma samples. Expression of alpha2,3-sialyltransferases ST3Gal-I, ST3Gal-II, and
enzyme activity of alpha2,3-sialyltransferase was significantly increased (P < 0.001) in
carcinoma specimens compared with normal mucosa. ST3Gal-I
mRNA expression was significantly increased (P = 0.05) in cases showing invasion of lymph vessels. Expression of ST6GalNAc-II was significantly increased (P = 0.04) in cases with
metastases to lymph nodes along the vascular trunk. Moreover, ST6GalNAc-II expression provides an prognostic factor for patient survival (log rank, P = 0.02). In an attempt to study the functional relevance of the
glycosyltransferases for TF biosynthesis, SW480 colorectal cells were transfected with each of the
enzymes, and cell surface expression of the TF glycotope was examined by flow cytometry. The presence of TF was not altered by transfection of the cells with either
sialyltransferase ST3Gal-I or ST3Gal-II. However, successful transfection with core 2 beta1,6-N-acetylglucosaminyltransferase led to reduced expression of TF. In contrast, increased cell surface expression of TF was found after ST6GalNAc-II transfection. Thus, expression of TF on the cell surface of SW480
colorectal carcinoma cells depends on the ratio of core 2 beta1,6-N-acetylglucosaminyltransferase and ST6GalNAc-II. Earlier immunohistological studies demonstrated that TF is a prognostic factor for patient survival. Our results suggest that
sialyltransferase ST6GalNAc-II is of crucial relevance for the prognostic significance of TF.