Overexpression of sialyltransferase CMP-sialic Acid : Gal beta 1,3GalNAc-Ralpha 6-sialyltransferase is related to poor patient survival in human colorectal carcinomas

Thomsen-Friedenreich (TF)-related blood group antigens, such as TF, Tn, and their sialylated variants, belong to a family of tumor-associated carbohyd rates, The aim of the present study was to examine tumor-associated alterat ions of glycosyltransferases involved in the biosynthesis of the TF glycoto pe in colorectal carcinomas. To this end, glycosyltransferase expression wa s examined in 40 cases of colorectal carcinoma specimens classified accordi ng to the WHO/Union International Contre Cancer guidelines and in "normal" mucosa of the same patients. Occurrence of TF glycotope was examined by imm unohistochemistry with the monoclonal antibody A78-G/A7. Expression of sial yltransferases CMP-sialic acid:Gal beta1,3GalNAc-R alpha3-sialyltransferase I and II (ST3Gal-I and ST3Gal-II) and CMP-sialic acid: Gal beta1,3GalNAc-R alpha6-sialyltransferase (ST6GalNAc-II) and of core 2 beta1,6-N-acetylgluc osaminyltransferase was determined by reverse transcription-PCR in the same cryostat sections used for immunohistochemistry. Additionally, alpha2,3-si alyltransferase enzyme activity was studied in each of these tissues. The T F glycotope was detected in 7% of the normal mucosa, but in 57% of the carc inoma samples. Expression of alpha2,3-sialyltransferases ST3Gal-I, ST3Gal-I I, and enzyme activity of alpha2,3-sialyltransferase was significantly incr eased (P < 0.001) in carcinoma specimens compared with normal mucosa, ST3Ga l-I mRNA expression was significantly increased (P = 0.05) in cases showing invasion of lymph vessels. Expression of ST6GalNAc-II was significantly in creased (P = 0.04) in cases with metastases to lymph nodes along the vascul ar trunk. Moreover, ST6GalNAc-II expression provides an prognostic factor f or patient survival (log rank, P = 0.02), In an attempt to study the functi onal relevance of the glycosyltransferases for TF biosynthesis, SW480 color ectal cells were transfected with each of the enzymes, and cell surface exp ression of the TF glycotope was examined by flow cytometry, The presence of TF was not altered by transfection of the cells with either sialyltransfer ase ST3Gal-I or ST3Gal-II, However, successful transfection with core 2 pl, 6-N-acetylglucosaminyltransferase led to reduced expression of TF, In contr ast, increased cell surface expression of TF was found after ST6GalNAc-II t ransfection, Thus, expression of TF on the cell surface of SW480 colorectal carcinoma cells depends on the ratio of core 2 beta1,6-N-acetylglucosaminy ltransferase and ST6GalNAc-II. Earlier immunohistological studies demonstra ted that TF is a prognostic factor for patient survival. Our results sugges t that sialyltransferase ST6GalNAc-II is of crucial relevance for the progn ostic significance of TF.