O-GLYCAN BIOSYNTHESIS IN HUMAN COLORECTAL ADENOMA CELLS DURING PROGRESSION TO CANCER

A human colonic adenoma cell line PC/AA derived from a familial polypo sis coli patient was passaged in culture to form an intermediate prema lignant clonogenic variant AA/C1 and, upon treatment with differentiat ing and carcinogenic agents, a cell line AA/C1/SB10 which is tumourige nic in nude mice. These three mucin-secreting cell lines have been use d as a model to study the changes in O-glycan biosynthesis during the progression to cancer. Several glycosyltransferases involved in the sy nthesis, elongation and termination of the common O-glycan core struct ures were found to decrease in the progression sequence towards adenoc arcinoma. Higher activity of a number of enzymes was seen in the inter mediate cell line. O-glycan biosynthesis in the original PC/AA cell li ne was closest to the normal human colonic phenotype, since al four co mmon mucin O-glycan cores and their extended structures could be synth esized; core 3 beta 3-GlcNAc-transferase and alpha 6-sialyltransferase acting on GalNAc-mucin were still detectable and core 2 beta 6-GlcNAc -transferase activity was accompanied by core 4 and I beta 6-GlcNAc-tr ansferase activities. During progression towards adenocarcinoma, the e xpression of alpha 6-sialyltransferase, core 3 beta 3-GlcNAc-transfera se, core 4 and I beta 6-GlcNAc-transferases were turned off. Using mon oclonal antibodies, Tn antigen, sialyl-Tn antigen, O-acetyl-sialomucin and sialyl-Le(a) determinants were not detected in secreted or cellul ar mucin isolated from any of the cell lines. The exposure of MUC1 epi topes was seen in the malignant line, whereas sialyl-Le(a) determinant s were found only in the premalignant PC/AA line. Sulfotransferase act ivities using core 1 substrate, Gal beta 1-3GalNAc alpha-benzyl, were high in PC/AA cells and progressively decreased upon development to ad enocarcinoma, and this decrease correlated with mucin sulfation. In su mmary, the synthesis of less abundant, sialylated, fucosylated and ext ended, unbranched core 1 structures should be facilitated in the malig nant cells. This is the first report of glycosyltransferase changes in human premalignant cells developing to tumourigenic cells. The data d emonstrate that these cell lines are an excellent model to study the c hanges and regulation of mucin oligosaccharide biosynthesis during pro gression to cancer.