Enhancement of metastatic ability by ectopic expression of ST6GalNAcI on a gastric cancer cell line in a mouse model.

ST6GalNAcI is a sialyltransferase responsible for the synthesis of sialyl Tn (sTn) antigen which is expressed in a variety of adenocarcinomas including gastric cancer especially in advanced cases, but the roles of ST6GalNAcI and sTn in cancer progression are largely unknown. We generated sTn-expressing human gastric cancer cells by ectopic expression of ST6GalNAcI to evaluate metastatic ability of these cells and prognostic effect of ST6GalNAcI and sTn in a mouse model, and identified sTn carrier proteins to gain insight into the function of ST6GalNAcI and sTn in gastric cancer progression. A green fluorescent protein-tagged human gastric cancer cell line was transfected with ST6GalNAcI to produce sTn-expressing cells, which were transplanted into nude mice. STn-positive gastric cancer cells showed higher intraperitoneal metastatic ability in comparison with sTn-negative control, resulting in shortened survival time of the mice, which was mitigated by anti-sTn antibody administration. Then, sTn-carrying proteins were immunoprecipitated from culture supernatants and lysates of these cells, and identified MUC1 and CD44 as major sTn carriers. It was confirmed that MUC1 carries sTn also in human advanced gastric cancer tissues. Identification of sTn carrier proteins will help understand mechanisms of metastatic phenotype acquisition of gastric cancer cells by ST6GalNAcI and sTn.