Clinical relevance of sialyltransferases ST6GAL-I and ST3GAL-III in gastric cancer

Aberrant glycosylation of membrane components due to specific alterations of glycosyltransferase activity is a common feature of carcinoma cells and is usually associated with invasion and metastasis. In a prospective study, the enzyme activity of the sialyltransferases ST6GAL-I and ST3GAL-III was studied in gastric cancer and normal mucosa in 55 patients by a radiometric assay. Cellular localization of sialyltransferase ST6GAL-I mRNA expression was studied by in situ hybridization. Sialyltransferase ST6GAL-I mRNA expression was mainly localized to epithelial cells. ST6GAL-I enzyme activity was enhanced within the tumor tissue. Significant correlations were found between the presence of signet ring cells and enhanced ST6GAL-I activity in the tumor tissue (p = 0.047) or in the mucosa (p = 0.024), and between signet ring cells and ST3GAL-III activity in the mucosa (p < 0.001). Multivariate Cox analysis demonstrated that only lymph node metastases (p = 0.044) had a significant influence on tumor-related survival. ST3GAL-III and ST6GAL-I activity showed no independent prognostic relevance in multivariate analysis, but high levels of ST3GAL-III and ST6GAL-I in the tumor tissue correlated with secondary local tumor recurrence (p = 0.005; p = 0.012). Interestingly, also the nonmalignant and uninvolved mucosa of tumor patients was altered on the molecular level and in some cases showed enhanced sialyltransferase levels indicative of the alteration of glycosylation very early during tumorigenesis.