As the observed changes in O-glycan synthesis can be associated with changes in the expression of specific glycosyltransferases, core 1 β1,3-galactosyltransferase, core 2 β1,6-N-acetylglucosaminyltransferase (C2GnT1) and β-galactoside α2,3-sialyltransferase (ST3Gal I), we studied their expression in parental, vector-transfected and MUC1-transfected MDA-MB-231 and 4T1 cells as well as T47D cells transduced with small hairpin RNA targeted MUC1 mRNA.