BioProject

Sialic acids on vertebrate cell surfaces mediate many biological roles. Altered expression of certain sialic acid types or their linkages can have prognostic significance in human cancer. More...

Sialic acids on vertebrate cell surfaces mediate many biological roles. Altered expression of certain sialic acid types or their linkages can have prognostic significance in human cancer. A classic but unexplained example is enhanced α2-6-sialylation on N-glycans, resulting from over-expression of the Golgi enzyme β-galactoside:α2-6-sialyltransferase (ST6Gal-I). Previous data supporting a role for the resulting Siaα2-3Galβ1-4GlcNAc (Sia6LacNAc) structure in tumor biology were based on in vitro studies in transfected carcinoma cells, in which increased Sia6LacNAc on β1-integrins enhanced their binding to ligands, and stimulated cell motility. Here we examine for the first time the in vivo role of the ST6Gal-I enzyme in the growth and differentiation of spontaneous mammary cancers in mice transgenic for an MMTV-promoter-driven polyoma-middle-T antigen, a tumor in which beta1-integrin function is important for tumorigenesis, and in maintaining the proliferative state of tumor cells. Tumors induced in St6gal1 null animals were more differentiated in comparison to those in the wild-type background, both by histological analysis and by protein expression profiles. Furthermore, we show the St6gal1 null tumors have selectively altered expression of genes associated with focal adhesion signaling, and have decreased phosphorylation of FAK, a downstream target of β1-integrins. This first in vivo evidence for a role of ST6Gal-I in tumor progression was confirmed using a novel approach, which conditionally restored St6gal1 in cell lines derived from the null tumors. These findings indicate a role for ST6Gal-I as a mediator of tumor progression, with its expression causing a less differentiated phenotype, via enhanced β1-integrin function. Keywords: sialic acid, genetic modification, mouse mammary carcinoma Overall design: Messenger RNA from tumors arising in wild-type or St6gal1 null littermates was used for the gene expression analysis on the Mouse Genome 430 2.0 Array (Affymetrix). Six PyV-mT St6gal1 null and wild-type tumor pairs were used, in four independent pools of three tumors each. Each sample is a pool of three different tumors from three different animals. For the first set of microarray analysis samples GSM239969 and GSM239970 were being compared, and in the second set, samples GSM239971 and GSM239972 were compared. Less...