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Alpha2-6-linked Sialic Acids on N-Glycans Modulate Carcinoma Differentiation In Vivo

ABSTRACT: 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

ORGANISM(S): Mus musculus

PROVIDER: GSE9447 | GEO | 2008/01/01

SECONDARY ACCESSION(S): PRJNA103203

REPOSITORIES: GEO

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Project description: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 Î±2-6-sialylation on N-glycans, resulting from over-expression of the Golgi enzyme Î²-galactoside:Î±2-6-sialyltransferase (ST6Gal-I). Previous data supporting a role for the resulting SiaÎ±2-3GalÎ²1-4GlcNAc (Sia6LacNAc) structure in tumor biology were based on in vitro studies in transfected carcinoma cells, in which increased Sia6LacNAc on Î²1-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 Î²1-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 Î²1-integrin function. Experiment 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.

Project description:Primary myelofibrosis (PMF) is a myeloproliferative neoplasm prone to leukemic transformation, for which limited treatment is available. Amongst individuals diagnosed with PMF, the most prevalent mutation is the JAK2V617F somatic point mutation that activates the Janus kinase 2 (JAK2) enzyme. Our earlier reports on hyperactivity of β1 integrin and enhanced adhesion activity of the α2β1 complex in JAK2V617F megakaryocytes (MKs) led us to examine the new hypothesis that this mutation leads to post-translational modification via changes in glycosylation. Samples were derived from immunoprecipitation of MKs obtained from Vav1-hJAK2V617F and wild type mice. Immunoprecipitated fractions were separated by SDS-PAGE and analyzed using LC-MS/MS techniques in a bottom-up glycoproteomics workflow. In the immunoprecipitate, glycopeptiforms corresponding to 11 out of the 12 potential N-glycosylation sites of integrin β1, and to all nine potential glycosylation sites of integrin α2, were observed. Glycopeptiforms were compared across WT and JAK2V617F phenotypes for both integrins. The overall trend observed is that JAK2V617F mutation in PMF MKs leads to changes in β1 glycosylation; in most cases, it results in an increase in the integrated area of glycopeptiforms. We also observed that, in mutated MKs, changes in integrin α2 glycosylation were more substantial than those observed for integrin β1 glycosylation, a finding that suggests that altered integrin α2 glycosylation may also affect activation. Additionally, the identification of proteins associated to the cytoskeleton that were co-immunoprecipitated with integrins α2 and β1 demonstrated the potential of the methodology employed in this study to provide some insight, at the peptide level, into the consequences of integrin activation in MKs. The extensive and detailed glycosylation patterns we uncovered provide a basis for future functional studies of each site in control cells as compared to JAK2V617F mutated cells.

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Alpha2-6-linked Sialic Acids on N-Glycans Modulate Carcinoma Differentiation In Vivo

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