Involvement of O-glycosylation defining oncofetal fibronectin in epithelial-mesenchymal transition process

Abstract

The process termed "epithelial-mesenchymal transition" (EMT) was originally discovered in ontogenic development, and has been shown to be one of the key steps in tumor cell progression and metastasis. Recently, we showed that the expression of some glycosphingolipids (GSLs) is down-regulated during EMT in human and mouse cell lines. Here, we demonstrate the involvement of GalNAc-type (or mucintype) O-glycosylation in EMT process, induced with transforming growth factor β (TGF-β) in human prostate epithelial cell lines. We found that: (i) TGF-β treatment caused up-regulation of oncofetal fibronectin (onfFN), which is defined by mAb FDC6, and expressed in cancer or fetal cells/tissues, but not in normal adult cells/tissues. The reactivity of mAb FDC6 requires the addition of an O-glycan at a specific threonine, inside the type III homology connective segment (IIICS) domain of FN. (ii) This change is associated with typical EMT characteristics; i.e., change from epithelial to fibroblastic morphology, enhanced cell motility, decreased expression of a typical epithelial cell marker, E-cadherin, and enhanced expression of mesenchymal markers. (iii) TGF-β treatment up-regulated mRNA level of FN containing the IIICS domain and GalNAc-T activity for the IIICS domain peptide substrate containing the FDC6 onfFN epitope. (iv) Knockdown of GalNAc-T6 and T3 inhibited TGF-β-induced up-regulation of onfFN and EMT process. (v) Involvement of GSLs was not detectable with the EMT process in these cell lines. These findings indicate the important functional role of expression of onfFN, defined by sitespecific O-glycosylation at IIICS domain, in the EMT process.O-glycosylated fibronectin | siRNA G lycoconjugates, such as glycosphingolipids (GSLs) and N-and O-linked glycoproteins, have been shown to play important roles in embryogenesis (1), tumorigenesis, and cancer progression (2). Specific types of glycosyl residues modulate particular signaling pathways and regulate cell phenotypes. For example, GM3 inhibits epithelial growth factor receptor (EGFR) activation (3, 4); GM2 associated with tetraspanine CD82 inhibits the activation of the hepatocyte growth factor receptor cMet (5); and O-Fucose glycans modulate Notch signaling, which controls the fate of many cell types (6-8).Epithelial-mesenchymal transition (EMT) was initially observed during early embryonic development and organ formation (9-11). Accumulating evidence has shown that the EMT process plays a key role in disease development, particularly in cancer progression to metastasis (10-14) and fibrosis (15). During EMT, cells lose their apical-basal polarity, change morphology to fibroblastic, display reduced expression of epithelial cell marker molecules such as E-cadherin (Ecad), and enhance expression of mesenchymal cell marker molecules such as fibronectin (FN), N-cadherin (Ncad), vimentin, and matrix-metalloproteinases (MMPs). When combined, these effects result in increased cell motility (10-15).Our recent studies found a reduction in specific GSLs (Gg4 and/ or GM2) in ...

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Probing isoform-specific functions of polypeptide GalNAc-transferases using zinc finger nuclease glycoengineered SimpleCells

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N- and O-Glycosylation in the Murine Synaptosome

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