The O-GalNAcylating enzyme GALNT5 mediates carcinogenesis and progression of cholangiocarcinoma via activation of AKT/ERK signaling

Mucin type O-glycosylation is a posttranslational modification of membrane and secretory proteins. Transferring of N-acetylgalactosamine, the first sugar of O-glycosylation, is catalyzed by one of the 20 isoforms of polypeptide N-acetylgalactosaminyltransferases (GALNTs). In this study, Vicia villosa lectin (VVL), a lectin that recognizes O-GalNAcylated glycans, was used to detect VVL-binding glycans (VBGs) in cholangiocarcinoma (CCA). The elevation of VBGs in tumor tissues of the liver fluke associated with CCA from hamsters and patients was noted. VBGs were detected in hyperplastic/dysplastic bile ducts and CCA but not in normal biliary epithelia and hepatocytes, indicating the association of VBGs with CCA development and progression. GALNT5 was shown to be the major isoform found in human CCA cell lines with high VBG expression. Suppression of GALNT5 expression using siRNA significantly reduced VBG expression, signifying the connection of GALNT5 and VBGs observed. Knocked-down GALNT5 expression considerably inhibited proliferation, migration and invasion of CCA cells. Increased expression of GALNT5 using pcDNA3.1-GALNT5 expression vector induced invasive phenotypes in CCA cells with low GALNT5 expression. Increasing of claudin-1 and decreasing of slug and vimentin expression together with inactivation of Akt/Erk signaling were noted in GALNT5 knocked-down cells. These observations were reversed in GALNT5 over-expressing cells. GALNT5-modulated progression of CCA cells was shown to be, in part, via GALNT5-mediated autocrine/paracrine factors that stimulated activations of Akt/Erk signaling and the epithelial to mesenchymal transition process. GALNT5 and its O-GalNAcylated products may have important roles in promoting progression of CCA and could possibly be novel targets for treatment of metastatic CCA.