Abstract
C1GALT1 controls the crucial step of GalNAc-type O-glycosylation and is associated with both physiologic and pathologic conditions, including cancers. EPH receptors comprise the largest family of receptor tyrosine kinases (RTKs) and modulate a diverse range of developmental processes and human diseases. However, the role of C1GALT1 in the signaling of EPH receptors remains largely overlooked. Here, we showed that C1GALT1 high expression in gastric adenocarcinomas correlated with adverse clinicopathologic features and is an independent prognostic factor for poor overall survival. Silencing or loss of C1GALT1 inhibited cell viability, migration, invasion, tumor growth and metastasis, as well as increased apoptosis and cytotoxicity of 5-fluorouracil in AGS and MKN45 cells. Phospho-RTK array and western blot analysis showed that C1GALT1 depletion suppressed tyrosine phosphorylation of EPHA2 induced by soluble Ephrin A1-Fc. O-glycans on EPHA2 were modified by C1GALT1 and both S277A and T429A mutants, which are O-glycosites on EPHA2, dramatically enhanced phosphorylation of Y588, suggesting that not only overall O-glycan structures but also site-specific O-glycosylation can regulate EPHA2 activity. Furthermore, depletion of C1GALT1 decreased Ephrin A1-Fc induced migration and reduced Ephrin A1 binding to cell surfaces. The effects of C1GALT1 knockdown or knockout on cell invasiveness in vitro and in vivo were phenocopied by EPHA2 knockdown in gastric cancer cells. These results suggest that C1GALT1 promotes phosphorylation of EPHA2 and enhances soluble Ephrin A1-mediated migration primarily by modifying EPHA2 O-glycosylation. Our study highlights the importance of GalNAc-type O-glycosylation in EPH receptor-regulated diseases and identifies C1GALT1 as a potential therapeutic target for gastric cancer.
Highlights
Supplementary information The online version of this article contains supplementary material, which is available to authorized users.Gastric cancer is the third leading cause of cancer-related deaths in the world [1]
These results suggest that C1GALT1 is significantly overexpressed in gastric adenocarcinomas compared with their adjacent nontumor tissues
C1GALT1-mediated cell growth was suppressed by lapatinib, a dual inhibitor for EGFR and HER2 (Supplementary Fig. S4). These results suggest that C1GALT1 knockdown modifies Oglycosylation and decreases 10% fetal bovine serum (FBS)-mediated phosphorylation of multiple receptor tyrosine kinases (RTKs) including EGFR and HER2 in gastric cancer cells
Summary
Surgery remains the main treatment for operable gastric cancer. New therapeutic approaches are currently being researched, such as monoclonal antibodies that target HER2 and immune. Taipei, Taiwan 6 Department of Medical Research, National Taiwan University. Taipei, Taiwan 7 Department of Life Science, National Taiwan University, Taipei, Taiwan 8 Department of Surgery, E-DA Hospital, Kaohsiung City, Taiwan. Mucin-type O-glycosylation modifies proteins in the gastrointestinal tract, and this modification is initiated through the transfer of Nacetylgalactosamine (GalNAc) to serine or threonine residues forming Tn antigen [4]. This reaction is catalyzed by a large group of enzymes named UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferases (GALNTs) [5]. T-antigen is modified by other glycosyltransferases to form complex O-glycans [7]
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