title: Mucin biosynthesis: epidermal growth factor downregulates core 2 enzymes in a human airway adenocarcinoma cell line.
abstract: Enzymes which exhibit core 2 beta1,6 N-acetylglucosaminyltransferase (C2GnT) activity play important roles in physiologic processes including the inflammatory response and immune system function, and C2GnT activity is regulated during processes, such as T cell activation and cellular differentiation. In this study, we have examined the regulation of C2GnT activity in the H292 airway epithelial cell line by epidermal growth factor (EGF), which has been previously shown to upregulate expression of the airway mucin MUC5AC in this cell line. We found that EGF suppressed C2GnT activity in a time- and dose-dependent fashion, and also suppressed core 4 beta1,6 N-acetylglucosaminyltransferase (C4GnT) activity. Consistent with the suppression of C4GnT activity, Northern blotting results showed that EGF preferentially inhibited the M isoform of C2GnT, which forms core 2, core 4, and blood group I beta1,6 branched carbohydrate structures, while the L isoform, which forms only the core 2 structure, was only modestly affected. Furthermore, EGF treatment resulted in a shift in the carbohydrate structure of FLAG-tagged MUC1 expressed in the cells from core 2-based toward core 1-based structures, consistent with the inhibitory effects of EGF on C2GnT. Transforming growth factor alpha mimicked the effect of EGF on C2GnT, implicating the EGF receptor (EGF-R) in C2GnT suppression, and the EGF-R tyrosine kinase inhibitor AG1478 blocked C2GnT suppression, confirming the role of EGF-R in the inhibition of C2GnT expression. Also, PD98059, a specific inhibitor of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK)1/2 in the Ras-mitogen-activated protein kinase pathway, completely blocked the EGF suppressive effect, suggesting possible involvement of the Ras-mitogen-activated protein kinase pathway in EGF-mediated downregulation of C2GnT. The results of this study suggest that exposure of airway cells to EGF may result in remodeling of mucin carbohydrate structure, potentially altering the biological properties of the cells.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, Nebraska 68198-4525, USA.
authors.forename: Paul V
authors.initials: PV
authors.lastname: Beum
authors.forename: Dhundy R
authors.initials: DR
authors.lastname: Bastola
authors.forename: Pi-Wan
authors.initials: PW
authors.lastname: Cheng
mesh_terms: D000230:Adenocarcinoma / Q000378:metabolism*; D002240:Carbohydrate Sequence; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000378:metabolism* / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D008969:Molecular Sequence Data; D018396:Mucin-1 / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D009077:Mucins / Q000096:biosynthesis*; D017351:N-Acetylglucosaminyltransferases / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D012142:Respiratory Tract Neoplasms / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D004791:Enzyme Inhibitors; D005419:Flavonoids; D007093:Imidazoles; D018396:Mucin-1; D009077:Mucins; D011725:Pyridines; D012333:RNA, Messenger; D004815:Epidermal Growth Factor; D017351:N-Acetylglucosaminyltransferases; C053024:beta-1,3-galactosyl-O-glycosyl-glycoprotein beta-1,6-acetylglucosaminyl transferase; C476018:core 4 beta1,6 N-acetylglucosaminyltransferase, human; C482128:MAP2K2 protein, human; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C482125:MAP2K1 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases; C090942:4-(4-fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)imidazole; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one