title: Transforming growth factor-beta and epidermal growth factor synergistically stimulate epithelial to mesenchymal transition (EMT) through a MEK-dependent mechanism in primary cultured pig thyrocytes.
abstract: Enhancement of tumor cell growth and invasiveness by transforming growth factor-beta (TGF-beta) requires constitutive activation of the ras/MAPK pathway. Here we have investigated how MEK activation by epidermal growth factor (EGF) influences the response of fully differentiated and growth-arrested pig thyroid epithelial cells in primary culture to TGF-beta1. The epithelial tightness was maintained after single stimulation with EGF or TGF-beta1 (both 10 ng/ml) for 48 hours. In contrast, co-stimulation abolished the transepithelial resistance and increased the paracellular flux of [(3)H]inulin within 24 hours. Reduced levels of the tight junction proteins claudin-1 and occludin accompanied the loss of barrier function. N-cadherin, expressed only in few cells of untreated or single-stimulated cultures, was at the same time increased 30-fold and co-localised with E-cadherin at adherens junctions in all cells. After 48 hours of co-stimulation, both E- and N-cadherin were downregulated and the cells attained a fibroblast-like morphology and formed multilayers. TGF-beta1 only partially inhibited EGF-induced Erk phosphorylation. The MEK inhibitor U0126 prevented residual Erk phosphorylation and abrogated the synergistic responses to TGF-beta1 and EGF. The observations indicate that concomitant growth factor-induced MEK activation is necessary for TGF-beta1 to convert normal thyroid epithelial cells to a mesenchymal phenotype.
authors.affiliation: Institute of Anatomy and Cell Biology, Göteborg University, Göteborg, Sweden. mats.grande@anatcell.gu.se
authors.forename: Mats
authors.initials: M
authors.lastname: Grände
authors.forename: Asa
authors.initials: A
authors.lastname: Franzen
authors.forename: Jan-Olof
authors.initials: JO
authors.lastname: Karlsson
authors.forename: Lars E
authors.initials: LE
authors.lastname: Ericson
authors.forename: Nils-Erik
authors.initials: NE
authors.lastname: Heldin
authors.forename: Mikael
authors.initials: M
authors.lastname: Nilsson
mesh_terms: D022005:Adherens Junctions / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D000818:Animals; D015820:Cadherins / Q000187:drug effects / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D048429:Cell Size / Q000187:drug effects / Q000502:physiology; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D062445:Claudin-1; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D004347:Drug Interactions / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000378:metabolism* / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000201:enzymology* / Q000648:ultrastructure; D048369:MAP Kinase Kinase 1; D008565:Membrane Proteins / Q000187:drug effects / Q000378:metabolism; D008648:Mesoderm / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008854:Microscopy, Electron; D020929:Mitogen-Activated Protein Kinase Kinases / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism; D009361:Neoplasm Invasiveness / Q000235:genetics* / Q000503:physiopathology; D062793:Occludin; D017346:Protein Serine-Threonine Kinases / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D034421:Sus scrofa; D013961:Thyroid Gland / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D019108:Tight Junctions / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D016212:Transforming Growth Factor beta / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D015820:Cadherins; D062445:Claudin-1; D004791:Enzyme Inhibitors; D008565:Membrane Proteins; D062793:Occludin; D016212:Transforming Growth Factor beta; D004815:Epidermal Growth Factor; D017346:Protein Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases