title: Mitogen-activated protein kinase (MAPK) pathway regulates branching by remodeling epithelial cell adhesion.
abstract: Although the growth factor (GF) signaling guiding renal branching is well characterized, the intracellular cascades mediating GF functions are poorly understood. We studied mitogen-activated protein kinase (MAPK) pathway specifically in the branching epithelia of developing kidney by genetically abrogating the pathway activity in mice lacking simultaneously dual-specificity protein kinases Mek1 and Mek2. Our data show that MAPK pathway is heterogeneously activated in the subset of G1- and S-phase epithelial cells, and its tissue-specific deletion results in severe renal hypodysplasia. Consequently to the deletion of Mek1/2, the activation of ERK1/2 in the epithelium is lost and normal branching pattern in mutant kidneys is substituted with elongation-only phenotype, in which the epithelium is largely unable to form novel branches and complex three-dimensional patterns, but able to grow without primary defects in mitosis. Cellular characterization of double mutant epithelium showed increased E-cadherin at the cell surfaces with its particular accumulation at baso-lateral locations. This indicates changes in cellular adhesion, which were revealed by electron microscopic analysis demonstrating intercellular gaps and increased extracellular space in double mutant epithelium. When challenged to form monolayer cultures, the mutant epithelial cells were impaired in spreading and displayed strong focal adhesions in addition to spiky E-cadherin. Inhibition of MAPK activity reduced paxillin phosphorylation on serine 83 while remnants of phospho-paxillin, together with another focal adhesion (FA) protein vinculin, were augmented at cell surface contacts. We show that MAPK activity is required for branching morphogenesis, and propose that it promotes cell cycle progression and higher cellular motility through remodeling of cellular adhesions.
authors.affiliation: Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
authors.forename: Anneliis
authors.initials: A
authors.lastname: Ihermann-Hella
authors.affiliation: Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
authors.forename: Maria
authors.initials: M
authors.lastname: Lume
authors.affiliation: Department of Pathology, University of Oulu, Oulu, Finland.
authors.forename: Ilkka J
authors.initials: IJ
authors.lastname: Miinalainen
authors.affiliation: Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
authors.forename: Anniina
authors.initials: A
authors.lastname: Pirttiniemi
authors.affiliation: Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
authors.forename: Yujuan
authors.initials: Y
authors.lastname: Gui
authors.affiliation: Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
authors.forename: Johan
authors.initials: J
authors.lastname: Peränen
authors.affiliation: Centre de Recherche en Cancérologie de l'Université Laval, CRCHUQ, Hôtel-Dieu de Québec, Québec, Canada.
authors.forename: Jean
authors.initials: J
authors.lastname: Charron
authors.affiliation: Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
authors.forename: Mart
authors.initials: M
authors.lastname: Saarma
authors.affiliation: Department of Genetics and Development, Columbia University Medical Center, New York, New York, United States of America.
authors.forename: Frank
authors.initials: F
authors.lastname: Costantini
authors.affiliation: Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
authors.forename: Satu
authors.initials: S
authors.lastname: Kuure
mesh_terms: D000818:Animals; D004847:Epithelial Cells / Q000378:metabolism; D022001:Focal Adhesions / Q000235:genetics*; D007668:Kidney / Q000254:growth & development* / Q000378:metabolism; D048369:MAP Kinase Kinase 1 / Q000235:genetics* / Q000378:metabolism; D048370:MAP Kinase Kinase 2 / Q000235:genetics* / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000235:genetics; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics; D009024:Morphogenesis / Q000235:genetics; D010766:Phosphorylation; D015398:Signal Transduction / Q000235:genetics; D016596:Vinculin / Q000378:metabolism
chemical_list: D016596:Vinculin; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C482127:Map2k1 protein, mouse; C482129:Map2k2 protein, mouse