title: RhoA, Rac1, and Cdc42 exert distinct effects on epithelial barrier via selective structural and biochemical modulation of junctional proteins and F-actin.
abstract: Epithelial intercellular junctions regulate cell-cell contact and mucosal barrier function. Both tight junctions (TJs) and adherens junctions (AJs) are regulated in part by their affiliation with the F-actin cytoskeleton. The cytoskeleton in turn is influenced by Rho family small GTPases such as RhoA, Rac1, and Cdc42, all of which constitute eukaryotic targets for several pathogenic organisms. With a tetracycline-repressible system to achieve regulated expression in Madin-Darby canine kidney (MDCK) epithelial cells, we used dominant-negative (DN) and constitutively active (CA) forms of RhoA, Rac1, and Cdc42 as tools to evaluate the precise contribution of each GTPase to epithelial structure and barrier function. All mutant GTPases induced time-dependent disruptions in epithelial gate function and distinct morphological alterations in apical and basal F-actin pools. TJ proteins occludin, ZO-1, claudin-1, claudin-2, and junctional adhesion molecule (JAM)-1 were dramatically redistributed in the presence of CA RhoA or CA Cdc42, whereas only claudins-1 and -2 were redistributed in response to CA Rac1. DN Rac1 expression also induced selective redistribution of claudins-1 and -2 in addition to JAM-1, whereas DN Cdc42 influenced only claudin-2 and DN RhoA had no effect. AJ protein localization was unaffected by any mutant GTPase, but DN Rac1 induced a reduction in E-cadherin detergent solubility. All CA GTPases increased the detergent solubility of claudins-1 and -2, but CA RhoA alone reduced claudin-2 and ZO-1 partitioning to detergent-insoluble membrane rafts. We conclude that Rho family GTPases regulate epithelial intercellular junctions via distinct morphological and biochemical mechanisms and that perturbations in barrier function reflect any imbalance in active/resting GTPase levels rather than simply loss or gain of GTPase activity.
authors.affiliation: Epithelial Pathobiology Research Unit, Department of Pathology and Lab Medicine, Emory University, Atlanta, GA 30322, USA. bruwer@uni-muenster.de
authors.forename: Matthias
authors.initials: M
authors.lastname: Bruewer
authors.forename: Ann M
authors.initials: AM
authors.lastname: Hopkins
authors.forename: Michael E
authors.initials: ME
authors.lastname: Hobert
authors.forename: Asma
authors.initials: A
authors.lastname: Nusrat
authors.forename: James L
authors.initials: JL
authors.lastname: Madara
mesh_terms: D000199:Actins / Q000378:metabolism*; D022005:Adherens Junctions / Q000378:metabolism; D000818:Animals; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000502:physiology; D062445:Claudin-1; D057167:Claudins; D003902:Detergents; D004285:Dogs; D004847:Epithelial Cells / Q000378:metabolism*; D007668:Kidney / Q000166:cytology; D021962:Membrane Microdomains / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D016296:Mutagenesis / Q000502:physiology; D010750:Phosphoproteins / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism; D012995:Solubility; D019108:Tight Junctions / Q000378:metabolism*; D062826:Zonula Occludens-1 Protein; D020764:cdc42 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D000199:Actins; C568108:CLDN1 protein, human; C491875:CLDN2 protein, human; D015815:Cell Adhesion Molecules; D062445:Claudin-1; D057167:Claudins; D003902:Detergents; D008565:Membrane Proteins; D010750:Phosphoproteins; D011956:Receptors, Cell Surface; C569042:TJP1 protein, human; D062826:Zonula Occludens-1 Protein; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein