title: Paracingulin regulates the activity of Rac1 and RhoA GTPases by recruiting Tiam1 and GEF-H1 to epithelial junctions.
abstract: Small GTPases control key cellular events, including formation of cell-cell junctions and gene expression, and are regulated by activating and inhibiting factors. Here, we characterize the junctional protein paracingulin as a novel regulator of the activity of two small GTPases, Rac1 and RhoA, through the functional interaction with their respective activators, Tiam1 and GEF-H1. In confluent epithelial monolayers, paracingulin depletion leads to increased RhoA activity and increased expression of mRNA for the tight junction protein claudin-2. During tight junction assembly by the calcium-switch, Rac1 shows two transient peaks of activity, at earlier (10-20 min) and later (3-8 h) time points. Paracingulin depletion reduces such peaks of Rac1 activation in a Tiam1-dependent manner, resulting in a delay in junction formation. Paracingulin physically interacts with GEF-H1 and Tiam1 in vivo and in vitro, and it is required for their efficient recruitment to junctions, based on immunofluorescence and biochemical experiments. Our results provide the first description of a junctional protein that interacts with GEFs for both Rac1 and RhoA, and identify a novel molecular mechanism whereby Rac1 is activated during junction formation.
authors.affiliation: Department of Molecular Biology, University of Geneva, CH-1211 Geneva, Switzerland.
authors.forename: Laurent
authors.initials: L
authors.lastname: Guillemot
authors.forename: Serge
authors.initials: S
authors.lastname: Paschoud
authors.forename: Lionel
authors.initials: L
authors.lastname: Jond
authors.forename: Andrea
authors.initials: A
authors.lastname: Foglia
authors.forename: Sandra
authors.initials: S
authors.lastname: Citi
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism / Q000502:physiology*; D057167:Claudins; D003598:Cytoskeletal Proteins; D004285:Dogs; D004848:Epithelium / Q000378:metabolism*; D017629:Gap Junctions; D005786:Gene Expression Regulation; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D008954:Models, Biological; D012333:RNA, Messenger / Q000378:metabolism; D064067:Rho Guanine Nucleotide Exchange Factors; D013347:Subcellular Fractions / Q000378:metabolism; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; D062825:Zonula Occludens Proteins; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*
chemical_list: C577356:ARHGEF2 protein, human; C533277:CGNL1 protein, human; C491875:CLDN2 protein, human; D002352:Carrier Proteins; D057167:Claudins; D003598:Cytoskeletal Proteins; D020662:Guanine Nucleotide Exchange Factors; D008565:Membrane Proteins; D012333:RNA, Messenger; D064067:Rho Guanine Nucleotide Exchange Factors; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; C087334:TIAM1 protein, human; C111873:TJP3 protein, human; D062825:Zonula Occludens Proteins; D020830:rac1 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein