title: Phosphorylation-mediated 14-3-3 protein binding regulates the function of the rho-specific guanine nucleotide exchange factor (RhoGEF) Syx.
abstract: Syx is a Rho-specific guanine nucleotide exchange factor (GEF) that localizes at cell-cell junctions and promotes junction stability by activating RhoA and the downstream effector Diaphanous homolog 1 (Dia1). Previously, we identified several molecules, including 14-3-3 proteins, as Syx-interacting partners. In the present study, we show that 14-3-3 isoforms interact with Syx at both its N- and C-terminal regions in a phosphorylation-dependent manner. We identify the protein kinase D-mediated phosphorylation of serine 92 on Syx, and additional phosphorylation at serine 938, as critical sites for 14-3-3 association. Our data indicate that the binding of 14-3-3 proteins inhibits the GEF activity of Syx. Furthermore, we show that phosphorylation-deficient, 14-3-3-uncoupled Syx exhibits increased junctional targeting and increased GEF activity, resulting in the strengthening of the circumferential junctional actin ring in Madin-Darby canine kidney cells. These findings reveal a novel means of regulating junctional Syx localization and function by phosphorylation-induced 14-3-3 binding and further support the importance of Syx function in maintaining stable cell-cell contacts.
authors: Department of Cancer Biology, Mayo Clinic Comprehensive Cancer Center, Jacksonville, Florida 32224, USA.
authors: Siu P
authors: SP
authors: Ngok
authors: Rory
authors: R
authors: Geyer
authors: Antonis
authors: A
authors: Kourtidis
authors: Peter
authors: P
authors: Storz
authors: Panos Z
authors: PZ
authors: Anastasiadis
mesh_terms: D048948:14-3-3 Proteins / Q000235:genetics / Q000378:metabolism*; D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002450:Cell Communication / Q000502:physiology*; D004285:Dogs; D000080865:Formins; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D010766:Phosphorylation / Q000502:physiology; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D055550:Protein Stability; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000502:physiology
chemical_list: D048948:14-3-3 Proteins; D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C108962:DIAPH1 protein, human; C491464:Diap1 protein, mouse; D000080865:Formins; D020662:Guanine Nucleotide Exchange Factors; D020033:Protein Isoforms; C511269:Syx protein, mouse