title: The Rho1p exchange factor Rgf1p signals upstream from the Pmk1 mitogen-activated protein kinase pathway in fission yeast.
abstract: The Schizosaccharomyces pombe exchange factor Rgf1p specifically regulates Rho1p during polarized growth. Rgf1p activates the beta-glucan synthase (GS) complex containing the catalytic subunit Bgs4p and is involved in the activation of growth at the second end, a transition that requires actin reorganization. In this work, we investigated Rgf1p signaling and observed that Rgf1p acted upstream from the Pck2p-Pmk1p MAPK signaling pathway. We noted that Rgf1p and calcineurin play antagonistic roles in Cl(-) homeostasis; rgf1Delta cells showed the vic phenotype (viable in the presence of immunosuppressant and chlorine ion) and were unable to grow in the presence of high salt concentrations, both phenotypes being characteristic of knockouts of the MAPK components. In addition, mutations that perturb signaling through the MAPK pathway resulted in defective cell integrity (hypersensitivity to caspofungin and beta-glucanase). Rgf1p acts by positively regulating a subset of stimuli toward the Pmk1p-cell integrity pathway. After osmotic shock and cell wall damage HA-tagged Pmk1p was phosphorylated in wild-type cells but not in rgf1Delta cells. Finally, we provide evidence to show that Rgf1p regulates Pmk1p activation in a process that involves the activation of Rho1p and Pck2p, and we demonstrate that Rgf1p is unique in this signaling process, because Pmk1p activation was largely independent of the other two Rho1p-specific GEFs, Rgf2p and Rgf3p.
authors.affiliation: Instituto de Microbiología Bioquímica, CSIC/Universidad de Salamanca and Departamento de Microbiología y Genética, Universidad de Salamanca, Campus Miguel de Unamuno, 37007 Salamanca, Spain.
authors.forename: Patricia
authors.initials: P
authors.lastname: Garcia
authors.forename: Virginia
authors.initials: V
authors.lastname: Tajadura
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Sanchez
mesh_terms: D000935:Antifungal Agents / Q000494:pharmacology; D000077336:Caspofungin; D002473:Cell Wall / Q000648:ultrastructure; D054714:Echinocandins / Q000494:pharmacology; D004789:Enzyme Activation; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D006358:Hot Temperature; D006861:Hydrogen Peroxide / Q000378:metabolism; D055666:Lipopeptides; D020935:MAP Kinase Signaling System / Q000502:physiology*; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D009997:Osmotic Pressure; D016877:Oxidants / Q000378:metabolism; D010641:Phenotype; D012568:Schizosaccharomyces / Q000187:drug effects / Q000502:physiology*; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics / Q000378:metabolism*; D013012:Sorbitol / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D000935:Antifungal Agents; D054714:Echinocandins; D020662:Guanine Nucleotide Exchange Factors; D055666:Lipopeptides; D016877:Oxidants; C511265:Rgf1 protein, S pombe; D029702:Schizosaccharomyces pombe Proteins; D013012:Sorbitol; D006861:Hydrogen Peroxide; D020928:Mitogen-Activated Protein Kinases; C516338:Pmk1 protein, S pombe; C524689:Spc1 protein, S pombe; D020741:rho GTP-Binding Proteins; C511156:rho1 protein, S pombe; D000077336:Caspofungin