title: GATA Factor Regulation in Excess Nitrogen Occurs Independently of Gtr-Ego Complex-Dependent TorC1 Activation.
abstract: The TorC1 protein kinase complex is a central component in a eukaryotic cell's response to varying nitrogen availability, with kinase activity being stimulated in nitrogen excess by increased intracellular leucine. This leucine-dependent TorC1 activation requires functional Gtr1/2 and Ego1/3 complexes. Rapamycin inhibition of TorC1 elicits nuclear localization of Gln3, a GATA-family transcription activator responsible for the expression of genes encoding proteins required to transport and degrade poor nitrogen sources, e.g., proline. In nitrogen-replete conditions, Gln3 is cytoplasmic and Gln3-mediated transcription minimal, whereas in nitrogen limiting or starvation conditions, or after rapamycin treatment, Gln3 is nuclear and transcription greatly increased. Increasing evidence supports the idea that TorC1 activation may not be as central to nitrogen-responsive intracellular Gln3 localization as envisioned previously. To test this idea directly, we determined whether Gtr1/2- and Ego1/3-dependent TorC1 activation also was required for cytoplasmic Gln3 sequestration and repressed GATA factor-mediated transcription by abolishing the Gtr-Ego complex proteins. We show that Gln3 is sequestered in the cytoplasm of gtr1Δ, gtr2Δ, ego1Δ, and ego3Δ strains either long term in logarithmically glutamine-grown cells or short term after refeeding glutamine to nitrogen-limited or -starved cells; GATA factor-dependent transcription also was minimal. However, in all but a gtr1Δ, nuclear Gln3 localization in response to nitrogen limitation or starvation was adversely affected. Our data demonstrate: (i) Gtr-Ego-dependent TorC1 activation is not required for cytoplasmic Gln3 sequestration in nitrogen-rich conditions; (ii) a novel Gtr-Ego-TorC1 activation-independent mechanism sequesters Gln3 in the cytoplasm; (iii) Gtr and Ego complex proteins participate in nuclear Gln3-Myc(13) localization, heretofore unrecognized functions for these proteins; and (iv) the importance of searching for new mechanisms associated with TorC1 activation and/or the regulation of Gln3 localization/function in response to changes in the cells' nitrogen environment.
authors.affiliation: Department of Microbiology, Immunology and Biochemistry, University of Tennessee Health Science Center, Memphis, Tennessee 38163.
authors.forename: Jennifer J
authors.initials: JJ
authors.lastname: Tate
authors.affiliation: Institut de Recherches Microbiologiques J.-M. Wiame, Laboratoire de Microbiologie Université Libre de Bruxelles, Brussels B1070, Belgium.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Georis
authors.affiliation: Department of Microbiology, Immunology and Biochemistry, University of Tennessee Health Science Center, Memphis, Tennessee 38163.
authors.forename: Rajendra
authors.initials: R
authors.lastname: Rai
authors.affiliation: Institut de Recherches Microbiologiques J.-M. Wiame, Laboratoire de Microbiologie Université Libre de Bruxelles, Brussels B1070, Belgium.
authors.forename: Fabienne
authors.initials: F
authors.lastname: Vierendeels
authors.affiliation: Institut de Recherches Microbiologiques J.-M. Wiame, Laboratoire de Microbiologie Université Libre de Bruxelles, Brussels B1070, Belgium.
authors.forename: Evelyne
authors.initials: E
authors.lastname: Dubois
authors.affiliation: Department of Microbiology, Immunology and Biochemistry, University of Tennessee Health Science Center, Memphis, Tennessee 38163 tcooper@uthsc.edu.
authors.forename: Terrance G
authors.initials: TG
authors.lastname: Cooper
mesh_terms: D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D050980:GATA Transcription Factors / Q000378:metabolism*; D017930:Genes, Reporter; D005838:Genotype; D005973:Glutamine / Q000378:metabolism; D000076222:Mechanistic Target of Rapamycin Complex 1; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D046912:Multiprotein Complexes / Q000378:metabolism*; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: D050980:GATA Transcription Factors; C121263:GTR2 protein, S cerevisiae; C552591:Gse1 protein, S cerevisiae; C121262:Gtr1 protein, S cerevisiae; C501979:MEH1 protein, S cerevisiae; D008565:Membrane Proteins; D046912:Multiprotein Complexes; D029701:Saccharomyces cerevisiae Proteins; D005973:Glutamine; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D020559:Monomeric GTP-Binding Proteins; D009584:Nitrogen
keywords: Ego1/3 complex; Gln3 localization; Gtr1/2 complex; Tor complex one (TORC1); nitrogen catabolite repression (NCR); nitrogen limitation; nitrogen starvation