title: In Saccharomyces cerevisiae an unbalanced level of tyrosine phosphorylation down-regulates the Ras/PKA pathway.
abstract: The role of tyrosyl phosphorylation/dephosphorylation in the budding yeast Saccharomyces cerevisiae, whose genome does not encode typical tyrosine kinases, has long remained elusive. Nevertheless, several protein kinases phosphorylating poly(TyrGlu) substrates have been identified. In this work, we use the expression of the low molecular weight tyrosine phosphatase Stp1 from the distantly related yeast Schizosaccharomyces pombe, as a tool to investigate whether an unbalanced level of protein tyrosine phosphorylation affects S. cerevisiae growth and metabolism. We correlate the previously reported down-regulation of the phosphotyrosine level brought about by overexpression of Stp1 with a large number of phenotypes indicative of down-regulation of the Ras pathway. These phenotypes include reduction in both glucose- and acidification-induced GTP loading of the Ras2 protein and cAMP signaling, impaired growth on a non-fermentable carbon source, alteration of cell cycle parameters, delayed recovery from nitrogen starvation, increased heat-shock resistance, attenuated pseudohyphal and invasive growth. Genetic data suggest that Stp1 acts either at, or above, the level of Ras2, possibly on the Ira proteins. Consistently, Stp1 was found to bind to immunoprecipitated Ira2. Since a catalytically inactive mutant form of Stp1 (Stp1(C11S)) effectively binds to Ira2 without producing any effect on yeast physiology, we conclude that down-regulation of the Ras pathway by Stp1 requires its phosphatase activity. In conclusion, our data suggest a possible cross-talk between tyrosine phosphorylation and the Ras pathway in yeast.
authors.affiliation: Dipartimento di Scienze Biochimiche, Università degli Studi di Firenze, Firenze, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Magherini
authors.forename: Stefano
authors.initials: S
authors.lastname: Busti
authors.forename: Tania
authors.initials: T
authors.lastname: Gamberi
authors.forename: Elena
authors.initials: E
authors.lastname: Sacco
authors.forename: Giovanni
authors.initials: G
authors.lastname: Raugei
authors.forename: Gianpaolo
authors.initials: G
authors.lastname: Manao
authors.forename: Giampietro
authors.initials: G
authors.lastname: Ramponi
authors.forename: Alessandra
authors.initials: A
authors.lastname: Modesti
authors.forename: Marco
authors.initials: M
authors.lastname: Vanoni
mesh_terms: D002453:Cell Cycle / Q000502:physiology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D015536:Down-Regulation; D000431:Ethanol / Q000378:metabolism; D044385:GTP-Binding Protein alpha Subunits / Q000235:genetics / Q000378:metabolism; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D010641:Phenotype; D010766:Phosphorylation; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D014443:Tyrosine / Q000378:metabolism*; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C109334:GPR1 protein, S cerevisiae; D044385:GTP-Binding Protein alpha Subunits; D020690:GTPase-Activating Proteins; C064960:IRA2 protein, S cerevisiae; D043562:Receptors, G-Protein-Coupled; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; D000431:Ethanol; D014443:Tyrosine; D006003:Glycogen; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D017027:Protein Tyrosine Phosphatases; C509508:Stp1 protein, S pombe; C083907:Gpa2 protein, S cerevisiae; C540695:gpa2 protein, S pombe; C489015:RAS2 protein, S cerevisiae; D018631:ras Proteins