title: The yeast Sks1p kinase signaling network regulates pseudohyphal growth and glucose response.
abstract: The yeast Saccharomyces cerevisiae undergoes a dramatic growth transition from its unicellular form to a filamentous state, marked by the formation of pseudohyphal filaments of elongated and connected cells. Yeast pseudohyphal growth is regulated by signaling pathways responsive to reductions in the availability of nitrogen and glucose, but the molecular link between pseudohyphal filamentation and glucose signaling is not fully understood. Here, we identify the glucose-responsive Sks1p kinase as a signaling protein required for pseudohyphal growth induced by nitrogen limitation and coupled nitrogen/glucose limitation. To identify the Sks1p signaling network, we applied mass spectrometry-based quantitative phosphoproteomics, profiling over 900 phosphosites for phosphorylation changes dependent upon Sks1p kinase activity. From this analysis, we report a set of novel phosphorylation sites and highlight Sks1p-dependent phosphorylation in Bud6p, Itr1p, Lrg1p, Npr3p, and Pda1p. In particular, we analyzed the Y309 and S313 phosphosites in the pyruvate dehydrogenase subunit Pda1p; these residues are required for pseudohyphal growth, and Y309A mutants exhibit phenotypes indicative of impaired aerobic respiration and decreased mitochondrial number. Epistasis studies place SKS1 downstream of the G-protein coupled receptor GPR1 and the G-protein RAS2 but upstream of or at the level of cAMP-dependent PKA. The pseudohyphal growth and glucose signaling transcription factors Flo8p, Mss11p, and Rgt1p are required to achieve wild-type SKS1 transcript levels. SKS1 is conserved, and deletion of the SKS1 ortholog SHA3 in the pathogenic fungus Candida albicans results in abnormal colony morphology. Collectively, these results identify Sks1p as an important regulator of filamentation and glucose signaling, with additional relevance towards understanding stress-responsive signaling in C. albicans.
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan, United States of America.
authors.forename: Cole
authors.initials: C
authors.lastname: Johnson
authors.affiliation: Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan, United States of America.
authors.forename: Hye Kyong
authors.initials: HK
authors.lastname: Kweon
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan, United States of America.
authors.forename: Daniel
authors.initials: D
authors.lastname: Sheidy
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan, United States of America.
authors.forename: Christian A
authors.initials: CA
authors.lastname: Shively
authors.affiliation: Department of Pathology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America; Department of Computational Medicine and Bioinformatics, University of Michigan Medical School, Ann Arbor, Michigan, United States of America.
authors.forename: Dattatreya
authors.initials: D
authors.lastname: Mellacheruvu
authors.affiliation: Department of Pathology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America; Department of Computational Medicine and Bioinformatics, University of Michigan Medical School, Ann Arbor, Michigan, United States of America.
authors.forename: Alexey I
authors.initials: AI
authors.lastname: Nesvizhskii
authors.affiliation: Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan, United States of America; Department of Computational Medicine and Bioinformatics, University of Michigan Medical School, Ann Arbor, Michigan, United States of America; Department of Chemistry, University of Michigan, Ann Arbor, Michigan, United States of America.
authors.forename: Philip C
authors.initials: PC
authors.lastname: Andrews
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan, United States of America.
authors.forename: Anuj
authors.initials: A
authors.lastname: Kumar
mesh_terms: D002454:Cell Differentiation / Q000235:genetics; D005947:Glucose / Q000378:metabolism*; D025301:Hyphae / Q000235:genetics* / Q000254:growth & development; D009584:Nitrogen / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics*; D015398:Signal Transduction / Q000235:genetics*
chemical_list: D029701:Saccharomyces cerevisiae Proteins; C104462:SKS1 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; D005947:Glucose; D009584:Nitrogen