title: Saccharomyces cerevisiae Tti2 Regulates PIKK Proteins and Stress Response.
abstract: The TTT complex is composed of the three essential proteins Tel2, Tti1, and Tti2 The complex is required to maintain steady state levels of phosphatidylinositol 3-kinase-related kinase (PIKK) proteins, including mTOR, ATM/Tel1, ATR/Mec1, and TRRAP/Tra1, all of which serve as regulators of critical cell signaling pathways. Due to their association with heat shock proteins, and with newly synthesized PIKK peptides, components of the TTT complex may act as cochaperones. Here, we analyze the consequences of depleting the cellular level of Tti2 in Saccharomyces cerevisiae We show that yeast expressing low levels of Tti2 are viable under optimal growth conditions, but the cells are sensitive to a number of stress conditions that involve PIKK pathways. In agreement with this, depleting Tti2 levels decreased expression of Tra1, Mec1, and Tor1, affected their localization and inhibited the stress responses in which these molecules are involved. Tti2 expression was not increased during heat shock, implying that it does not play a general role in the heat shock response. However, steady state levels of Hsp42 increase when Tti2 is depleted, and tti2L187P has a synthetic interaction with exon 1 of the human Huntingtin gene containing a 103 residue polyQ sequence, suggesting a general role in protein quality control. We also find that overexpressing Hsp90 or its cochaperones is synthetic lethal when Tti2 is depleted, an effect possibly due to imbalanced stoichiometry of a complex required for PIKK assembly. These results indicate that Tti2 does not act as a general chaperone, but may have a specialized function in PIKK folding and/or complex assembly.
authors.affiliation: Department of Biochemistry, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, N6A5C1 Canada.
authors.forename: Kyle S
authors.initials: KS
authors.lastname: Hoffman
authors.affiliation: Department of Pathology, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, N6A5C1, Canada.
authors.forename: Martin L
authors.initials: ML
authors.lastname: Duennwald
authors.affiliation: Department of Biology, The University of Western Ontario, London, Ontario, N6A5B7 Canada.
authors.forename: Jim
authors.initials: J
authors.lastname: Karagiannis
authors.affiliation: Department of Biochemistry, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, N6A5C1 Canada.
authors.forename: Julie
authors.initials: J
authors.lastname: Genereaux
authors.affiliation: Department of Biochemistry, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, N6A5C1 Canada.
authors.forename: Alexander S
authors.initials: AS
authors.lastname: McCarton
authors.affiliation: Department of Biochemistry, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, N6A5C1 Canada cbrandl@uwo.ca.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Brandl
mesh_terms: D000483:Alleles; D002470:Cell Survival / Q000235:genetics; D015870:Gene Expression; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013312:Stress, Physiological / Q000235:genetics
chemical_list: D018841:HSP90 Heat-Shock Proteins; D018832:Molecular Chaperones; D029701:Saccharomyces cerevisiae Proteins; C576144:Tti2 protein, S cerevisiae
keywords: PIKK proteins; TTT complex; chaperone; heat shock response; protein expression