title: Hypoxia abolishes transience of the heat-shock response in the methylotrophic yeast Hansenula polymorpha.
abstract: The heat-shock response is conserved amongst practically all organisms. Almost invariably, the massive heat-shock protein (Hsp) synthesis that it induces is subsequently down-regulated, making this a transient, not a sustained, stress response. This study investigated whether the heat-shock response displays any unusual features in the methylotrophic yeast Hansenula polymorpha, since this organism exhibits the highest growth temperature (49-50 degrees C) identified to date for any yeast and grows at 47 degrees C without either thermal death or detriment to final biomass yield. Maximal levels of Hsp induction were observed with a temperature upshift of H. polymorpha from 30 degrees C to 47-49 degrees C. This heat shock induces a prolonged growth arrest, heat-shock protein synthesis being down-regulated long before growth resumes at such high temperatures. A 30 degrees C to 49 degrees C heat shock also induced thermotolerance, although H. polymorpha cells in balanced growth at 49 degrees C were intrinsically thermotolerant. Unexpectedly, the normal transience of the H. polymorpha heat-shock response was suppressed completely by imposing the additional stress of hypoxia at the time of the 30 degrees C to 49 degrees C temperature upshift. Hypoxia abolishing the transience of the heat-shock response appears to operate at the level of Hsp gene transcription, since the heat-induced Hsp70 mRNA was transiently induced in a heat-shocked normoxic culture but displayed sustained induction in a culture deprived of oxygen at the time of temperature upshift.
authors.affiliation: Laboratorio di Genetica Microbica, DiSA, Università Politecnica delle Marche, 60131 Ancona, Italy.
authors.forename: Emanuela
authors.initials: E
authors.lastname: Guerra
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, UK.
authors.forename: Poh Poh
authors.initials: PP
authors.lastname: Chye
authors.affiliation: Laboratorio di Genetica Microbica, DiSA, Università Politecnica delle Marche, 60131 Ancona, Italy.
authors.forename: Enrico
authors.initials: E
authors.lastname: Berardi
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, UK.
authors.forename: Peter W
authors.initials: PW
authors.lastname: Piper
mesh_terms: D002453:Cell Cycle / Q000187:drug effects; D015966:Gene Expression Regulation, Fungal; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D018869:Heat-Shock Response / Q000187:drug effects*; D006358:Hot Temperature; D010100:Oxygen / Q000494:pharmacology*; D010843:Pichia / Q000187:drug effects / Q000254:growth & development* / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013696:Temperature
chemical_list: D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D012333:RNA, Messenger; D010100:Oxygen