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PLoS ONE (2008); 3(2):e1598
Hsf1 Activation Inhibits Rapamycin Resistance and TOR Signaling in Yeast Revealed by Combined Proteomic and Genetic Analysis-
Bandhakavi S, Xie H, O'Callaghan B, Sakurai H, Kim DH, Griffin TJ
Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota, United States of America-
Abstract: TOR kinases integrate environmental and nutritional signals to regulate cell growth in eukaryotic organisms- Here, we describe results from a study combining quantitative proteomics and comparative expression analysis in the budding yeast, S- cerevisiae, to gain insights into TOR function and regulation- We profiled protein abundance changes under conditions of TOR inhibition by rapamycin treatment, and compared this data to existing expression information for corresponding gene products measured under a variety of conditions in yeast- Among proteins showing abundance changes upon rapamycin treatment, almost 90% of them demonstrated homodirectional -i-e-, in similar direction- transcriptomic changes under conditions of heat-oxidative stress- Because the known downstream responses regulated by Tor1-2 did not fully explain the extent of overlap between these two conditions, we tested for novel connections between the major regulators of heat-oxidative stress response and the TOR pathway- Specifically, we hypothesized that activation of regulator-s- of heat-oxidative stress responses phenocopied TOR inhibition and sought to identify these putative TOR inhibitor-s-- Among the stress regulators tested, we found that cells -hsf1-R206S, F256S and ssa1-3 ssa2-2- constitutively activated for heat shock transcription factor 1, Hsf1, inhibited rapamycin resistance- Further analysis of the hsf1-R206S, F256S allele revealed that these cells also displayed multiple phenotypes consistent with reduced TOR signaling- Among the multiple Hsf1 targets elevated in hsf1-R206S, F256S cells, deletion of PIR3 and YRO2 suppressed the TOR-regulated phenotypes- In contrast to our observations in cells activated for Hsf1, constitutive activation of other regulators of heat-oxidative stress responses, such as Msn2-4 and Hyr1, did not inhibit TOR signaling- Thus, we propose that activated Hsf1 inhibits rapamycin resistance and TOR signaling via elevated expression of specific target genes in S- cerevisiae- Additionally, these results highlight the value of comparative expression analyses between large-scale proteomic and transcriptomic datasets to reveal new regulatory connections-
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Chris Stark, Bobby-Joe Breitkreutz, Teresa Reguly, Lorrie Boucher, Ashton Breitkreutz, Mike Tyers.
Nucleic Acids Res. Jan 1;34:D535-9.