title: Proteasomal degradation of Rpn4 in Saccharomyces cerevisiae is critical for cell viability under stressed conditions.
abstract: The proteasome homeostasis in Saccharomyces cerevisiae is regulated by a negative feedback loop in which the transcription factor Rpn4 induces the proteasome genes and is rapidly degraded by the assembled proteasome. In addition to the proteasome genes, Rpn4 regulates numerous other genes involved in a wide range of cellular pathways. Therefore, the Rpn4-proteasome negative feedback circuit not only controls proteasome abundance, but also gauges the expression of other Rpn4 target genes. Our previous work has shown that Rpn4-induced gene expression is critical for cell viability under stressed conditions. Here we investigate whether proteasomal degradation of Rpn4 is also important for cell survival in response to stress. To this end, we generate a stabilized Rpn4 mutant (Rpn4*) that retains its transcription activity. We find that expression of Rpn4* severely reduces cell viability in response to various genotoxic and proteotoxic agents. This detrimental effect can be eliminated by a point mutation that abolishes the transcription activity of Rpn4*, suggesting that overexpression of some Rpn4 target genes weakens the cell's ability to cope with stress. Moreover, we demonstrate that inhibition of Rpn4 degradation causes synthetic growth defects when combined with proteasome impairment resulting from mutation of a proteasome gene or accumulation of misfolded endoplasmic reticulum membrane proteins. Rpn4 thus represents an important stress-responsive mediator whose degradation as well as availability are critical for cell survival under stressed conditions.
authors.affiliation: Department of Pathology, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.
authors.forename: Xiaogang
authors.initials: X
authors.lastname: Wang
authors.forename: Haiming
authors.initials: H
authors.lastname: Xu
authors.forename: Seung-Wook
authors.initials: SW
authors.lastname: Ha
authors.forename: Donghong
authors.initials: D
authors.lastname: Ju
authors.forename: Youming
authors.initials: Y
authors.lastname: Xie
mesh_terms: D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D009153:Mutagens / Q000633:toxicity; D017354:Point Mutation; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism*; D017510:Protein Folding / Q000187:drug effects; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013312:Stress, Physiological / Q000187:drug effects; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D004268:DNA-Binding Proteins; D008565:Membrane Proteins; D009153:Mutagens; C119430:RPN4 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D046988:Proteasome Endopeptidase Complex