Disruption of Rpn4-Induced Proteasome Expression in Saccharomyces cerevisiae Reduces Cell Viability Under Stressed Conditions

Abstract

The proteasome homeostasis in Saccharomyces cerevisiae is regulated by a negative feedback circuit in which the transcription activator Rpn4 upregulates the proteasome genes and is rapidly degraded by the assembled proteasome. Previous studies have shown that rpn4D cells are sensitive to a variety of stresses. However, the contribution of the loss of Rpn4-induced proteasome expression to the rpn4D phenotypes remains unclear because Rpn4 controls numerous genes other than the proteasome genes. Here we construct a yeast strain in which one of the essential proteasome genes, PRE1, is no longer induced by Rpn4. We show that the active proteasome level is lower in this strain than in the wild-type counterpart. Moreover, we demonstrate that loss of Rpn4-induced proteasome expression leads to cell-cycle delay in G 2 /M and sensitizes cells to various stresses. To our knowledge, this is the first report that explicitly reveals the physiological function of Rpn4-induced proteasome expression. This study also provides a tool for understanding the interactions between proteasome homeostasis and other cellular processes.

Proteasomal Degradation of Rpn4 in Saccharomyces cerevisiae Is Critical for Cell Viability Under Stressed Conditions

“…It is worthy of note that rpn4D cells are also hypersensitive to the stressors that impair the growth and viability of RPN4* cells, such as UV, MMS, t-BuOOH, and ste6-G38D (Figures 3 and 5; also see Wang et al 2008). Thus, both availability and degradation of Rpn4 are critical for cell survival under stressed conditions.…”

“…(B) A fivefold serial dilution assay was applied to compare the sensitivity of RPN4, RPN4*, and rpn4D cells to tunicamycin (0.25 mg/ml). ( Jelinsky et al 2000;Ng et al 2000;Owsianik et al 2002;Haugen et al 2004;London et al 2004;Hahn et al 2006;Hanna et al 2007;Salin et al 2008;Teixeira et al 2008;Wang et al 2008;Metzger and Michaelis 2009). RPN4 is activated by a variety of stressors; and Rpn4 in turn upregulates a large number of stress-responsive genes, including the proteasome genes and others involved in protein ubiquitylation, DNA repair, and other cellular processes.…”

“…Thus, Rpn4 is considered to be an important stress-responsive mediator. In fact, it has been shown that rpn4D cells are sensitive to different stressing agents ( Jelinsky et al 2000;Ng et al 2000;London et al 2004;Hanna et al 2007;Wang et al 2008).…”

Regulation of PSMB5 Protein and β Subunits of Mammalian Proteasome by Constitutively Activated Signal Transducer and Activator of Transcription 3 (STAT3)

“…3, B and C). Previous studies in yeast showed that loss of one of the proteasome genes reduced proteasome assembly and activity (33). Because PSMB5 protein levels decreased due to inhibition of p-STAT3, we hypothesized that chymotrypsin-like activity would reflect the reduction of subunit expression.…”

Roles for Gcn5 in promoting nucleosome assembly and maintaining genome integrity

“…67,68 Rpn4 is transcription factor that regulates expression of proteasome genes. In addition, Rpn4 is regulated by various forms of cellular stress 69 and localizes to double strand break sites.…”