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Proteasomes, Sir2, and Hxk2 form an interconnected aging network that impinges on the AMPK/Snf1-regulated transcriptional repressor Mig1.

Yao Y, Tsuchiyama S, Yang C, Bulteau AL, He C, Robison B, Tsuchiya M, Miller D, Briones V, Tar K, Potrero A, Friguet B, Kennedy BK, Schmidt M - PLoS Genet. (2015)

Bottom Line: This pro-longevity effect might be mediated by improved protein homeostasis, as this protease is an integral module of the protein homeostasis network.We found that the premature induction of respiration in cells with increased proteasome activity originates from enhanced turnover of Mig1, an AMPK/Snf1 regulated transcriptional repressor that prevents the induction of genes required for respiration.Collectively, the results argue for a model in which elevated proteasome activity leads to the uncoupling of Snf1-mediated Mig1 regulation, resulting in a premature activation of respiration and thus the induction of a mitohormetic response, beneficial to lifespan.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, New York, United States of America.

ABSTRACT
Elevated proteasome activity extends lifespan in model organisms such as yeast, worms and flies. This pro-longevity effect might be mediated by improved protein homeostasis, as this protease is an integral module of the protein homeostasis network. Proteasomes also regulate cellular processes through temporal and spatial degradation of signaling pathway components. Here we demonstrate that the regulatory function of the proteasome plays an essential role in aging cells and that the beneficial impact of elevated proteasome capacity on lifespan partially originates from deregulation of the AMPK signaling pathway. Proteasome-mediated lifespan extension activity was carbon-source dependent and cells with enhancement proteasome function exhibited increased respiratory activity and oxidative stress response. These findings suggested that the pro-aging impact of proteasome upregulation might be related to changes in the metabolic state through a premature induction of respiration. Deletion of yeast AMPK, SNF1, or its activator SNF4 abrogated proteasome-mediated lifespan extension, supporting this hypothesis as the AMPK pathway regulates metabolism. We found that the premature induction of respiration in cells with increased proteasome activity originates from enhanced turnover of Mig1, an AMPK/Snf1 regulated transcriptional repressor that prevents the induction of genes required for respiration. Increasing proteasome activity also resulted in partial relocation of Mig1 from the nucleus to the mitochondria. Collectively, the results argue for a model in which elevated proteasome activity leads to the uncoupling of Snf1-mediated Mig1 regulation, resulting in a premature activation of respiration and thus the induction of a mitohormetic response, beneficial to lifespan. In addition, we observed incorrect Mig1 localization in two other long-lived yeast aging models: cells that overexpress SIR2 or deleted for the Mig1-regulator HXK2. Finally, compromised proteasome function blocks lifespan extension in both strains. Thus, our findings suggest that proteasomes, Sir2, Snf1 and Hxk2 form an interconnected aging network that controls metabolism through coordinated regulation of Mig1.

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Cells with increased proteasome abundance exhibit features indicative of prematurely activated Snf1/AMP kinase signaling.The mRNA levels of the glucose repressed genes GAL1, HXK1 and SUC2 were tested via quantitative RT-PCR. mRNA was prepared after cells were grown in galactose for 4 h in WT, rpn4Δ, ubr2Δ, or rpn4Δ ubr2Δ cells. The data were corrected for the housekeeping gene ACT1 and presented relative to WT expression as the mean +/- SEM of three biological replicates. P-values represent the statistical significance relative to WT expression and were assessed by an Ordinary one-way Annova using the GraphPad Prism software. P-values: * p < 0.05, ** p < 0.01, *** p < 0.001.
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pgen.1004968.g003: Cells with increased proteasome abundance exhibit features indicative of prematurely activated Snf1/AMP kinase signaling.The mRNA levels of the glucose repressed genes GAL1, HXK1 and SUC2 were tested via quantitative RT-PCR. mRNA was prepared after cells were grown in galactose for 4 h in WT, rpn4Δ, ubr2Δ, or rpn4Δ ubr2Δ cells. The data were corrected for the housekeeping gene ACT1 and presented relative to WT expression as the mean +/- SEM of three biological replicates. P-values represent the statistical significance relative to WT expression and were assessed by an Ordinary one-way Annova using the GraphPad Prism software. P-values: * p < 0.05, ** p < 0.01, *** p < 0.001.

Mentions: A typical response in yeast after cells switch from fermentation to respiration is the rapid nuclear accumulation of the stress and nutrient responsive transcription factor Msn2 [42], since this metabolic switch results in oxidative stress due to increased respiratory chain activity. We therefore reasoned that the increased respiratory activity of ubr2Δ cells should lead to increased nuclear localization of Msn2. In agreement with this hypothesis, we observed that ~ 50% of cells grown under fermentation conditions displayed nuclear localization of Msn2 (S3 Fig.). In addition, the ubr2Δ strain exhibits the induction of genes such as SUC2, HXK1 and GAL1 that are typically derepressed upon glucose withdrawal, while the rpn4Δ strain exhibited reduced expression of these genes (Fig. 3). These data corroborate that cells with more proteasome activity exhibit a metabolic shift towards respiratory metabolism.


Proteasomes, Sir2, and Hxk2 form an interconnected aging network that impinges on the AMPK/Snf1-regulated transcriptional repressor Mig1.

Yao Y, Tsuchiyama S, Yang C, Bulteau AL, He C, Robison B, Tsuchiya M, Miller D, Briones V, Tar K, Potrero A, Friguet B, Kennedy BK, Schmidt M - PLoS Genet. (2015)

Cells with increased proteasome abundance exhibit features indicative of prematurely activated Snf1/AMP kinase signaling.The mRNA levels of the glucose repressed genes GAL1, HXK1 and SUC2 were tested via quantitative RT-PCR. mRNA was prepared after cells were grown in galactose for 4 h in WT, rpn4Δ, ubr2Δ, or rpn4Δ ubr2Δ cells. The data were corrected for the housekeeping gene ACT1 and presented relative to WT expression as the mean +/- SEM of three biological replicates. P-values represent the statistical significance relative to WT expression and were assessed by an Ordinary one-way Annova using the GraphPad Prism software. P-values: * p < 0.05, ** p < 0.01, *** p < 0.001.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4309596&req=5

pgen.1004968.g003: Cells with increased proteasome abundance exhibit features indicative of prematurely activated Snf1/AMP kinase signaling.The mRNA levels of the glucose repressed genes GAL1, HXK1 and SUC2 were tested via quantitative RT-PCR. mRNA was prepared after cells were grown in galactose for 4 h in WT, rpn4Δ, ubr2Δ, or rpn4Δ ubr2Δ cells. The data were corrected for the housekeeping gene ACT1 and presented relative to WT expression as the mean +/- SEM of three biological replicates. P-values represent the statistical significance relative to WT expression and were assessed by an Ordinary one-way Annova using the GraphPad Prism software. P-values: * p < 0.05, ** p < 0.01, *** p < 0.001.
Mentions: A typical response in yeast after cells switch from fermentation to respiration is the rapid nuclear accumulation of the stress and nutrient responsive transcription factor Msn2 [42], since this metabolic switch results in oxidative stress due to increased respiratory chain activity. We therefore reasoned that the increased respiratory activity of ubr2Δ cells should lead to increased nuclear localization of Msn2. In agreement with this hypothesis, we observed that ~ 50% of cells grown under fermentation conditions displayed nuclear localization of Msn2 (S3 Fig.). In addition, the ubr2Δ strain exhibits the induction of genes such as SUC2, HXK1 and GAL1 that are typically derepressed upon glucose withdrawal, while the rpn4Δ strain exhibited reduced expression of these genes (Fig. 3). These data corroborate that cells with more proteasome activity exhibit a metabolic shift towards respiratory metabolism.

Bottom Line: This pro-longevity effect might be mediated by improved protein homeostasis, as this protease is an integral module of the protein homeostasis network.We found that the premature induction of respiration in cells with increased proteasome activity originates from enhanced turnover of Mig1, an AMPK/Snf1 regulated transcriptional repressor that prevents the induction of genes required for respiration.Collectively, the results argue for a model in which elevated proteasome activity leads to the uncoupling of Snf1-mediated Mig1 regulation, resulting in a premature activation of respiration and thus the induction of a mitohormetic response, beneficial to lifespan.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, New York, United States of America.

ABSTRACT
Elevated proteasome activity extends lifespan in model organisms such as yeast, worms and flies. This pro-longevity effect might be mediated by improved protein homeostasis, as this protease is an integral module of the protein homeostasis network. Proteasomes also regulate cellular processes through temporal and spatial degradation of signaling pathway components. Here we demonstrate that the regulatory function of the proteasome plays an essential role in aging cells and that the beneficial impact of elevated proteasome capacity on lifespan partially originates from deregulation of the AMPK signaling pathway. Proteasome-mediated lifespan extension activity was carbon-source dependent and cells with enhancement proteasome function exhibited increased respiratory activity and oxidative stress response. These findings suggested that the pro-aging impact of proteasome upregulation might be related to changes in the metabolic state through a premature induction of respiration. Deletion of yeast AMPK, SNF1, or its activator SNF4 abrogated proteasome-mediated lifespan extension, supporting this hypothesis as the AMPK pathway regulates metabolism. We found that the premature induction of respiration in cells with increased proteasome activity originates from enhanced turnover of Mig1, an AMPK/Snf1 regulated transcriptional repressor that prevents the induction of genes required for respiration. Increasing proteasome activity also resulted in partial relocation of Mig1 from the nucleus to the mitochondria. Collectively, the results argue for a model in which elevated proteasome activity leads to the uncoupling of Snf1-mediated Mig1 regulation, resulting in a premature activation of respiration and thus the induction of a mitohormetic response, beneficial to lifespan. In addition, we observed incorrect Mig1 localization in two other long-lived yeast aging models: cells that overexpress SIR2 or deleted for the Mig1-regulator HXK2. Finally, compromised proteasome function blocks lifespan extension in both strains. Thus, our findings suggest that proteasomes, Sir2, Snf1 and Hxk2 form an interconnected aging network that controls metabolism through coordinated regulation of Mig1.

Show MeSH