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The mitochondrial ribosomal protein of the large subunit, Afo1p, determines cellular longevity through mitochondrial back-signaling via TOR1.

Heeren G, Rinnerthaler M, Laun P, von Seyerl P, Kössler S, Klinger H, Hager M, Bogengruber E, Jarolim S, Simon-Nobbe B, Schüller C, Carmona-Gutierrez D, Breitenbach-Koller L, Mück C, Jansen-Dürr P, Criollo A, Kroemer G, Madeo F, Breitenbach M - Aging (Albany NY) (2009)

Bottom Line: Despite the respiratory deficiency the mutant has paradoxical increase in growth rate compared to generic petite mutants.A comparison of the single and double mutant strains for afo1 and fob1 shows that the longevity phenotype of afo1 is independent of the formation of ERCs (ribosomal DNA minicircles).AFO1/MRPL25 function establishes a new connection between mitochondria, metabolism and aging.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, Division of Genetics, University of Salzburg, 5020 Salzburg, Austria.

ABSTRACT
Yeast mother cell-specific aging constitutes a model of replicative aging as it occurs in stem cell populations of higher eukaryotes. Here, we present a new long-lived yeast deletion mutation,afo1 (for aging factor one), that confers a 60% increase in replicative lifespan. AFO1/MRPL25 codes for a protein that is contained in the large subunit of the mitochondrial ribosome. Double mutant experiments indicate that the longevity-increasing action of the afo1 mutation is independent of mitochondrial translation, yet involves the cytoplasmic Tor1p as well as the growth-controlling transcription factor Sfp1p. In their final cell cycle, the long-lived mutant cells do show the phenotypes of yeast apoptosis indicating that the longevity of the mutant is not caused by an inability to undergo programmed cell death. Furthermore, the afo1 mutation displays high resistance against oxidants. Despite the respiratory deficiency the mutant has paradoxical increase in growth rate compared to generic petite mutants. A comparison of the single and double mutant strains for afo1 and fob1 shows that the longevity phenotype of afo1 is independent of the formation of ERCs (ribosomal DNA minicircles). AFO1/MRPL25 function establishes a new connection between mitochondria, metabolism and aging.

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Double mutant                                            experiments of afo1Δ                                                    and                                            tor1Δ. The TOR1 gene is involved                                            in nutrient sensing and lifespan determination in yeast [5]. The double                                            mutant was constructed in an isogenic cross between the two single mutants                                            in the BY background. Lifespans of the wild type, both single mutants and                                            the double mutant were determined by micromanipulation. The experiment                                            shows that an intact TOR1 gene is needed for the lifespan                                            elongation observed in the afo1Δ strain as the                                            lifespan of the afo1Δ,                                                    tor1Δ double                                            mutant strain is not significantly different (p<0.02) from the lifespan                                            of the tor1Δ                                                    single                                            mutant strain.
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Figure 5: Double mutant experiments of afo1Δ and tor1Δ. The TOR1 gene is involved in nutrient sensing and lifespan determination in yeast [5]. The double mutant was constructed in an isogenic cross between the two single mutants in the BY background. Lifespans of the wild type, both single mutants and the double mutant were determined by micromanipulation. The experiment shows that an intact TOR1 gene is needed for the lifespan elongation observed in the afo1Δ strain as the lifespan of the afo1Δ, tor1Δ double mutant strain is not significantly different (p<0.02) from the lifespan of the tor1Δ single mutant strain.

Mentions: Two independent lines of evidence revealed that the afo1 deletion confers longevity and oxidative stress resistance through the TOR1 signaling pathway. First, we chromosomally integrated a C-terminally GFP-labeled version of the transcription factor, Sfp1p, at the SFP1 locus under the control of the native promotor in strains afo1Δ, BY4741 WT and BY4741 ρ0. Sfp1p is activated by the TOR1 and PKA pathways and is regulated by shuttling between the nucleus in its active form and the cytoplasm upon deactivation. Sfp1p is a major regulator of cytoplasmic ribosome synthesis and, consequently, of cellular growth [6]. As expected, addition of the Tor1p inhibitor rapamycin to WT cells induced the translocation of Sfp1p from the nucleus to the cytoplasm. In the bona fide BY4741 ρ0strain, Sfp1p was found constitutively in the cytoplasm, even in the absence of rapamycin. In stark contrast, in the afo1Δ mutant, Sfp1p was constitutively present in the nucleus, and rapamycin failed to induce the nucleo-cytoplasmic translocation of Sfp1p (Figure 4A). Similar results were obtained with an alternative Tor1p inhibitor, arsenite [17]. Arsenite induced the nucleocyto-plasmic translocation of Sfp1p in WT cells, while Sfp1p stayed in the cytoplasm of ρ0cells and in the nuclei of afo1 mutant cells, irrespective of the addition of arsenite (Figure 4B). Rapamycin failed to inhibit the growth of afo1 mutant cells [18]. Altogether, these data suggested that TOR1 signaling might govern the longevity of afo1 cells. The relation between TOR1 and AFO1 was further explored by epistasis experiments using double mutants (Figure 5). The lifespan of the double deletion strain (afo1Δ, tor1Δ) was similar to the lifespan of the tor1 deletion strain, i.e. about 15% longer than wild type (in good agreement with [11]). However, the double mutant afo1Δ,tor1Δ strain aged more rapidly than the single mutant afo1Δ strain (Figure 5). We conclude that a functional TOR1 gene is needed for exerting the lifespan-prolonging effect of afo1Δ.


The mitochondrial ribosomal protein of the large subunit, Afo1p, determines cellular longevity through mitochondrial back-signaling via TOR1.

Heeren G, Rinnerthaler M, Laun P, von Seyerl P, Kössler S, Klinger H, Hager M, Bogengruber E, Jarolim S, Simon-Nobbe B, Schüller C, Carmona-Gutierrez D, Breitenbach-Koller L, Mück C, Jansen-Dürr P, Criollo A, Kroemer G, Madeo F, Breitenbach M - Aging (Albany NY) (2009)

Double mutant                                            experiments of afo1Δ                                                    and                                            tor1Δ. The TOR1 gene is involved                                            in nutrient sensing and lifespan determination in yeast [5]. The double                                            mutant was constructed in an isogenic cross between the two single mutants                                            in the BY background. Lifespans of the wild type, both single mutants and                                            the double mutant were determined by micromanipulation. The experiment                                            shows that an intact TOR1 gene is needed for the lifespan                                            elongation observed in the afo1Δ strain as the                                            lifespan of the afo1Δ,                                                    tor1Δ double                                            mutant strain is not significantly different (p<0.02) from the lifespan                                            of the tor1Δ                                                    single                                            mutant strain.
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Figure 5: Double mutant experiments of afo1Δ and tor1Δ. The TOR1 gene is involved in nutrient sensing and lifespan determination in yeast [5]. The double mutant was constructed in an isogenic cross between the two single mutants in the BY background. Lifespans of the wild type, both single mutants and the double mutant were determined by micromanipulation. The experiment shows that an intact TOR1 gene is needed for the lifespan elongation observed in the afo1Δ strain as the lifespan of the afo1Δ, tor1Δ double mutant strain is not significantly different (p<0.02) from the lifespan of the tor1Δ single mutant strain.
Mentions: Two independent lines of evidence revealed that the afo1 deletion confers longevity and oxidative stress resistance through the TOR1 signaling pathway. First, we chromosomally integrated a C-terminally GFP-labeled version of the transcription factor, Sfp1p, at the SFP1 locus under the control of the native promotor in strains afo1Δ, BY4741 WT and BY4741 ρ0. Sfp1p is activated by the TOR1 and PKA pathways and is regulated by shuttling between the nucleus in its active form and the cytoplasm upon deactivation. Sfp1p is a major regulator of cytoplasmic ribosome synthesis and, consequently, of cellular growth [6]. As expected, addition of the Tor1p inhibitor rapamycin to WT cells induced the translocation of Sfp1p from the nucleus to the cytoplasm. In the bona fide BY4741 ρ0strain, Sfp1p was found constitutively in the cytoplasm, even in the absence of rapamycin. In stark contrast, in the afo1Δ mutant, Sfp1p was constitutively present in the nucleus, and rapamycin failed to induce the nucleo-cytoplasmic translocation of Sfp1p (Figure 4A). Similar results were obtained with an alternative Tor1p inhibitor, arsenite [17]. Arsenite induced the nucleocyto-plasmic translocation of Sfp1p in WT cells, while Sfp1p stayed in the cytoplasm of ρ0cells and in the nuclei of afo1 mutant cells, irrespective of the addition of arsenite (Figure 4B). Rapamycin failed to inhibit the growth of afo1 mutant cells [18]. Altogether, these data suggested that TOR1 signaling might govern the longevity of afo1 cells. The relation between TOR1 and AFO1 was further explored by epistasis experiments using double mutants (Figure 5). The lifespan of the double deletion strain (afo1Δ, tor1Δ) was similar to the lifespan of the tor1 deletion strain, i.e. about 15% longer than wild type (in good agreement with [11]). However, the double mutant afo1Δ,tor1Δ strain aged more rapidly than the single mutant afo1Δ strain (Figure 5). We conclude that a functional TOR1 gene is needed for exerting the lifespan-prolonging effect of afo1Δ.

Bottom Line: Despite the respiratory deficiency the mutant has paradoxical increase in growth rate compared to generic petite mutants.A comparison of the single and double mutant strains for afo1 and fob1 shows that the longevity phenotype of afo1 is independent of the formation of ERCs (ribosomal DNA minicircles).AFO1/MRPL25 function establishes a new connection between mitochondria, metabolism and aging.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, Division of Genetics, University of Salzburg, 5020 Salzburg, Austria.

ABSTRACT
Yeast mother cell-specific aging constitutes a model of replicative aging as it occurs in stem cell populations of higher eukaryotes. Here, we present a new long-lived yeast deletion mutation,afo1 (for aging factor one), that confers a 60% increase in replicative lifespan. AFO1/MRPL25 codes for a protein that is contained in the large subunit of the mitochondrial ribosome. Double mutant experiments indicate that the longevity-increasing action of the afo1 mutation is independent of mitochondrial translation, yet involves the cytoplasmic Tor1p as well as the growth-controlling transcription factor Sfp1p. In their final cell cycle, the long-lived mutant cells do show the phenotypes of yeast apoptosis indicating that the longevity of the mutant is not caused by an inability to undergo programmed cell death. Furthermore, the afo1 mutation displays high resistance against oxidants. Despite the respiratory deficiency the mutant has paradoxical increase in growth rate compared to generic petite mutants. A comparison of the single and double mutant strains for afo1 and fob1 shows that the longevity phenotype of afo1 is independent of the formation of ERCs (ribosomal DNA minicircles). AFO1/MRPL25 function establishes a new connection between mitochondria, metabolism and aging.

Show MeSH
Related in: MedlinePlus