A Defect in Protein Farnesylation Suppresses a Loss of <i>Schizosaccharomyces pombe tsc2+</i>, a Homolog of the Human Gene Predisposing to Tuberous Sclerosis Complex

Nakase, Yukiko; Fukuda, Keiko; Chikashige, Yuji; Tsutsumi, Chihiro; Morita, Daisuke; Kawamoto, Shinpei; Ohnuki, Mari; Hiraoka, Yasushi; Matsumoto, Tomohiro

doi:10.1534/genetics.106.056895

Cited by 31 publications

(44 citation statements)

References 52 publications

(40 reference statements)

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“…These results indicate that the growth defect of Dtsc2 cells is mainly due to leucine auxotrophy. Consistently, it is demonstrated that leu1-32 Dtsc2 failed to grow on PM media containing 40-200 mg/ml leucine Nakase et al 2006). As reported previously (van Slegtenhorst et al 2004;Nakase et al 2006) and as shown in Figure 1C, the prototrophic Dtsc2 cells displayed canavanine resistance.…”

Section: Miscellaneous Methodssupporting

confidence: 88%

“…In fission yeast, several lines of evidence have demonstrated that Tsc2 functions as GAP for the small GTPase Rhb1 (van Slegtenhorst et al 2004(van Slegtenhorst et al , 2005Urano et al 2005;Nakase et al 2006), and Rhb1 positively regulates Tor2 activity (Urano et al 2005;Uritani et al 2006). Based on these reports we reasoned that isolation of the mutant strains that phenocopy Dtsc2 cells will identify novel negative regulators of Tor2.…”

Section: Resultsmentioning

confidence: 99%

“…Studies using budding yeast have extensively enhanced our knowledge about TOR signaling; however, in this model there are no Tsc homologs. In contrast, in fission yeast Schizosaccharomyces pombe, Tsc1 and Tsc2 form a complex that acts as a GTPase activating protein (GAP) for the small GTPase Rhb1 (Rheb homolog) (van Slegtenhorst et al 2004;Nakase et al 2006), and Rhb1 physically associates with Tor2 in a GTP-dependent manner (Urano et al 2005;Uritani et al 2006). Recently, Nakashima et al ( , 2012 demonstrate that, similar to mammalian mTORC1-S6K-S6, the TORC1 (Tor2)-Psk1-Rps6 constitutes a nutrient-dependent signaling pathway.…”

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confidence: 99%

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TORC1 Signaling Is Governed by Two Negative Regulators in Fission Yeast

Liu

Zhang

et al. 2013

Genetics

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The target of rapamycin (TOR) is a highly conserved protein kinase that regulates cell growth and metabolism. Here we performed a genome-wide screen to identify negative regulators of TOR complex 1 (TORC1) in Schizosaccharomyces pombe by isolating mutants that phenocopy Dtsc2, in which TORC1 signaling is known to be up-regulated. We discovered that Dnpr2 displayed similar phenotypes to Dtsc2 in terms of amino acid uptake defects and mislocalization of the Cat1 permease. However, Dnpr2 and Dtsc2 clearly showed different phenotypes in terms of rapamycin supersensitivity and Isp5 transcription upon various treatments. Furthermore, we showed that Tor2 controls amino acid homeostasis at the transcriptional and post-transcriptional levels. Our data reveal that both Npr2 and Tsc2 negatively regulate TORC1 signaling, and Npr2, but not Tsc2, may be involved in the feedback loop of a nutrient-sensing pathway.T HE target of rapamycin (TOR) plays vitally important roles in regulating cell growth and metabolism. TOR interacts with several proteins to form two structurally and functionally distinct complexes named TOR complex 1 (TORC1) and 2 (TORC2) Sabatini 2009, 2012). In response to environmental cues, TORC1 controls cell growth and differentiation by coordinating diverse cellular processes including transcription, translation, and autophagy. Research on TORC1 has generated a model of the complex TOR signaling network (Huang and Manning 2009;Orlova and Crino 2010;Laplante and Sabatini 2012). In the regulation of TORC1 signaling, four major signals have been identified, namely growth factors (insulin, IGF, etc.), energy status (AMP/ATP ratio), oxygen levels, and nutrients (amino acids) Sabatini 2009, 2012). In mammals, the tuberous sclerosis complex 1 and 2 (TSC1-TSC2) serves as a key point of signal integration. The growth factors stimulate TORC1 signaling via PI3K-Akt/ PKB-mediated phosphoinhibition of TSC2 (Inoki et al. 2002;Manning et al. 2002). The energy starvation inhibits TORC1 signaling via AMPK-dependent phosphoactivation of TSC2 (Inoki et al. 2003). Then, TSC2 negatively regulates TORC1 activity by converting GTP-bound Rheb (Ras homolog enriched in brain) into its inactive GDP-bound state (Inoki et al. 2003;Tee et al. 2003). The amino acids, in particular the branched-chain amino acid leucine, positively regulate TORC1. The TORC1 signaling remains sensitive to amino acid deprivation in TSC2 2/2 cells (Nobukuni et al. 2005), indicating that the activation of TORC1 by amino acids is independent of TSC2. Recently, it was demonstrated that TORC1 responds to amino acid availability via mechanisms involving Rag GTPases (Sancak et al. 2008). In the presence of amino acids, the Rag GTPases interact with TORC1, thereby promoting the translocation of TORC1 to the lysosomal membranes and facilitating Rheb's activation of TORC1 (Sancak et al. 2010).In budding yeast Saccharomyces cerevisiae, TOR1 and TOR2 genes were originally identified as the targets of rapamycin, and mutations in TOR1 or TOR2 genes confer resi...

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Section: Miscellaneous Methodssupporting

confidence: 88%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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TORC1 Signaling Is Governed by Two Negative Regulators in Fission Yeast

Liu

Zhang

et al. 2013

Genetics

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“…Unlike budding yeast, fission yeast encodes apparent orthologues of mammalian TSC1 and TSC2. Furthermore, genetic studies in fission yeast are consistent with TSC and Rheb orthologues functioning, respectively, to antagonize and stimulate a TORC1-like activity (Mach et al, 2000;Yang et al, 2001;Tabancay et al, 2003;van Slegtenhorst et al, 2004;Urano et al, 2005;Nakase et al, 2006). There is considerable debate regarding the mechanisms by which Rheb regulates mTORC1 (Wullschleger et al (2006) and described elsewhere in this issue); perhaps studies in a genetically tractable organism like S. pombe will help settle these controversies.…”

Section: Future Directionsmentioning

confidence: 95%

Cell growth control: little eukaryotes make big contributions

2006

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The story of rapamycin is a pharmaceutical fairytale. Discovered as an antifungal activity in a soil sample collected on Easter Island, this macrocyclic lactone and its derivatives are now billion dollar drugs, used in, and being evaluated for, a number of clinical applications. Taking advantage of its antifungal property, the molecular Target Of Rapamycin, TOR, was first described in the budding yeast Saccharomyces cerevisiae. TORs encode large, Ser/Thr protein kinases that reside in two distinct, structurally and functionally conserved, multi-protein complexes. In yeast, these complexes coordinate many different aspects of cell growth. TOR complex 1, TORC1, promotes protein synthesis and other anabolic processes, while inhibiting macroautophagy and other catabolic and stress-response processes. TORC2 primarily regulates cell polarity, although additional readouts of this complex are beginning to be characterized. TORC1 appears to be activated by nutrient cues and inhibited by stresses and rapamycin; however, detailed mechanisms are not known. In contrast, TORC2 is insensitive to rapamycin and physiological regulators of this complex have yet to be defined. Given the unsurpassed resources available to yeast researchers, this simple eukaryote continues to contribute to our understanding of eukaryotic cell growth in general and TOR function in particular

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“…Like mammalian cells, Rhb1p is down-regulated by the Tsc1p/Tsc2p complex (21,22). Mutations in the tsc genes result in a delayed response to nitrogen starvation as well as defects in amino acid uptake (21)(22)(23)(24)(25). The fission yeast genome encodes two TOR proteins, Tor1p and Tor2p (26,27).…”

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confidence: 99%

Point mutations in TOR confer Rheb-independent growth in fission yeast and nutrient-independent mammalian TOR signaling in mammalian cells

Urano

Sato

Matsuo

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

133

149

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Rheb is a unique member of the Ras superfamily GTP-binding proteins. We as well as others previously have shown that Rheb is a critical component of the TSC/TOR signaling pathway. In fission yeast, Rheb is encoded by the rhb1 gene. Rhb1p is essential for growth and directly interacts with Tor2p. In this article, we report identification of 22 single amino acid changes in the Tor2 protein that enable growth in the absence of Rhb1p. These mutants also exhibit decreased mating efficiency. Interestingly, the mutations are located in the C-terminal half of the Tor2 protein, clustering mainly within the FAT and kinase domains. We noted some differences in the effect of a mutation in the FAT domain (L1310P) and in the kinase domain (E2221K) on growth and mating. Although the Tor2p mutations bypass Rhb1p's requirement for growth, they are incapable of suppressing Rhb1p's requirement for resistance to stress and toxic amino acids, pointing to multiple functions of Rhb1p. In mammalian systems, we find that mammalian target of rapamycin (mTOR) carrying analogous mutations (L1460P or E2419K), although sensitive to rapamycin, exhibits constitutive activation even when the cells are starved for nutrients. These mutations do not show significant difference in their ability to form complexes with Raptor, Rictor, or mLST8. Furthermore, we present evidence that mutant mTOR can complex with wild-type mTOR and that this heterodimer is active in nutrient-starved cells.constitutive active TOR ͉ FAT domain ͉ kinase domain ͉ mating ͉ TORC1

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A Defect in Protein Farnesylation Suppresses a Loss of Schizosaccharomyces pombe tsc2+, a Homolog of the Human Gene Predisposing to Tuberous Sclerosis Complex

Cited by 31 publications

References 52 publications

TORC1 Signaling Is Governed by Two Negative Regulators in Fission Yeast

TORC1 Signaling Is Governed by Two Negative Regulators in Fission Yeast

Cell growth control: little eukaryotes make big contributions

Point mutations in TOR confer Rheb-independent growth in fission yeast and nutrient-independent mammalian TOR signaling in mammalian cells

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