Distinctive Responses to Nitrogen Starvation in the Dominant Active Mutants of the Fission Yeast Rheb GTPase

Murai, Tomoka; Nakase, Yukiko; Fukuda, Keiko; Chikashige, Yuji; Tsutsumi, Chihiro; Hiraoka, Yasushi; Matsumoto, Tomohiro

doi:10.1534/genetics.109.105379

Cited by 27 publications

(32 citation statements)

References 42 publications

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“…5C), which correlates with the decrease in cat1 ϩ level (Fig. 3A) and with previous observations that demonstrated canavanine resistance of tor2 temperature-sensitive alleles (48). A slight additive defect in the uptake of arginine is observed in ⌬isp7 tor2-51 mutant cells, under either semipermissive or restrictive conditions (Fig.…”

Section: Resultssupporting

confidence: 90%

“…However, the relationship between Gtr1/2 and TORC1 is complex. Thus, for example tor2-ts cells are canavanine resistant (48), while ⌬gtr1 and ⌬gtr2 cells are canavanine sensitive (53). Recently, it was suggested that Tor2 has opposing effects on Cat1 activity; thus, while the transcript of cat1 ϩ is positively regulated by Tor2, the localization of Cat1 at the plasma membrane is negatively regulated through endocytosis (53).…”

Section: Resultsmentioning

confidence: 99%

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Isp7 Is a Novel Regulator of Amino Acid Uptake in the TOR Signaling Pathway

Laor

Cohen

Pasmanik‐Chor

et al. 2014

Molecular and Cellular Biology

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c TOR proteins reside in two distinct complexes, TOR complexes 1 and 2 (TORC1 and TORC2), that are central for the regulation of cellular growth, proliferation, and survival. TOR is also the target for the immunosuppressive and anticancer drug rapamycin. In Schizosaccharomyces pombe, disruption of the TSC complex, mutations in which can lead to the tuberous sclerosis syndrome in humans, results in a rapamycin-sensitive phenotype under poor nitrogen conditions. We show here that the sensitivity to rapamycin is mediated via inhibition of TORC1 and suppressed by overexpression of isp7 ؉ , a member of the family of 2-oxoglutarate-Fe(II)-dependent oxygenase genes. The transcript level of isp7 ؉ is negatively regulated by TORC1 but positively regulated by TORC2. Yet we find extensive similarity between the transcriptome of cells disrupted for isp7؉ and cells mutated in the catalytic subunit of TORC1. Moreover, Isp7 regulates amino acid permease expression in a fashion similar to that of TORC1 and opposite that of TORC2. Overexpression of isp7 ؉ induces TORC1-dependent phosphorylation of ribosomal protein Rps6 while inhibiting TORC2-dependent phosphorylation and activation of the AGC-like kinase Gad8. Taken together, our findings suggest a central role for Isp7 in amino acid homeostasis and the presence of isp7 ؉ -dependent regulatory loops that affect both TORC1 and TORC2.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Isp7 Is a Novel Regulator of Amino Acid Uptake in the TOR Signaling Pathway

Laor

Cohen

Pasmanik‐Chor

et al. 2014

Molecular and Cellular Biology

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Section: Mutation or Inhibition Of Tor2 Activity Leads To Canavanine mentioning

confidence: 63%

“…We confirmed that the expression of the tor2 + gene under its endogenous promoter from a multicopy plasmid suppressed canavanine resistance of tor2-287 mutant cells ( Figure 2B), indicating that canavanine resistance is due to the tor2 mutation. Consistently, Murai et al (2009) demonstrated that another Tor2 allele, the tor2-ts6 mutant, was resistant to canavanine.Next, we examined several tor2 point mutants in which the wild-type tor2 + gene was replaced with a mutation on its chromosomal locus. The tor2 L1310P and tor2 E2221K mutants have activating mutations , and the tor2 S1837E mutation has an inactivating mutation in the residue crucial for the binding between the FRB domain in TOR and the FKBP12-rapamycin complex (Nakashima et al 2010).…”

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confidence: 63%

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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“…, which have been identified as hyperactivating mutations in fission yeast (Murai et al, 2009;Urano et al, 2005), from the chromosomal rhb1 + locus. Phosphorylation of p27 in rhb1 V17A but not in the wild-type rhb1 + or rhb1 K120R was significantly resistant to nitrogen starvation, similar to that in tsc2 cells (Fig.…”

Section: K120rmentioning

confidence: 99%

Fission yeast TORC1 regulates phosphorylation of ribosomal S6 proteins in response to nutrients and its activity is inhibited by rapamycin

Nakashima

Sato

Tamanoi

2010

Journal of Cell Science

116

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SummaryCellular activities are regulated by environmental stimuli through protein phosphorylation. Target of rapamycin (TOR), a serine/threonine kinase, plays pivotal roles in cell proliferation and cell growth in response to nutrient status. In Schizosaccharomyces pombe, TORC1, which contains Tor2, plays crucial roles in nutrient response. Here we find a nitrogen-regulated phosphoprotein, p27, in S. pombe using the phospho-Akt substrate antibody. Response of p27 phosphorylation to nitrogen availability is mediated by TORC1 and the TSCRhb1 signaling, but not by TORC2 or other nutrient stress-related pathways. Database and biochemical analyses indicate that p27 is identical to ribosomal protein S6 (Rps6). Ser235 and Ser236 in Rps6 are necessary for Rps6 phosphorylation by TORC1. These Rps6 phosphorylations are dispensable for cell viability. Rps6 phosphorylation by TORC1 also responds to availability of glucose and is inhibited by osmotic and oxidative stresses. Rapamycin inhibits the ability of TORC1 to phosphorylate Rps6, owing to interaction of the rapamycin-FKBP12 complex with the FRB domain in Tor2. Rapamycin also leads to a decrease in cell size in a TORC1-dependent manner. Our findings demonstrate that the nutrient-responsive and rapamycin-sensitive TORC1-S6 signaling exists in S. pombe, and that this pathway plays a role in cell size control.

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Distinctive Responses to Nitrogen Starvation in the Dominant Active Mutants of the Fission Yeast Rheb GTPase

Cited by 27 publications

References 42 publications

Isp7 Is a Novel Regulator of Amino Acid Uptake in the TOR Signaling Pathway

Isp7 Is a Novel Regulator of Amino Acid Uptake in the TOR Signaling Pathway

TORC1 Signaling Is Governed by Two Negative Regulators in Fission Yeast

Fission yeast TORC1 regulates phosphorylation of ribosomal S6 proteins in response to nutrients and its activity is inhibited by rapamycin

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