Nitrogen Regulates AMPK to Control TORC1 Signaling

Davie, Elizabeth A. Colby; Forte, Gabriella; Petersen, Janni

doi:10.1016/j.cub.2014.12.034

Cited by 72 publications

(129 citation statements)

References 51 publications

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“…In wholecell extracts, we detected a specific band for wild-type cells grown in low (0.2%) glucose but not in high (3%) glucose (Fig. 1C), consistent with previous studies (21,26). This band was absent in ssp2Δ cells and migrated at the predicted higher molecular weight in lysates from cells expressing the fusion protein Ssp2-13-myc (Fig.…”

Section: Resultssupporting

confidence: 90%

“…Mutations in ssp1 ϩ lead to pleiotropic defects, including energy stress, cell cycle progression, and cell polarity (19)(20)(21)(22)(23), consistent with activation of fission yeast ARKs for diverse cellular functions. Genetic experiments place Ssp1 upstream of Ssp2/AMPK␣ for growth in low glucose (22,24,25), and Ssp1 is required for phosphorylation of Ssp2 under low-nitrogen or low-glucose conditions (21,26). Further, we recently identified Ssp1 as the sole upstream kinase for the activation loop of Cdr2 (27), an ARK that regulates cell size at division.…”

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confidence: 99%

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Phosphatases Generate Signal Specificity Downstream of Ssp1 Kinase in Fission Yeast

Deng

Lee

Schutt

et al. 2017

Molecular and Cellular Biology

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AMPK-related protein kinases (ARKs) coordinate cell growth, proliferation, and migration with environmental status. It is unclear how specific ARKs are activated at specific times. In the fission yeast Schizosaccharomyces pombe, the CaMKKlike protein kinase Ssp1 promotes cell cycle progression by activating the ARK Cdr2 according to cell growth signals. Here, we demonstrate that Ssp1 activates a second ARK, Ssp2/AMPK␣, for cell proliferation in low environmental glucose. Ssp1 activates these two related targets by the same biochemical mechanism: direct phosphorylation of a conserved residue in the activation loop (Cdr2-T166 and Ssp2-T189). Despite a shared upstream kinase and similar phosphorylation sites, Cdr2 and Ssp2 have distinct regulatory input cues and distinct functional outputs. We investigated this specificity and found that distinct protein phosphatases counteract Ssp1 activity toward its different substrates. We identified the PP6 family phosphatase Ppe1 as the primary phosphatase for Ssp2-T189 dephosphorylation. The phosphatase inhibitor Sds23 acts upstream of PP6 to regulate Ssp2-T189 phosphorylation in a manner that depends on energy but not on the intact AMPK heterotrimer. In contrast, Cdr2-T166 phosphorylation is regulated by protein phosphatase 2A but not by the Sds23-PP6 pathway. Thus, our study provides a phosphatase-driven mechanism to induce specific physiological responses downstream of a master protein kinase.KEYWORDS AMPK, Cdr2, Ssp1, fission yeast, kinase, phosphatase, pombe C ells control proliferation, polarized growth, and migration according to nutrient and environmental status. These processes must be tightly regulated during normal growth and development, and loss of this coordination is coupled with distinct steps in the initiation and maturation of tumors (1, 2). The AMP-activated protein kinase (AMPK)-related kinase (ARK) subfamily of protein kinases is essential for coordination of cell growth, proliferation, and migration with environmental status (3). Human cells express at least 13 members of this conserved kinase subfamily, including the metabolic sensor AMPK, the cytoskeletal kinase MARK1/Par-1, and the SAD kinases that regulate cell growth and polarity (4). Given their functions in diverse cell biological processes, it is remarkable that all ARKs can be activated by a shared upstream activating kinase, which phosphorylates the activation loop of ARK kinase domains to turn them "on" (4). To meet the needs of a rapidly changing environment, different ARKs need to be turned on and off at different times. This leads to a simple question: how does a common activation mechanism activate different ARKs at different times?The defining member of the ARK subfamily is AMPK. This conserved heterotrimeric complex is activated by low cellular energy status, typically the result of low levels of environmental nutrients (5). AMPK activation shifts cells toward catabolism and promotes the Warburg effect in cancer cells (5-7). The AMPK heterotrimer consists of a catalytic ␣ subun...

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Section: Resultssupporting

confidence: 90%

mentioning

confidence: 99%

Phosphatases Generate Signal Specificity Downstream of Ssp1 Kinase in Fission Yeast

Deng

Lee

Schutt

et al. 2017

Molecular and Cellular Biology

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“…TORC1 is essential for growth in S. pombe and plays a critical role in regulating the switch between growth and sexual development in response to nitrogen starvation. Consistently, disruption of S. pombe TORC1 results in many features characteristic of nitrogenstarved cells (5)(6)(7)(8), and TORC1-dependent phosphorylation of the small ribosomal protein Rps6 is diminished under nitrogen starvation (9).…”

Section: Target Of Rapamycin (Tor)mentioning

confidence: 67%

“…Interestingly, most if not all of the cellular functions of S. pombe TORC2 are mediated via phosphorylation and activation of its downstream substrate Gad8, an AGC (PKA, PKG, and PKC kinases)-like kinase with structural and functional similarities to AKT, the most well established substrate kinase of mTORC2 (11,14,15). Although S. pombe TORC1 is responsive to the availability of nitrogen or amino acids (5)(6)(7)(8)16), we (17) and the Shiozaki and co-workers (18) have recently shown that S. pombe TORC2 responds to the availability of glucose. Upon glucose withdrawal or shift from glucose to a less favorable carbon source such as glycerol, there is a reduction of TORC2-dependent phosphorylation of Gad8 at serine 546 (equivalent to serine 473 in AKT) and concomitant reduced Gad8 kinase activity (17,18).…”

Section: Target Of Rapamycin (Tor)mentioning

confidence: 99%

Gad8 Protein Is Found in the Nucleus Where It Interacts with the MluI Cell Cycle Box-binding Factor (MBF) Transcriptional Complex to Regulate the Response to DNA Replication Stress

Cohen

Kupiec

Weisman

2016

Journal of Biological Chemistry

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The target of rapamycin (TOR) kinase is found at the core of two evolutionarily conserved complexes known as TOR complexes 1 and 2 (TORC1 and TORC2). In fission yeast, TORC2 is dispensable for proliferation under optimal growth conditions but is required for starvation and stress responses. We have previously reported that loss of function of TORC2 renders cells highly sensitive to DNA replication stress; however, the mechanism underlying this sensitivity is unknown. TORC2 has one known direct substrate, the kinase Gad8, which is related to AKT in human cells. Here we show that both TORC2 and its substrate Gad8 are found in the nucleus and are bound to the chromatin. We also demonstrate that Gad8 physically interacts with the MluI cell cycle box-binding factor (MBF) transcription complex that regulates the G 1 /S progression and the response to DNA stress. In mutant cells lacking TORC2 or Gad8, the binding of the MBF complex to its cognate promoters is compromised, and the induction of MBF target genes in response to DNA replication stress is reduced. Consistently, the protein levels of Cdt2 and Cig2, two MBF target genes, are reduced in the absence of TORC2-Gad8 signaling. Taken together, our findings highlight critical functions of TORC2 in the nucleus and suggest a role in surviving DNA replication stress via transcriptional regulation of MBF target genes. Target of rapamycin (TOR)2 is an atypical protein kinase that was isolated as the target of the immunosuppressive and anticancer drug rapamycin. TOR proteins play a central role in growth, proliferation, and survival and can be found in two distinct and evolutionarily conserved complexes, TORC1 and TORC2 (1-3). The two TOR complexes are key regulators of cellular growth; however, they respond to different stimuli and phosphorylate distinct sets of protein substrates (1-3). Human cells contain a single TOR protein, known as mTOR, which functions as the catalytic subunit of both mTORC1 and mTORC2. In the fission yeast, Schizosaccharomyces pombe, there are two genes encoding for TOR proteins. Tor1 interacts with Ste20 (Rictor in human cells) and Sin1 (mSin1 in human cells) to form TORC2, whereas Tor2 interacts with Mip1 (Raptor in human cells) to form TORC1 (4). TORC1 is essential for growth in S. pombe and plays a critical role in regulating the switch between growth and sexual development in response to nitrogen starvation. Consistently, disruption of S. pombe TORC1 results in many features characteristic of nitrogenstarved cells (5-8), and TORC1-dependent phosphorylation of the small ribosomal protein Rps6 is diminished under nitrogen starvation (9).S. pombe TORC2 is not essential for growth but is required for cell survival under a wide variety of stress conditions, including high or low temperatures, oxidative or osmotic stress, and DNA damage or replication stresses (10, 11). TORC2 is also essential for entrance into a stationary (G 0 -like) phase and sexual development, two processes that occur in response to nutritional starvation. Under normal growth ...

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“…In addition, cell growth and cell cycle progression are dependent on availability of nitrogen and other nutrients and subsequent signalling via target of rapamycin complex 1 (Takahara and Maeda, 2012). In fungi, there is evidence for active sensing of extracellular nitrogen because response to nitrogen stress was independent from intracellular ATP/AMP levels (Davie et al, 2015).…”

Section: Nitrogen Sensingmentioning

confidence: 99%

Fungal sensing of host environment

Braunsdorf

Mailänder-Sánchez²,

Schaller

2016

Cellular Microbiology

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Summary To survive inside a host, fungi have to adapt to a changing and often hostile environment and therefore need the ability to recognize what is going on around them. To adapt to different host niches, they need to sense external conditions such as temperature, pH and to recognize specific host factors. The ability to respond to physiological changes inside the host, independent of being in a commensal, pathogenic or even symbiotic context, implicates mechanisms for sensing of specific host factors. Because the cell wall is constantly in contact with the surrounding, fungi express receptors on the surface of their cell wall, such as pheromone receptors, which have important roles, besides mediating chemotropism for mating. We are not restricting the discussion to the human host because the receptors and mechanisms used by different fungal species to sense their environment are often similar even for plant pathogens. Furthermore, the natural habitat of opportunistic pathogenic fungi with the potential to cause infection in a human host is in soil and on plants. While the hosts' mechanisms of sensing fungal pathogens have been addressed in the literature, the focus of this review is to fill the gap, giving an overview on fungal sensing of a host‐(ile) environment. Expanding our knowledge on host–fungal interactions is extremely important to prevent and treat diseases of pathogenic fungi, which are important issues in human health and agriculture but also to understand the delicate balance of fungal symbionts in our ecosystem.

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Nitrogen Regulates AMPK to Control TORC1 Signaling

Cited by 72 publications

References 51 publications

Phosphatases Generate Signal Specificity Downstream of Ssp1 Kinase in Fission Yeast

Phosphatases Generate Signal Specificity Downstream of Ssp1 Kinase in Fission Yeast

Gad8 Protein Is Found in the Nucleus Where It Interacts with the MluI Cell Cycle Box-binding Factor (MBF) Transcriptional Complex to Regulate the Response to DNA Replication Stress

Fungal sensing of host environment

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