The general amino acid control pathway regulates mTOR and autophagy during serum/glutamine starvation

Organisms have evolved elaborate mechanisms to adjust intracellular nutrient levels in response to fluctuating availability of exogenous nutrients. During starvation, cells can enhance amino acid uptake and synthesis through the general amino acid control (GAAC) pathway, whereas nonessential cellular contents are recycled by autophagy. How these two pathways are coordinated in response to starvation is currently unknown. Here we show that the GAAC pathway couples exogenous amino acid availability with autophagy. Starvation caused deactivation of mTOR, which then activated autophagy. In parallel, serum/glutamine starvation activated the GAAC pathway, which up-regulated amino acid transporters, leading to increased amino acid uptake. This elevated the intracellular amino acid level, which in turn reactivated mTOR and suppressed autophagy. Knockdown of activating transcription factor 4, the major transcription factor in the GAAC pathway, or of SLC7A5, a leucine transporter, caused impaired mTOR reactivation and much higher levels of autophagy. Thus, the GAAC pathway modulates autophagy by regulating amino acid uptake and mTOR reactivation during serum/glutamine starvation.

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Complementary α-arrestin - Rsp5 ubiquitin ligase complexes control selective nutrient transporter endocytosis in response to amino acid availability

10.1101/2020.04.24.059832 ◽

2020 ◽

Author(s):

Vasyl Ivashov ◽

Johannes Zimmer ◽

Sinead Schwabl ◽

Jennifer Kahlhofer ◽

Sabine Weys ◽

...

Keyword(s):

Amino Acid ◽

Ubiquitin Ligase ◽

Amino Acid Transporters ◽

General Amino Acid Control ◽

Amino Acid Availability ◽

Acid Control ◽

Genome Wide ◽

A Genome ◽

Lysine Residues ◽

Nutrient Transporter

AbstractHow cells adjust transport across their membranes is incompletely understood. Previously, we have shown that S.cerevisiae broadly re-configures the nutrient transporters at the plasma membrane in response to amino acid availability, through selective endocytosis of sugar- and amino acid transporters (AATs) (Müller et al., 2015). A genome-wide screen now revealed that Art2/Ecm21, a member of the α-arrestin family of Rsp5 ubiquitin ligase adaptors, is required for the simultaneous endocytosis of four AATs and induced during starvation by the general amino acid control pathway. Art2 uses a basic patch to recognize C-terminal acidic sorting motifs in these AATs and instructs Rsp5 to ubiquitinate proximal lysine residues. In response to amino acid excess, Rsp5 instead uses TORC1-activated Art1 to detect N-terminal acidic sorting motifs within the same AATs, which initiates exclusive substrate-induced endocytosis of individual AATs. Thus, amino acid availability activates complementary α-arrestin-Rsp5-complexes to control selective endocytosis for nutrient acquisition.

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Amino Acid Transporters on the Guard of Cell Genome and Epigenome

Cancers ◽

10.3390/cancers13010125 ◽

2021 ◽

Vol 13 (1) ◽

pp. 125

Author(s):

Uğur Kahya ◽

Ayşe Sedef Köseer ◽

Anna Dubrovska

Keyword(s):

Amino Acid ◽

Cancer Metabolism ◽

Tumor Imaging ◽

Redox Homeostasis ◽

Amino Acid Uptake ◽

Metabolic Reprogramming ◽

Tumor Evolution ◽

Amino Acid Transporters ◽

Acid Uptake ◽

Growth And Survival

Tumorigenesis is driven by metabolic reprogramming. Oncogenic mutations and epigenetic alterations that cause metabolic rewiring may also upregulate the reactive oxygen species (ROS). Precise regulation of the intracellular ROS levels is critical for tumor cell growth and survival. High ROS production leads to the damage of vital macromolecules, such as DNA, proteins, and lipids, causing genomic instability and further tumor evolution. One of the hallmarks of cancer metabolism is deregulated amino acid uptake. In fast-growing tumors, amino acids are not only the source of energy and building intermediates but also critical regulators of redox homeostasis. Amino acid uptake regulates the intracellular glutathione (GSH) levels, endoplasmic reticulum stress, unfolded protein response signaling, mTOR-mediated antioxidant defense, and epigenetic adaptations of tumor cells to oxidative stress. This review summarizes the role of amino acid transporters as the defender of tumor antioxidant system and genome integrity and discusses them as promising therapeutic targets and tumor imaging tools.

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Influence of organic cations on basic amino-acid uptake by human placental villi

Reproduction Fertility and Development ◽

10.1071/rd9951491 ◽

1995 ◽

Vol 7 (6) ◽

pp. 1491

Author(s):

RB Krishna ◽

J Dancis ◽

M Levitz

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Basic Amino Acid ◽

Amino Acid Uptake ◽

Progressive Increase ◽

Amino Acid Transporters ◽

Acid Uptake ◽

Chorionic Villi ◽

Basic Amino Acids ◽

Kinetics Of

Human placental chorionic villi were incubated for 30 min with [3H]lysine or [3H]arginine and the distribution ratios (intracellular:extracellular concentrations) were determined. The ratios remained unchanged when Na+ in Earle's buffered salt solution was replaced with Li+. When Na+ was replaced with choline there was a significant increase is distribution ratios (lysine 1.34 +/- 0.33 v. 3.99 +/- 0.15, arginine 1.95 +/- 0.37 v. 5.05 +/- 1.16). Leucine, a neutral amino acid with a Na(+)-independent transport system, was unaffected by choline substitution. The distribution ratio for alanine, which is Na(+)-dependent, was reduced (2.50 +/- 0.41 v. 1.45 +/- 0.20). Two other quarternary amines, acetyl-beta-methylcholine and tetraethylammonium chloride (TEA) caused similar increases in the distribution ratios of the basic amino acids. Hordenine, a tertiary amine, was less effective and there was little or no effect with ephedrine, a secondary amine. The choline effect was first observable at concentrations of 105 mM. With TEA, there was a progressive increase in distribution ratios beginning at 29 mM. Lysine efflux was measured after incubation of villi with lysine in Earle's buffer or choline buffer. Lysine was rapidly released to the fresh medium with 25% more retained in choline-exposed villi. The amines may cause alterations in the kinetics of basic amino-acid transporters or may modify other aspects of placental physiology permitting an increase retention of the basic amino acids.

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The role of amino acid transporters in inherited and acquired diseases

Biochemical Journal ◽

10.1042/bj20101912 ◽

2011 ◽

Vol 436 (2) ◽

pp. 193-211 ◽

Cited By ~ 109

Author(s):

Stefan Bröer ◽

Manuel Palacín

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Mammalian Cells ◽

Neuronal Excitability ◽

Tumour Progression ◽

Building Blocks ◽

Amino Acid Uptake ◽

Whole Body ◽

Amino Acid Transporters ◽

Acid Uptake

Amino acids are essential building blocks of all mammalian cells. In addition to their role in protein synthesis, amino acids play an important role as energy fuels, precursors for a variety of metabolites and as signalling molecules. Disorders associated with the malfunction of amino acid transporters reflect the variety of roles that they fulfil in human physiology. Mutations of brain amino acid transporters affect neuronal excitability. Mutations of renal and intestinal amino acid transporters affect whole-body homoeostasis, resulting in malabsorption and renal problems. Amino acid transporters that are integral parts of metabolic pathways reduce the function of these pathways. Finally, amino acid uptake is essential for cell growth, thereby explaining their role in tumour progression. The present review summarizes the involvement of amino acid transporters in these roles as illustrated by diseases resulting from transporter malfunction.

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Adaptive responses to peroxynitrite: increased glutathione levels and cystine uptake in vascular cells

AJP Cell Physiology ◽

10.1152/ajpcell.2000.279.4.c1168 ◽

2000 ◽

Vol 279 (4) ◽

pp. C1168-C1176 ◽

Cited By ~ 24

Author(s):

Barbara J. Buckley ◽

A. Richard Whorton

Keyword(s):

Amino Acid ◽

Close Correlation ◽

Amino Acid Uptake ◽

Acid Uptake ◽

Vascular Cells ◽

Adaptive Responses ◽

Amino Acid Availability ◽

Copper Zinc ◽

Copper Zinc Superoxide Dismutases ◽

Extracellular Sodium

We and others recently demonstrated increased glutathione levels, stimulated cystine uptake, and induced γ-glutamylcysteinyl synthase (γ-GCS) in vascular cells exposed to nitric oxide donors. Here we report the effects of peroxynitrite on glutathione levels and cystine uptake. Treatment of bovine aortic endothelial and smooth muscle cells with 3-morpholinosydnonimine (SIN-1), a peroxynitrite donor, resulted in transient depletion of glutathione followed by a prolonged increase beginning at 8–9 h. Concentration-dependent increases in glutathione of up to sixfold occurred 16–18 h after 0.05–2.5 mM SIN-1. Responses to SIN-1 were inhibited by copper-zinc superoxide dismutases and manganese(III)tetrakis(1-methyl-4-pyridyl)porphyrin pentachloride, providing evidence for peroxynitrite involvement. Because glutathione synthesis is regulated by amino acid availability, we also studied cystine uptake. SIN-1 treatment resulted in a prolonged increase in cystine uptake beginning at 6–9 h. Increases in cystine uptake after SIN-1 were blocked by inhibitors of protein and RNA synthesis, by extracellular glutamate but not by extracellular sodium. These studies suggest induction of the xc − pathway of amino acid uptake. A close correlation over time was observed for increases in cystine uptake and glutathione levels. In summary, vascular cells respond to chronic peroxynitrite exposure with adaptive increases in cellular glutathione and cystine transport.

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Amino Acid Transporters in Plant Cells: A Brief Review

Plants ◽

10.3390/plants9080967 ◽

2020 ◽

Vol 9 (8) ◽

pp. 967

Author(s):

Guangzhe Yang ◽

Qiuxing Wei ◽

Hao Huang ◽

Jixing Xia

Keyword(s):

Amino Acid ◽

Intracellular Transport ◽

Abiotic Stress Tolerance ◽

Amino Acid Uptake ◽

Phloem Loading ◽

Amino Acid Transporters ◽

Acid Uptake ◽

Potential Applications ◽

Phloem Loading And Unloading ◽

Development Regulation

Amino acids are not only a nitrogen source that can be directly absorbed by plants, but also the major transport form of organic nitrogen in plants. A large number of amino acid transporters have been identified in different plant species. Despite belonging to different families, these amino acid transporters usually exhibit some general features, such as broad expression pattern and substrate selectivity. This review mainly focuses on transporters involved in amino acid uptake, phloem loading and unloading, xylem-phloem transfer, import into seed and intracellular transport in plants. We summarize the other physiological roles mediated by amino acid transporters, including development regulation, abiotic stress tolerance and defense response. Finally, we discuss the potential applications of amino acid transporters for crop genetic improvement.

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4F2hc stabilizes GLUT1 protein and increases glucose transport activity

AJP Cell Physiology ◽

10.1152/ajpcell.00416.2010 ◽

2011 ◽

Vol 300 (5) ◽

pp. C1047-C1054 ◽

Cited By ~ 20

Author(s):

Haruya Ohno ◽

Yusuke Nakatsu ◽

Hideyuki Sakoda ◽

Akifumi Kushiyama ◽

Hiraku Ono ◽

...

Keyword(s):

Amino Acid ◽

Glucose Uptake ◽

Glucose Transporter ◽

Fluorescent Protein ◽

Amino Acid Uptake ◽

Amino Acid Transporters ◽

Acid Uptake ◽

Mrna Levels ◽

Glucose Transporter 1 ◽

Glut1 Protein

Glucose transporter 1 (GLUT1) is widely distributed throughout various tissues and contributes to insulin-independent basal glucose uptake. Using a split-ubiquitin membrane yeast two-hybrid system, we newly identified 4F2 heavy chain (4F2hc) as a membrane protein interacting with GLUT1. Though 4F2hc reportedly forms heterodimeric complexes between amino acid transporters, such as LAT1 and LAT2, and regulates amino acid uptake, we investigated the effects of 4F2hc on GLUT1 expression and the associated glucose uptake. First, FLAG-tagged 4F2hc and hemagglutinin-tagged GLUT1 were overexpressed in human embryonic kidney 293 cells and their association was confirmed by coimmunoprecipitation. The green fluorescent protein-tagged 4F2hc and DsRed-tagged GLUT1 showed significant, but incomplete, colocalization at the plasma membrane. In addition, an endogenous association between GLUT1 and 4F2hc was demonstrated using mouse brain tissue and HeLa cells. Interestingly, overexpression of 4F2hc increased the amount of GLUT1 protein in HeLa and HepG2 cells with increased glucose uptake. In contrast, small interfering RNA (siRNA)-mediated 4F2hc gene suppression markedly reduced GLUT1 protein in both cell types, with reduced glucose uptake. While GLUT1 mRNA levels were not affected by overexpression or gene silencing of 4F2hc, GLUT1 degradation after the addition of cycloheximide was significantly suppressed by 4F2hc overexpression and increased by 4F2hc siRNA treatment. Taken together, these observations indicate that 4F2hc is likely to be involved in GLUT1 stabilization and to contribute to the regulation of not only amino acid but also glucose metabolism.

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The tea plant CsLHT1 and CsLHT6 transporters take up amino acids, as a nitrogen source, from the soil of organic tea plantations

Horticulture Research ◽

10.1038/s41438-021-00615-x ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Fang Li ◽

Chunxia Dong ◽

Tianyuan Yang ◽

Shilai Bao ◽

Wanping Fang ◽

...

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Amino Acid Content ◽

Amino Acid Uptake ◽

Amino Acid Transporters ◽

Acid Uptake ◽

Tea Plantation ◽

Tea Plantations ◽

Organic Tea ◽

Tea Plants

AbstractOrganic tea is more popular than conventional tea that originates from fertilized plants. Amino acids inorganic soils constitute a substantial pool nitrogen (N) available for plants. However, the amino-acid contents in soils of tea plantations and how tea plants take up these amino acids remain largely unknown. In this study, we show that the amino-acid content in the soil of an organic tea plantation is significantly higher than that of a conventional tea plantation. Glutamate, alanine, valine, and leucine were the most abundant amino acids in the soil of this tea plantation. When 15N-glutamate was fed to tea plants, it was efficiently absorbed and significantly increased the contents of other amino acids in the roots. We cloned seven CsLHT genes encoding amino-acid transporters and found that the expression of CsLHT1, CsLHT2, and CsLHT6 in the roots significantly increased upon glutamate feeding. Moreover, the expression of CsLHT1 or CsLHT6 in a yeast amino-acid uptake-defective mutant, 22∆10α, enabled growth on media with amino acids constituting the sole N source. Amino-acid uptake assays indicated that CsLHT1 and CsLHT6 are H+-dependent high- and low-affinity amino-acid transporters, respectively. We further demonstrated that CsLHT1 and CsLHT6 are highly expressed in the roots and are localized to the plasma membrane. Moreover, overexpression of CsLHT1 and CsLHT6 in Arabidopsis significantly improved the uptake of exogenously supplied 15N-glutamate and 15N-glutamine. Taken together, our findings are consistent with the involvement of CsLHT1 and CsLHT6 in amino-acid uptake from the soil, which is particularly important for tea plants grown inorganic tea plantations.

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Complementary α-arrestin-ubiquitin ligase complexes control nutrient transporter endocytosis in response to amino acids

eLife ◽

10.7554/elife.58246 ◽

2020 ◽

Vol 9 ◽

Cited By ~ 2

Author(s):

Vasyl Ivashov ◽

Johannes Zimmer ◽

Sinead Schwabl ◽

Jennifer Kahlhofer ◽

Sabine Weys ◽

...

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Ubiquitin Ligase ◽

Amino Acid Transporters ◽

General Amino Acid Control ◽

Amino Acid Availability ◽

Genome Wide ◽

A Genome ◽

Lysine Residues ◽

Nutrient Transporter

How cells adjust nutrient transport across their membranes is incompletely understood. Previously, we have shown that S. cerevisiae broadly re-configures the nutrient transporters at the plasma membrane in response to amino acid availability, through endocytosis of sugar- and amino acid transporters (AATs) (Müller et al., 2015). A genome-wide screen now revealed that the selective endocytosis of four AATs during starvation required the α-arrestin family protein Art2/Ecm21, an adaptor for the ubiquitin ligase Rsp5, and its induction through the general amino acid control pathway. Art2 uses a basic patch to recognize C-terminal acidic sorting motifs in AATs and thereby instructs Rsp5 to ubiquitinate proximal lysine residues. When amino acids are in excess, Rsp5 instead uses TORC1-activated Art1 to detect N-terminal acidic sorting motifs within the same AATs, which initiates exclusive substrate-induced endocytosis. Thus, amino acid excess or starvation activate complementary α-arrestin-Rsp5-complexes to control selective endocytosis and adapt nutrient acquisition.

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Is gamma-actin a regulator of amino acid transport?

AJP Cell Physiology ◽

10.1152/ajpcell.1996.270.6.c1647 ◽

1996 ◽

Vol 270 (6) ◽

pp. C1647-C1655 ◽

Cited By ~ 7

Author(s):

G. Lin ◽

J. I. McCormick ◽

R. M. Johnstone

Keyword(s):

Amino Acid ◽

Cell Line ◽

Amino Acid Transport ◽

Normal Growth ◽

Amino Acid Uptake ◽

Xenopus Laevis Oocytes ◽

Amino Acid Transporters ◽

Acid Uptake ◽

Acid Transport ◽

Dependent Transport

A mutated yeast cell line incapable of growth in minimal medium with proline as the sole nitrogen source was restored to normal growth by transfection with a cDNA from mouse Ehrlich cells. The cloned cDNA (E51) was found to be 90% homologous to gamma-actin. Immediately after transfection with E51 cDNA, both alpha-aminoisobutyric acid (AIB) and proline uptake in the mutated yeast were increased, particularly at pH 5. The expression of the same E51 cDNA also enhanced amino acid uptake in Xenopus laevis oocytes after injection into the Xenopus nuclei. A mutated mammalian lymphocyte cell line (GF-17), deficient in system A transport, also showed increased Na(+)-dependent transport after transfection with E51 cDNA. Whereas the mock transfected GF-17 cells failed to grow in the selection medium, the transfectants with E51 cDNA grew better than the untransfected cells. The data are consistent with the conclusion that expression of E51 cDNA can modify inactive, endogenous amino acid transporters, permitting substantial amino acid uptake in cells deficient in amino acid transporter(s) and permitting rapid cell growth. The data suggest that the gamma-actin-like protein coded for by E51 cDNA may play a significant regulatory role in amino acid transport.

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