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

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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Alanine uptake activates hepatocellular chloride channels

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1997.273.4.g849 ◽

1997 ◽

Vol 273 (4) ◽

pp. G849-G853 ◽

Cited By ~ 6

Author(s):

Steven D. Lidofsky ◽

Richard M. Roman

Keyword(s):

Amino Acid ◽

Mammalian Cells ◽

Chloride Channels ◽

Amino Acid Uptake ◽

Experimental Models ◽

Cell Swelling ◽

Acid Uptake ◽

Adaptive Responses ◽

Anion Channels

Cells involved in the retrieval and metabolic conversion of amino acids undergo significant increases in size in response to amino acid uptake. The resultant adaptive responses to cell swelling are thought to include increases in membrane K+ and Cl− permeability through activation of volume-sensitive ion channels. This viewpoint is largely based on experimental models of hypotonic swelling, but few mammalian cells experience hypotonic challenge in vivo. Here we have examined volume regulatory responses in a physiological model of cell-swelling alanine uptake in immortalized hepatocytes. Alanine-induced cell swelling was followed by a decrease in cell volume that was temporally associated with an increase in membrane Cl− currents. These currents were dependent both on alanine concentration and Na+, suggesting that currents were stimulated by Na+-coupled alanine uptake. Cl− currents were outwardly rectifying, exhibited an anion permeability sequence of I− > Br− > Cl−, and were inhibited by the Cl− channel blocker 5-nitro-2-(3-phenylpropylamino)benzoic acid, features similar to those reported for a widely distributed class of volume-sensitive anion channels evoked by experimental hypotonic stress. These findings suggest that volume-sensitive anion channels participate in adaptive responses to amino acid uptake and provide such channels with a new physiological context.

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

The Journal of Cell Biology ◽

10.1083/jcb.201403009 ◽

2014 ◽

Vol 206 (2) ◽

pp. 173-182 ◽

Cited By ~ 92

Author(s):

Rui Chen ◽

Yilong Zou ◽

Dongxue Mao ◽

Daxiao Sun ◽

Guanguang Gao ◽

...

Keyword(s):

Transcription Factor ◽

Amino Acid ◽

Amino Acid Level ◽

Amino Acid Uptake ◽

Amino Acid Transporters ◽

Acid Uptake ◽

General Amino Acid Control ◽

Amino Acid Availability ◽

Acid Control ◽

Activating Transcription Factor 4

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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Faculty Opinions recommendation of Light enhanced amino acid uptake by dominant bacterioplankton groups in surface waters of the Atlantic Ocean.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1126015.583128 ◽

2008 ◽

Author(s):

John Hobbie

Keyword(s):

Amino Acid ◽

Atlantic Ocean ◽

Surface Waters ◽

Amino Acid Uptake ◽

Acid Uptake

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Molecular Imaging of Brain Tumor-Associated Epilepsy

Diagnostics ◽

10.3390/diagnostics10121049 ◽

2020 ◽

Vol 10 (12) ◽

pp. 1049

Author(s):

Csaba Juhász ◽

Sandeep Mittal

Keyword(s):

Brain Tumor ◽

Amino Acid ◽

Brain Tumors ◽

Treatment Strategies ◽

Amino Acid Uptake ◽

Seizure Outcome ◽

Acid Uptake ◽

Positron Emission ◽

Oncology Practice ◽

Glioneuronal Tumors

Epilepsy is a common clinical manifestation and a source of significant morbidity in patients with brain tumors. Neuroimaging has a pivotal role in neuro-oncology practice, including tumor detection, differentiation, grading, treatment guidance, and posttreatment monitoring. In this review, we highlight studies demonstrating that imaging can also provide information about brain tumor-associated epileptogenicity and assist delineation of the peritumoral epileptic cortex to optimize postsurgical seizure outcome. Most studies focused on gliomas and glioneuronal tumors where positron emission tomography (PET) and advanced magnetic resonance imaging (MRI) techniques can detect metabolic and biochemical changes associated with altered amino acid transport and metabolism, neuroinflammation, and neurotransmitter abnormalities in and around epileptogenic tumors. PET imaging of amino acid uptake and metabolism as well as activated microglia can detect interictal or peri-ictal cortical increased uptake (as compared to non-epileptic cortex) associated with tumor-associated epilepsy. Metabolic tumor volumes may predict seizure outcome based on objective treatment response during glioma chemotherapy. Advanced MRI, especially glutamate imaging, can detect neurotransmitter changes around epileptogenic brain tumors. Recently, developed PET radiotracers targeting specific glutamate receptor types may also identify therapeutic targets for pharmacologic seizure control. Further studies with advanced multimodal imaging approaches may facilitate development of precision treatment strategies to control brain tumor-associated epilepsy.

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Polyribonucleotide Synthesis and Bacterial Amino Acid Uptake: the Work of Leon A. Heppel

Journal of Biological Chemistry ◽

10.1016/s0021-9258(17)47471-0 ◽

2007 ◽

Vol 282 (18) ◽

pp. e13-e15

Author(s):

Nicole Kresge ◽

Robert D. Simoni ◽

Robert L. Hill

Keyword(s):

Amino Acid ◽

Amino Acid Uptake ◽

Acid Uptake

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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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