Amino Acid Depletion Research Articles

AMPK activation protects astrocytes from hypoxia‑induced cell death.

Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a major cellular energy sensor that is activated by an increase in the AMP/adenosine triphosphate (ATP) ratio. This causes the initiation of adaptive cellular programs, leading to the inhibition of anabolic pathways and increasing ATP synthesis. AMPK indirectly inhibits mammalian target of rapamycin (mTOR) complex 1 (mTORC1), a serine/threonine kinase and central regulator of cell growth and metabolism, which integrates various growth inhibitory signals, such as the depletion of glucose, amino acids, ATP and oxygen. While neuroprotective approaches by definition focus on neurons, that are more sensitive under cell stress conditions, astrocytes play an important role in the cerebral energy homeostasis during ischemia. Therefore, the protection of astrocytic cells or other glial cells may contribute to the preservation of neuronal integrity and function. In the present study, it was thus hypothesized that a preventive induction of energy deprivation-activated signaling pathways via AMPK may protect astrocytes from hypoxia and glucose deprivation. Hypoxia-induced cell death was measured in a paradigm of hypoxia and partial glucose deprivation in vitro in the immortalized human astrocytic cell line SVG. Both the glycolysis inhibitor 2-deoxy-d-glucose (2DG) and the AMPK activator A-769662 induced the phosphorylation of AMPK, resulting in mTORC1 inhibition, as evidenced by a decrease in the phosphorylation of the target ribosomal protein S6 (RPS6). Treatment with both 2DG and A-769662 also decreased glucose consumption and lactate production. Furthermore, A-769662, but not 2DG induced an increase in oxygen consumption, possibly indicating a more efficient glucose utilization through oxidative phosphorylation. Hypoxia-induced cell death was profoundly reduced by treatment with 2DG or A-769662. On the whole, the findings of the present study demonstrate, that AMPK activation via 2DG or A-769662 protects astrocytes under hypoxic and glucose-depleted conditions.

Microbial enzymes for deprivation of amino acid metabolism in malignant cells: biological strategy for cancer treatment.

Amino acid deprivation therapy (AADT) is emerging as a promising strategy for the development of novel therapeutics against cancer. This biological therapy relies upon the differences in the metabolism of cancer and normal cells. The rapid growth of tumors results in decreased expression of certain enzymes leading to auxotrophy for some specific amino acids. These auxotrophic tumors are targeted by amino acid-depleting enzymes. The depletion of amino acid selectively inhibits tumor growth as the normal cells can synthesize amino acids by their usual machinery. The enzymes used in AADT are mostly obtained from microbes for their easy availability. Microbial L-asparaginase is already approved by FDA for the treatment of acute lymphoblastic leukemia. Arginine deiminase and methionase are under clinical trials and the therapeutic potential of lysine oxidase, glutaminase and phenylalanine ammonia lyase is also being explored. The present review provides an overview of microbial amino acid depriving enzymes. Various attributes of these enzymes like structure, mode of action, production, formulations, and targeted cancers are discussed. The challenges faced and the combat strategies to establish AADT in standard cancer armamentarium are also reviewed.Key Points • Amino acid deprivation therapy is a potential therapy for auxotrophic tumors. • Microbial enzymes are used due to their ease of manipulation and high productivity. • Enzyme properties are improved by PEGylation, encapsulation, and genetic engineering. • AADT can be employed as combinational therapy for better containment of cancer.

Plasma metabolomics of the time resolved response to Opisthorchis felineus infection in an animal model (golden hamster, Mesocricetus auratus).

BackgroundOpisthorchiasis is a hepatobiliary disease caused by flukes of the trematode family Opisthorchiidae. Opisthorchiasis can lead to severe hepatobiliary morbidity and is classified as a carcinogenic agent. Here we investigate the time-resolved metabolic response to Opisthorchis felineus infection in an animal model.MethodologyThirty golden hamsters were divided in three groups: severe infection (50 metacercariae/hamster), mild infection (15 metacercariae/hamster) and uninfected (vehicle-PBS) groups. Each group consisted of equal number of male and female animals. Plasma samples were collected one day before the infection and then every two weeks up to week 22 after infection. The samples were subjected to 1H Nuclear Magnetic Resonance (NMR) spectroscopy and multivariate statistical modelling.Principal findingsThe time-resolved study of the metabolic response to Opisthorchis infection in plasma in the main lines agrees with our previous report on urine data. The response reaches its peak around the 4th week of infection and stabilizes after the 10th week. Yet, unlike the urinary data there is no strong effect of the gender in the data and the intensity of infection is presented in the first two principal components of the PCA model. The main trends of the metabolic response to the infection in blood plasma are the transient depletion of essential amino acids and an increase in lipoprotein and cholesterol concentrations.ConclusionsThe time resolved metabolic signature of Opisthorchis infection in the hamster’s plasma shows a coherent shift in amino acids and lipid metabolism. Our work provides insight into the metabolic basis of the host response on the helminth infection.

Tumor hypermetabolism confers resistance to immunotherapy.

Advances in our understanding of tumor immune biology and development of cancer immunotherapies have led to improved outcomes for patients that suffer from aggressive cancers such as metastatic melanoma. Despite these advances, a significant proportion of patients still fail to benefit, and as a result, attention has shifted to understanding how cancer cells escape immune destruction. Of particular interest is the metabolic landscape of the tumor microenvironment, as recent studies have demonstrated how both competition for essential nutrients and depletion of specific amino acids can promote T cell dysfunction. Here, we will discuss the major energetic pathways engaged by both T cells and cancer cells, metabolic substrates present in the tumor microenvironment, and emerging therapeutic strategies that seek to improve T cell metabolic fitness and bolster the antitumor immune response.

PHD1 controls muscle mTORC1 in a hydroxylation-independent manner by stabilizing leucyl tRNA synthetase

mTORC1 is an important regulator of muscle mass but how it is modulated by oxygen and nutrients is not completely understood. We show that loss of the prolyl hydroxylase domain isoform 1 oxygen sensor in mice (PHD1KO) reduces muscle mass. PHD1KO muscles show impaired mTORC1 activation in response to leucine whereas mTORC1 activation by growth factors or eccentric contractions was preserved. The ability of PHD1 to promote mTORC1 activity is independent of its hydroxylation activity but is caused by decreased protein content of the leucyl tRNA synthetase (LRS) leucine sensor. Mechanistically, PHD1 interacts with and stabilizes LRS. This interaction is promoted during oxygen and amino acid depletion and protects LRS from degradation. Finally, elderly subjects have lower PHD1 levels and LRS activity in muscle from aged versus young human subjects. In conclusion, PHD1 ensures an optimal mTORC1 response to leucine after episodes of metabolic scarcity.

Proteasome inhibition in multiple myeloma: lessons for other cancers.

Cellular protein homeostasis (proteostasis) depends on the controlled degradation of proteins that are damaged or no longer required by the ubiquitin-proteasome system (UPS). The 26S proteasome is the principal executer of substrate-specific proteolysis in eukaryotic cells and regulates a myriad of cellular functions. Proteasome inhibitors were initially developed as chemical tools to study proteasomal function but rapidly became widely used anticancer drugs that are now used at all stages of treatment for the bone marrow cancer multiple myeloma (MM). Here, we review the mechanisms of action of proteasome inhibitors that underlie their preferential toxicity to MM cells, focusing on endoplasmic reticulum stress, depletion of amino acids, and effects on glucose and lipid metabolism. We also discuss mechanisms of resistance to proteasome inhibition such as autophagy and metabolic rewiring and what lessons we may learn from the success and failure of proteasome inhibition in MM for treating other cancers with proteostasis-targeting drugs.

Integrated Systems Level Examination of Proteasome Inhibitor Stress Recovery in Myeloma Cells Reveals Druggable Vulnerabilities Linked to Multiple Metabolic Processes

Proteasome inhibitors (PIs) form the backbone of multiple myeloma (MM) treatment regimens used at diagnosis and relapse, but their clinical benefit is limited by varying degrees of resistance. The mechanisms that protect MM cells (MMCs) from PI-induced cell death are only partly understood, and experimental resistance studies often rely on the prolonged exposure of MMCs to relatively low levels of PIs. However, patients receive PI doses that result in high but short plasma peaks. Given that each PI dose reduces a patient's MMC load until a plateau is reached, one can assume that each PI dose kills some MMCs by triggering overwhelming stress. This proposition implies that a proportion of MMCs not only survive but also resolve PI-induced stress. We hypothesised that the mechanisms of PI-induced stress recovery require a redistribution of cellular resources, and that this process triggers specific recovery-associated and potentially druggable vulnerabilities. To test this hypothesis, we obtained a global systems-level view of the cellular response to proteasome inhibition by performing a multi-omics 10-day time-course experiment. To mimic in vivo pharmacokinetics and anti-MM effects, RPMI-8226 MMCs were treated with a 1h pulse of carfilzomib (CFZ; 750nmol/L), which reduced the number of viable MMCs to a nadir of approximately 50% on day +2, followed by a return to pretreatment baseline levels of viable cells by day +6. Levels of ubiquitinated proteins as a readout of effective proteasome inhibition peaked on day +1 and returned to baseline levels on day +6. Samples for transcriptome analysis by RNA-seq, proteome analysis by a multiplexed tandem mass tag (TMT)-based approach, and global metabolomic profiling by ultrahigh performance liquid chromatography-tandem mass spectroscopy (LC-MS) were collected 2h prior to the CFZ pulse (day 0) and on days +1, +2, +4, +6, +8, and +10. The results demonstrate extensive and kinetically complex changes of the MMC transcriptome, proteome and metabolome that did not fully return to baseline by day +10. Conventional and advanced computational analyses of RNA-seq data (including biological homogeneity score-validated graph-based clustering of temporal patterns combined with gene enrichment and KEGG/GO pathway analysis) revealed different patterns of involvement of multiple and functionally diverse pathways. Perhaps most notably, RNA-seq data revealed extensive metabolic pathway responses while cells were dying and throughout recovery. Consistently, metabolomic profiling by LC-MS showed wide-ranging metabolite changes. These included rapid intracellular depletion of glucose, which was paralleled by the accumulation of lactate and pyruvate and lasted until day +8. Consistently, the major glucose uptake regulator TXNIP stood out as upregulated during recovery, which was accompanied by the predicted downregulation of the glucose transporter GLUT1. These findings were confirmed by real-time PCR and immunoblotting in RPMI-8226 and other MMC lines. Moreover, pharmacological inhibition of glucose and lactate metabolising enzymes and transmembrane transport enhanced MMC killing by CFZ, confirming profound and druggable changes in glucose and energy metabolism during PI stress recovery. We also observed prolonged depletion of a number of amino acids, including glutamine, which was paralleled by depletion of glutamate and TCA cycle intermediates. Moreover, we found RNA-seq and real-time PCR/immunoblot-based evidence for an amino acid response (AAR) during stress recovery that was driven by the amino acid sensing kinase GCN2 (EIF2AK4). The preclinical GCN2 inhibitor GCN2iB was effective at blocking the AAR and enhanced MMC killing in a panel of CFZ-treated MMC lines. This effect was particularly pronounced during the intermediate stages of recovery, in line with the kinetics of amino acid depletion and the AAR. Thus, our observations define the complex and prolonged cellular responses that characterise the recovery of MMCs from proteasome inhibition. They reveal wide-ranging metabolic changes that persist far beyond immediate stress survival and highlight the dependence of MMCs on the GCN2-driven AAR to overcome PI stress. The findings demonstrate that the mechanisms of PI recovery trigger druggable vulnerabilities, providing the basis for ongoing investigations into sequential therapeutic interventions to enhance responses to PIs. Disclosures Caputo: GSK: Research Funding. Kaiser:Abbvie, Celgene, Takeda, Janssen, Amgen, Abbvie, Karyopharm: Consultancy; Celgene, Janssen: Research Funding; Takeda, Janssen, Celgene, Amgen: Honoraria, Other: Travel Expenses. Auner:Karyopharm: Consultancy; Takeda: Consultancy; Amgen: Other: Consultancy and Research Funding.

P38-Mitogen Activated Kinases Mediate a Developmental Regulatory Response to Amino Acid Depletion and Associated Oxidative Stress in Mouse Blastocyst Embryos.

Maternal starvation coincident with preimplantation development has profound consequences for placental-fetal development, with various identified pathologies persisting/manifest in adulthood; the ‘Developmental Origin of Health and Disease’ (DOHaD) hypothesis/model. Despite evidence describing DOHaD-related incidence, supporting mechanistic and molecular data relating to preimplantation embryos themselves are comparatively meager. We recently identified the classically recognized stress-related p38-mitogen activated kinases (p38-MAPK) as regulating formation of the extraembryonic primitive endoderm (PrE) lineage within mouse blastocyst inner cell mass (ICM). Thus, we wanted to assay if PrE differentiation is sensitive to amino acid availability, in a manner regulated by p38-MAPK. Although blastocysts appropriately mature, without developmental/morphological or cell fate defects, irrespective of amino acid supplementation status, we found the extent of p38-MAPK inhibition induced phenotypes was more severe in the absence of amino acid supplementation. Specifically, both PrE and epiblast (EPI) ICM progenitor populations remained unspecified and there were fewer cells and smaller blastocyst cavities. Such phenotypes could be ameliorated, to resemble those observed in groups supplemented with amino acids, by addition of the anti-oxidant NAC (N-acetyl-cysteine), although PrE differentiation deficits remained. Therefore, p38-MAPK performs a hitherto unrecognized homeostatic early developmental regulatory role (in addition to direct specification of PrE), by buffering blastocyst cell number and ICM cell lineage specification (relating to EPI) in response to amino acid availability, partly by counteracting induced oxidative stress; with clear implications for the DOHaD model.

Macronutrient Valuation: A Novel Tool to Study Food Preference and Choice

In a study published in this issue of the Journal, Buckley et al. (1) develop a computerized task to measure macronutrient valuation that they define as the “value that humans place on a calorie derived from fat, carbohydrate, and protein.” In the same paper, they then use the new method to explore how protein valuation correlates with body composition in a separate sample of community-dwelling elderly. The authors suggest that macronutrient valuation is a driver for food preference that might contribute to explaining food choices. According to this framework, preference for highly palatable and sweet foods might for instance result from a higher valuation of carbohydrates and fats, whereas higher protein valuation might explain preference for foods that are rich in protein. Studying protein valuation from this point of view is of particular interest: although our capacity to choose high-protein containing foods is essential for health, we cannot rely on a consciously perceptible sensory stimulus, as is the case with texture for fat (2) or sweet taste for sugars. Indeed, despite evidence about the red color (3) or umami taste (4) being markers of dietary protein, there is no specific sensory characteristic that is shared among all high-protein containing foods. Therefore, it is more likely that our ability to choose dietary protein sources is based on conditioning that occurs throughout our life when we experience association between consumption of specific foods (here, sources of dietary protein) and beneficial nutritional outcome (here, suppression of amino acid depletion). Although precise mechanisms that lead to such conditioning remain to be discovered, studies in rodents and humans demonstrate that animals compose their diet in a way to ensure sufficient protein intakes, and a diet that is depleted in protein or essential amino acids provokes aversion and lower intakes as a result of experienced metabolic distress (5). In a natural setting, measure of protein valuation could thus be a useful method to explore how humans choose dietary sources of protein for their diet.

CRISPR/Transposon gene integration (CRITGI) can manage gene expression in a retrotransposon-dependent manner

The fine-tuning of gene expression contributes to both basic science and applications. Here, we develop a novel gene expression technology termed CRITGI (CRISPR/Transposon gene integration). CRITGI uses CRISPR/Cas9 to integrate multiple copies of the plasmid pTy1 into Ty1 loci, budding yeast retrotransposons. The pTy1 plasmid harbors a Ty1 consensus sequence for integration, a gene of interest with its own promoter and a selection marker gene. Interestingly, the expression of the pTy1 gene in Ty1 loci could be induced in synthetic complete amino acid depletion medium, which could activate the selection marker gene on pTy1. The induction or repression of the gene on pTy1 depended on Ty1 transcription. Activation of the selection marker gene on pTy1 triggered Ty1 transcription, which led to induction of the gene on pTy1. The gene on pTy1 was not transcribed with Ty1 mRNA; the transcription required its own promoter. Furthermore, the trimethylation of histone H3 on lysine 4, a landmark of transcriptionally active chromatin, accumulated at the 5′ end of the gene on pTy1 following selection marker gene activation. Thus, CRITGI is a unique gene regulation system to induce the genes on pTy1 in amino acid depletion medium and utilizes Ty1 transcription to create a chromatin environment favorable for the transcription of the genes on pTy1.

Leaf metabolic signatures induced by real and simulated herbivory in black mustard (Brassica nigra)

IntroductionThe oxylipin methyl jasmonate (MeJA) is a plant hormone active in response signalling and defence against herbivores. Although MeJA is applied experimentally to mimic herbivory and induce plant defences, its downstream effects on the plant metabolome are largely uncharacterized, especially in the context of primary growth and tissue-specificity of the response.ObjectivesWe investigated the effects of MeJA-simulated and real caterpillar herbivory on the foliar metabolome of the wild plant Brassica nigra and monitored the herbivore-induced responses in relation to leaf ontogeny.MethodsAs single or multiple herbivory treatments, MeJA- and mock-sprayed plants were consecutively exposed to caterpillars or left untreated. Gas chromatography (GC) and liquid chromatography (LC) time-of-flight mass-spectrometry (TOF-MS) were combined to analyse foliar compounds, including central primary and specialized defensive plant metabolites.ResultsPlant responses were stronger in young leaves, which simultaneously induced higher chlorophyll levels. Both MeJA and caterpillar herbivory induced similar, but not identical, accumulation of tricarboxylic acids (TCAs), glucosinolates (GSLs) and phenylpropanoids (PPs), but only caterpillar feeding led to depletion of amino acids. MeJA followed by caterpillars caused higher induction of defence compounds, including a three-fold increase in the major defence compound allyl-GSL (sinigrin). When feeding on MeJA-treated plants, caterpillars gained less weight indicative of the reduced host-plant quality and enhanced resistance.ConclusionsThe metabolomics approach showed that plant responses induced by herbivory extend beyond the regulation of defence metabolism and are tightly modulated throughout leaf development. This leads to a new understanding of the plant metabolic potential that can be exploited for future plant protection strategies.

Identification of Novel, Potent, and Orally Available GCN2 Inhibitors with Type I Half Binding Mode.

General control nonderepressible 2 (GCN2) is a master regulator kinase of amino acid homeostasis and important for cancer survival in the tumor microenvironment under amino acid depletion. We initiated studies aiming at the discovery of novel GCN2 inhibitors as first-in-class antitumor agents and conducted modification of the substructure of sulfonamide derivatives with expected type I half binding on GCN2. Our synthetic strategy mainly corresponding to the αC-helix allosteric pocket of GCN2 led to significant enhancement in potency and a good pharmacokinetic profile in mice. In addition, compound 6d, which showed slow dissociation in binding on GCN2, demonstrated antiproliferative activity in combination with the asparagine-depleting agent asparaginase in an acute lymphoblastic leukemia (ALL) cell line, and it also displayed suppression of GCN2 pathway activation with asparaginase treatment in the ALL cell line and mouse xenograft model.

Immunoregulatory Interplay Between Arginine and Tryptophan Metabolism in Health and Disease.

Over evolution, some amino-acid catabolic pathways have become critical checkpoints in immunity (1–3). The associated immunoregulatory effects rely on the depletion of specific amino acids in the microenvironment and/or generation of biologically active metabolites (4). Consumption of l-arginine (Arg) by arginase 1 (ARG1) represents a well-known immunoregulatory mechanism exploited by M2 macrophages (5) and myeloid-derived suppressor cells (MDSCs) (6–8) in tumor settings. ARG1 is also expressed by human neutrophils (9). Indoleamine 2,3-dioxygenase 1 (IDO1)—a powerful immunosuppressive enzyme catalyzing the first, rate limiting step in l-tryptophan (Trp) catabolism—depletes Trp and produces immunoregulatory molecules collectively known as kynurenines (10–13). High IDO1 expression and catalytic activity occur in dendritic cells (DCs)—professional antigen presenting cells—in response to interferon-γ (IFN-γ) (8, 10, 11). Unlike ARG1, IDO1 is also endowed with non-enzymatic signaling activity in DCs that, in the presence of transforming growth factor-β (TGF-β) in microenvironments, leads to durable immunoregulatory effects (14, 15). In conventional DCs (cDCs), a relay pathway—marked by the sequential activation of ARG1 and IDO1—promotes a potent immunoregulatory phenotype (8, 16, 17). In this setting, spermidine, i.e., a polyamine produced downstream of the ARG1-dependent pathway (18), is capable of triggering IDO1 phosphorylation and signaling, and thus may represent the critical molecular interconnection between the two enzymes (8, 16). Here, we discuss the possible protective vs. pathogenetic roles of the interplay between IDO1 and ARG1 in reprogramming immune cell functions in neoplasia and autoimmune diseases.

Abstract 3656: The mTOR-activating GATOR2 complex is essential in PAX3-FOXO1-positive rhabdomyosarcoma

Abstract Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood, and can be genomically classified into fusion-positive and fusion-negative subsets. The former is driven by PAX3-FOXO1 or related chimeric transcription factors and has few other genetic alterations; the latter harbors recurrent mutations within the PI3K-RAS pathway. Despite these fundamental differences in cancer initiating events, current therapeutic approaches are identical between the two groups aside from chemotherapy intensification for some fusion-positive patients given their poorer outcomes. Current pharmacologic strategies do not permit direct targeting of the PAX3-FOXO1 oncoprotein, so we undertook a CRISPRi genetic screen to identify genes whose loss was toxic to PAX3-FOXO1+ RMS cells, but tolerated in cells with knockdown of the fusion protein. We hypothesized that this would identify targetable dependencies created by PAX3-FOXO1 expression that might permit precision therapy for fusion positive RMS. Through this screen, we identified two genes within the mTOR-activating GATOR2 complex, MIOS and WDR24, as essential for the growth of PAX3-FOXO1 positive RMS cells. We find that loss of MIOS is toxic to fusion-positive RMS cells due to a loss of mTORC1 signaling that normally initiates from signals of amino acid sufficiency. Restoration of mTORC1 activation by amino acids could be achieved by genetic suppression of either DEPDC5, a component of the RAG GAP GATOR1 complex that is normally inhibited by GATOR2, or of TSC1, which suppresses mTORC1 activity in the absence of PI3K signaling. Either genetic alteration completely rescued fusion positive RMS cells from the deleterious effects of MIOS loss. Correspondingly, we found that a fusion-negative RMS cell line with an activating NRAS mutation was insensitive to MIOS loss, suggesting that in this genetic context, amino acid signaling through GATOR2 is no longer necessary to activate mTORC1 and promote RMS survival. In contrast, loss of WDR24 was toxic to both fusion positive and fusion negative RMS cells, and could not be rescued by genetic reactivation of mTORC1. Preliminary data demonstrate alterations in lysosome size and quantity after WDR24 suppression, adding to existing data in Drosophila that this gene plays a critical, mTOR-independent role in lysosome biogenesis, and showing that this role supports RMS survival. As mTOR inhibitors are being tested in frontline phase 3 studies in North America, our work lends timely molecular insight into how the genetic basis of distinct RMS subtypes can influence the signals that promote mTORC1 function to support cancer cell survival. Based on our finding that amino acid activation of mTORC1 is a fusion-positive dependency, we are now testing combined mTOR inhibition with amino acid depletion as a precision therapeutic strategy in preclinical models of this aggressive childhood cancer. Citation Format: Amit J. Sabnis, David V. Allegakoen, Trever G. Bivona. The mTOR-activating GATOR2 complex is essential in PAX3-FOXO1-positive rhabdomyosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3656.

EGFR-Pak Signaling Selectively Regulates Glutamine Deprivation-Induced Macropinocytosis

Macropinocytosis has emerged as an important nutrient-scavenging pathway that supports tumor cell fitness. By internalizing extracellular protein and targeting it for lysosomal degradation, this endocytic pathway functions as an amino acid supply route, permitting tumor cell growth and survival despite the nutrient-poor conditions of the tumor microenvironment. Here, we provide evidence that a subset of pancreatic ductal adenocarcinoma (PDAC) tumors are wired to integrate contextual metabolic inputs to regulate macropinocytosis, dialing up or down this uptake pathway depending on nutrient availability. We find that regional depletion of amino acids coincides with increased levels of macropinocytosis and that the scarcity of glutamine uniquely drives this process. Mechanistically, this stimulation of macropinocytosis depends on the nutrient stress-induced potentiation of epidermal growth factor receptor signaling that, through the activation of Pak, controls the extent of macropinocytosis in these cells. These results provide a mechanistic understanding of how nutritional cues can control protein scavenging in PDAC tumors.

Signal Transduction in Ribosome Biogenesis: A Recipe to Avoid Disaster.

Energetically speaking, ribosome biogenesis is by far the most costly process of the cell and, therefore, must be highly regulated in order to avoid unnecessary energy expenditure. Not only must ribosomal RNA (rRNA) synthesis, ribosomal protein (RP) transcription, translation, and nuclear import, as well as ribosome assembly, be tightly controlled, these events must be coordinated with other cellular events, such as cell division and differentiation. In addition, ribosome biogenesis must respond rapidly to environmental cues mediated by internal and cell surface receptors, or stress (oxidative stress, DNA damage, amino acid depletion, etc.). This review examines some of the well-studied pathways known to control ribosome biogenesis (PI3K-AKT-mTOR, RB-p53, MYC) and how they may interact with some of the less well studied pathways (eIF2α kinase and RNA editing/splicing) in higher eukaryotes to regulate ribosome biogenesis, assembly, and protein translation in a dynamic manner.

SUN-323 Somatostatin Analogue: An Effective Treatment for Pseudoglucagonoma Syndrome

INTRODUCTION: Pseudoglucagonoma syndrome (PS) refers to the presence of necrolytic migratory erythema (NME), despite normal glucagon levels, and absence of a glucagon-secreting tumor. We present a case of PS successfully treated with octreotide. CASE PRESENTATION: A 42-year-old woman with history of Roux-en-Y bypass surgery, performed 14 years ago, presented to the ER with abdominal pain and rash. Two months before presentation, she took 3 days of furosemide for ankle edema. On the third day of treatment, she developed a painful rash with blisters on the feet that progressed to the arms. She stopped furosemide and consulted our ER. There, her exam showed normal vitals signs and a fatigued-appearing patient. Her skin exam was remarkable for a painful, erythematous, scaling rash with vesicles and bullae in the intergluteal cleft, upper and lower extremities. Initial labs showed decreased albumin levels (1.9 g/dl), and normocytic anemia. Skin biopsy was consistent with zinc deficiency causing acrodermatitis enteropathica vs. NME. An abdominal CT revealed a 2.6 cm mass in the pancreatic head, compatible with pancreatic neoplasm, as well as changes of pancreatitis. Lab results showed deficiency in fat-soluble vitamins, zinc and copper. Infectious and rheumatologic evaluations were negative. Two fasting glucagon levels were normal (185 ng/L and 141 ng/L). A biopsy of the pancreatic mass was unable to be performed because she refused. At this point PS was included as a differential diagnosis and the rash has not improved despite repletion of vitamins and minerals. As a result, empiric immediate-release octreotide trial was started. The starting dose was 50mcg IV twice a day and a rapid titration (1 week) to 200mcg TID over the course of 1 week. Improvement of the skin lesion were observed 24 hours after starting octreotide. DISCUSSION: PS has been associated with malignancies, liver disease, infections, malabsorption, pulmonary or renal glucagonoma and pancreatitis. The pathogenesis of NME is not clear, but is believed to be multifactorial, involving excess of glucagon, deficiency of amino acid, zinc and/or free fatty acids. One hypothesis of glucagon as a cause of NME is that glucagon induces glycogenolysis and gluconeogenesis that may lead to epidermal amino acid depletion, necrolysis, and activation of inflammatory mediators. However, octreotide has been reported to improve NME in patients without glucagonoma, demonstrating that response is independent of glucagon levels. The first step for treatment is to correct the underlying pathology. Octreotide should be considered as second line of treatment. We recommend starting with a low dose of immediate-release octreotide, and increase for a maximum dose of 200 mcg TID. This dose can be maintained until resolution of symptoms and then switched to long-acting release octreotide.

Sestrin2 Negatively Regulates Casein Synthesis through the SH3BP4-mTORC1 Pathway in Response to AA Depletion or Supplementation in Cow Mammary Epithelial Cells.

Sestrin2 (SESN2) negatively regulates the mammalian target of rapamycin complex 1 (mTORC1) pathway and casein synthesis in response to amino acid (AA) depletion in cow mammary epithelial cells (CMECs); however, the underlying mechanism is unclear. In the current study, the regulation of SESN2 on AA-mediated β-casein (CSN2) synthesis in CMECs and its mechanism were investigated. Overexpression and silencing of SESN2 demonstrated that SESN2 negatively regulated AA-mediated expression of CSN2 and mTORC1 pathway. Co-immunoprecipitation analysis showed that SESN2 interacted with SH3 domain-binding protein 4 (SH3BP4). Overexpression and silencing of SH3BP4 demonstrated that SH3BP4 negatively regulated AA-mediated expression of CSN2 and mTORC1 pathway and that SESN2 negatively regulated expression of CSN2 and mTORC1 pathway through the SH3BP4 in the presence and absence of AA. The absence or presence of AA demonstrated that AA negatively regulated expression and nuclear localization of activating transcription factor 4 (ATF4). Overexpression and silencing of ATF4 demonstrated that AA negatively regulated SESN2 expression through ATF4. Together, these results indicate that SESN2 negatively regulates the mTORC1 pathway and subsequent CSN2 synthesis through the SH3BP4 in response to AA absence or presence in CMECs.

Amino Acid Degrading Enzymes and their Application in Cancer Therapy.

Amino acids are essential components in various biochemical pathways. The deprivation of certain amino acids is an antimetabolite strategy for the treatment of amino acid-dependent cancers which exploits the compromised metabolism of malignant cells. Several studies have focused on the development and preclinical and clinical evaluation of amino acid degrading enzymes, namely L-asparaginase, L-methionine γ-lyase, L-arginine deiminase, L-lysine α-oxidase. Further research into cancer cell metabolism may therefore define possible targets for controlling tumor growth. The purpose of this review was to summarize recent progress in the relationship between amino acids metabolism and cancer therapy, with a particular focus on Lasparagine, L-methionine, L-arginine and L-lysine degrading enzymes and their formulations, which have been successfully used in the treatment of several types of cancer. We carried out a structured search among literature regarding to amino acid degrading enzymes. The main aspects of search were in vitro and in vivo studies, clinical trials concerning application of these enzymes in oncology. Most published research are on the subject of L-asparaginase properties and it's use for cancer treatment. L-arginine deiminase has shown promising results in a phase II trial in advanced melanoma and hepatocellular carcinoma. Other enzymes, in particular Lmethionine γ-lyase and L-lysine α-oxidase, were effective in vitro and in vivo. The findings of this review revealed that therapy based on amino acid depletion may have the potential application for cancer treatment but further clinical investigations are required to provide the efficacy and safety of these agents.

Metabolomic foundation for differential responses of lipid metabolism to nitrogen and phosphorus deprivation in an arachidonic acid-producing green microalga

The green oleaginous microalga Lobosphaera incisa accumulates storage lipids triacylglycerols (TAG) enriched in the long-chain polyunsaturated fatty acid arachidonic acid under nitrogen (N) deprivation. In contrast, under phosphorous (P) deprivation, the production of the monounsaturated oleic acid prevails. We compared physiological responses, ultrastructural, and metabolic consequences of L. incisa acclimation to N and P deficiency to provide novel insights into the key determinants of ARA accumulation. Differential responses to nutrient deprivation on growth performance, carbon-to-nitrogen stoichiometry, membrane lipid composition and TAG accumulation were demonstrated. Ultrastructural analyses suggested a dynamic role for vacuoles in sustaining cell homeostasis under conditions of different nutrient availability and their involvement in autophagy in L. incisa. Paralleling ARA-rich TAG accumulation in lipid droplets, N deprivation triggered intensive chloroplast dismantling and promoted catabolic processes. Metabolome analysis revealed depletion of amino acids and pyrimidines, and repression of numerous biosynthetic hubs to favour TAG biosynthesis under N deprivation. Under P deprivation, despite the relatively low growth penalties, the presence of the endogenous P reserves and the characteristic lipid remodelling, metabolic signatures of energy deficiency were revealed. Metabolome adjustments to P deprivation included depletion in ATP and phosphorylated nucleotides, increased levels of TCA-cycle intermediates and osmoprotectants. We conclude that characteristic cellular and metabolome adjustments tailor the adaptive responses of L. incisa to N and P deprivation modulating its LC-PUFA production.