Host cell glutamine metabolism as a potential antiviral target

A virus minimally contains a nucleic acid genome packaged by a protein coat. The genome and capsid together are known as the nucleocapsid, which has an envelope containing a lipid bilayer (mainly phospholipids) originating from host cell membranes. The viral envelope has transmembrane proteins that are usually glycoproteins. The proteins in the envelope bind to host cell receptors, promoting membrane fusion and viral entry into the cell. Virus-infected host cells exhibit marked increases in glutamine utilization and metabolism. Glutamine metabolism generates ATP and precursors for the synthesis of macromolecules to assemble progeny viruses. Some compounds derived from glutamine are used in the synthesis of purines and pyrimidines. These latter compounds are precursors for the synthesis of nucleotides. Inhibitors of glutamine transport and metabolism are potential candidate antiviral drugs. Glutamine is also an essential nutrient for the functions of leukocytes (lymphocyte, macrophage, and neutrophil), including those in virus-infected patients. The increased glutamine requirement for immune cell functions occurs concomitantly with the high glutamine utilization by host cells in virus-infected patients. The development of antiviral drugs that target glutamine metabolism must then be specifically directed at virus-infected host cells to avoid negative effects on immune functions. Therefore, the aim of this review was to describe the landscape of cellular glutamine metabolism to search for potential candidates to inhibit glutamine transport or glutamine metabolism.

Biphasic regulation of glutamine consumption by WNT during osteoblast differentiation

Osteoblasts are the principal bone forming cells. As such, osteoblasts have enhanced demand for amino acids to sustain high rates of matrix synthesis associated with bone formation. The precise systems utilized by osteoblasts to meet these synthetic demands are not well understood. WNT signaling is known to rapidly stimulate glutamine uptake during osteoblast differentiation. Using a cell biology approach, we identified two amino acid transporters, Slc7a7 and Slc1a5, as the primary transporters of glutamine in response to WNT. Slc1a5 mediates the majority of glutamine uptake, whereas Slc7a7 mediates the rapid increase in glutamine uptake in response to WNT. Mechanistically, WNT signals through the canonical/β-catenin dependent pathway to rapidly induce Slc7a7 expression. Conversely, Slc1a5 expression is regulated by the transcription factor ATF4 downstream of the mTORC1 pathway. Targeting either Slc1a5 or Slc7a7 using shRNA reduced WNT induced glutamine uptake and prevented osteoblast differentiation. Collectively these data highlight the critical nature of glutamine transport for WNT induced osteoblast differentiation.

Targeting Glutamine Addiction in Gliomas

The most common malignant brain tumors are those of astrocytic origin, gliomas, with the most aggressive glioblastoma (WHO grade IV) among them. Despite efforts, medicine has not made progress in terms of the prognosis and life expectancy of glioma patients. Behind the malignant phenotype of gliomas lies multiple genetic mutations leading to reprogramming of their metabolism, which gives those highly proliferating cells an advantage over healthy ones. The so-called glutamine addiction is a metabolic adaptation that supplements oxidative glycolysis in order to secure neoplastic cells with nutrients and energy in unfavorable conditions of hypoxia. The present review aims at presenting the research and clinical attempts targeting the different metabolic pathways involved in glutamine metabolism in gliomas. A brief description of the biochemistry of glutamine transport, synthesis, and glutaminolysis, etc. will forego a detailed comparison of the therapeutic strategies undertaken to inhibit glutamine utilization by gliomas.

364 Impact of porcine reproductive and respiratory syndrome virus challenge and deoxynivalenol on intestinal integrity and nutrient transport

Porcine reproductive and respiratory syndrome (PRRS) virus infections and mycotoxin contaminated feedstuffs are two common issues facing the pork industry as both act, independently, to antagonize pig intestinal function, growth performance, and health. However, the combined impact of PRRS and mycotoxin exposure on pig intestinal health and function has not been investigated. Therefore, the objective of this experiment was to examine the impact of the mycotoxin deoxynivalenol (DON) on the intestinal integrity and function of PRRS infected pigs, employing an ex vivo model. Jejunum samples were collected from PRRS naïve (control; n = 6) and 21 day post inoculated PRRS virus infected (n = 8) gilts (10 weeks of age). In duplicate, explants were mounted into modified Ussing Chambers and incubated with or without 25 mM DON for 45 minutes prior to assessment of transepithelial resistance (TER), mucosal to serosal macromolecule (FD4) flux, and active glucose and glutamine transport. Data were analyzed using the mixed model procedure of SAS and a split plot design to examine the fixed effects of PRRS, DON, and their interaction. There were no PRRS by DON interactions for any ex vivo parameters assessed. Irrespective of DON, PRRS jejunum segments had decreased TERs (57%, P < 0.001), increased FD4 flux (P = 0.005), and tended to have increased active glucose transport (P = 0.093) compared with uninfected controls. Irrespective of PRRS status, DON increased FD4 flux (113%, P = 0.013), and tended to increase active glucose transport (P = 0.088) compared with jejunal explants not treated with DON. However, TERs and active glutamine transport did not differ due to DON treatment. Taken together, these data highlight the impacts that viral health challenge and mycotoxin contamination have on aspects of intestinal integrity and function. However, it does not appear that PRRS challenged pigs are more sensitive to the effects of DON than their healthy counterparts.

SN1 Transporter Regulation by Sp1 in Ammonia-Treated Mouse Cortical Astrocytes: Role of Sp1 Phosphorylation Status

The involvement of astrocytic SN1 (SNAT3) transporter in ammonia-induced L-glutamine retention was recently documented in mouse cultured astrocytes. Here we investigated the involvement of specificity protein 1 (Sp1) transcription factor in SN1 regulation in ammonium chloride (&ldquo;ammonia&rdquo;)-treated astrocytes. Sp1 expression and its cellular localization were determined using real-time qPCR, Western blot and confocal microscopy, respectively. Sp1 binding to Snat3 promoter was analyzed by chromatin immunoprecipitation. Ammonia-induced Sp1 regulatory role in SN1-mediated [3H]glutamine transport was verified using siRNA and mithramycin A. The involvement of protein kinase C (PKC) isoforms in Sp1 level/phosphorylation status was verified using siRNA technology. Sp1 translocation to the nuclei and its enhanced binding to Snat3 promoter, along with Sp1 dependence of system N-mediated [3H]glutamine transport were observed in astrocytes upon ammonia exposure. Ammonia decreased the level of phosphorylated Sp1, and the effect was reinforced by long-term incubation with PKC modulator, phorbol 12-myristate 13-acetate, a treatment likely to dephosphorylate Sp1. Furthermore, &nbsp;silencing of PKC&delta; isoform abolished the increase of Sp1 level by ammonia. Collectively, the results demonstrate the regulatory role of Sp1 in regulation of SN1 expression and activity in ammonia-treated astrocytes and implicate altered Sp1 phosphorylation status in this capacity.

SLC1A5 Silencing Inhibits Esophageal Cancer Growth via Cell Cycle Arrest and Apoptosis

Background/Aims: Solute-linked carrier family A1 member 5 (SLC1A5), which has high affinity to neutral amino acids, is essential for glutamine transport and amino acid metabolism in various cancers. However, the role of SLC1A5 in esophageal cancer has not been reported. Methods: SLC1A5 expression in esophageal cancer tissues was detected by immunohistochemistry and western blotting. The effects of SLC1A5 knockdown on the growth, cell cycle, viability, and glutamine metabolism of esophageal cancer cells were investigated with flow cytometry and western blotting. Furthermore, the consequences of SLC1A5 knockdown on tumor growth and survival were also evaluated in vivo using mice carrying esophageal cancer xenografts. Results: SLC1A5 was expressed in 86.5% (32/37) of the cancer tissues from esophageal cancer patients. Moreover, SLC1A5 expression in the cancerous tissues was significantly higher than that in the paired adjacent normal tissues. SLC1A5 knockdown with siRNA (PZ siRNA) in TE-1 cells in vitro significantly decreased cell growth and reduced both leucine and glutamine transport, leading to inhibition of mTORC1 signaling. Additionally, siRNA-mediated SLC1A5 knockdown resulted in cell cycle arrest and apoptosis of TE-1 cells. The survival rate of athymic (nu/nu) male nude mice carrying tumors formed from TE-1 cells transfected with SLC1A5 siRNA (PZ siRNA) was also significantly improved compared with mice carrying tumors formed from TE-1 cells transfected with control siRNA. Tumor size/weight was also significantly lower for the former mice group of mice. Conclusion: Our data indicate that SLC1A5 plays an important role in esophageal cancer both in vivo and in vitro. The inhibition of esophageal cancer growth by targeting SLC1A5 could, therefore, be used as a preoperative therapy for esophageal cancer.