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      Latent KSHV Infected Endothelial Cells Are Glutamine Addicted and Require Glutaminolysis for Survival

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          Abstract

          Kaposi’s Sarcoma-associated Herpesvirus (KSHV) is the etiologic agent of Kaposi’s Sarcoma (KS). KSHV establishes a predominantly latent infection in the main KS tumor cell type, the spindle cell, which is of endothelial cell origin. KSHV requires the induction of multiple metabolic pathways, including glycolysis and fatty acid synthesis, for the survival of latently infected endothelial cells. Here we demonstrate that latent KSHV infection leads to increased levels of intracellular glutamine and enhanced glutamine uptake. Depletion of glutamine from the culture media leads to a significant increase in apoptotic cell death in latently infected endothelial cells, but not in their mock-infected counterparts. In cancer cells, glutamine is often required for glutaminolysis to provide intermediates for the tri-carboxylic acid (TCA) cycle and support for the production of biosynthetic and bioenergetic precursors. In the absence of glutamine, the TCA cycle intermediates alpha-ketoglutarate (αKG) and pyruvate prevent the death of latently infected cells. Targeted drug inhibition of glutaminolysis also induces increased cell death in latently infected cells. KSHV infection of endothelial cells induces protein expression of the glutamine transporter, SLC1A5. Chemical inhibition of SLC1A5, or knockdown by siRNA, leads to similar cell death rates as glutamine deprivation and, similarly, can be rescued by αKG. KSHV also induces expression of the heterodimeric transcription factors c-Myc-Max and related heterodimer MondoA-Mlx. Knockdown of MondoA inhibits expression of both Mlx and SLC1A5 and induces a significant increase in cell death of only cells latently infected with KSHV, again, fully rescued by the supplementation of αKG. Therefore, during latent infection of endothelial cells, KSHV activates and requires the Myc/MondoA-network to upregulate the glutamine transporter, SLC1A5, leading to increased glutamine uptake for glutaminolysis. These findings expand our understanding of the required metabolic pathways that are activated during latent KSHV infection of endothelial cells, and demonstrate a novel role for the extended Myc-regulatory network, specifically MondoA, during latent KSHV infection.

          Author Summary

          KSHV is the etiologic agent of KS, the most common tumor of AIDS patients worldwide. Currently, there are no therapeutics available to directly treat latent KSHV infection. This study reveals that latent KSHV infection induces endothelial cells to become glutamine addicted, similarly to cancer cells. Extracellular glutamine is required to feed the TCA cycle through glutaminolysis, a process called anaplerosis. KSHV induces protein expression of the glutamine transporter SLC1A5 and SLC1A5 expression is required for the survival of latently infected cells. KSHV also induces the expression of the proto-oncogene Myc and its binding partner Max, as well as, the nutrient-sensing transcription factor, MondoA and its binding partner Mlx. MondoA regulates SLC1A5 and glutaminolysis during latent KSHV infection, and its expression is required for the survival of latently infected endothelial cells. These studies show that glutaminolysis and a single glutamine transporter, under the regulation of MondoA, are required for the survival of latently infected cells, providing novel druggable targets for latently infected endothelial cells. This work supports that a cancer-like metabolic signature is established by latent KSHV infection, opening the door to further therapeutic targeting specifically of KSHV latently infected cells.

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          Most cited references 30

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          Cancer cell metabolism: Warburg and beyond.

          Described decades ago, the Warburg effect of aerobic glycolysis is a key metabolic hallmark of cancer, yet its significance remains unclear. In this Essay, we re-examine the Warburg effect and establish a framework for understanding its contribution to the altered metabolism of cancer cells.
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            The transcription factor Myc controls metabolic reprogramming upon T lymphocyte activation.

            To fulfill the bioenergetic and biosynthetic demand of proliferation, T cells reprogram their metabolic pathways from fatty acid β-oxidation and pyruvate oxidation via the TCA cycle to the glycolytic, pentose-phosphate, and glutaminolytic pathways. Two of the top-ranked candidate transcription factors potentially responsible for the activation-induced T cell metabolic transcriptome, HIF1α and Myc, were induced upon T cell activation, but only the acute deletion of Myc markedly inhibited activation-induced glycolysis and glutaminolysis in T cells. Glutamine deprivation compromised activation-induced T cell growth and proliferation, and this was partially replaced by nucleotides and polyamines, implicating glutamine as an important source for biosynthetic precursors in active T cells. Metabolic tracer analysis revealed a Myc-dependent metabolic pathway linking glutaminolysis to the biosynthesis of polyamines. Therefore, a Myc-dependent global metabolic transcriptome drives metabolic reprogramming in activated, primary T lymphocytes. This may represent a general mechanism for metabolic reprogramming under patho-physiological conditions. Copyright © 2011 Elsevier Inc. All rights reserved.
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              Q's next: the diverse functions of glutamine in metabolism, cell biology and cancer.

              Several decades of research have sought to characterize tumor cell metabolism in the hope that tumor-specific activities can be exploited to treat cancer. Having originated from Warburg's seminal observation of aerobic glycolysis in tumor cells, most of this attention has focused on glucose metabolism. However, since the 1950s cancer biologists have also recognized the importance of glutamine (Q) as a tumor nutrient. Glutamine contributes to essentially every core metabolic task of proliferating tumor cells: it participates in bioenergetics, supports cell defenses against oxidative stress and complements glucose metabolism in the production of macromolecules. The interest in glutamine metabolism has been heightened further by the recent findings that c-myc controls glutamine uptake and degradation, and that glutamine itself exerts influence over a number of signaling pathways that contribute to tumor growth. These observations are stimulating a renewed effort to understand the regulation of glutamine metabolism in tumors and to develop strategies to target glutamine metabolism in cancer. In this study we review the protean roles of glutamine in cancer, both in the direct support of tumor growth and in mediating some of the complex effects on whole-body metabolism that are characteristic of tumor progression.
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                Author and article information

                Affiliations
                [1 ]Molecular and Cellular Biology Program, University of Washington, Seattle, Washington, United States of America
                [2 ]Department of Microbiology, University of Washington, Seattle, Washington, United States of America
                [3 ]Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America
                University of North Carolina at Chapel Hill, UNITED STATES
                Author notes

                The authors have declared that no competing interests exist.

                Conceived and designed the experiments: ELS PAC ML. Performed the experiments: ELS PAC ABT. Analyzed the data: ELS PAC ML. Wrote the paper: ELS ML.

                Contributors
                Role: Editor
                Journal
                PLoS Pathog
                PLoS Pathog
                plos
                plospath
                PLoS Pathogens
                Public Library of Science (San Francisco, CA USA )
                1553-7366
                1553-7374
                21 July 2015
                July 2015
                : 11
                : 7
                26197457 4510438 10.1371/journal.ppat.1005052 PPATHOGENS-D-15-00288

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

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                Figures: 8, Tables: 0, Pages: 18
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                Funding
                Research for this publication was supported by grants to ML from the National Cancer Institute (RO1CA189986) and the National Dental and Craniofacial Institute (PO1DE02195). ELS was supported by a National Science Foundation graduate research fellowship (DGE-0718124 and DGE-1256082). PAC was supported by NCI/NIH grant (RO1CA57138). ABT was supported by NIH PREP (R25GM086304-02). The content of this report is solely our responsibility and does not necessarily represent the official views of the National Institutes of Health. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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                Research Article
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                Infectious disease & Microbiology

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