Viral hijacking of cellular metabolism.

This review discusses the current state of the viral metabolism field and gaps in knowledge that will be important for future studies to investigate. We discuss metabolic rewiring caused by viruses, the influence of oncogenic viruses on host cell metabolism, and the use of viruses as guides to identify critical metabolic nodes for cancer anabolism. We also discuss the need for more mechanistic studies identifying viral proteins responsible for metabolic hijacking and for in vivo studies of viral-induced metabolic rewiring. Improved technologies for detailed metabolic measurements and genetic manipulation will lead to important discoveries over the next decade

Viral Reprogramming of Metabolism as an Approach to Identify Metabolic Vulnerabilities in Cancer

Cancer cells and viruses reprogram cell metabolism towards increased nutrient uptakeand anabolism. Unlike cancer cells, viruses undergo intense selection for efficiency, onlyupregulating metabolic nodes critical for their rapid replication. Viruses are therefore powerfultools to identify essential metabolic pathways in cancer cells. A previous study from our labreported that adenovirus infection increases host cell anabolic glucose metabolism. Specificglycolytic genes are activated by binding of viral protein E4ORF1 with cellular transcriptionfactor MYC, which is upregulated in many cancers. Here, we show that adenovirus infectionalso upregulates glutamine metabolism through E4ORF1-induced MYC activation, leading toincreased levels of glutaminase and glutamine transporters. Inhibition of glutaminase reducesoptimal replication of adenovirus and other diverse viruses, including HSV-1 and influenza.Glutaminase inhibitors are also currently in clinical trials to treat certain types of cancers. Thisstudy serves as a proof-of-principle that metabolic enzymes and pathways important for adenovirus infection converge on critical metabolic enzymes in cancer.The specific compilation of metabolic genes altered by adenovirus infection, that mayalso be critical for cancer cell proliferation, is currently undefined. We find that adenovirusinfection leads to upregulation of an enzyme involved in fructose metabolism, ketohexokinase,which supports optimal virus replication and lung tumor growth. We further show that lungcancer cells can convert glucose via the polyol pathway into fructose, which can then bemetabolized by ketohexokinase. Our model for how ketohexokinase promotes anabolism is byallowing cells to bypass negative feedback on a heavily regulated enzyme in glycolysis,phosphofructokinase, and allowing increased glucose utilization into nucleotides. Since KHKdeficiency is a clinically benign, targeting KHK in lung cancer have limited systemic toxicities in patients.Finally, numerous viruses in addition to adenovirus have been found to reprogram host cell metabolism, but whether the flavivirus Zika virus alters metabolism and whether viruses have unique effects on different host cells remains unclear. We find that Zika virus differentially alters glucose metabolism in both human cells and mosquito cells by increasing glucose use in the TCA cycle in human cells, while increasing glucose utilization into the pentose phosphate pathway in mosquito cells. Zika virus infection of human cells leads to selective depletion of nucleotide triphosphates, leading to AMP-activated protein kinase activation and cell death. Our findings suggest that the differential metabolic reprogramming during Zika virus infection of human versus mosquito cells determines whether or not cell death occurs and demonstrates that viruses can have contrasting effects depending on the host cell. Taken together, this dissertation (i) describes virally induced metabolic changes in both adenovirus and Zika virus and (ii) utilizes the evolutionary efficiency of adenovirus infection as an approach to identify important metabolic enzymes in anabolism and cancer

In vivo genetic dissection of tumor growth and the Warburg effect.

A well-characterized metabolic landmark for aggressive cancers is the reprogramming from oxidative phosphorylation to aerobic glycolysis, referred to as the Warburg effect. Models mimicking this process are often incomplete due to genetic complexities of tumors and cell lines containing unmapped collaborating mutations. In order to establish a system where individual components of oncogenic signals and metabolic pathways can be readily elucidated, we induced a glycolytic tumor in the Drosophila wing imaginal disc by activating the oncogene PDGF/VEGF-receptor (Pvr). This causes activation of multiple oncogenic pathways including Ras, PI3K/Akt, Raf/ERK, Src and JNK. Together this network of genes stabilizes Hifα (Sima) that in turn, transcriptionally up-regulates many genes encoding glycolytic enzymes. Collectively, this network of genes also causes inhibition of pyruvate dehydrogenase (PDH) activity resulting in diminished ox-phos levels. The high ROS produced during this process functions as a feedback signal to consolidate this metabolic reprogramming

Differential Metabolic Reprogramming by Zika Virus Promotes Cell Death in Human versus Mosquito Cells

Zika virus is a pathogen that poses serious consequences, including congenital microcephaly. Although many viruses reprogram host cell metabolism, whether Zika virus alters cellular metabolism and the functional consequences of Zika-induced metabolic changes remain unknown. Here, we show that Zika virus infection differentially reprograms glucose metabolism in human versus C6/36 mosquito cells by increasing glucose use in the tricarboxylic acid cycle in human cells versus increasing glucose use in the pentose phosphate pathway in mosquito cells. Infection of human cells selectively depletes nucleotide triphosphate levels, leading to elevated AMP/ATP ratios, AMP-activated protein kinase (AMPK) phosphorylation, and caspase-mediated cell death. AMPK is also phosphorylated in Zika virus-infected mouse brain. Inhibiting AMPK in human cells decreases Zika virus-mediated cell death, whereas activating AMPK in mosquito cells promotes Zika virus-mediated cell death. These findings suggest that the differential metabolic reprogramming during Zika virus infection of human versus mosquito cells determines whether cell death occurs

MYC-induced reprogramming of glutamine catabolism supports optimal virus replication.

Viruses rewire host cell glucose and glutamine metabolism to meet the bioenergetic and biosynthetic demands of viral propagation. However, the mechanism by which viruses reprogram glutamine metabolism and the metabolic fate of glutamine during adenovirus infection have remained elusive. Here, we show MYC activation is necessary for adenovirus-induced upregulation of host cell glutamine utilization and increased expression of glutamine transporters and glutamine catabolism enzymes. Adenovirus-induced MYC activation promotes increased glutamine uptake, increased use of glutamine in reductive carboxylation and increased use of glutamine in generating hexosamine pathway intermediates and specific amino acids. We identify glutaminase (GLS) as a critical enzyme for optimal adenovirus replication and demonstrate that GLS inhibition decreases replication of adenovirus, herpes simplex virus 1 and influenza A in cultured primary cells. Our findings show that adenovirus-induced reprogramming of glutamine metabolism through MYC activation promotes optimal progeny virion generation, and suggest that GLS inhibitors may be useful therapeutically to reduce replication of diverse viruses