Upregulation of ATP Citrate Lyase Phosphorylation and Neutral Lipid Synthesis through Viral Growth Factor Signaling during Vaccinia Virus Infection

Like all other viruses, poxviruses rely on host cells to provide metabolites and energy. Vaccinia virus (VACV), the prototype poxvirus, induces profound metabolic alterations in host cells. We previously showed that VACV infection increases the tricarboxylic acid (TCA) cycle intermediates, including citrate, that can be transported to the cytosol to be converted to acetyl-CoA for de novo fatty acid biosynthesis. ATP citrate lyase (ACLY) is a pivotal enzyme converting citrate to acetyl-CoA. Here, we report that VACV infection stimulates the S455 phosphorylation of ACLY, a post-translational modification that stimulates ACLY activity. We demonstrate that the chemical and genetic inhibition of ACLY severely suppresses VACV replication. Remarkably, we found that virus growth factor (VGF)-induced signaling is essential for the VACV-mediated upregulation of ACLY phosphorylation. Furthermore, the upregulation of ACLY phosphorylation during VACV infection is dependent on the activation of the cellular Akt kinase that phosphorylates ACLY. Finally, we report that VGF-induced ACLY phosphorylation via the EGFR-Akt pathway is important for VACV stimulations of neutral lipid droplet synthesis. These findings identified a previously unknown way of rewiring cell metabolism by a virus and a novel function for VGF in the governance of virus-host interactions through the induction of a key enzyme at the crossroads of the TCA cycle and fatty acid de novo biosynthesis. Our study also provides a mechanism for the role played by VGF and its downstream signaling cascades in the modulation of lipid metabolism in VACV-infected cells. Importance ATP citrate lyase is a key metabolic enzyme that sits at the crossroads of glucose, glutamine, and lipid metabolism. However, how virus infection affects this protein is unclear. Using chemical, genetic, and metabolic approaches we show that VACV, the prototype poxvirus, increases the phosphorylation of ACLY in primary human fibroblasts in a VGF-dependent manner. We further show that the VGF-EGFR-Akt signaling pathway is vital for VACV-induced lipid droplet synthesis. Our findings identified ACLY as a potential target for novel antiviral development against pathogenic poxviruses. Our study also expands the role of growth factor signaling in boosting VACV replication by targeting multiple metabolic pathways.