Hypoxia-inducible factor 1α (HIF1α) Suppresses Virus Replication in Human Cytomegalovirus Infection by Limiting Kynurenine Synthesis

Human cytomegalovirus (HCMV) replication depends on the activities of several host regulators of metabolism. Hypoxia-inducible factor 1α (HIF1α) was previously proposed to support virus replication through its metabolic regulatory function. HIF1α protein levels rise in response to HCMV infection in non-hypoxic conditions, but its effect on HCMV replication was not investigated. We addressed the role of HIF1α in HCMV replication by generating primary human cells with HIF1α knocked out using CRISPR/Cas9. When HIF1α was absent, we found that HCMV replication was enhanced, showing that HIF1α suppresses viral replication. We used untargeted metabolomics to determine if HIF1α regulates metabolite concentrations in HCMV infected cells. We discovered that in HCMV-infected cells, HIF1α suppresses intracellular and extracellular concentrations of kynurenine. HIF1α also suppressed the expression of the indoleamine 2,3-dioxygenase 1 (IDO1) rate-limiting enzyme in kynurenine synthesis. In addition to its role in tryptophan metabolism, kynurenine acts as a signaling messenger by activating aryl hydrocarbon receptor (AhR). Inhibiting AhR reduces HCMV replication while activating AhR with an exogenous ligand increases virus replication. Moreover, we found that feeding kynurenine to cells promotes HCMV replication. We conclude that HIF1α suppresses HCMV replication, at least in part, by regulating KYN levels and AhR activity. Overall, our findings indicate that HIF1α reduces HCMV replication by regulating metabolism and metabolite signaling.