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

Abstract

Human cytomegalovirus (HCMV) replication depends on the activities of several host regulators of metabolism. Hypoxia-inducible factor 1 (HIF1) was previously proposed to support virus replication through its metabolic regulatory function. HIF1 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 HIF1 in HCMV replication by generating primary human cells with HIF1 knocked out using CRISPR/Cas9. When HIF1 was absent, we found that HCMV replication was enhanced, showing that HIF1 suppresses viral replication. We used untargeted metabolomics to determine if HIF1 regulates metabolite concentrations in HCMV infected cells. We discovered that in HCMV-infected cells, HIF1 suppresses intracellular and extracellular concentrations of kynurenine. HIF1 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 HCMV replication. Moreover, we found that feeding kynurenine to cells promotes HCMV replication. Overall, our findings indicate that HIF1 reduces HCMV replication by regulating metabolism and metabolite signaling. ImportanceViruses, like human cytomegalovirus (HCMV), reprogram cellular metabolism using host metabolic regulators to support virus replication. Alternatively, in response to infection, the host can use metabolism to limit virus replication. Here, our findings show that the host uses hypoxia-inducible factor 1 (HIF1) as a metabolic regulator to reduce HCMV replication. Further, we found that HIF1 suppresses kynurenine synthesis, a metabolite that can promote HCMV replication by signaling through the aryl hydrocarbon receptor (AhR). In infected cells, the rate-limiting enzyme in kynurenine synthesis, indoleamine 2,3-dioxygenase 1 (IDO1), is suppressed by a HIF1-dependent mechanism. Our findings describe a functional connection between HIF1, IDO1, and AhR that allows HIF1 to limit HCMV replication through metabolic regulation, advancing our understanding of virus-host interactions.