A role of hypoxia-inducible factor 1 alpha in Murine Gammaherpesvirus 68 (MHV68) lytic replication and reactivation from latency.

Darlah M López-Rodríguez,Varvara Kirillov,Laurie T Krug,Samita Andreansky,Enrique A Mesri,Yan Yuan

doi:10.1371/journal.ppat.1008192

Abstract

The hypoxia-inducible factor 1 alpha (HIF1α) protein and the hypoxic microenvironment are critical for infection and pathogenesis by the oncogenic gammaherpesviruses (γHV), Kaposi sarcoma herpes virus (KSHV) and Epstein-Barr virus (EBV). However, understanding the role of HIF1α during the virus life cycle and its biological relevance in the context of host has been challenging due to the lack of animal models for human γHV. To study the role of HIF1α, we employed the murine gammaherpesvirus 68 (MHV68), a rodent pathogen that readily infects laboratory mice. We show that MHV68 infection induces HIF1α protein and HIF1α-responsive gene expression in permissive cells. siRNA silencing or drug-inhibition of HIF1α reduce virus production due to a global downregulation of viral gene expression. Most notable was the marked decrease in many viral genes bearing hypoxia-responsive elements (HREs) such as the viral G-Protein Coupled Receptor (vGPCR), which is known to activate HIF1α transcriptional activity during KSHV infection. We found that the promoter of MHV68 ORF74 is responsive to HIF1α and MHV-68 RTA. Moreover, Intranasal infection of HIF1αLoxP/LoxP mice with MHV68 expressing Cre- recombinase impaired virus expansion during early acute infection and affected lytic reactivation in the splenocytes explanted from mice. Low oxygen concentrations accelerated lytic reactivation and enhanced virus production in MHV68 infected splenocytes. Thus, we conclude that HIF1α plays a critical role in promoting virus replication and reactivation from latency by impacting viral gene expression. Our results highlight the importance of the mutual interactions of the oxygen-sensing machinery and gammaherpesviruses in viral replication and pathogenesis.

Highlights

Many pathogenic viruses need to adapt to different physiological oxygen levels for efficient infection of the host by controlling the host’s oxygen-sensing transcriptional machinery centered around the regulation of the hypoxia-inducible factors, the main transcriptional regulators of the hypoxia-stimulated genes
We study the role of HIF1α using the mouse gammaherpesvirus 68 (MHV68) that readily infects laboratory mice
We demonstrate that Murine Gammaherpesvirus 68 (MHV68) infection upregulates HIF1α during replication and inactivation of HIF1α transcriptional activity significantly decreased viral gene expression, which results in impaired virus production in vitro

Summary

Introduction

Many pathogenic viruses need to adapt to different physiological oxygen levels for efficient infection of the host by controlling the host’s oxygen-sensing transcriptional machinery centered around the regulation of the hypoxia-inducible factors, the main transcriptional regulators of the hypoxia-stimulated genes. Hypoxia Inducible Factor 1 alpha (HIF1α) is a eukaryotic cellular transcription factor whose main role is to support the adaptation of cells and tissues to lower oxygen concentrations. In the presence of oxygen, HIF1α is rapidly targeted for degradation by the ubiquitin complex via proline hydroxylation [2]. HIF1α binds the constitutively expressed HIF1β forming a heterodimeric helix-loop-helix transcriptional complex. The HIF1 heterodimer recognizes the DNA-binding motif known as the hypoxia-response element (HRE) within the promoter of target genes. This leads to the expression of proteins such as vascular endothelial growth factors, glucose transporters, and erythropoietin required to adapt to low oxygen levels [3]

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