Mechanism of interferon stimulated gene induction in HIV-1 infected macrophages

Abstract

Viruses manipulate the complex interferon and interferon stimulated gene (ISG) system in different ways. We have previously shown that HIV inhibits type I and III interferons in its key target cells but directly stimulates a subset of >20 ISGs in macrophages and dendritic cells many of which are antiviral. Here we examined the mechanism of induction of ISGs and showed this occurred in two phases. The first phase was transient (0-24hpi) induced mainly by extracellular vesicles, and one of its component proteins HSP90α, contained within the HIV inoculum. The second dominant and persistent phase (>48hpi) was induced via newly transcribed HIV RNA and sensed via RIGI, as shown by the reduction in ISG expression after the knock down of the RIGI adaptor, MAVS, by siRNA and the inhibition of both the initiation and elongation of HIV transcription, by shRNA transcriptional silencing. We further defined the induction pathway, showing sequential HIV RNA stimulation via Tat, RIGI, MAVS, IRF1 and IRF7 also identified by siRNA knockdown. IRF1 also plays a key role in the first phase. We also showed that the ISGs, IFITs 1-3 inhibited HIV production, measured as extracellular infectious virus. All induced antiviral ISGs probably lead to restriction of HIV replication in macrophages, contributing to a persistent, non-cytopathic infection while the inhibition of interferon facilitates spread to adjacent cells. Both may influence the size of macrophage HIV reservoirs in vivo. Elucidating the mechanisms of ISG induction may help devise immunotherapeutic strategies to limit the size of these reservoirs. IMPORTANCE HIV, like other viruses, manipulates the antiviral interferon and interferon stimulated gene (ISG) system to facilitate its initial infection and establishment of viral reservoirs. HIV specifically inhibits all type l and lll interferons in its target cells, including, macrophages, dendritic cells and T cells. It also induces a subset of over 20 ISGs of differing composition in each cell target. This occurs in two temporal phases in macrophages. Extracellular vesicles contained within the inoculum induced the first and transient phase of ISGs. Newly transcribed HIV RNA induced the second and dominant ISG phase and here the full induction pathway is defined. Therefore, HIV nucleic acids, which are potent inducers of interferon and ISGs, are initially concealed and antiviral ISGs are not fully induced until replication is well established. Theses antiviral ISGs may contribute to the persistent infection in macrophages and to the establishment of viral reservoirs in vivo.