A maturation defective HIV-1 activates cGAS

BackgroundDetection of viruses by host pattern recognition receptors induces the expression of type I interferon (IFN) and IFN-stimulated genes (ISGs), which suppress viral replication. Retroviruses such as HIV-1 are subject to sensing by both RNA and DNA sensors, and whether there are any particular features of the viral genome or reverse transcripts that facilitate or enhance this sensing is currently unknown. ResultsWhilst investigating the determinants of innate detection of HIV-1 we noticed that infection of THP-1 cells or primary macrophages with a virus expressing Gag fused to a reporter gene (luciferase or GFP) induced a robust IFN and ISG response that was not observed with an equivalent virus with similar genome length and composition, but expressing wild-type Gag. Innate immune activation by Gag-fusion HIV-1 was dependent on reverse transcription and DNA sensor cGAS, suggesting activation of an IFN response by viral DNA. Further investigation of the Gag-fusion viral particles revealed maturation defects, as evidenced by incomplete Gag cleavage and a diminished capacity to saturate restriction factor TRIM5, likely due to aberrant particle formation. We propose that expression of the Gag fusion protein disturbs the correct cleavage and maturation of wild-type Gag, yielding viral particles that are unable to effectively shield viral DNA from detection by innate sensors including cGAS. ConclusionsThese data highlight the crucial role of capsid in innate evasion and support growing literature that disruption of Gag cleavage and capsid formation induces a viral DNA- and cGAS-dependent innate immune response. Together these data demonstrate a protective role for capsid and suggest that antiviral activity of capsid-targeting antivirals may benefit from enhanced innate and adaptive immunity in vivo.