IP6‐stabilised HIV capsids evade cGAS/STING‐mediated host immune sensing

Abstract

HIV‐1 uses inositol hexakisphosphate (IP6) to build a metastable capsid capable of delivering its genome into the host nucleus. Here, we show that viruses that are unable to package IP6 lack capsid protection and are detected by innate immunity, resulting in the activation of an antiviral state that inhibits infection. Disrupting IP6 enrichment results in defective capsids that trigger cytokine and chemokine responses during infection of both primary macrophages and T‐cell lines. Restoring IP6 enrichment with a single mutation rescues the ability of HIV‐1 to infect cells without being detected. Using a combination of capsid mutants and CRISPR‐derived knockout cell lines for RNA and DNA sensors, we show that immune sensing is dependent upon the cGAS–STING axis and independent of capsid detection. Sensing requires the synthesis of viral DNA and is prevented by reverse transcriptase inhibitors or reverse transcriptase active‐site mutation. These results demonstrate that IP6 is required to build capsids that can successfully transit the cell and avoid host innate immune sensing.

Cell-free assays reveal the HIV-1 capsid protects reverse transcripts from cGAS

“…This protection appears to be mediated by intact, or largely intact capsids because cGAS recognition increases dramatically when capsids are disrupted by heat, reduced IP6 concentrations, or destabilizing mutations in the viral capsid. Our observation that capsid integrity and stability can strongly modulate cGAS-mediated detection of HIV-1 is consistent with a growing body of literature indicating that the capsid sequence has a substantial impact on sensitivity to innate immune sensors 6,11,12,19,21 , and that IP6 perturbations or improper capsid formation can promote cGAS activation 5,20 . We suggest that our in vitro system can be useful in characterizing these effects, and also in determining how host factors promote capsid uncoating and cDNA exposure.…”

“…This upregulates hundreds of IFN-stimulated genes (ISGs), many of which can potently restrict HIV-1 infection [15][16][17][18] . Capsid structural integrity apparently influences the degree to which cGAS recognizes viral DNA, as specific CA mutations and CA-binding proteins are linked with increased or decreased IFN responses during infection 5,6,11,12,[19][20][21][22][23][24] . However, the parameters that regulate exposure of viral DNA and its detection by cGAS remain unclear.…”

HIV Infection: Shaping the Complex, Dynamic, and Interconnected Network of the Cytoskeleton

“…In a good way for its life cycle, the HIV-1 core mimics MT regulators in a very similar manner [235]. Notably, it is plausible that the alteration of the HIV-1 core interaction with these cytoskeleton-associated motors could provoke abnormal virus trafficking [236] and facilitate the recognition of the viral material by antiviral cellular sensors (i.e., TRIM5α or TLRs (toll-like receptors)) [143,149,150,152,[237][238][239][240][241][242], thus activating immune cellular responses to inhibit viral infection/replication [36,[243][244][245][246][247][248], as reported for unstable HIV-1 cores [143,144,236,249,250]. These facts reinforce the relevance of MT stability [71,163,164,166,214] and nuclear core uncoating for viral infection (comprehensively reviewed in [37]).…”

HIV-1 capsid stability and reverse transcription are finely balanced to minimize sensing of reverse transcription products via the cGAS-STING pathway

“…In the more commonly used THP-1 monocytic cell line model, WT HIV-1 has been reported to induce a range of innate immune responses, likely due to differences in cell culture and stimulation conditions, virus preparation, and the effective multiplicity of infection (MOI) ( 18 , 33 , 35 – 38 ). In THP-1 cells, CA mutations that prevent the recruitment of cellular cofactors CPSF6 and cyclophilin A ( 20 ) or alter CA-sp1 proteolytic cleavage ( 35 ) can enhance innate immune sensing, whereas IP6-mediated stabilization of the CA lattice ( 39 ) or CA mutations that confer resistance to the destabilizing effects of the CA-targeting compound PF74 can result in evasion of sensing ( 33 ). Unequivocally, cGAS-STING-mediated recognition of incoming viruses seems to be the main pathway that triggers innate immune activation in HIV-1-infected THP-1 cells and macrophages ( 18 , 33 , 35 – 39 ).…”