Abstract
BackgroundHIV-1 capsid influences viral uncoating and nuclear import. Some capsid is detected in the nucleus but it is unclear if it has any function. We reported that the antibiotic Coumermycin-A1 (C-A1) inhibits HIV-1 integration and that a capsid mutation confers resistance to C-A1, suggesting that capsid might affect post-nuclear entry steps.ResultsHere we report that C-A1 inhibits HIV-1 integration in a capsid-dependent way. Using molecular docking, we identify an extended binding pocket delimited by two adjacent capsid monomers where C-A1 is predicted to bind. Isothermal titration calorimetry confirmed that C-A1 binds to hexameric capsid. Cyclosporine washout assays in Jurkat CD4+ T cells expressing engineered human TRIMCyp showed that C-A1 causes faster and greater escape from TRIMCyp restriction. Sub-cellular fractionation showed that small amounts of capsid accumulated in the nuclei of infected cells and C-A1 reduced the nuclear capsid. A105S and N74D capsid mutant viruses did not accumulate capsid in the nucleus, irrespective of C-A1 treatment. Depletion of Nup153, a nucleoporin located at the nuclear side of the nuclear pore that binds to HIV-1 capsid, made the virus less susceptible to TRIMCyp restriction, suggesting that Nup153 may help maintain some integrity of the viral core in the nucleus. Furthermore C-A1 increased binding of CPSF6, a nuclear protein, to capsid.ConclusionsOur results indicate that capsid is involved in post-nuclear entry steps preceding integration.Electronic supplementary materialThe online version of this article (doi:10.1186/s12977-016-0262-0) contains supplementary material, which is available to authorized users.
Highlights
HIV-1 capsid influences viral uncoating and nuclear import
C‐A1 inhibits HIV‐1 integration We previously reported that C-A1 inhibited HIV-1 integration [38]
We previously suggested that C-A1 targeted capsid because serial passaging of HIV-1 in the presence of the drug resulted in the emergence of a drug-resistant virus with the A105S capsid mutation
Summary
HIV-1 capsid influences viral uncoating and nuclear import. We reported that the antibiotic Coumermycin-A1 (C-A1) inhibits HIV-1 integration and that a capsid mutation confers resistance to C-A1, suggesting that capsid might affect post-nuclear entry steps. Following HIV-1 entry into cells, capsid proteins are shed from the conical core, a step called uncoating, and the viral RNA genome is reverse transcribed into a double stranded DNA molecule. It is not always clear how capsid impacts on such steps. We detected low amounts of HIV-1 capsid inside nuclei of infected CD4 T cells [24], an observation later confirmed and extended by several groups [25,26,27], suggesting a more direct
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