| Summary: | After entry into a target cell, HIV-1 must traverse the cytoplasm and enter the nucleus in order to integrate into host chromatin. Until recently, the viral CA core was thought to play a passive role in infection, simply delivering its contents to the cytoplasm soon after entry. However, CA has recently been found to interact with and/or determine interaction with several nuclear entry cofactors. In this study, we investigate the consequences of CA interacting with the host mRNA-processing factor CPSF6. We provide evidence that the interaction between CA and cytoplasmic CPSF6 during early infection dictates the downstream nuclear entry pathway and integration site selection of HIV-1, despite not affecting viral titre in cell lines. We identify clinically relevant CTL escape mutations that lie within the CPSF6 binding pocket of CA and alter the relationship of HIV-1 with the CPSF6-dependent nuclear entry pathway. The phenotypes of these mutants suggest that conservation of this pathway is important in vivo but also that the pathway differs between cell types. In addition, we examine the antiviral mechanisms of C-terminal truncations of CPSF6 and the small-molecule CPSF6 peptidomimetics PF74 and BI-1. We design a series of compounds predicted to interact with the CPSF6-binding pocket of CA and screen them for antiviral activity as well as the ability to alter the nuclear entry pathway of HIV-1. Of particular interest are a compound that exhibits a very different inhibition profile from PF74/BI-1 and a compound that causes the virus to use a CPSF6-independent nuclear entry pathway without reducing viral titre. Together, the findings in this study confirm and characterise the role of CPSF6 as an HIV-1 cofactor and demonstrate that drugs targeting the CA-CPSF6 interaction could inhibit the virus through multiple different mechanisms.
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