Characterization of INI1-interaction defective IN mutants during HIV-1 replication
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The HIV-1 life cycle is regulated by numerous cellular host factors that can either aid or inhibit viral replication. Integrase interactor-1 (INI1/hSNF5), a core component of the SWI/SNF chromatin remodeling complex, was the first host protein identified as a direct binding partner of HIV-1 integrase (IN). Since its discovery, INI1 has been shown to play multiple roles in the context of HIV-1 replication. INI1, along with the associated Sin3a-HDAC1 complex, are incorporated into HIV-1 virions, but not other retroviruses, and this encapsidation is required for particles to be infectious. Furthermore, INI1 is required in producer cells for viral particle production. These "proviral" functions of INI1 are in contrast to reports suggesting that INI1 has an antiviral role during early events of the HIV-1 life cycle. The reasons for these dual effects are currently unknown.;To further delineate the role of INI1 during HIV-1 replication, we identified a panel of INI1-interaction-defective IN (IID-IN) mutants and tested their ability to replicate when incorporated into full-length molecular clones of HIV-1. All mutant viruses were defective for multiday replication, and moreover the degree of defect in replication correlated with the degree of defect to INI1-binding. Virions harboring highly defective IID-IN mutations were defective for in vivo reverse transcription and integration, as measured by qPCR. Partially defective mutants proceeded through all steps of early events, but were partially impaired for integration. While mutant virions exhibited variable defects in virion morphology, no defects in reverse transcriptase activity, capsid stability or uncoating in vitro were observed. Among the highly defective mutants, D202G displayed a selective defect in binding INI1 but not to binding other host factors. A previously identified IN mutant, W235E, that is only blocked for in vivo integration, also revealed a severe and selective defect in binding to INI1. Taken together, these studies indicate that IID-IN mutants fall into two categories: those that are blocked at reverse transcription and those that are blocked at integration. Our data collectively highlight the importance of the IN-INI1 interaction during early post-entry events of the HIV-1 life cycle.