Recruitment of a SAP18-HDAC1 Complex into HIV-1 Virions and Its Requirement for Viral Replication

Abstract

HIV-1 integrase (IN) is a virally encoded protein required for integration of viral cDNA into host chromosomes. INI1/hSNF5 is a component of the SWI/SNF complex that interacts with HIV-1 IN, is selectively incorporated into HIV-1 (but not other retroviral) virions, and modulates multiple steps, including particle production and infectivity. To gain further insight into the role of INI1 in HIV-1 replication, we screened for INI1-interacting proteins using the yeast two-hybrid system. We found that SAP18 (Sin3a associated protein 18 kD), a component of the Sin3a-HDAC1 complex, directly binds to INI1 in yeast, in vitro and in vivo. Interestingly, we found that IN also binds to SAP18 in vitro and in vivo. SAP18 and components of a Sin3A-HDAC1 complex were specifically incorporated into HIV-1 (but not SIV and HTLV-1) virions in an HIV-1 IN–dependent manner. Using a fluorescence-based assay, we found that HIV-1 (but not SIV) virion preparations harbour significant deacetylase activity, indicating the specific recruitment of catalytically active HDAC into the virions. To determine the requirement of virion-associated HDAC1 to HIV-1 replication, an inactive, transdominant negative mutant of HDAC1 (HDAC1 ^H141A) was utilized. Incorporation of HDAC1 ^H141A decreased the virion-associated histone deacetylase activity. Furthermore, incorporation of HDAC1 ^H141A decreased the infectivity of HIV-1 (but not SIV) virions. The block in infectivity due to virion-associated HDAC1 ^H141A occurred specifically at the early reverse transcription stage, while entry of the virions was unaffected. RNA-interference mediated knock-down of HDAC1 in producer cells resulted in decreased virion-associated HDAC1 activity and a reduction in infectivity of these virions. These studies indicate that HIV-1 IN and INI1/hSNF5 bind SAP18 and selectively recruit components of Sin3a-HDAC1 complex into HIV-1 virions. Furthermore, HIV-1 virion-associated HDAC1 is required for efficient early post-entry events, indicating a novel role for HDAC1 during HIV-1 replication.

Author Summary

The interaction between the host and HIV-1 virus is a dynamic process. While some host cellular proteins mount antiviral response, HIV-1 utilizes other host proteins for its propagation. It is crucial to understand the role of host proteins in HIV-1 replication for successful development of strategies to combat AIDS. INI1/hSNF5 is a cellular protein that directly binds to an HIV-1 protein, integrase (IN). It is selectively encapsidated into HIV-1 virions and is required for the subsequent viral replication. However, how INI1 mediates its effects is not completely understood. Here we report a novel finding that INI1 as well as IN directly binds to SAP18 (Sin3a-associated protein of 18 kD), a component of the cellular Sin3a/HDAC (Histone Deacetylase) complex. The HDAC complexes are multiprotein epigenetic modifiers known to affect cellular transcription. In this report we find that along with INI1, SAP18 and the components of the Sin3a-HDAC1 complex are specifically recruited into HIV-1 virions. In addition, we find that virion-associated deacetylase activity is required for efficient reverse transcription in target cells. These studies indicate that HIV-1 IN protein may recruit HDAC1 complex into the virions for utilizing them in the subsequent stages of replication. Our findings provide new insight into the roles of cellular HDAC1 complex in HIV-1 replication and provide a novel paradigm to understand host-virus dynamic interaction.