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 (HDAC1H141A) was utilized. Incorporation of HDAC1H141A decreased the virion-associated histone deacetylase activity. Furthermore, incorporation of HDAC1H141A decreased the infectivity of HIV-1 (but not SIV) virions. The block in infectivity due to virion-associated HDAC1H141A 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.

HIV-1 Vpr Protein Induces Proteasomal Degradation of Chromatin-associated Class I HDACs to Overcome Latent Infection of Macrophages

“…The study also showed that the virion incorporation of HDAC1 plays a role in efficient early post-entry events (38). Since Vpr has already been shown to incorporate one of its target proteins, UNG2, into viral particles (39), it is worth examining whether Vpr plays a role in incorporation of HDACs into the virions or if there is a link between degradation and virion incorporation of HDACs.…”

INI1/hSNF5-interaction defective HIV-1 IN mutants exhibit impaired particle morphology, reverse transcription and integration in vivo

“…HIV-1 particles containing the catalytically inactive HDAC1 H141A mutant show reduced deacetylase activity and reduced infectivity. The block due to the presence of the HDAC1 H141A mutant appears to be at or prior to reverse transcription in the target cells [29]. These observations are corroborated by the findings that producer cells lacking INI1 show greatly reduced HIV-1 particle production and that the few particles produced are defective for reverse transcription [26].…”

“…INI1 binds to SAP18 (Sin3a associated protein of 18 KD), a component of the Sin3a-HDAC1 complex. In addition to INI1, components of the Sin3a/HDAC1 repressor complex, including SAP18 and HDAC1, are incorporated into HIV-1 virions [29]. HIV-1 particles containing the catalytically inactive HDAC1 H141A mutant show reduced deacetylase activity and reduced infectivity.…”

Molecular Crosstalk between HIV-1 Integration and Host Proteins – Implications for Therapeutics

“…As described above, INI1/hSNF5 has been shown to be specifically encapsidated into HIV-1 virions, probably through the IN region of Gag-Pol (Yung et al, 2001(Yung et al, , 2004. In addition, a recent study demonstrates that the IN-INI1/hSNF1 interaction selectively recruits SAP18 and HDAC1, components of the Sin3a-HDAC complex, into the HIV-1 virion, increasing the infectivity of the virions (Sorin et al, 2009). Although Huwe1 is an E3 ubiquitin ligase, our study suggests that enzymatic activity of Huwe1 is not involved in the ubiquitination and subsequent proteasomal-degradation of IN and Gag-Pol .…”