Specificity of Interaction of INI1/hSNF5 with Retroviral Integrases and Its Functional Significance

Abstract

Integrase interactor 1 (INI1)/hSNF5 is a host factor that directly interacts with human immunodeficiency virus type 1 (HIV-1) integrase and is incorporated into HIV-1 virions. Here, we show that while INI1/hSNF5 is completely absent from purified microvesicular fractions, it is specifically incorporated into HIV-1 virions with an integrase-to-INI1/hSNF5 stoichiometry of approximately 2:1 (molar ratio). In addition, we show that INI1/hSNF5 is not incorporated into related primate lentiviral and murine retroviral particles despite the abundance of the protein in producer cells. We have found that the specificity in incorporation of INI1/hSNF5 into HIV-1 virions is directly correlated with its ability to exclusively interact with HIV-1 integrase but not with other retroviral integrases. This specificity is also reflected in our finding that the transdominant mutant S6, harboring the minimal integrase interaction domain of INI1/hSNF5, blocks HIV-1 particle production but not that of the other retroviruses in 293T cells. Taken together, these results suggest that INI1/hNSF5 is a host factor restricted for HIV-1 and that S6 acts as a highly specific and potent inhibitor of HIV-1 replication.Despite the effectiveness of highly active antiretroviral therapy in controlling human immunodeficiency virus type 1 (HIV-1) replication, the emergence of drug-resistant viruses in infected patients and the severe side effects caused by the currently used drug regimen necessitate continued search for new and improved therapeutic strategies for controlling AIDS (12, 42). HIV-1-encoded proteins such as integrase (IN) and cellular proteins that are implicated in the HIV-1 life cycle are attractive targets for the development of antivirals (22,38).IN catalyzes the integration of viral cDNA into the host genomic DNA, a process that is essential for the replication of all retroviruses and a step that results in the latent form of the virus (8). During the life cycle of a retrovirus, IN is produced as part of the Gag-Pol polyprotein, which is assembled into virions and subsequently cleaved into individual components during maturation (8). IN consists of three distinct structural domains (2), the N-terminal zinc-binding domain (HHCC), the central core domain with a highly conserved D,D(35)E motif required for the catalytic activity, and the less highly conserved C-terminal domain. Although crystal structure data exist for single and double domains of IN, no structural data exist yet for the entire IN protein (18). Various biochemical and genetic approaches have been used to demonstrate the multimerization of IN (1, 16, 25), but the exact nature of the IN multimer is still unknown (11,24).Studies of IN have demonstrated that it may affect steps in viral replication besides integration itself. For example, the presence of IN mutations affects viral morphology, particle formation, particle release, and infectivity (9, 17, 43). Deletions or mutations in the Zn finger region of IN (for example, H12A) have been shown to result in decreased parti...

Uneven Genetic Robustness of HIV-1 Integrase

“…Moreover, CA must also form interactions with a wide variety of host proteins (62)(63)(64). While IN forms critical interactions with LEDGF (65,66), as well as interactions with TRN-SR2(TNPO3) (35,67) and INI-1/hSNF5 (36,68), and also undergoes multimerization processes (21,(69)(70)(71), the larger number of specialized CA-CA interactions that mediate accurate virion assembly may make CA exceptionally fragile (Fig. 3A to E) (11).…”

“…Importantly, mutagenesis studies utilizing complementation have indicated the likelihood that IN forms a functional multimer (31)(32)(33). Other mutagenesis studies have also suggested a critical role for IN-binding cellular cofactors, for example, lens epithelium-derived growth factor (LEDGF) (34) and possibly transportin SR-2 (TRN-SR2, or TNPO3) (35) and integrase interactor (INI) 1/hSNF5 (36). Further work using scanning or site-directed mutagenesis has revealed individual IN amino acids that are likely to be involved in DNA binding or other critical IN functions (22,(37)(38)(39)(40)(41)(42)(43)(44).…”

Vector integration: Location, location, location

“…Lysine 4 and 9 of H3 are methylated at transcriptional start sites 15 and both H3 and H4 have varying acetylation patterns depending on whether they are in open reading frames or intergenic regions 16 Other chromosomal proteins also redistribute with transcription and at least one, the INI/SNF5 complex, has been shown to interact with HIV-1 integrase. 17 Any or all of these factors (and others) might affect integration site choice.…”

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

“…4B, right). 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).…”

“…Moreover, expression of the S6 fragment in Jurkat T cells protected the cells against HIV-1 replication (Yung et al, 2001). Although this inhibitory effect was not detected in full-length INI1/hSNF5, the WT INI1/hSNF5 has been shown to be incorporated into virions during virus production (Yung et al, 2001;Yung et al, 2004). Given the recent report that depletion of endogenous INI1/hSNF5 did not affect the transduction efficiency of an HIV-1-based vector, this suggests that INI1/hSNF5 is likely implicated in post-integration steps, rather than the integration step as we shall see below, particularly in HIV-1 production (Ariumi et al, 2006).…”