HIV-1 integrase (IN) is

Similar to all other viruses, human immunodeficiency virus type 1 (HIV-1) depends heavily on cellular factors for its successful replication. In this study we have investigated the interaction of HIV-1 integrase (IN) with several host nuclear import factors using co-immunoprecipitation assays. Our results indicate that IN interacts specifically with host importin 7 (Imp7) in vivo, but does not interact with importin 8 (Imp8) or importin ␣ (Rch1). To carry out a successful infection, human immunodeficiency virus type 1 (HIV-1) 4 takes advantage of various host cellular proteins and cellular pathways. The interaction between cellular proteins and viral components takes place during various steps of the HIV-1 life cycle, including viral DNA nuclear import. The most striking feature of HIV-1 is its ability to replicate in non-dividing cells. This feature depends on the ability of the virus to transport its cDNA, as part of a large preintegration complex (PIC), from the cytoplasm to the nucleus by an active and energy-dependent process (1-3). However, the mechanism by which the PIC translocates across the nuclear membrane into the nucleus of non-dividing cells is still not fully understood. It has been shown that three HIV-1 PIC-associated proteins including MAp17, IN, and Vpr possess karyophilic properties, and contribute to nuclear translocation of viral PICs. This action is accomplished through their interactions with karyophilic cellular proteins, thereby directing the PIC through the nuclear pore complex (4 -10). In addition, a cis-acting element named the central DNA flap, which is located in the 3Ј region of the pol gene sequence, was also shown to contribute to HIV-1 nuclear import in both dividing and non-dividing cells (11)(12)(13)(14). Nuclear import of proteins in mammalian cells can be mediated by several distinct pathways. The importin ␣/␤ heterodimer meditates nuclear import of proteins harboring a classical nuclear localization signal, which either contains a cluster of basic amino acids or two basic clusters separated by 10 -20 amino acids (bipartite nuclear localization signal) (for reviews see Refs. 15 and 16). Also, importin ␤ (Imp␤) was shown to bind to and import HIV-1 proteins, such as HIV-1 Tat, Rev, and HTLV Rex, independently of importin ␣ (Imp␣) (17-21). Similarly, transportin, an Imp␤-related receptor, imports its substrates (heterogeneous nuclear ribonucleoproteins) by directly binding to the glycine-rich M9 domain of the protein (22,23). Based on the similarity to Imp␤, several other nuclear import factors, including Imp7 and Imp8, have also been identified (24). Imp7 is one of several cellular importins that bind to and mediate nuclear import of ribosomal proteins in mammalian cells, and it was also found to translocate other proteins, such as glucocorticoid receptor and histone H1 into the nucleus (18,(25)(26)(27). In the case of histone H1, Jakel et al. (27) have demonstrated that two receptors, Imp␤ and Imp7,

cThe cytidine deaminase APOBEC3G (A3G) exerts a multifaceted antiviral effect against HIV-1 infection. First, A3G was shown to be able to terminate HIV infection by deaminating the cytosine residues to uracil in the minus strand of the viral DNA during reverse transcription. Also, a number of studies have indicated that A3G inhibits HIV-1 reverse transcription by a non-editingmediated mechanism. However, the mechanism by which A3G directly disrupts HIV-1 reverse transcription is not fully understood. In the present study, by using a cell-based coimmunoprecipitation (Co-IP) assay, we detected the direct interaction between A3G and HIV-1 reverse transcriptase (RT) in produced viruses and in the cotransfected cells. The data also suggested that their interaction did not require viral genomic RNA bridging or other viral proteins. Additionally, a deletion analysis showed that the RT-binding region in A3G was located between amino acids 65 and 132. Overexpression of the RT-binding polypeptide A3G 65-132 was able to disrupt the interaction between wild-type A3G and RT, which consequently attenuated the anti-HIV effect of A3G on reverse transcription. Overall, this paper provides evidence for the physical and functional interaction between A3G and HIV-1 RT and demonstrates that this interaction plays an important role in the action of A3G against HIV-1 reverse transcription. Several host proteins have been identified as intrinsic restriction factors because of their ability to inhibit HIV replication and/or dissemination (2, 31, 41, 52). Among them, the apolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like 3G (APOBEC3G; here referred to as A3G) is the one that restricts HIV-1 replication through more than one mechanism (17,32,37,38,40). In the absence of the HIV-1 viral infectivity factor (Vif), A3G is incorporated into progeny viruses through its interaction with the nucleocapsid (NC) domain of the Gag protein and/or viral RNA (1,15,56,63). Once these progeny viruses initiate new infection, the incorporated A3G will deaminate the cytidine to uridine in the viral minus-strand DNA during reverse transcription, resulting in hypermutation in the provirus. As a result, the HIV-1 proviral DNA will be no longer functional or degrade rapidly (21,32,38,64). Additionally, the mutated proviral DNA may produce defective or truncated viral polypeptides that represent a significant source of major histocompatibility complex class I (MHC-I)-restricted epitopes to activate HIV-1-specific CD8 ϩ cytotoxic T lymphocytes (CTLs) (12).Reverse transcription catalyzed by HIV-1 reverse transcriptase (RT) is a critical step for HIV-1 to establish its replication cycle. In infected cells, RT employs tRNA 3Lys and the polypurine tract as primers and converts the viral genomic RNA into doublestranded viral DNA (23). This process is catalyzed by both the DNA polymerase and RNase H activities of RT (23,49). Interestingly, in addition to the deaminase activity, A3G has also been shown to directly inhibit HIV-1 reverse transcription by a non...

HIV-1 employs the cellular nuclear import machinery to actively transport its preintegration complex (PIC) into the nucleus for integration of the viral DNA. Several viral karyophilic proteins and cellular import factors have been suggested to contribute to HIV-1 PIC nuclear import and replication. However, how HIV interacts with different cellular machineries to ensure efficient nuclear import of its preintegration complex in dividing and nondividing cells is still not fully understood. In this study, we have investigated different importin ␣ (Imp␣) family members for their impacts on HIV-1 replication, and we demonstrate that short hairpin RNA (shRNA)-mediated Imp␣3 knockdown (KD) significantly impaired HIV infection in HeLa cells, CD4؉ C8166 T cells, and primary macrophages. Moreover, quantitative real-time PCR analysis revealed that Imp␣3-KD resulted in significantly reduced levels of viral 2-long-terminal repeat (2-LTR) circles but had no effect on HIV reverse transcription. All of these data indicate an important role for Imp␣3 in HIV nuclear import. In an attempt to understand how Imp␣3 participates in HIV nuclear import and replication, we first demonstrated that the HIV-1 karyophilic protein integrase (IN) was able to interact with Imp␣3 both in a 293T cell expression system and in HIV-infected CD4 ؉ C8166 T cells. Deletion analysis suggested that a region (amino acids [aa] 250 to 270) in the C-terminal domain of IN is involved in this viral-cellular protein interaction. Overall, this study demonstrates for the first time that Imp␣3 is an HIV integrase-interacting cofactor that is required for efficient HIV-1 nuclear import and replication in both dividing and nondividing cells.HIV-1 replicates productively in nondividing cells, such as monocytes (49,61,74), macrophages (23,37,59,65,71), dendritic cells (47,64), and resting CD4 ϩ T lymphocytes (86), through its ability to undergo active nuclear import by hijacking the host nuclear import machinery. Moreover, active nuclear import is not only required for nondividing-cell infection but also plays a role in the infection of proliferating cells (35). This ability of HIV-1 to enter the nucleus at interphase may contribute significantly to the very high replication rate observed in infected individuals (30,70,73) and is one of the crucial steps in HIV-1 replication, which plays a leading role in the establishment of infection and AIDS pathogenesis.The viral double-stranded DNA (dsDNA), which associates with viral and cellular proteins, forms a high-molecular-mass nucleoprotein complex called the preintegration complex (PIC) in the cytosol of an infected cell (15,51). This large complex has to actively enter the nucleus through the intact nuclear membrane in order to be integrated. At the molecular level, the active nuclear import ability of HIV-1 is attributed to the karyophilic properties of viral PICs. It is known that several viral nucleophilic proteins, including integrase (IN), matrix (MA), and Vpr, are associated with this nucleoprotein complex and pla...

In this study, reverse transcriptase (RT)-and integrase (IN)-