Interaction of Human Immunodeficiency Virus Type 1 Integrase with Cellular Nuclear Import Receptor Importin 7 and Its Impact on Viral Replication

Abstract

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,

The HIV-1 Integrase Mutant R263A/K264A Is 2-fold Defective for TRN-SR2 Binding and Viral Nuclear Import

“…Lysine 264 was found to be acetylated by p300 by Cereseto et al (60). Importin 7 and importin-␣3 have both been implicated as nuclear import factors for HIV through a direct interaction with IN (14,54). Although importin 7 was later invalidated as HIV-1 nuclear import factor (11), Arg 263 and Lys 264 were reported as interacting amino acids.…”

“…Nuclear import in the human cell is orchestrated by a plethora of karyopherins, comprising both broad spectrum and highly specialized transporters. Several of these have been suggested to take part in HIV nuclear import, in particular importin-␣/␤ (8 -10), importin-␣3 (11), and importin-7 (12)(13)(14)(15). In 2008, transportin-SR2 (TRN-SR2, transportin-3, Tnpo3), encoded by the TNPO3 gene, was independently identified as a cellular cofactor of HIV in two genome-wide siRNA screens (16,17) and picked up as a specific binding partner of HIV IN (18).…”

Transportin 3 and importin α are required for effective nuclear import of HIV-1 integrase in virus-infected cells

“…In addition to importin α and TNPO3, there are two additional pathways that have been implicated in PIC nuclear transport. These include the nuclear import receptor importin 7, 19,20,55 and the direct interaction with Nup153, 34,56 which is one of the NPC proteins. 57 The current results as well as previous results 20,21,34,52,56,58 may imply that these two pathways could also be required to ensure PIC nuclear transport as a multi nuclear import complex.…”

“…Several cellular nuclear-import receptors have been suggested to be involved in the process of PIC nuclear import. Among them are the importin α/β heterodimer, [14][15][16][17][18] importin 7 19,20 and transportin 3 (TPNO3/transportin-SR2, an importin β-like receptor). [21][22][23] Various viral karyophilic proteins, such as the Matrix (MA), Vpr and IN, 3,[24][25][26][27][28][29][30] have been suggested to actively translocate the PIC into the host-cell nucleus.…”

Multifunctional facets of retrovirus integrase

“…In the cytoplasm, IN cleaves a dinucleotide from the 3' OH ends of blunt DNA before transport of the PIC into the nucleus ( Figure 5). HIV IN also appears to play a role in the nuclear transport of the PIC along with other viral and cellular proteins [28,29] . After transport, IN inserts the 3' OH recessed DNA ends into the cellular DNA genome.…”