Nuclear Export of Vpr Is Required for Efficient Replication of Human Immunodeficiency Virus Type 1 in Tissue Macrophages

Abstract

Retroviruses must gain access to the host cell nucleus for subsequent replication and viral propagation. Human immunodeficiency virus type 1 (HIV-1) and other primate lentiviruses are distinguished from the gammaretroviruses by their ability to infect nondividing cells such as macrophages, an important viral reservoir in vivo. Rather than requiring nuclear membrane breakdown during cell division, the HIV-1 preintegration complex (PIC) enters the nucleus by traversing the central aqueous channel of the limiting nuclear pore complex. The HIV-1 PIC contains three nucleophilic proteins, matrix, integrase, and Vpr, all of which have been implicated in nuclear targeting. The mechanism by which Vpr can display such nucleophilic properties and yet also be available for incorporation into virions assembling at the plasma membrane is unresolved. We recently characterized Vpr as a nucleocytoplasmic shuttling protein that contains two novel nuclear import signals and an exportin-1-dependent nuclear export signal (NES). We now demonstrate that mutation of this NES impairs the incorporation of Vpr into newly formed virions. Furthermore, we find that the Vpr NES is required for efficient HIV replication in tissue macrophages present in human spleens and tonsils. These findings underscore how the nucleocytoplasmic shuttling of Vpr not only contributes to nuclear import of the HIV-1 PIC but also enables Vpr to be present in the cytoplasm for incorporation into virions, leading to enhancement of viral spread within nondividing tissue macrophages.Human immunodeficiency virus type 1 (HIV-1) and other primate lentiviruses are able to infect nondividing cells, notably terminally differentiated macrophages (41), an important viral reservoir within the infected host (31,34,53). This biological feature distinguishes the lentiviruses from the oncoretroviruses (or gammaretroviruses), in which cell division associated with nuclear membrane dissolution is required for infection (33,42,62). HIV-1 is also able to infect resting, nondividing T cells in lymphoid tissues (13). These nondividing T cells may contribute to the establishment of protected reservoirs in the host, undermining attempts to eradicate virusproducing cells in the long term (5,6,15,56,77).After entry by fusion and uncoating, the viral reverse transcriptase complex traverses the cytoplasm while reverse transcribing the two strands of RNA into DNA (20), forming the viral preintegration complex (PIC). The nuclear envelope forms a barrier that the PIC must negotiate. The nuclear envelope is studded with nuclear pore complexes (NPCs) that form a conduit with a central aqueous channel mediating bidirectional transport of many macromolecules. The NPC corresponds to a 125-MDa structure comprising 50 to 100 polypeptides. Many of these proteins are members of the nucleoporin family characterized by FG repeats (46). During active transport, the central aqueous channel accommodates protein complexes as large as 25 nm in diameter. However, the HIV-1 PIC exhibits a Stokes diameter of 56 n...

Macrophages and HIV-1: dangerous liaisons

“…This was potentially explained in recent experiments using a Vpr mutant that does not affect nuclear import but that impairs the nuclear export of Vpr and its incorporation into virions. The efficient nuclear export of Vpr enhances viral replication in cultured macrophages (Sherman et al, 2003). HIV-2 and SIV contain two related genes, vpr and vpx.…”

HIV-1 Induces Telomerase Activity in Monocyte-Derived Macrophages, Possibly Safeguarding One of Its Reservoirs

“…It is yet unclear whether the reactivation of telomerase in MDM could be an indirect effect of HIV infection as a consequence of the activation of cellular proteins, like Sp1 and Akt (60,77), or if it is directly mediated by viral proteins, like Vpr and/or Nef. On the one hand, Vpr, which is strictly required for HIV replication in MDM, regulates the shuttling of macromolecules between the nucleus and cytoplasm and can act as a transcriptional factor (8,41,72). On the other hand, Nef can protect MDM from apoptosis triggered by HIV and contributes to efficient viral replication as well (37,59).…”

Mechanistic Differences in RNA-dependent DNA Polymerization and Fidelity between Murine Leukemia Virus and HIV-1 Reverse Transcriptases

“…The generality of this idea needs to be further explored by analyzing more RT proteins isolated from different retroviruses. Furthermore, note that, in order to complete viral replication in nondividing cells, HIV-1 also requires a viral accessory protein, viral protein R (Vpr), which enables the pre-integration complex containing the synthesized proviral DNA to enter the nucleus through the nuclear membrane that remains intact in nondividing cells (55,56). In contrast, other retroviruses, which infect dividing cells, do not require this transport mechanism because the pre-integration complex of these viruses can access chromosomes during mitosis where the nuclear membrane barrier disintegrates.…”