Nuclear Export of Simian Immunodeficiency Virus Vpx Protein

Abstract

Lentiviruses, human immunodeficiency viruses (HIVs), and simian immunodeficiency viruses (SIVs) are distinguished from oncoretroviruses by their ability to infect nondividing cells such as macrophages. Retroviruses must gain access to the host cell nucleus for replication and propagation. HIV and SIV preintegration complexes (PIC) enter nuclei after traversing the central aqueous channel of the limiting nuclear pore complex without membrane breakdown. Among the nucleophilic proteins, namely, matrix, integrase, Vpx, and Vpr, present in HIV type 2/SIV PIC, Vpx is implicated in nuclear targeting and is also available for incorporation into budding virions at the plasma membrane. The mechanisms of these two opposite functions are not known. We demonstrate that Vpx is a nucleocytoplasmic shuttling protein and contains two novel noncanonical nuclear import signals and a leptomycin B-sensitive nuclear export signal. In addition, Vpx interacts with the cellular tyrosine kinase Fyn through its C-terminal proline-rich motif. Furthermore, our data indicate that Fyn kinase phosphorylates Vpx and regulates its export from nucleus. Replacement of conserved tryptophan residues within domain 41 to 63 and tyrosine residues at positions 66, 69, and 71 in Vpx impairs its nuclear export, virion incorporation, and SIV replication in macrophages. Nuclear export is essential to ensure the availability of Vpx in the cytoplasm for incorporation into virions, leading to efficient viral replication within nondividing cells.

Identification and Characterization of Three Novel Nuclear Export Signals in the Influenza A Virus Nucleoprotein

“…As shown in Fig. 1, EGFP alone was localized in both the nucleus and the cytoplasm, which is consistent with the observation in previous reports (15,26,39), since its molecular mass (26 kDa) is below the size exclusion limit (ϳ40 kDa) for passive diffusion through the nuclear pores. However, of the seven sequences tested, three (NP-pNES , NP-pNES [183][184][185][186][187][188][189][190][191][192][193][194][195][196][197], and NP-pNES[248-274]) shifted the EGFP to the cytoplasm, suggesting that these NP-NESs are sufficient to direct the fusion protein from the nucleus to cytoplasm.…”

Characterization of Simian Immunodeficiency Virus SIV SM /Human Immunodeficiency Virus Type 2 Vpx Function in Human Myeloid Cells

“…In our hands, the intracellular distribution of Vpx is more heterogeneous than previously appreciated (5,10,24,27), and in DCs, where it exerts a specific function, Vpx is excluded from the nucleus, suggesting that nuclear localization is not important for the action of Vpx. Vpx has been reported to possess a nuclear export signal that can be disrupted upon the simultaneous mutations of three tryptophan residues at positions 49, 53, and 56 (39). However, a previous study failed to reveal a nuclear export signal in Vpx (5), and in our hands, the W49/53/56A Vpx mutant displays a WT intracellular distribution and is not retained exclusively in the nucleus, arguing against a nuclear export signal in Vpx.…”

“…At least two possibilities can explain these results. First, Vpx may exert a positive effect on viral infectivity through both a DCAF1-dependent and -independent mechanism and thus make use of DCAF1 during the infection of macrophages (39) but not during the infection of THP-1 cells (this study). These differences may relate to cell-type-specific functions of E3-ubiquitin ligase adaptors in the cell metabolism and physiology and may reflect an exquisite ability of Vpx to adapt to specific changes in the intracellular milieu.…”

Multifaceted activity of HIV Vpr/Vpx proteins: the current view of their virological functions

“…It has also been reported by us and others that Vpr-deleted viruses of the HIV-2 group grow as well as wildtype virus in MDMs [23][24][25]. In sharp contrast to HIV-1 Vpr and HIV-2 Vpr, HIV-2/SIV Vpx is essential for viral replication in MDMs [8,9,23,24,[26][27][28][29][30][31]. A typical example of these observations is shown in Figure 3A.…”