Novel Nuclear Import of Vpr Promoted by Importin α Is Crucial for Human Immunodeficiency Virus Type 1 Replication in Macrophages

Abstract

Monocytes/macrophages are major targets of human immunodeficiency virus type 1 (HIV-1) infection. The viral preintegration complex (PIC) of HIV-1 enters the nuclei of monocyte-derived macrophages, but very little PIC migrates into the nuclei of immature monocytes. Vpr, one of the accessory gene products of HIV-1, is essential for the nuclear import of PIC in these cells, although the role of Vpr in the entry mechanism of PIC remains to be clarified. We have shown previously that Vpr is targeted to the nuclear envelope and then transported into the nucleus by importin ␣ alone, in an importin ␤-independent manner. Here we demonstrate that the nuclear import of Vpr is strongly promoted by the addition of cytoplasmic extract from macrophages but not of that from monocytes and that the nuclear import activity is lost with immunodepletion of importin ␣ from the cytoplasmic extract. Immunoblot analysis and real-time PCR demonstrate that immature monocytes express importin ␣ at low levels, whereas the expression of three major importin ␣ isoforms markedly increases upon their differentiation into macrophages, indicating that the expression of importin ␣ is required for nuclear import of Vpr. Furthermore, interaction between importin ␣ and the N-terminal ␣-helical domain of Vpr is indispensable, not only for the nuclear import of Vpr but also for HIV-1 replication in macrophages. This study suggests the possibility that the binding of Vpr to importin ␣, preceding a novel nuclear import process, is a potential target for therapeutic intervention.

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

“…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. Thus, inhibition of only one of these nuclear import pathways should result in partial decrease in the level of the HIV PIC nuclear import but should not block it completely.…”

Cellular and viral determinants of retroviral nuclear entry

“…Viral protein R, or Vpr, has many functions: it regulates apoptosis, arrests the cell cycle at the G2 stage by binding to DDB1 and Cul4-associated factor 1 (DCAF1), and RNA splicing (Nitahara-Kasahara et al 2007;Kogan and Rappaport 2011). Despite the absence of a functional NLS, it exhibits karyophilic properties during PIC nuclear transport.…”

Human immunodeficiency virus type 1 Vpr: functions and molecular interactions

“…For example, in the presence of importin-a, the nuclear localization of Vpr increases. It has been suggested that interaction of Vpr with importin-a facilitates its nuclear localization (Gallay et al, 1996(Gallay et al, , 1997Nitahara-Kasahara et al, 2007).…”