Implication of the Lymphocyte-Specific Nuclear Body Protein Sp140 in an Innate Response to Human Immunodeficiency Virus Type 1

Abstract

The viral infectivity factor (Vif) of human immunodeficiency virus type 1 (HIV-1) neutralizes an unidentified antiviral pathway that occurs only in nonpermissive (NP) cells. Using a yeast two-hybrid screen of a human lymphocyte cDNA library, we identified several potential Vif partners. One, the nuclear body protein Sp140, was found specifically in all NP cells (n ‫؍‬ 12 cell lines tested; P < 0.001), and HIV-1 infection induced its partial dispersal from nuclear bodies into cytosolic colocalization with Vif. Our results implicate Sp140 in a response to HIV-1 that may be related to or coordinated with the pathway that inactivates HIV-1 lacking vif.The Vif protein encoded by human immunodeficiency virus type 1 (HIV-1) is a 23,000-M r phosphoprotein that has been detected in the cytosol and nucleus in association with membranes, intermediate filaments, the viral Gag polyprotein, and the viral genomic RNA (8,10,17,23,25,27,43,55). It enhances the infectivity but not the quantity of HIV-1 virions released from nonpermissive (NP) cells, including T lymphocytes and macrophages and some leukemic T-cell lines, by 20-to 100-fold, but it is unnecessary in permissive (P) cells (7,13,22,39,44,53). Although the HIV-1 lacking vif that is made in P cells efficiently infects NP cells, the NP cells release noninfectious HIV-1 virions that appear to have a normal protein and RNA composition but that are irreversibly altered in a manner that inhibits reverse transcription in target cells (9,13,17,24,36,44,53).Two lines of evidence suggest that for Vif to function, the protein must interact with an unknown cellular factor that occurs in NP cells. Recently, we and others found that the NP phenotype is dominant in P ϫ NP heterokaryons (31,42). This implies that NP cells contain a pathway for inactivating HIV-1, that this pathway is absent or incomplete in P cells, and that Vif neutralizes this pathway. Additionally, it was reported that Vif proteins of primate lentiviruses function only in the lymphocytes of species closely related to the viral hosts (41). This finding implies that for Vif to function, rather than associating with a viral factor, the protein must bind to a cellular factor that changes during evolution (41). Consequently, we hypothesized that P cells lack this Vif-binding target factor and/or another component or components of the pathway that inactivates HIV-1 lacking vif.We used the L40 yeast system (26) with full-length HXB2 strain Vif as bait in a two-hybrid screen of a human leukocyte Matchmaker cDNA library (Clontech, Palo Alto, Calif.). This system provides high-level expression of LexA-B domain (BD)-bait and Ga14-A domain (AD)-prey proteins, thereby enhancing weak bait-prey associations. Although several prey were of potential interest, we focused principally on Sp140 because it is lymphocyte and macrophage specific and is induced by gamma interferon (3,4,15). Additionally, Sp140 is closely related to the widely expressed protein Sp100, which has been implicated in defenses against other viruses and associates...

Analysis of HIV-1 Viral Infectivity Factor-mediated Proteasome-dependent Depletion of APOBEC3G

“…This discrepancy was explained when more YFP-Vif appeared to localize to the cytoplasm when immunolocalized with either ␣-Vif or ␣-GFP, which suggests that cytoplasmic Vif is more amenable to immunostaining. Altogether these results demonstrated that a more substantial fraction of Vif localizes to the nucleus than described previously and are consistent with previous findings that show Vif interacts with nuclear proteins Sp140 (43) and ZIN (44).…”

The Human Immunodeficiency Virus Type 1 Vif Protein Reduces Intracellular Expression and Inhibits Packaging of APOBEC3G (CEM15), a Cellular Inhibitor of Virus Infectivity

“…A variety of Vif-interacting host factors have since been identified. These include vimentin (20), Hck (17), sp140 (28), and CEM15 (36). In fact, expression of Hck and CEM15 appeared to be associated with inhibition of viral infectivity in a Vif-dependent manner (17,36).…”

Ring Finger Protein ZIN Interacts with Human Immunodeficiency Virus Type 1 Vif

“…Indeed a number of cellular factors have been shown to interact with Vif. These include tyrosine kinase Hck (14), an ATP-binding protein, HP68 (45), and lymphocyte-specific nuclear body protein Sp140 (25). However, the biological significance of these cellular factors in relation to their association with Vif is not clear.…”