Browsing by keyword "Nef"

Now showing items 1-3 of 3

    • A Long Cytoplasmic Loop Governs the Sensitivity of the Anti-viral Host Protein SERINC5 to HIV-1 Nef
      Dai, Weiwei; Usami, Yoshiko; Wu, Yuanfei; Gottlinger, Heinrich G. (2018-01-23)
      We recently identified the multipass transmembrane protein SERINC5 as an antiviral protein that can potently inhibit HIV-1 infectivity and is counteracted by HIV-1 Nef. We now report that the anti-HIV-1 activity, but not the sensitivity to Nef, is conserved among vertebrate SERINC5 proteins. However, a Nef-resistant SERINC5 became Nef sensitive when its intracellular loop 4 (ICL4) was replaced by that of Nef-sensitive human SERINC5. Conversely, human SERINC5 became resistant to Nef when its ICL4 was replaced by that of a Nef-resistant SERINC5. In general, ICL4 regions from SERINCs that exhibited resistance to a given Nef conferred resistance to the same Nef when transferred to a sensitive SERINC, and vice versa. Our results establish that human SERINC5 can be modified to restrict HIV-1 infectivity even in the presence of Nef.

    • Potent Enhancement of HIV-1 Replication by Nef in the Absence of SERINC3 and SERINC5
      Wu, Yuanfei; Olety, Balaji; Weiss, Eric R.; Popova, Elena; Yamanaka, Hikaru; Gottlinger, Heinrich G. (2019-06-11)
      It has recently emerged that HIV-1 Nef counteracts the antiviral host proteins SERINC3 and SERINC5. In particular, SERINC5 inhibits the infectivity of progeny virions when incorporated. SERINC3 and SERINC5 are also counteracted by the unrelated murine leukemia virus glycosylated Gag (glycoGag) protein, which possesses a potent Nef-like activity on HIV-1 infectivity. We now report that a minimal glycoGag termed glycoMA can fully substitute for Nef in promoting HIV-1 replication in Jurkat T lymphoid cells, indicating that Nef enhances replication in these cells mainly by counteracting SERINCs. In contrast, the SERINC antagonist glycoMA was unable to substitute for Nef in MOLT-3 T lymphoid cells, in which HIV-1 replication was highly dependent on Nef, and remained so even in the absence of SERINC3 and SERINC5. As in MOLT-3 cells, glycoMA was unable to substitute for Nef in stimulating HIV-1 replication in primary human cells. Although the ability of Nef mutants to promote HIV-1 replication in MOLT-3 cells correlated with the ability to engage endocytic machinery and to downregulate CD4, Nef nevertheless rescued virus replication under conditions where CD4 downregulation did not occur. Taken together, our observations raise the possibility that Nef triggers the endocytosis of a novel antiviral factor that is active against both laboratory-adapted and primary HIV-1 strains. IMPORTANCE The Nef protein of HIV-1 and the unrelated glycoGag protein of a murine leukemia virus similarly prevent the uptake of antiviral host proteins called SERINC3 and SERINC5 into HIV-1 particles, which enhances their infectiousness. We now show that although both SERINC antagonists can in principle similarly enhance HIV-1 replication, glycoGag is unable to substitute for Nef in primary human cells and in a T cell line called MOLT-3. In MOLT-3 cells, Nef remained crucial for HIV-1 replication even in the absence of SERINC3 and SERINC5. The pronounced effect of Nef on HIV-1 spreading in MOLT-3 cells correlated with the ability of Nef to engage cellular endocytic machinery and to downregulate the HIV-1 receptor CD4 but nevertheless persisted in the absence of CD4 downregulation. Collectively, our results provide evidence for a potent novel restriction activity that affects even relatively SERINC-resistant HIV-1 isolates and is counteracted by Nef.

    • SERINC5: Its Sensitivity to Nef and Restriction of HIV-1
      Dai, Weiwei (2018-08-06)
      The accessory protein Nef of human immunodeficiency virus type 1 (HIV-1) has long been known to enhance the infectivity of HIV-1 progeny virions. The multipass transmembrane proteins serine incorporator 3 (SERINC3) and SERINC5 were recently identified as novel antiviral proteins that restrict HIV-1 infectivity. Nef enhances HIV-1 infectivity by removing SERINCs from the plasma membrane, which prevents their incorporation into progeny HIV-1 virions. To exploit this potent intrinsic antiretroviral factor for potential therapy development, it is critical to explore the determinants in SERINC5 that govern its downregulation by Nef and its restriction on HIV-1 infectivity. Here I report that the ability to inhibit HIV-1 infectivity is conserved among vertebrate SERINC5 proteins, whereas the sensitivity to downregulation by Nef is not. However, a Nef-resistant SERINC5 became Nef-sensitive when its intracellular loop 4 (ICL4) was replaced by that of Nef-sensitive human SERINC5. Conversely, human SERINC5 became resistant to Nef when its ICL4 was replaced by that of a Nef-resistant SERINC5. In general, ICL4 regions from SERINCs that exhibited resistance to a given Nef conferred resistance to the same Nef when transferred to a sensitive SERINC, and vice versa. I demonstrate that human SERINC5 can be modified to restrict HIV-1 infectivity even in the presence of Nef. Moreover, by generating chimeras between SERINC5 and SERINC2, which does not exhibit antiretroviral activity, I demonstrate that SERINC5’s inhibitory function, unlike the sensitivity to Nef, requires the participation of more than one region. Helix 4 and extracellular loop 5 (ECL5) of SERINC5 are both required for the potent restriction of HIV-1 infectivity. In contrast, a large amino-terminal portion of SERINC5 is not required for its antiretroviral activity of SERINC5. The determinants in ECL5 disperse throughout the loop. Furthermore, the ECL5 of SERINC5 is a hotspot region that determines the Env-dependent antiretroviral activity of SERINC5.