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Reassessment of the capacity of the HIV-1 Env cytoplasmic domain to trigger NF-κB activation
Virology Journal volume 15, Article number: 35 (2018)
The cytoplasmic domain of lentiviral Envelopes (EnvCD) ensures Env incorporation into nascent virions and regulates Env trafficking to and from the plasma membrane. It has also been reported to promote transcription from the viral LTR both directly and indirectly. Noticeably, the HIV-1 and SIVmac239 EnvCDs were described to trigger nuclear translocation of NF-κB (Postler, Cell Host Microbes 2012). Given the paramount importance of identifying viral and host factors regulating HIV transcription, cellular signaling pathways and latency, and given that viral replication capacity is dependent on Env, we asked whether HIV EnvCDs from different HIV-1 subtypes differently modulated NF-κB. To that aim, we evaluated the ability of primary HIV-1 Envs from subtypes B and C to activate the NF-κB pathway. Primary subtype B and C Envs all failed to activate the NF-κB pathway. In contrast, when the EnvCD of HIV-1 Envs was fused to the the CD8-α chain, it induced ~ 10-fold increase in NF-κB induction, and this increase was much stronger with a truncated form of the HIV EnvCD lacking the 76 C-terminal residues and containing the proposed TAK-1 binding domain. Our results indicate that the HIV-1 EnvCD is unlikely to trigger the NF-κB pathway in its native trimeric form.
The cytoplasmic domain (CD) of lentiviral envelopes (Env) is unusually long (~ 150 residues) compared to other retroviruses (< 50 residues)  and reviewed in [2,3,4,5]. It comprises a disordered sequence with a tyrosine-based internalization signal immediately downstream of the membrane-spanning-domain (MSD), an immunodominant epitope and three amphipathic α-helices (lentiviral lytic peptides, LLP-2, LLP-3 and LLP-1). Despite considerable sequence variation, the physicochemical and structural properties of peptides spanning the LLP regions are believed to be conserved across HIV types and subtypes .
The EnvCD ensures Env incorporation into the nascent virion [7,8,9,10,11,12,13,14,15,16]. It also regulates Env trafficking to and from the plasma membrane [17, 18] through the endolysosomal and Trans-Golgi-Network (TGN) by interacting with multiple cellular factors, including AP1–3, TIP47, Rab9, Rab11A/FIP1C and retromer components Vps26 and Vps35 [19,20,21,22,23,24,25]. Different groups have reported that the EnvCD could also enhance viral transcription, by relieving RhoA-mediated transcriptional inhibition through the interaction of LLP-3 with p155-RhoGEF [26, 27] and by affecting the stability of the precursor of luman, a repressor of Tat-mediated HIV transcription . The HIV-1 and SIVmac239 EnvCDs were also reported to induce the nuclear translocation of NF-κB p65/RelA . For HIV-1, residues 759–770, encompassing the Y768HRL motif at the N-terminus of LLP-2 interact with TAK-1, leading to phosphorylation of IκB .
In vitro, differences in viral replication capacity across subtypes map to the viral Env [30,31,32,33,34]. Because NF-κB activates T-lymphocytes and the viral promoter LTR contains NF-κB binding sites , we asked whether primary HIV-1 Envs from subtypes B and C differently trigger the NF-κB pathway.
To evaluate NF-κB induction by different primary HIV-1 Envs, HEK293T cells were cotransfected with a NF-κB-Firefly-Luciferase reporter plasmid and a panel of 13 HIV-1 full-length Envs cloned in pCDNA3.1: we used HIV-1 EnvNL4.3 , EnvNLAD8 , EnvHXB2, subtype B  and subtype C [39, 40] Envs. EnvNL4.3 harboring a STOP codon at position 710 (EnvΔCD) was used as negative control. All vectors express the two Rev exons. Transfection efficiency was assessed by Flow Cytometry and confirmed protein expression 37 and 48 h post-transfection, with a decrease by 48 h post-transfection (Additional file 1: Figure S1A), probably reflecting Env-induced cell death. To normalize for transfection efficiency, a plasmid expressing CMV-Renilla-Luciferase (Promega pGL4.74 hRLuc) was included in all experiments. NF-κB-Luciferase induction by each of the viral Envs was normalized using the corresponding Renilla-Luciferase signal, and calculated as the fold-change relative to the empty vector (mock), as in . As shown in Fig. 1a, TNF-α (Sigma) readily induced a ~ 2 log increase in NF-κB-Luciferase, validating the system. However, neither of the HIV-1 Envs triggered NF-κB activity (p > 0.05, Kruskal-Wallis test): NF-κB-Luciferase induction ranged from 0.79 to 1.5 for subtype B Envs and from 0.36 to 1.16 for subtype C Envs 37 h post-transfection and from 0.36 to 1.04 for subtype B Envs and 0.31 to 0.80 for subtype C Envs 48 h post-transfection. Variations in NF-κB-Luciferase (Fig. 1a) did not recapitulate Env expression levels (Additional file 1: Figure S1A). When NF-κB-Luciferase induction was further normalized to Env expression levels (MFI) to account for variability in Env expression levels, NF-κB-Luciferase triggered by the viral Envs never exceeded the levels induced by the mock control (p > 0.05, Kruskal-Wallis test) (Additional file 2: Figure S2A), reflecting basal cell activation levels upon transfection and confirming that native Envs do not trigger NF-κB. Limiting serum in HEK293T cell cultures (1% Fetal Bovine Serum) to ensure minimal basal activation did not change NF-κB induction (not shown). Of note, while the HIV-1 Env ectodomain has been reported to trigger NF-κB and apoptosis [41,42,43], this phenomenon requires CD4 and CXCR4 or a co-receptor. Here we investigated NF-κB-induction in cells that do not express the viral receptor CD4, excluding a similar phenomenon. The capacity of the HIV-1 Envs to induce transcription from the LTR was then assessed by transfecting TZM-bl cells with the same Env expression vectors. TZM-bl cells are CD4+ CXCR4+ HeLa-derived cells expressing the Firefly Luciferase and the β-galactosidase genes under the control of the viral promoter LTR. Tat-containing Env expression vectors (EnvNL4.3 + Tat, EnvNLAD8 + Tat) were used as positive controls and the CMV-Renilla-Luciferase vector was included for normalization. LTR-driven transcription was induced by the Tat-containing vectors, as expected, but not by the Env expression vectors, ranging from 0.25 to 1.51 and from 0.30 to 1.26 for subtype B and C Envs respectively (p > 0.05, Kruskal-Wallis test) (Fig. 1b).
One major difference between our experimental set-up and that of Postler et al.  lies in the use of Env expression vectors versus CD8-EnvCD chimeras, respectively. To verify the impact of the ectodomain on the ability of the EnvCD to trigger the NF-κB pathway, we cotransfected HEK293T cells with the NF-κB-Luciferase reporter and a construct containing the EnvCD of HXB2 (residues 707–756) fused to the extracellular and transmembrane domains of the CD8-α chain (residues 1–211) , a kind gift from C Berlioz-Torrent. A CD8-α construct bearing a STOP codon downstream of the transmembrane domain (CD8STOP) was used as a negative control . The CMV-Renilla-Luciferase vector was included for normalization and the fold-change in NF-κB-Luciferase induction was compared (Kruskal-Wallis test). As expected, the CD8-EnvCDHXB2 chimera induced a ~ 10-fold increase in NF-κB-dependent-Luciferase expression relative to the CD8STOP construct 37 h (p < 0.001) and 48 h (p < 0.01) post-transfection (Fig. 2a), in agreement with the findings of Postler et al. using a similar chimera . Using a CD8-EnvCD chimera truncated just downstream of the Y768HRL motif, CD8-EnvCDHXB2–780 (residues 707–780 of HIV-1 EnvCDHXB2), NF-κB-Luciferase activity was ~ 16-fold and ~ 40-fold higher relative to CD8STOP 37 and 48 h post-transfection, respectively (p < 0.001) (Fig. 2a), while a CD8-EnvCD chimera truncated just upstream of the motif of interest, CD8-EnvCDHXB2–760 (residues 707–760 of HIV-1 EnvCDHXB2) did not activate the NF-κB pathway (Fig. 2a), again recapitulating the results of Postler et al. using a CD8-EnvCD construct lacking the 74 C-terminal residues . When NF-κB induction was further normalized to CD8-EnvCD expression levels, CD8-CDHXB2, CD8-EnvCD780 and CD8-SIVmac239 maintained the capacity to activate NF-κB compared to the CD8STOP construct (Additional file 2: Figure S2B). Taken together, these results show that the HIV-1 EnvCD triggers the NF-κB pathway only when expressed downstream of CD8-α, but not in its wild-type form downstream of the isogenic Env ectodomain. We then verified the intracellular localization of the Env-based and CD8-based constructs. As shown in Fig. 2b, EnvNL4.3 and EnvHXB2 colocalized nicely with CD8-EnvCDHXB2 and EnvΔCD colocalized with CD8STOP, arguing against the possibility that different intracellular localization accounts for this dichotomy. We also evaluated the ability of CD8-α-based chimeras fused to the EnvCDs of SIVmac239, MLV and HTLV-1 fused to the CD8-α chain  to trigger NF-κB. The CD8-EnvCDSIVmac239 induced a ~ 26-fold (p < 0.05) and 36-fold (p < 0.01) increase in NF-κB-Luciferase 37 and 48 h post-transfection, respectively, compared to CD8STOP (Fig. 2a). The short EnvCDs of MLV and HTLV had no impact on NF-κB activity (p > 0.05) (Fig. 2a), probably because they lack LLP domains. NF-κB induction by CD8-EnvCDHXB2 and CD8-EnvCDHXB2–780 was higher 48 h post-transfection than 37 h post-transfection, while NF-κB induction by CD8-EnvCDSIVmac239 was weaker 48 h post-transfection, probably reflecting EnvCDSIVmac239 toxicity.
Given that T lymphocyte activation is a prerequisite to HIV replication and that the viral promoter LTR contains NF-κB binding sites, identifying the factors that do promote viral transcription and induce apoptosis in a physiological setting is of major importance. It has been proposed that together with Nef, the EnvCD could provide CD4+ T-lymphocytes the two independent triggers necessary for cell activation and viral replication in vivo. Our results clearly argue against the possibility that the HIV-1 EnvCD might trigger the NF-κB pathway during HIV-1 infection. One possible explanation to the differences observed using CD8-EnvCD chimeras and full length HIV-1 Envs is that differences in conformational dynamics dictate the ability of the HIV-1 EnvCD to trigger the NF-κB pathway. Determinants involved in NF-κB induction might remain cryptic in the trimeric native form of Env while becoming exposed in the context of CD8-EnvCD chimeras. The N-terminal domain of the constructs (Env-ectodomain or CD8-α) may affect the conformation of the EnvCD. The reverse has been reported in that truncations of the HIV-1 or SIVmac239 EnvCDs affect the conformation of the corresponding extracellular domain and its susceptibility to neutralization [44, 45]. The levels of Env oligomerization may further modify the determinants of Env which are exposed. In the CD8-EnvCD chimeras, the EnvCD is most likely mono- or dimeric given that CD8 is dimeric . In the native Env, the EnvCD is mainly trimeric. These possibilities are in line with the observation that truncated forms of the EnvCD are more potent NF-κB pathway activators than the full-length Env. While CD8-α-based chimeras and truncated proteins are powerful tools to dissect the biochemical properties and molecular interactions of retroviral EnvCDs, they have limitations, including potential conformational discrepancies with the native protein, as this study documents, and the fact that truncated EnvCDs are counter-selected in vivo for Env incorporation is impaired . Further studies will be needed to fully appreciate the structure and functions of the HIV-1 EnvCD.
In conclusion, the EnvCD of HIV-1 seems to trigger NF-κB when expressed downstream of CD8-α, particularly when truncated forms of the EnvCD are used, but this effect does not extend to the native Env, arguing against the likelihood that the HIV EnvCD activates this pathway in its native form. The results reported in this study confirm the crucial role of the native trimeric structure of the HIV-1 Env protein and illustrate the need to interpret data obtained with chimeric constructs with the highest caution, first ensuring they extend to native proteins. Given that the viral Env is the target of neutralizing antibodies and given the chief role of cellular activation in the pathogenesis of HIV-AIDS, accurately identifying epitopes with potential biological functions is of major importance for the understanding of HIV pathology and for the design of protective vaccine and viral reservoir eradication strategies.
Envelope Cytoplasmic domain
Human Immunodeficiency Virus type 1
Human T-cell Leukemia virus type I
Lentiviral Lytic Peptide
Murine Leukemia Virus
Membrane Spanning Domain
Simian Immunodeficiency Virus
Hunter E, Swanstrom R. Retrovirus envelope glycoproteins. Curr Top Microbiol Immunol. 1990;157:187–253.
Checkley MA, Luttge BG, Freed EO. HIV-1 envelope glycoprotein biosynthesis, trafficking, and incorporation. J Mol Biol. 2011;410(4):582–608.
Steckbeck JD, Kuhlmann AS, Montelaro RC. C-terminal tail of human immunodeficiency virus gp41: functionally rich and structurally enigmatic. J Gen Virol. 2012. https://www.ncbi.nlm.nih.gov/pubmed/?term=steckbeck+and+2012.
Postler TS, Desrosiers RC. The tale of the long tail: the cytoplasmic domain of HIV-1 gp41. J Virol. 2012. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3536369/.
Santos da Silva E, Mulinge M, Perez Bercoff D. The frantic play of the concealed HIV envelope cytoplasmic tail. Retrovirology. 2013;10(1):54.
Steckbeck JD, et al. Highly conserved structural properties of the C-terminal tail of HIV-1 gp41 protein despite substantial sequence variation among diverse clades: implications for functions in viral replication. J Biol Chem. 2011;286(31):27156–66.
Gonzalez SA, Burny A, Affranchino JL. Identification of domains in the simian immunodeficiency virus matrix protein essential for assembly and envelope glycoprotein incorporation. J Virol. 1996;70(9):6384–9.
Freed EO, Martin MA. Domains of the human immunodeficiency virus type 1 matrix and gp41 cytoplasmic tail required for envelope incorporation into virions. J Virol. 1996;70(1):341–51.
Cosson P. Direct interaction between the envelope and matrix proteins of HIV-1. EMBO J. 1996;15(21):5783–8.
Lee YM, et al. Mutations in the matrix protein of human immunodeficiency virus type 1 inhibit surface expression and virion incorporation of viral envelope glycoproteins in CD4+ T lymphocytes. J Virol. 1997;71(2):1443–52.
Murakami T, Freed EO. Genetic evidence for an interaction between human immunodeficiency virus type 1 matrix and alpha-helix 2 of the gp41 cytoplasmic tail. J Virol. 2000;74(8):3548–54.
Piller SC, et al. Mutational analysis of conserved domains within the cytoplasmic tail of gp41 from human immunodeficiency virus type 1: effects on glycoprotein incorporation and infectivity. J Virol. 2000;74(24):11717–23.
Hourioux C, et al. Identification of the glycoprotein 41(TM) cytoplasmic tail domains of human immunodeficiency virus type 1 that interact with Pr55Gag particles. AIDS Res Hum Retrovir. 2000;16(12):1141–7.
Freed EO, Martin MA. Virion incorporation of envelope glycoproteins with long but not short cytoplasmic tails is blocked by specific, single amino acid substitutions in the human immunodeficiency virus type 1 matrix. J Virol. 1995;69(3):1984–9.
Mammano F, et al. Rescue of human immunodeficiency virus type 1 matrix protein mutants by envelope glycoproteins with short cytoplasmic domains. J Virol. 1995;69(6):3824–30.
Wyma DJ, Kotov A, Aiken C. Evidence for a stable interaction of gp41 with Pr55(gag) in immature human immunodeficiency virus type 1 particles. J Virol. 2000;74(20):9381–7.
Rowell JF, Stanhope PE, Siliciano RF. Endocytosis of endogenously synthesized HIV-1 envelope protein. Mechanism and role in processing for association with class II MHC. J Immunol. 1995;155(1):473–88.
Bultmann A, et al. Identification of two sequences in the cytoplasmic tail of the human immunodeficiency virus type 1 envelope glycoprotein that inhibit cell surface expression. J Virol. 2001;75(11):5263–76.
Ohno H. Interaction of tyrosine-based sorting signals with clathrin-associated proteins. Science. 1995;269:1872–5.
Berlioz-Torrent C, et al. Interactions of the cytoplasmic domains of human and simian retroviral transmembrane proteins with components of the clathrin adaptor complexes modulate intracellular and cell surface expression of envelope glycoproteins. J Virol. 1999;73(2):1350–61.
Wyss S, et al. The highly conserved C-terminal dileucine motif in the cytosolic domain of the human immunodeficiency virus type 1 envelope glycoprotein is critical for its association with the AP-1 clathrin adaptor [correction of adapter]. J Virol. 2001;75(6):2982–92.
Blot G, et al. Targeting of the human immunodeficiency virus type 1 envelope to the trans-Golgi network through binding to TIP47 is required for env incorporation into virions and infectivity. J Virol. 2003;77(12):6931–45.
Murray JL, et al. Rab9 GTPase is required for replication of human immunodeficiency virus type 1, filoviruses, and measles virus. J Virol. 2005;79(18):11742–51.
Qi M, et al. A tyrosine-based motif in the HIV-1 envelope glycoprotein tail mediates cell-type- and Rab11-FIP1C-dependent incorporation into virions. Proc Natl Acad Sci U S A. 2015;112(24):7575–80.
Groppelli E, et al. Retromer regulates HIV-1 envelope glycoprotein trafficking and incorporation into virions. PLoS Pathog. 2014;10(10):e1004518.
Zhang H, et al. Functional interaction between the cytoplasmic leucine-zipper domain of HIV-1 gp41 and p115-RhoGEF. Curr Biol. 1999;9(21):1271–4.
Wang L, et al. Modulation of HIV-1 replication by a novel RhoA effector activity. J Immunol. 2000;164(10):5369–74.
Blot G, et al. Luman, a new partner of HIV-1 TMgp41, interferes with tat-mediated transcription of the HIV-1 LTR. J Mol Biol. 2006;364(5):1034–47.
Postler TS, Desrosiers RC. The cytoplasmic domain of the HIV-1 glycoprotein gp41 induces NF-kappaB activation through TGF-beta-activated kinase 1. Cell Host Microbe. 2012;11(2):181–93.
Ball SC, et al. Comparing the ex vivo fitness of CCR5-tropic human immunodeficiency virus type 1 isolates of subtypes B and C. J Virol. 2003;77(2):1021–38.
Rangel HR, et al. Role of the human immunodeficiency virus type 1 envelope gene in viral fitness. J Virol. 2003;77(16):9069–73.
Pollakis G, et al. Phenotypic and genotypic comparisons of CCR5- and CXCR4-tropic human immunodeficiency virus type 1 biological clones isolated from subtype C-infected individuals. J Virol. 2004;78(6):2841–52.
Arien KK, et al. Replicative fitness of historical and recent HIV-1 isolates suggests HIV-1 attenuation over time. AIDS. 2005;19(15):1555–64.
Arts, E.J., Infection with subtype C HIV-1 of lower replicative fitness as compared to subtypes a and D leads to slower disease progression in Zimbabwean and Ugandan women. 2006.
Centlivre M, et al. HIV-1 clade promoters strongly influence spatial and temporal dynamics of viral replication in vivo. J Clin Invest. 2005;115(2):348–58.
Adachi A, et al. Production of acquired immunodeficiency syndrome-associated retrovirus in human and nonhuman cells transfected with an infectious molecular clone. J Virol. 1986;59(2):284–91.
Freed EO, Englund G, Martin MA. Role of the basic domain of human immunodeficiency virus type 1 matrix in macrophage infection. J Virol. 1995;69(6):3949–54.
Li M, et al. Human immunodeficiency virus type 1 env clones from acute and early subtype B infections for standardized assessments of vaccine-elicited neutralizing antibodies. J Virol. 2005;79(16):10108–25.
Williamson C, et al. Characterization and selection of HIV-1 subtype C isolates for use in vaccine development. AIDS Res Hum Retrovir. 2003;19(2):133–44.
Derdeyn CA, et al. Envelope-constrained neutralization-sensitive HIV-1 after heterosexual transmission. Science. 2004;303(5666):2019–22.
Perfettini JL, et al. NF-kappaB and p53 are the dominant apoptosis-inducing transcription factors elicited by the HIV-1 envelope. J Exp Med. 2004;199(5):629–40.
Perfettini JL, et al. Mechanisms of apoptosis induction by the HIV-1 envelope. Cell Death Differ. 2005;12(Suppl 1):916–23.
Perfettini JL, et al. Critical involvement of the ATM-dependent DNA damage response in the apoptotic demise of HIV-1-elicited syncytia. PLoS One. 2008;3(6):e2458.
Edwards TG, et al. Truncation of the cytoplasmic domain induces exposure of conserved regions in the ectodomain of human immunodeficiency virus type 1 envelope protein. J Virol. 2002;76(6):2683–91.
Durham ND, et al. Neutralization resistance of virological synapse-mediated HIV-1 infection is regulated by the gp41 cytoplasmic tail. J Virol. 2012;86(14):7484–95.
Pascale MC, et al. Assembly of the CD8alpha/p56(lck) protein complex in stably expressing rat epithelial cells. FEBS Lett. 2000;480(2–3):226–30.
Beaumont E, et al. Matrix and envelope coevolution revealed in a patient monitored since primary infection with human immunodeficiency virus type 1. J Virol. 2009;83(19):9875–89.
The authors are thankful to Clarisse Berlioz-Torrent for the generous gift of CD8-EnvCD constructs and to Uriel Hazan for fruitful discussions.
The current research was funded by Grant MESR#20131106 from Ministère de la Recherche et de l’Enseignement Supérieur du Luxembourg. CB is supported by a fellowship from the Fonds National de la Recherche du Luxembourg (FNR) (AFR-6012272). The funding bodies had no impact on study design, data interpretation or manuscript writing.
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Expression of Env and CD8-EnvCD 37 and 48 h post-transfection by Flow Cytometry. A. Expression of subtype B and C Env in HEK293T cells. 1.2 × 105 HEK293T cells in duplicate wells were cotransfected in the same conditions as in Fig. 1a with all Env expression vectors and the Luciferase expression vectors. The empty pcDNA3.1 vector was used as negative control (mock). Duplicate wells were pooled and Env expression was measured by flow cytometry 37 and 48 h post transfection using a 1:1 mixture of human anti-gp120 antibodies PGT121 + F105 (AIDS Research and Reagent program) and an APC-labelled mouse anti-human IgG secondary antibody (Lifetech A21445). Analyses were performed using FlowJo v10. The mean MFI of at least 3 independent experiments are reported. Error bars represent standard deviation. B. Expression of reference Env and CD8-EnvCD chimeras in HEK293T cells. 1.2 × 105 HEK293T cells in duplicate wells were cotransfected in the same conditions as in Fig. 2a with Env and CD8-EnvCD expression vectors and the luciferase expressing vectors. The empty pcDNA3.1 vector was used as negative control (mock). Duplicate wells were pooled and cells were stained either with the same 1:1 mixture of human anti-gp120 antibodies PGT121 + F105 and an APC-labelled mouse anti-human IgG secondary antibody or with a 510-labelled mouse anti-human CD8 antibody (Biolegend #301048). Analyses were performed using FlowJo v10. The mean MFI of at least 3 independent experiments are reported. Error bars represent standard deviation. (PDF 302 kb)
NF-κB induction relative to Env and CD8-EnvCD expression levels. A. NF-κB induction by subtype B and subtype C Envs relative to Env expression levels. NF-κB induction measured in HEK cells co-transfected with the subtype B or subtype C Envs, NF-κB-Luciferase and CMV-Renilla-Luciferase vectors (Fig. 1a and b) was normalized to Env expression levels (MFI, Additional file 1: Figure S1A) to account for differences in Env expression vectors. B. NF-κB induction by CD8-EnvCD relative to expression levels. NF-κB induction measured in HEK cells co-transfected with the CD8-EnvCD constructs, NF-κB-Luciferase and CMV-Renilla-Luciferase vectors (Fig. 2a and b) was normalized to CD8-EnvCD expression levels (MFI, Additional file 1: Figure S1B) to account for differences in expression vectors. It is noteworthy that this second normalization round is subject to differences in antibody affinity for Env, in Env expression kinetics and cycling dynamics, as well as in Env-induced cytotoxicity. This is particularly the case for the subtype B and C primary Envs, while CD8-EnvCD expression levels are less subject to differences in antibody affinity. (PDF 308 kb)
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Beraud, C., Lemaire, M. & Perez Bercoff, D. Reassessment of the capacity of the HIV-1 Env cytoplasmic domain to trigger NF-κB activation. Virol J 15, 35 (2018) doi:10.1186/s12985-018-0941-7
- Env cytoplasmic domain