Human Dlg protein binds to the envelope glycoproteins of human T-cell leukemia virus type 1 and regulates envelope mediated cell-cell fusion in T lymphocytes

Abstract

Human homologue of the Drosophila Dlg tumor suppressor (hDlg) is a widely expressed scaffold protein implicated in the organization of multi-protein complexes at cell adhesion sites such as the neuronal synapse. hDlg contains three PDZ domains that mediate its binding to the consensus motifs present at the C-termini of various cell surface proteins, thus inducing their clustering and/or stabilization at the plasma membrane. Using a yeast two-hybrid screen, we identified hDlg as a cellular binding partner of a viral membrane integral protein, the envelope glycoprotein (Env) of human T-cell leukemia virus type 1 (HTLV-1). HTLV-1 is a human retrovirus that infects CD4+ T lymphocytes and is preferentially transmitted via direct contacts between infected and target cells, through a structure referred to as the virological synapse. Here, we demonstrate that hDlg interacts with a classical PDZ domain-binding motif present at the C-terminus of the cytoplasmic domain of HTLV-1 Env and conserved in the related HTLV-2 virus. We further document that, in HTLV-1 infected primary T cells, hDlg and Env are concentrated in restricted areas of the plasma membrane, enriched in molecules involved in T-cell contacts. The presence of Gag proteins responsible for viral assembly and budding in these areas indicated that they constitute platforms for viral assembly and transmission. Finally, a mutant virus unable to bind hDlg exhibited a decreased ability to trigger Env mediated cell fusion between T lymphocytes. We thus propose that hDlg stabilizes HTLV-1 envelope glycoproteins at the virological synapse formed between infected and target cells, hence assisting the cell-to-cell transmission of the virus.

Novel Role for Interleukin-2 Receptor-Jak Signaling in Retrovirus Transmission

“…Indeed, we observed an almost threefold increase in syncytium formation in the presence of p12 or IL-2, but no change was seen in the expression of Env, which is intimately involved in syncytium formation. The human disc large protein (Dlg1) has been shown to interact with the envelope protein from HTLV-1, and this interaction is required for syncytium formation (9,62). Env also is known to undergo a number of other changes, including disulfide isomerization and a series of glycosylation events, that are required for syncytium formation (38,55).…”

PDZD8 Is a Novel Gag-Interacting Factor That Promotes Retroviral Infection

“…Another PDZ protein, Dlg1 (discs large protein), directly binds HIV-1 Gag and negatively regulates late steps of the viral life cycle (32). Dlg1 also interacts with human T-cell leukemia virus type-1 envelope glycoprotein and regulates cell-cell fusion in T lymphocytes (3). Furthermore, interaction between HIV-1 trans-activator protein Tat and the PDZ-like domain of SATB1 (special AT-rich sequence binding protein 1) has been suggested to function in viral propagation in T cells (25).…”

“…2A and B) compared to the control line, suggesting that overexpression of PDZD8 affects HIV-1 infection at an early stage. As different PDZ domain-containing proteins have been shown to play a role in infection by several retroviruses (3,21,25,32), we also tested the effects of PDZD8 on MuLV and simian immunodeficiency virus (SIV) infection. Control and PDZD8-overexpressing CHME3 cells were infected with various amounts of M-MuLV-puro (Moloney MuLV-based viral vector carrying the puromycin resistance marker) (30) and SIV-luc (SIV mac -based viral vector carrying a luciferase reporter) (43) pseudotyped with VSV-G glycoprotein.…”

Neuropilin-1 Is Involved in Human T-Cell Lymphotropic Virus Type 1 Entry

“…The HTLV-1-infected T-cell line CIB, which has been described previously (3) and which was established from a patient with HTLV-1-associated myelopathy, was cultivated in complete RPMI 1640 medium supplemented with 100 U/ml of interleukin 2 (IL-2) (Roche, France). Peripheral blood mononuclear cells from healthy donors were separated by Ficoll Hypaque density gradient centrifugation followed by isolation of primary T cells using the pan T-cell negative-selection kit (Miltenyi Biotec, France).…”