title: HIV-1 gp41 fusogenic function triggers autophagy in uninfected cells.
abstract: Cell-expressed HIV-1 envelope glycoproteins (gp120 and gp41, called Env) induce autophagy in uninfected CD4 T cells, leading to their apoptosis, a mechanism most likely contributing to immunodeficiency. The presence of CD4 and CXCR4 on target cells is required for this process, but Env-induced autophagy is independent of CD4 signaling. Here we demonstrate that CXCR4-mediated signaling pathways are not directly involved in autophagy and cell death triggering. Indeed, cells stably expressing mutated forms of CXCR4, unable to transduce different Gi-dependent and -independent signals, still undergo autophagy and cell death after coculture with effector cells expressing Env. After gp120 binding to CD4 and CXCR4, the N terminus fusion peptide (FP) of gp41 is inserted into the target membrane, and gp41 adopts a trimeric extended pre-hairpin intermediate conformation, target of HIV fusion inhibitors such as T20 and C34, before formation of a stable six-helix bundle structure and cell-to-cell fusion. Interestingly, Env-mediated autophagy is triggered in both single cells (hemifusion) and syncytia (complete fusion), and prevented by T20 and C34. The gp41 fusion activity is responsible for Env-mediated autophagy since the Val2Glu mutation in the gp41 FP totally blocks this process. On the contrary, deletion of the C-terminal part of gp41 enhances Env-induced autophagy. These results underline the major role of gp41 in inducing autophagy in the uninfected cells and indicate that the entire process leading to HIV entry into target cells through binding of Env to its receptors, CD4 and CXCR4, is responsible for autophagy and death in the uninfected, bystander cells.
authors.affiliation: CPBS, UM1, UM2, CNRS, Institut de Biologie, Montpellier, France.
authors.forename: Mélanie
authors.initials: M
authors.lastname: Denizot
authors.forename: Mihayl
authors.initials: M
authors.lastname: Varbanov
authors.forename: Lucile
authors.initials: L
authors.lastname: Espert
authors.forename: Véronique
authors.initials: V
authors.lastname: Robert-Hebmann
authors.forename: Sophie
authors.initials: S
authors.lastname: Sagnier
authors.forename: Elisabet
authors.initials: E
authors.lastname: Garcia
authors.forename: Marta
authors.initials: M
authors.lastname: Curriu
authors.forename: Robert
authors.initials: R
authors.lastname: Mamoun
authors.forename: Julià
authors.initials: J
authors.lastname: Blanco
authors.forename: Martine
authors.initials: M
authors.lastname: Biard-Piechaczyk
mesh_terms: D001343:Autophagy; D015704:CD4 Antigens / Q000235:genetics / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology* / Q000648:ultrastructure; D002460:Cell Line; D018920:Coculture Techniques; D015700:HIV Envelope Protein gp41 / Q000235:genetics / Q000276:immunology*; D015658:HIV Infections / Q000276:immunology*; D015497:HIV-1 / Q000276:immunology* / Q000502:physiology; D006801:Humans; D046529:Microscopy, Electron, Transmission; D019718:Receptors, CXCR4 / Q000235:genetics / Q000276:immunology; D014760:Viral Fusion Proteins / Q000276:immunology*; D053586:Virus Internalization
chemical_list: D015704:CD4 Antigens; C527276:CXCR4 protein, human; D015700:HIV Envelope Protein gp41; D019718:Receptors, CXCR4; D014760:Viral Fusion Proteins; C514787:gp41 protein, Human immunodeficiency virus 1