Human immunodeficiency virus type 1 Nef protein sensitizes CD4(+) T lymphoid cells to apoptosis via functional upregulation of the CD95/CD95 ligand pathway

Many viruses have evolved genes encoding proteins that regulate cell death by apoptosis. The human immunodeficiency virus type 1 (HIV-1) Nef protein a lters T-cell development and signaling and is required for optimal viral re plication and pathogenicity in vivo. To analyze the interference of Nef wit h cell survival, we used both regulated and constitutively expressed nef al leles in stably transfected T-cell lines. Nef-expressing cells were sensiti zed to cell death by apoptosis, which was specifically exacerbated by an an ti-CD95 IgM monoclonal antibody (MoAb). Flow cytometric analysis showed tha t the surface expression of both CD95 and CD95 ligand (CD95L) was upregulat ed by endogenous Nef expression. Nef-mediated apoptosis was almost complete ly suppressed by the addition in culture of an anti-CD95 Fab' IgG MoAb, whi ch specifically blocks CD95/CD95L interactions, Lastly, mutation of a proli ne motif in the core region of the nef gene, which disrupts its ability to interact with cellular kinases and reduces HIV-1 replication in vitro, comp letely abrogated the Nef-mediated induction of apoptosis as well as its abi lity to upregulate surface CD95 and CD95L. These findings may provide molec ular insight into the role of endogenous Nef in the T-cell depletion observ ed in vivo, particularly HIV-specific cytotoxic CD8(+) T cells. (C) 1999 by The American Society of Hematology.