Apoptosis enhancement by the HIV-1 Nef protein.
The HIV-1 nef gene, essential for AIDS pathogenesis, encodes a 27-kDa protein (Nef) whose biochemical and biological functions are unclear. It has been suggested that Nef expression contributes to the T cell depletion observed during the disease by promoting their apoptosis. We report that in CD4(+) human lymphoblastoid cell lines transfected with the nef cDNA obtained from three different HIV-1 strains, expression of the Nef protein enhances and accelerates the response to four unrelated apoptotic agents (staurosporine, anisomycin, camptothecin, and etoposide) but not to an anti-Fas agonist Ab. Nef reduces the expression of the anti-apoptotic proteins Bcl-2 and Bcl-X(L) and induces a striking enhancement of apoptotic hallmarks, including mitochondrial depolarization, exposure of phosphatidylserine on the cell surface, activation of caspase-3, and cleavage of the caspase target poly(ADP-ribose) polymerase. Interestingly, the peptide Z-Val-Ala-DL-Asp-fluoromethylketone (a broad-spectrum caspase inhibitor) reduces, but does not abolish, phosphatidylserine exposure, suggesting that Nef also activates a caspase-independent apoptotic pathway. Surprisingly, Nef expression increases DNA degradation but without causing oligonucleosomal fragmentation. An increased apoptotic response and down-modulation of Bcl-2/Bcl-X(L) following Nef expression are observed also in NIH-3T3 fibroblasts. These data show that Nef enhances programmed cell death in different cell types by affecting multiple critical components of the apoptotic machinery independently from the Fas pathway.
Rasola
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Division of Molecular Oncology, Institute for Cancer Research, University of Torino Medical School, Candiolo, Italy. arasola@ircc.unito.it
Gramaglia
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Boccaccio
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Comoglio
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D016475:3T3 Cells; D000276:Adjuvants, Immunologic / Q000502:physiology*; D000818:Animals; D017209:Apoptosis / Q000276:immunology*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D053938:DNA Fragmentation / Q000276:immunology; D004789:Enzyme Activation / Q000276:immunology; D015693:Gene Products, nef / Q000502:physiology*; D015497:HIV-1 / Q000276:immunology*; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008564:Membrane Potentials / Q000276:immunology; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D010718:Phosphatidylserines / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D013601:T-Lymphocytes / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D014407:Tumor Cells, Cultured; D051020:bcl-X Protein; D054311:nef Gene Products, Human Immunodeficiency Virus
D000276:Adjuvants, Immunologic; C494811:BCL2L1 protein, human; C494812:Bcl2l1 protein, mouse; D015693:Gene Products, nef; D010718:Phosphatidylserines; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein; D054311:nef Gene Products, Human Immunodeficiency Virus; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases