Apoptosis Enhancement by the HIV-1 Nef Protein

Abstract

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-XL 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-XL 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.

To kill or be killed: how HIV exhausts the immune system

“…However, T-cell priming for apoptosis is associated with the in vivo expression in both CD4 þ and CD8 þ T cells of the active forms of caspase-8 and caspase-3, 109 which can be induced in vitro by a number of HIV proteins, such as Tat, Env, Nef or Vpr. 62,49,71,63 Since T-cell activation is downmodulating the level of the apoptosis inhibitory protein FLIP (FLICE-like inhibitory protein), it was hypothesized that susceptibility of patients' T cells to AICD was associated with decreased c-FLIP expression. However, the levels of c-FLIP in purified CD4 þ and CD8 þ T cells from HIV þ donors do not differ from that of noninfected control donors.…”

Antibody Against Integrin Lymphocyte Function-Associated Antigen 1 Inhibits HIV Type 1 Infection in Primary Cells Through Caspase-8-Mediated Apoptosis

“…[76][77][78] While our studies did not identify specific HIV-1 proteins that lead to activation of caspase-8 to initiate apoptosis when the LFA-1/ICAM-1 interaction is blocked, induction of caspase activity has been attributed to HIV-1 Env, protease, and the accessory proteins tat, nef, vpr, and vpu. [35][36][37][38]44,45,[79][80][81] Our data showed that X4 tropic and dual tropic viruses induced LFA-1-dependent resistance to apoptosis but not R5 tropic viruses. This result suggests that proteins specifically associated with X4/dual tropic viruses may be responsible for the phenomenon.…”

“…It has been shown that caspases 3, 6, 8, and 9 are activated by various HIV-1 proteins. [35][36][37][38][39][40][41][42][43][44][45] Thus, caspases may represent a link between integrins and HIV-1 infection.…”

Evaluation of the in vitro antiretroviral potential of some Biginelli-type pyrimidines

“…HIV-1 infection in tissue-culture conditions leads to syncytium formation and single cell lysis which are called cytopathic eff ects (Dedera and Ratner, 1991). Th ere are reports of the cytostatic or cytotoxic eff ects of HIV-1 proteins Tat, Vif, Vpr, Nef, and protease in cultured cells (Bartz and Emerman, 1999;Chen et al, 1999;Okada et al, 1997;Rasola et al, 2001). However, lysis of cultured T cells infected by HIV-1 and depletion of these cells in simian immunodeficiency virus infected monkeys has been observed without these viral proteins (Cao et al, 1996;McCloskey et al, 1997).…”