Caspase Inhibition Activates HIV in Latently Infected Cells: ROLE OF TUMOR NECROSIS FACTOR RECEPTOR 1 AND CD95

Carsten Scheller,Sieghart Sopper,Peifeng Chen,Egbert Flory,Eleni Koutsilieri,Tomas Racek,Stephan Ludwig,Volker Ter Meulen,Christian Jassoy

doi:10.1074/jbc.m200763200

Abstract

Stimulation of tumor necrosis factor receptor 1 (TNF-R1) triggers both caspase-dependent and caspase-independent signaling activities. The caspase-dependent signaling pathway induces apoptotic cell death in susceptible cells, whereas the caspase-independent signaling cascade leads to activation of nuclear factor kappa B and induces antiapoptotic signaling activities. Stimulation of nuclear factor kappa B via TNF-R1 is known to activate human immunodeficiency virus (HIV) replication in infected cells. Here we show that the broad range caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (ZVAD) activates HIV replication in the chronically infected T-cell line ACH-2. Virus activation was caused by a sensitization of TNF-R1 toward endogenously produced tumor necrosis factor alpha (TNF-alpha). Neutralizing anti-TNF-alpha antibodies completely abolished the virus-inducing activity of ZVAD. Treatment of cells with TNF-alpha in the presence of ZVAD caused increased expression of TNF-alpha and induced enhanced virus replication. Activation of CD95, another member of the TNF receptor family, similarly triggered HIV replication, which was further enhanced in the presence of ZVAD. Our data show that caspase inhibitors sensitize both CD95 and TNF-R1 to mediate activation of HIV in latently infected cells. Activation of HIV replication in latent virus reservoirs is currently discussed as a therapeutic strategy to achieve eradication of HIV in patients treated with antiretroviral therapy. Our results point to a novel role for caspase inhibitors as activators of virus replication in vivo.

Highlights

Stimulation of tumor necrosis factor receptor 1 (TNFR1) triggers both caspase-dependent and caspase-independent signaling activities
We show that caspase inhibitors block death receptor-induced apoptosis but allow the execution of caspase-independent signaling pathways triggered by TNF-R1 or CD95 that lead to activation of NF-␬B and human immunodeficiency virus (HIV) in chronically infected T cells
To study any interfering effects between these two different signaling cascades on HIV replication, we blocked apoptotic TNF-R1 signaling with the peptidic broad range caspase inhibitor ZVAD

Summary

Caspase Inhibition Activates HIV in Latently Infected Cells

Stimulation of nuclear factor ␬B via TNF-R1 is known to activate human immunodeficiency virus (HIV) replication in infected cells. Our data show that caspase inhibitors sensitize both CD95 and TNF-R1 to mediate activation of HIV in latently infected cells. The other is mediated by caspase activity and induces apoptosis in susceptible cells [1,2,3] Another member of the TNF receptor family, CD95, has been recognized as a cell surface molecule mediating primarily apoptotic signaling [4]. We show that caspase inhibitors block death receptor-induced apoptosis but allow the execution of caspase-independent signaling pathways triggered by TNF-R1 or CD95 that lead to activation of NF-␬B and HIV in chronically infected T cells.

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION