HIV-1 Tat Induces Microvascular Endothelial Apoptosis Through Caspase Activation

Abstract

HIV-1 Tat, in addition to its critical role in viral transcription, is secreted from infected cells and can act as a proto-cytokine. We studied the effects of HIV-1 Tat in primary human microvascular endothelial cells of lung origin and found that it caused apoptosis. This apoptosis occurred without induction of either Fas or TNF, known mediators of programmed cell death. Tat, like Fas ligand, induced cleavage of chromatin structure, as evidenced by changes in DNA laddering, incorporation of fluorescein into the nicked chromosomal DNA (TUNEL assay), and mono- or oligonucleosomes. Furthermore, Tat treatment caused cleavage of poly(A/DP)-ribose polymerase, a substrate of caspases. Caspase-3, but not caspase-9, was activated following treatment of primary human microvascular endothelial cells of lung origin with either Tat or anti-Fas agonist Ab (anti-Fas). Inhibition of caspase-3 activity markedly reduced apoptosis. Although Fas-mediated apoptosis involved changes in Bcl-2, Bax, and Bad regulatory proteins, such alterations were not observed with Tat. Taken together, these data demonstrate that HIV-1 Tat is able to activate apoptosis in microvascular endothelium by a mechanism distinct from TNF secretion or the Fas pathway.

Langat Flavivirus Protease NS3 Binds Caspase-8 and Induces Apoptosis

“…Other RNA viruses encode more than one protein that induce apoptosis. Proteases 2A and 3C of poliovirus, envelope glycoproteins E1 and E2 of Sindbis virus, and four proteins of human immunodeficiency virus, gp120, gp41, Tat, and Vpr, induce apoptosis (1,8,9,14,16,22,39). While it is uncertain why viruses have more than one protein that induce apoptosis, different proteins may provide selective advantage for a virus in different environments.…”

Apoptotic death of striatal neurons induced by human immunodeficiency virus-1 Tat and gp120: Differential involvement of caspase-3 and endonuclease G

“…HIV-1 viral products can be released by infected microglia and astroglia (Ensoli et al, 1990;Munis et al, 1992;Robert-Guroff et al, 1990;Chang et al, 1997;Shutt and Soil, 1999;Jones et al, 1998;Jones et al, 2000), and can also induce the production and release of proinflammatory cytokines and cellular toxins in neural cells (Yeung et al, 1995;Adamson et al, 1996;Bagetta et al, 1996a;Kaul and Lipton, 1999;Nath et al, 1999). Numerous lines of evidence suggest that extracellular proinflammatory cytokines and cellular toxins can induce neuronal apoptosis (Gabuzda et al, 1986;Gendelman et al, 1994;Shi et al, 1998;New et al, 1998;Bagetta et al, 1999;Holden et al, 1999;Zheng et al, 1999;Park et al, 2001;Takahashi et al, 1996). Furthermore, several studies suggest that HIV-1 Tat and gp120 interact with neuronally-expressed receptors to activate multiple pro-apoptotic signaling cascades in neurons Moore et al, 1997;New et al, 1997;Shi et al, 1998;Piller et al, 1999;Bonavia et al, 2001;Corasaniti et al, 2001;Haughey et al, 2001).…”

“…HIV encephalitis (HIVE) often accompanies HIV dementia and is characterized by prominent microglial activation, neuronal losses, dendritic pruning, and decreased density of synapses (Masliah et al, 1996;Lipton, 1997). Apoptotic changes are seen with HIVE in both neurons and nonneuronal cells (Ramirez et al, 2001;Bonavia et al, 2001;Corasaniti et al, 2001;AdleBiassette et al, 1995;Gelbard et al, 1995;Petito and Roberts, 1995;Shi et al, 1996;Kaul et al, 2001;Shi et al, 1998;Park et al, 2001). HIV-1 is neurotoxic by inducing inflammation and through the direct release of toxic viral proteins such as Nef, Vpr, gp120 and Tat (Haughey et al, 2001;Brenneman et al, 1988;Dreyer et al, 1990;Adamson et al, 1996;New et al, 1997;Kruman et al, 1998;Yeung et al, 1998;Huang and Bond, 2000;Trillo-Pazos et al, 2000;Nath, 2002).…”

Evaluation of novel cell cycle inhibitors in mantle cell lymphoma

“…The level of chromatin cleavage due to apoptosis was quantitated by using the Fluorescein In Situ Cell Death Detection kit (Roche, IN, USA), as described (Park et al, 2001). To assess caspase-3-mediated apoptosis, a cell-permeable, irreversible inhibitor of caspase-3, Z-DEVD-FMK (R&D Systems, Minneapolis, MN, USA), and FMK-control (R&D Systems) were employed.…”

“…Cells stimulated with the indicated compounds were lysed in radioimmunoprecipitation assay buffer, and immunoblot analyses were performed, as described (Park et al, 2001).…”