HIV induces lymphocyte apoptosis by a p53‐initiated, mitochondrial‐mediated mechanism

Abstract

HIV-1 induces apoptosis and leads to CD4+ T-lymphocyte depletion in humans. It is still unclear whether HIV-1 kills infected cells directly or indirectly. To elucidate the mechanisms of HIV-1-induced apoptosis, we infected human CD4+ T cells with HIV-1. Enzymatic analysis with fluorometric substrates showed that caspase 2, 3, and 9 were activated in CD4+ T cells with peak levels 48 h after infection. Immunoblotting analysis confirmed the cleavage of pro-caspase 3 and 9, and of specific caspase substrates. Release of cytochrome c and apoptosis-inducing factor (AIF) from mitochondria was observed in HIV-infected cells. The cytochrome c and AIF release preceded the reduction of the mitochondrial transmembrane potential and nuclear chromatin condensation. H IV infection led to phosphorylation of p53 at the Ser15 residue, detectable as early as 24 h after infection. The p53 phosphorylation was followed by increased mRNA and protein expression of p21, Bax, HDM2, and p53. Up-regulation of surface FasL expression, accompanied by a down-regulation of Fas-associated proteins (FADD, DAXX, and RIP), was observed 72 h after infection. Our results suggest that HIV activates the p53 pathway, leading to cytochrome c and AIF release with ensuing caspase activation.

Mechanisms of apoptosis induction by the HIV-1 envelope

“…Infection of primary human lymphoblasts in vitro, with lymphotropic HIV-1 isolates, causes cell death mainly by syncytium formation, associated with a series of alterations that resemble those induced by Env in vitro, namely DC m loss, 46,67 mitochondrial release of Cyt c and AIF, 67,68 increased ROS production, 69 phosphorylation of p53 on serine 15, 55,67 phosphorylation of p53 on serine 46, 61 activation of p38 MAPK, 66 and the p53-dependent induction of Bax 67 and Puma. 61 The amount of Bax is found to be increased in the mitochondrion-enriched heavy membrane fraction of HIV-infected CD4 þ T cells as compared to uninfected controls.…”

“…61 The amount of Bax is found to be increased in the mitochondrion-enriched heavy membrane fraction of HIV-infected CD4 þ T cells as compared to uninfected controls. 45,67 In vitro, pharmacological inhibition of Cdk1 (with roscovitine), 55,62 mTOR (with rapamycin), 55,62 p38 MAPK (with SB203580 or other inhibitors), 66,70 or p53 (with cyclic pifithrin-a) 61,62 suppresses the apoptosis induced by HIV-1 infection, while caspase inhibition (with Z-VAD.fmk) has no or little cytoprotective effects. 45,68 Altogether, these data suggest that the cascade of events delineated above (cell fusion-activation of Cdk1/cyclin B-p53 phosphorylation on serine 15 and serine 46 by mTOR and p38 MAPKtranscriptional activation of p53 target genes such as Bax and Puma-Bax translocation to mitochondria with consequent MMP-caspase independent cell death) is induced by HIV-1 infection in vitro.…”

Differential Cell Killing by Lymphomagenic Murine Leukemia Viruses Occurs Independently of p53 Activation and Mitochondrial Damage

“…It has been observed that phosphorylation of Ser-15 at the amino terminus of p53 specifically occurs following DNA damage by such agents as ␥-irradiation, UV light, and hydroxyurea. The involvement of p53 in the induction of cell killing has been recently demonstrated for other retroviruses, such as HIV-1 and ts-1 Moloney MLV (5,18,23). Therefore, we tested the hypothesis that high levels of MCF13 MLV UVD can activate the intrinsic DNA damage pathway through p53 activation.…”

HIV: no PUMA no death?

“…5 Recent reports demonstrated that p53 and its target gene Bax are involved in the induction of apoptosis triggered by HIV in infected primary lymphocytes. 6,7 The role of p53 in HIV-induced cell death has now been more firmly validated by a recent report by Perfettini et al 8 in the Journal of Experimental Medicine. The same group had previously demonstrated the existence of a sequence of events during syncytia formation: 9 (i) activation of mammalian target of rapamycin (mTOR); (ii) mTOR-dependent phosphorylation of p53 at serine 15 and the induction of its target gene Bax; (iii) activation of a mitochondrial death pathway.…”