Akt Regulates the Activation-Induced Apoptosis of T Cells Mediated by HIV-1 gp120.

Multiple mechanisms contribute to the loss of CD4⁺ T cells in HIV-1 infected individuals. Activation-induced apoptosis of bystander T cells mediated by HIV-1 gp120 is one of the critical mechanisms leading to T cell loss in AIDS. Clinical studies have shown that T cells in the lymph nodes of HIV-1 infected individuals undergo activation-induced apoptosis. In the present study, we used a model where T cells undergo apoptosis after HIV-1 gp120/CD4 cross-linking in conjunction with CD3/T cell antigen receptor activation. We have shown that treatment with HIV-1 gp120 (10 nM) and anti-gp120 MoAb induces approximately 20–25% apoptosis in Jurkat T cells in the presence of immobilized anti-CD3 antibody. However, the molecular mechanism by which HIV-1 gp120 mediates the apoptosis of T cells is still unclear. We have also examined the role of Akt/Protein kinase B in HIV-1 gp120-induced apoptosis. Akt is a cell survival molecule that has been shown to block cell death. We observed a decrease in Akt phosphorylation upon gp120 treatment of Jurkat T cells and peripheral blood mononuclear cells (PBMCs). In contrast, only CD3 stimulation was shown to increase the phosphorylation of Akt. To further confirm the role of Akt in gp120-induced apoptosis, Jurkat T cells were transfected with HA epitope-tagged wild type Akt, dominant-negative Akt that lacks kinase activity, or with a control vector. The transfected cells were treated with gp120 and apoptosis was evaluated by Annexin-PI staining. The T cells expressing wild type Akt showed reduced gp120 apoptosis as compared to the vector control-expressing cells. Conversely, expression of a dominant-negative mutant of Akt accelerated cell death as compared to the vector control. We then further assessed the role of upstream regulators of Akt, such as PI-3 kinase. In this regard, we have shown that inhibition of PI-3 kinase leads to enhanced gp120-induced apoptosis. At present, we are elucidating downstream effectors of the Akt pathway. Taken together, these studies suggest that Akt plays a key role in HIV-1 gp120-induced apoptosis, and that identification of Akt-mediated signaling pathways may provide novel therapeutic targets to combat immune deficiency in AIDS.