A number of mechanisms have been proposed to explain the depletion of helper CD4+ cells in HIV-infected individuals. Gougeon and Montagnier suggested that loss of CD4+ cells in HIV-infected patients is associated with apoptosis. Current studies in our laboratory are directed toward understanding the mechanisms employed by cells undergoing programmed cell death. We have focused on the role of the HIV tat gene in this process. Tat can modulate the redox state of cells by altering the activity of various enzymes to shift the cellular state toward pro-oxidant conditions. We have shown that the altered redox state can cause cells to die by apoptosis. Currently, we are studying the regulation of the cell death mediated by the interactions of tat and TNF-alpha. We have generated two cell lines, HeLa and EAhy926, that contain constitutively activated tat. In these cells, tat potentiated TNF-induced activation of NF-kappa b, and cellular cytotoxicity. In addition, we have shown that TNF-induced cytotoxicity was mediated through TNFRI, because treatment of the cells with TNFRI neutralizing antibodies could rescue the cells from TNF-induced cell death. TNFRI expression was normally down-regulated in both HeLa and EAhyp26 cells following TNF treatment. However, TNFRI downregulation did not occur in the same cells expressing HIV tat. Furthermore, addition of recombinant, soluble HIV tat protein could induce the expression of TNFRI. Therefore, it is possible that the HIV tat protein may cause upregulation of TNFRI, the major receptor which mediates the effects of TNF. By increasing TNFRI, Tat is able to potentiate the effects of TNF. These effects most likely lead to changes of local homeostasis and may contribute to the AIDS disease development. In separate studies we are pursuing the apoptotic pathway in response to oxidative damage. In studies following the role of p53 in this process, we have found that this process also appears to require the p85 kinase as well as alterations in the Rb and E2F protein complexes.
