Requirement of calmodulin binding by HIV-1 gp160 for enhanced FAS-mediatedapoptosis

Accelerated apoptosis is one mechanism proposed for the loss of CD4+ T-lymp hocytes in human immunodeficiency virus type 1 (HIV-1) infection. The HIV-1 envelope glycoprotein, gp160, contains two C-terminal calmodulin-binding d omains. Expression of gp160 in Jurkat T-cells results in increased sensitiv ity to FAS- and ceramide-mediated apoptosis, The pro-apoptotic effect of gp 160 expression is blocked by two calmodulin antagonists, tamoxifen and trif luoperazine. This enhanced apoptosis in response to FAS antibody or C-2-cer amide is associated with activation of caspase 3, a critical mediator of ap optosis, A point mutation in the C-terminal calmodulin-binding domain of gp 160 (alanine 835 to tryptophan, A835W) eliminates gp160-dependent enhanced FAS-mediated apoptosis in transiently transfected cells, as well as in vitr o calmodulin binding to a peptide corresponding to the C-terminal calmoduli n-binding domain of gp160, Stable Tet-off Jurkat cell lines were developed that inducibly express wild type gp160 or gp160A835W, Increasing expression of wild type gp160, but not gp160A835W, correlates with increased calmodul in levels, increased apoptosis, and caspase 3 activation in response to ant i-FAS treatment. The data indicate that gp160-enhanced apoptosis is depende nt upon calmodulin up-regulation, involves the activation of caspase 3, and requires calmodulin binding to the C-terminal binding domain of gp160.