ROLE OF CALMODULIN IN HIV-POTENTIATED FAS-MEDIATED APOPTOSIS

The recently demonstrated extraordinary rate of turnover of T cells in human immunodeficiency virus (HIV)-1-infected patients and the appare ntly concomitant high rate of viral production and death are consisten t with a large amount of cell death directly due to infection. Apoptos is may be one of the major forms of cell death in HIV-1 infection. Man y apoptotic pathways depend on calcium and therefore would be expected to involve calmodulin. As the HIV-1 envelope glycoprotein, gp160, con tains two known calmodulin-binding domains, we investigated the possib ility that the cytoplasmic domain of the HIV-1 envelope protein gp160 could enhance Fas-mediated apoptosis, the major form of apoptosis in l ymphocytes. Our studies have shown that 1) transfection of H9 and MOLT -4 cells with a non-infectious HIV proviral clone, pFN, which expresse s wild-type gp160 leads to enhanced Fas-mediated apoptosis, 2) transfe ction of MOLT-4 cells with a pFN construct pFN Delta 147, which expres ses a carboxyl-terminally truncated gp160 lacking the calmodulin-bindi ng domains, produces less Fas-mediated apoptosis than transfection wit h pFN, and 3) the calmodulin antagonists trifluoperazine and tamoxifen completely inhibit the pFN enhancement of Fas-mediated apoptosis in M OLT-4 cells. We have replicated all of these results using the vectors pSRHS and pSRHS Delta 147, which express wild-type gp160 and truncate d gp160, respectively, in the absence of other viral proteins. These i nvestigations provide a mechanism by which HIV-1 may induce apoptosis and a possible intracellular target for future therapeutics.