Actin integrity is indispensable for CD95/Fas-induced apoptosis of HIV-specific CD8+ T cells

We have recently provided data suggesting a potential role for mitochondria and Bcl-2-family molecules in apoptosis sensitivity of HIV-specific CD8+ T cells. Here, we report on the role of filamentous (F) actin in this process. Disruption of actin by cytochalasin D (cytD) or lantrunculin A remarkably reduced CD95/Fas-induced apoptosis of HIV-specific CD8+ T cells while their spontaneous apoptosis was unaffected. This inhibition cannot be attributed to changes of CD95/Fas distribution or levels in these cells. Furthermore, cytD treatment reduced CD95/Fas-induced apoptosis of CD8+ T cells from HIV+ patients independently of their differentiation status. CD95/Fas-induced apoptosis of both CD38+ and CD38- HIV-specific CD8+ T cells was inhibited by cytD treatment indicating that actin mediates this apoptotic process independently of the activation level of these cells. CytD was found to reduce the activation of caspase-8 induced by short treatment of purified CD8+ T cells from HIV+ patients with anti-CD95/Fas. Our data reveal actin as a critical mediator of HIV-specific CD8+ T cell apoptosis; further analysis of the molecular mechanisms governing this process may potentially contribute to design new therapies targeting the enhancement of the immune system in HIV infection.