Brief Comment : Stable Expression of Human Immunodeficiency Virus Type 1 Nef Confers Resistance against Fas-Mediated Apoptosis

Abstract

To investigate the effect of Nef on Fas-mediated apoptosis, we compared T cells, both population and subclones stably expressing Nef from HIV-1_NL432, with Nef^- control cells. Fas-mediated apoptosis was significantly delayed in Nef⁺ cells as determined by annexin V staining and the percentage of apoptotic cells was lower in all Nef-expressing cells than in the control cells by a maximum of 10-fold. Next we measured cell surface levels of Fas to test whether the delayed apoptosis in Nef⁺ cells was due to reduced cell surface expression of Fas. We found that there was no significant difference in the surface level of Fas between the Nef⁺ and Nef^- cells. To further define the steps affected by Nef in the Fas signaling pathway, the activation of caspase-3 and caspase-8 was investigated. A reasonable correlation was found between the magnitude of apoptosis measured by annexin V staining and the enzymatic activity of caspase-3. The overall level of caspase-8 activity in Nef⁺ cells was also lower than in Nef^- cells, although the extent of inhibition was not as significant as seen for caspase-3. Overall, our results indicate that long-term stable expression of Nef, which mimicks persistent or latent infection in vivo, confers resistance against anti-Fas Ab-induced apoptosis through inhibition of caspase-3 and caspase-8 activation.