Apoptosis induction by interleukin-2-activated cytotoxic lymphocytes in a squamous cell carcinoma cell line and Daudi cells - involvement of reactive oxygen species-dependent cytochrome c and reactive oxygen species-independent apoptosis-inducing factors.

Investigation of the induction of apoptosis by cytotoxic lymphocytes has mainly focused on the signalling associated with Fas and its adaptor proteins. The signal pathway via mitochondria, however, has not been sufficiently elucidated in cytotoxic lymphocyte-induced apoptosis. We examined the release of mitochondrial proapoptotic factors by lymphokine-activated killer (LAK) cells in two cell lines. LAK cell-induced DNA fragmentation of the target cells was suppressed to approximately 50% of control levels by the addition of neutralizing monoclonal antibody to Fas and a granzyme B inhibitor. When intracellular reactive oxygen species (ROS) were scavenged, the LAK cell-induced DNA fragmentation was decreased to approximately 60% of the non-treated cell level. Co-cultivation of Daudi cells with LAK cells increased cytosolic and mitochondrial ROS levels. Activation of procaspase-3 and apoptosis by treatment of oral squamous cell carcinoma cells (OSC) with LAK cells was partially inhibited by pretreatment of OSC cells with ROS scavengers and mitochondrial complex inhibitors. Furthermore, cytochrome c and apoptosis-inducing factor (AIF) were released from mitochondria by OSC cell treatment with supernatants of LAK cells. The supernatant-induced cytochrome c release was suppressed by mitochondrial complex inhibitors, but the inhibitors did not inhibit the release of AIF. These results indicate that LAK cells induce target cell apoptosis via not only the Fas/Fas ligand system and granzyme B, but also ROS-dependent cytochrome c and ROS-independent AIF release.