Diacylglycerol kinase α regulates the secretion of lethal exosomes bearing Fas ligand during activation-induced cell death of T lymphocytes

Fas ligand ( FasL) mediates both apoptotic and inflammatory responses in the immune system. FasL function critically depends on the different forms of FasL; soluble Fas ligand lacking the transmembrane and cytoplasmic domains is a poor mediator of apoptosis, whereas full-length, membrane-associated FasL ( mFasL) is pro-apoptotic. mFasL can be released from T lymphocytes, via the secretion of mFasL-bearing exosomes. mFasL in exosomes retains its activity in triggering Fas-dependent apoptosis, providing an alternative mechanism of cell death that does not necessarily imply cell-to-cell contact. Diacylglycerol kinase alpha ( DGK alpha), a diacylglycerol ( DAG)-consuming enzyme, is involved in the attenuation of DAG-derived responses initiated at the plasma membrane that lead to T lymphocyte activation. Here we studied the role of DGK alpha on activation-induced cell death on a T cell line and primary T lymphoblasts. The inhibition of DGK alpha increases the secretion of lethal exosomes bearing mFas ligand and subsequent apoptosis. On the contrary, the overactivation of the DGK alpha pathway inhibits exosome secretion and subsequent apoptosis. DGK alpha was found associated with the trans-Golgi network and late endosomal compartments. Our results support the hypothesis that the DGK alpha effect on apoptosis occurs via the regulation of the release of lethal exosomes by the exocytic pathway, and point out that the spatial orchestration of the different pools of DAG ( plasma membrane and Golgi membranes) by DGK alpha is crucial for the control of cell activation and also for the regulation of the secretion of lethal exosomes, which in turn controls cell death.