A new role of diacylglycerol kinase alpha on the secretion of lethal exosomes bearing Fas ligand during activation-induced cell death of T lymphocytes.

Exosomes are small membrane vesicles that intracellularly accumulate into late or multivesicular endosomes (multivesicular bodies, MVB). Exosomes have a particular lipid and protein content, reflecting their origin as intraluminal vesicles of late endosomes. The stimulation of several hematopoietic cells induces the fusion of the limiting membrane of the MVB with the plasma membrane, leading to the release of exosomes towards the extracellular environment. In T lymphocytes, stimulation of the T cell receptor (TCR) induces the fusion of the MVBs with the plasma membrane and exosomes carrying several bio-active proteins are secreted. Among these proteins, the pro-apoptotic protein Fas ligand (FasL) is released as a non-proteolysed form (mFasL), associated to the exosomes. These mFasL-bearing exosomes may trigger the apoptosis of T lymphocytes. Here, we present evidences supporting a role of diacylglycerol kinase alpha (DGKalpha), a diacylglycerol (DAG)-consuming enzyme, on the secretion of exosomes carrying mFasL, and the subsequent activation-induced cell death (AICD) on a T cell line and primary T lymphoblasts.