Abstract
The death receptor Fas/CD95 initiates apoptosis by engaging diverse cellular organelles including endosomes. The link between Fas signaling and membrane traffic has remained unclear, in part because it may differ in diverse cell types. After a systematic investigation of all known pathways of endocytosis, we have clarified that Fas activation opens clathrin-independent portals in mature T cells. These portals drive rapid internalization of surface proteins such as CD59 and depend upon actin-regulating Rho GTPases, especially CDC42. Fas-enhanced membrane traffic invariably produces an accumulation of endocytic membranes around the Golgi apparatus, in which recycling endosomes concentrate. This peri-Golgi polarization has been documented by colocalization analysis of various membrane markers and applies also to active caspases associated with internalized receptor complexes. Hence, T lymphocytes show a diversion in the traffic of endocytic membranes after Fas stimulation that seems to resemble the polarization of membrane traffic after their activation.