Actin dependent CD95 internalization is specific for Type I cells.

CD95 Type I and Type II cells differ in the requirement for mitochondrial contribution to the execution of apoptosis. Mitochondria are required to amplify the apoptosis signal only in Type II cells. Here we show that CD95 internalizes in an actin dependent manner only in Type I cells and that the two CD95 apoptosis cell types differ in their threshold of active caspase-8 required to execute apoptosis. The data suggest that CD95 is linked to the cytoskeleton in different ways in the two cell types and that they have adapted to different levels of active caspase-8 generated at the activated receptor.