24p3 is a secreted protein that induces apoptosis in leukocytes. Recently, 24p3 has been shown to bind to iron-containing bacterial siderophores. In this issue of Cell, Devireddy et al. (2005) identify a receptor that internalizes 24p3. Internalization of iron bound to 24p3 prevents apoptosis. In contrast, internalization of the apo form of 24p3 that does not contain iron leads to cellular iron efflux and apoptosis via the proapoptotic protein Bim.
