24p3 and its receptor: dawn of a new iron age?

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, a receptor that internalizes 24p3 is identified. 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.