Abstract

A distinct group of receptors including DCC, UNC5, RET and Ptc1 is known to function in ligand‐dependent neuronal growth and differentiation or axon guidance. Acting as “dependence receptors”, they may also regulate neuronal cell survival by inducing apoptosis in the absence of cognate ligand. Receptor‐initiated apoptosis requires proteolytic (caspase) cleavage and exposure of a pro‐apoptotic region in the cytoplasmic domains of the receptors. In contrast, classical apoptosis induced by growth factor or cytokine deprivation involves loss of survival signaling without receptor cleavage. DCC, UNC5, RET and Ptc1 are downregulated or mutated in diverse cancers, and show properties characteristic of tumor suppressors, consistent with their ability to promote neuronal cell death. Dysfunctional dependence receptors have been linked to the loss of specific neurons in certain inherited and neurodegenerative diseases. Dependence receptor‐initiated apoptosis represents a novel paradigm for the controlled removal of specific cells during neural development and elimination of malignant cells that have strayed beyond regions of ligand availability. BioEssays 26:656–664, 2004. © 2004 Wiley Periodicals, Inc.