Apoptosis and Dependence Receptors: A Molecular Basis for Cellular Addiction

The Buck Institute for Age Research, Novato, and University of California, San Francisco, San Francisco, California; and Centre Genetique Moleculaire et Cellulaire, Equipe Labellisée "La Ligue," Centre National de la Recherche Scientifique UMR5534, University of Lyon, and the International Agency For Research in Cancer, Lyon, France Bredesen, Dale E., Patrick Mehlen, and Shahrooz Rabizadeh. Apoptosis and Dependence Receptors: A Molecular Basis for Cellular Addiction. Physiol Rev 84: 411–430, 2004; 10.1152/physrev.00027.2003.—Classical signal transduction is initiated by ligand-receptor interactions. We have described an alternative form of signal transduction that is initiated by the withdrawal of ligands from specific receptors referred to as dependence receptors. This process is widespread, featuring in developmental cell death, carcinogenesis (especially metastasis), neurodegeneration, and possibly subapoptotic events such as neurite retraction and somal atrophy. Initial mechanistic studies of dependence receptors suggest that these receptors form complexes that include specific caspases. Complex formation appears to be a function of ligand-receptor interaction, and dependence receptors appear to exist in at least two conformational states. Complex formation in the absence of ligand leads to caspase activation by a mechanism that in at least some cases is dependent on caspase cleavage of the receptor itself, releasing proapoptotic peptides. Thus these receptors may serve in caspase amplification, and in so doing create cellular states of dependence on their respective ligands. Address for reprint requests and other correspondence: D. E. Bredesen, The Buck Institute for Age Research, 8001 Redwood Blvd., Novato, CA 94945 (E-mail: dbredesen{at}buckinstitute.org ).