Arrestin: roles in the life and death of retinal neurons.

G protein-coupled receptors are a large family of signaling molecules that respond to a wide variety of extracellular stimuli. The receptors relay the information encoded by the ligand through the activation of heterotrimeric G proteins and intracellular effector molecules. To ensure the appropriate regulation of the signaling cascade, it is vital to properly inactivate the receptor. This inactivation is achieved, in part, by the binding of a soluble protein, arrestin, which uncouples the receptor from the downstream G protein. In addition to the inactivation of G protein-coupled receptors, arrestins have also been implicated in the endocytosis of receptors and cross talk with other signaling pathways. Due to its central role in cellular signaling, misregulation or misfunction of arrestin can have dramatic affects on cell viability and have direct implications in human disease.