Somatostatin (SRIF) is the major physiological inhibitor of growth hormone, insulin and glucagon release and therefore is an important regulator of human development, growth and metabolism. It aso controls neuronal activity in brain and is involved in the regulation of motor activity and cognition in rodents and humans. Alterations in SRIF transmission occur in Alzheimer's disease and may contribute to the pathophysiology of this neuropsychiatric disorder. SRIF induces its biological actions by interacting with membrane bound receptors which are coupled to second messenger systems and ion channels via G proteins. The objective of this proposal is to characterize the physical properties of the SRIF receptor in order to better understand the biochemical and cellular basis of action of this important neuropeptide. Our studies in the past granting period showed that carbohydrates in the receptor were essential for agonist binding, that the protein kinase BARK could induce the desensitization of the receptor in vitro and that the SRIF receptor selectively couples to the G proteins Gia1, Gia3 and Goa. Based on these results, we will focus our investigations on 3 major physical aspects of the SRIF receptor. We will identify the mechanism by which carbohydrates in the receptor influence high affinity agonist binding; the importance of SRIF receptor phosphorylation in causing SRIF desensitization and the nature of the interaction of SRIF receptors with G proteins which link the receptor to cellular effector systems. In addition, we will continue our efforts to clone SRIF receptor cDNA. using our recently developed antibody against the SRIF receptor, to reveal the primary structure of the SRIF receptor. This will allow us to identify specific regions and amino acid sequences in the receptor involved in its functional activity and will also allow us to investigate the basis for the structural diversity of SRIF receptor subtypes. These studies will provide a better understanding of the molecular basis of action of SRIF which will be important in elucidating the physiological role of SRIF in the brain and will be critical for the development of new therapeutic agents for the treatment of neuropsychiatric disorders with altered SRIF transmission such as Alzheimer's disease.
