The role of specific receptor domains in signal transduction by the VIP2 receptor

Receptors for the neuropeptides VIP and P ACAP belong to a novel sub-family of G protein-coupled receptors, the secretin/ calcitonin/ parathyroid hormone receptor family. The rat VIP2 receptor was recently cloned in this laboratory and the present project was carried out to characterise the signalling mechanisms used by this receptor and define the role of crucial receptor domains. These studies have primarily involved the transient expression of receptors in host cells. The results demonstrated for the first time that both the VIP1 and VIP2 receptors can stimulate phospholipase C (PLC) in addition to adenylate cyclase (AC) and that this stimulation occurs by a pertussis toxin(PTx)-sensitive mechanism. Correspondingly, GTP,.S modulation of ligand-binding to the VIP2 receptor in COS 7 cell membranes was shown to be partially PTx-sensitive, suggesting an interaction of the receptor with a PTx-sensitive G protein. An epitope-tagged human VIP2 receptor was expressed in COS 7 cells and imrnunoprecipitated with its associated G proteins for Western-blotting studies. Immunoreactivity for Gaq, Ga5 and a member of the G<Xif o/ t/ z family, other than Gan or G