DIFFERENTIAL SIGNAL-TRANSDUCTION BY 5 SPLICE VARIANTS OF THE PACAP RECEPTOR

THE two forms of pituitary adenylyl cyclase-activating polypeptide (PA CAP-27 and -38) are neuropeptides of the secretin/glucagon/vasoactive intestinal polypeptide/growth-hormone-releasing hormone family and reg ulate hormone release from the pituitary and adrenal gland1-3. They ma y also be involved in spermatogenesis4, and PACAP-38 potently stimulat es neuritogenesis and survival of cultured rat sympathetic neuroblast5 ,6 and promotes neurite outgrowth of PC-12 cells7. The PACAP type-I re ceptor (found in hypothalamus, brain stem, pituitary, adrenal gland an d testes), specific for PACAP, is positively coupled to adenylyl cycla se and phospholipase C. The recently cloned type II receptor does not discriminate between PACAP and vasoactive intestinal polypeptide and i s coupled to only adenylyl cyclase8. Here we have used a new expressio n cloning strategy, based on the induction of a reporter gene by cycli c AMP, to isolate a complementary DNA encoding the type-I PACAP recept or. On transfection of this cDNA, both PACAP-27 and -38 stimulate aden ylyl cyclase with similar EC50 values (50% effective concentration, 0. 1-0.4 nM), whereas only PACAP-38 stimulates phospholipase C with high potency (EC50 = 15 nM). Four other splice variants were isolated with insertions at the C-terminal end of the third intracellular loop. Expr ession of these cDNAs revealed altered patterns of adenylyl cyclase an d phospholipase C stimulation, suggesting a novel mechanism for fine t uning of signal transduction.