Direct cAMP signaling through G-protein-coupled receptors mediates growth cone attraction induced by pituitary adenylate cyclase-activating polypeptide.
Developing axons are guided to their appropriate targets by environmental cues through the activation of specific receptors and intracellular signaling pathways. Here we report that gradients of pituitary adenylate cyclase-activating polypeptide (PACAP), a neuropeptide widely expressed in the developing nervous system, induce marked attraction of Xenopus growth cones in vitro. PACAP exerted its chemoattractive effects through PAC1, a PACAP-selective G-protein-coupled receptor (GPRC) expressed at the growth cone. Furthermore, the attraction depended on localized cAMP signaling because it was completely blocked either by global elevation of intracellular cAMP levels using forskolin or by inhibition of protein kinase A using specific inhibitors. Moreover, local direct elevation of intracellular cAMP by focal photolysis of caged cAMP compounds was sufficient to induce growth cone attraction. On the other hand, blockade of Ca2+, phospholipase C, or phosphatidyl inositol-3 kinase signaling pathways did not affect PACAP-induced growth cone attraction. Finally, PACAP-induced attraction also involved the Rho family of small GTPases and required local protein synthesis. Taken together, our results establish cAMP signaling as an independent pathway capable of mediating growth cone attraction induced by a physiologically relevant peptide acting through GPCRs. Such a direct cAMP pathway could potentially operate in other guidance systems for the accurate wiring of the nervous system.
Guirland
Carmine
C
Department of Neuroscience and Cell Biology, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway, New Jersey 08852, USA.
Buck
Kenneth B
KB
Gibney
Jean A
JA
DiCicco-Bloom
Emanuel
E
Zheng
James Q
JQ
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes; D019204:GTP-Binding Proteins / Q000378:metabolism; D020439:Growth Cones / Q000187:drug effects / Q000502:physiology*; D009479:Neuropeptides / Q000494:pharmacology*; D018377:Neurotransmitter Agents / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000378:metabolism; D051236:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide; D051237:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I; D011979:Receptors, Pituitary Hormone / Q000378:metabolism*; D015290:Second Messenger Systems / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013116:Spinal Cord / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism; D014981:Xenopus; D029867:Xenopus Proteins; D020741:rho GTP-Binding Proteins / Q000378:metabolism
D002118:Calcium; D000242:Cyclic AMP; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D019204:GTP-Binding Proteins; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D011500:Protein Synthesis Inhibitors; D011956:Receptors, Cell Surface; D051236:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide; D051237:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I; D011979:Receptors, Pituitary Hormone; D010738:Type C Phospholipases; D029867:Xenopus Proteins; D020741:rho GTP-Binding Proteins; C495404:ADCYAP1 protein, Xenopus