Pituitary adenylate cyclase-activating polypeptide (PACAP)/PAC1HOP1 receptor activation coordinates multiple neurotrophic signaling pathways: Akt activation through phosphatidylinositol 3-kinase gamma and vesicle endocytosis for neuronal survival.
MAPK and Akt pathways are predominant mediators of trophic signaling for many neuronal systems. Among the vasoactive intestinal peptide/secretin/glucagon family of related peptides, pituitary adenylate cyclase-activating polypeptide (PACAP) binding to specific PAC(1) receptor isoforms can engage multiple signaling pathways and promote neuroprotection through mechanisms that are not well understood. Using a primary sympathetic neuronal system, the current studies demonstrate that PACAP activation of PAC(1)HOP1 receptors engages both MAPK and Akt neurotrophic pathways in an integrated program to facilitate neuronal survival after growth factor withdrawal. PACAP not only stimulated prosurvival ERK1/2 and ERK5 activation but also abrogated SAPK/JNK and p38 MAPK signaling in parallel. In contrast to the potent and rapid effects of PACAP in ERK1/2 phosphorylation, PACAP stimulated Akt phosphorylation in a late phase of PAC(1)HOP1 receptor signaling. From inhibitor and immunoprecipitation analyses, the PACAP/PAC(1)HOP1 receptor-mediated Akt responses did not represent transactivation mechanisms but appeared to depend on G alpha(q)/phosphatidylinositol 3-kinase gamma activity and vesicular internalization pathways. Phosphatidylinositol 3-kinase gamma-selective inhibitors blocked PACAP-stimulated Akt phosphorylation in primary neuronal cultures and in PAC(1)HOP1-overexpressing cell lines; RNA interference-mediated knockdown of the receptor effectors attenuated PACAP-mediated Akt activation. Similarly, perturbation of endocytic pathways also blocked Akt phosphorylation. Between ERK and Akt pathways, PACAP-stimulated Akt signaling was the primary cascade that attenuated cultured neuron apoptosis after growth factor withdrawal. The partitioning of PACAP-mediated Akt signaling in endosomes may be a key mechanism contributing to the high spatial and temporal specificity in signal transduction necessary for survival pathways.
May
Victor
V
Departments of Anatomy and Neurobiology and of Pharmacology, The University of Vermont College of Medicine, Burlington, Vermont 05405. Electronic address: victor.may@uvm.edu.
Lutz
Eve
E
University of Strathclyde, Strathclyde Institute of Pharmacy and Biomedical Sciences, Royal College, 204 George Street, Glasgow G1 1XW, Scotland, United Kingdom.
MacKenzie
Christopher
C
University of Strathclyde, Strathclyde Institute of Pharmacy and Biomedical Sciences, Royal College, 204 George Street, Glasgow G1 1XW, Scotland, United Kingdom.
Schutz
Kristin C
KC
Departments of Anatomy and Neurobiology and of Pharmacology, The University of Vermont College of Medicine, Burlington, Vermont 05405.
Dozark
Kate
K
Departments of Anatomy and Neurobiology and of Pharmacology, The University of Vermont College of Medicine, Burlington, Vermont 05405.
Braas
Karen M
KM
Departments of Anatomy and Neurobiology and of Pharmacology, The University of Vermont College of Medicine, Burlington, Vermont 05405.
D000818:Animals; D002470:Cell Survival; D058544:Class Ib Phosphatidylinositol 3-Kinase; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism; D005260:Female; D007527:Isoenzymes / Q000378:metabolism; D009474:Neurons / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide / Q000378:metabolism*; D020033:Protein Isoforms; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D051237:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I / Q000378:metabolism*; D015398:Signal Transduction; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D007527:Isoenzymes; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D020033:Protein Isoforms; D051237:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I; D019869:Phosphatidylinositol 3-Kinases; D058544:Class Ib Phosphatidylinositol 3-Kinase; D051057:Proto-Oncogene Proteins c-akt; D048051:p38 Mitogen-Activated Protein Kinases