Pituitary Adenylate Cyclase-activating Polypeptide (PACAP)/PAC₁HOP1 Receptor Activation Coordinates Multiple Neurotrophic Signaling Pathways: Akt ACTIVATION THROUGH PHOSPHATIDYLINOSITOL 3-KINASE γ AND VESICLE ENDOCYTOSIS FOR NEURONAL SURVIVAL

• Published in: The Journal of biological chemistry Vol. 285; no. 13; pp. 9749 - 9761
• Main Authors: May, Victor, Lutz, Eve, MacKenzie, Christopher, Schutz, Kristin C, Dozark, Kate, Braas, Karen M
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 26.03.2010
• Subjects: Animals; Cell Survival; Class Ib Phosphatidylinositol 3-Kinase; Endocytosis; Endosomes - metabolism; Female; Isoenzymes - metabolism; Neurobiology; Neurons - metabolism; p38 Mitogen-Activated Protein Kinases - metabolism; Phosphatidylinositol 3-Kinases - metabolism; Phosphorylation; Pituitary Adenylate Cyclase-Activating Polypeptide - metabolism; Protein Isoforms; Proto-Oncogene Proteins c-akt - metabolism; Rats; Rats, Sprague-Dawley; Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I - metabolism; Signal Transduction
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M109.043117

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 PAC₁ 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 PAC₁HOP1 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 PAC₁HOP1 receptor signaling. From inhibitor and immunoprecipitation analyses, the PACAP/PAC₁HOP1 receptor-mediated Akt responses did not represent transactivation mechanisms but appeared to depend on Gαq/phosphatidylinositol 3-kinase γ activity and vesicular internalization pathways. Phosphatidylinositol 3-kinase γ-selective inhibitors blocked PACAP-stimulated Akt phosphorylation in primary neuronal cultures and in PAC₁HOP1-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.