Pituitary Adenylate Cyclase-activating Polypeptide (PACAP)/PAC1HOP1 Receptor Activation Coordinates Multiple Neurotrophic Signaling Pathways

Abstract

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.

Role of transglutaminase 2 in PAC1 receptor mediated protection against hypoxia-induced cell death and neurite outgrowth in differentiating N2a neuroblastoma cells

“…The broad spectrum PKC inhibitor Ro 318220 inhibited PACAP-27-induced TG2 activity, indicating that Gq-protein coupling is involved in PAC1 receptor-mediated TG2 activation. The PAC1 receptor also activates ERK1/2, JNK1/2, p38 MAPK and PKB (Monaghan et al, 2008;May et al, 2010, Castorina et al, 2014. In this study we observed PACAP-27-induced activation of ERK1/2, JNK1/2, and PKB but not p38 MAPK.…”

“…Likewise, PACAP is widely recognized as a neuroprotective peptide and potential therapeutic agent for the treatment of cerebral ischaemia and various neurodegenerative disorders (Reglodi et al, 2011;Lee and Seo, 2014). The mechanisms of PACAP/PAC1 receptorinduced neuroprotection are complex and involve multiple signalling pathways that include PKA, PKB, ERK1/2, NF-кB and Ca 2+ mobilization (May et al, 2010;Baxter et al, 2011;Manecka et al, 2013). In this study we have shown for the first time a role for TG2 in PAC1 receptor-induced cytoprotection in differentiating mouse N2a and human SH-SY5Y neuroblastoma cells.…”

“…The PAC1 receptor is a member of the GPCR superfamily which activates adenylyl cyclase/cAMP/PKA (via Gsprotein coupling) and phospholipase C/DAG/PKC (via Gq-protein coupling) dependent signalling pathways (Dickson and Finlayson, 2009;Vaudry et al, 2009). The PAC1 receptor also triggers the activation of several other protein kinase cascades such as ERK1/2, JNK1/2, p38 MAPK and PKB (Monaghan et al, 2008;May et al, 2010, Castorina et al 2014. Since some of these protein kinase pathways are associated with modulation of TG activity (PKA, PKC and ERK1/2) it is conceivable that the PAC1 receptor regulates TG activity.…”

Pituitary Adenylate Cyclase-Activating Polypeptide Causes Tyrosine Phosphorylation of the Epidermal Growth Factor Receptor in Lung Cancer Cells

“…PACAP activation of PAC1 HOP1 caused ERK1/2 and ERK5 activation, but abrogated stress-activated protein/c-Jun NH 2 -terminal kinase and p38 mitogen-activated protein kinase signaling (May et al, 2010). PACAP caused ERK1/2 and ERK5 phosphorylation of primary sympathetic neurons within minutes and phosphorylation of AKT within hours (May et al, 2010).…”

“…PACAP activation of PAC1 HOP1 caused ERK1/2 and ERK5 activation, but abrogated stress-activated protein/c-Jun NH 2 -terminal kinase and p38 mitogen-activated protein kinase signaling (May et al, 2010). PACAP caused ERK1/2 and ERK5 phosphorylation of primary sympathetic neurons within minutes and phosphorylation of AKT within hours (May et al, 2010). We are investigating whether PACAP causes AKT phosphorylation in NSCLC cells, but we recently found that PACAP causes focal adhesion kinase and paxillin tyrosine phosphorylation within minutes after the addition to NCI-H838 cells (Moody et al, 2012).…”