Departments of Anatomy and Neurobiology and of Pharmacology, The University of Vermont College of Medicine, Burlington, Vermont 05405.
University of Strathclyde, Strathclyde Institute of Pharmacy and Biomedical Sciences, Royal College, 204 George Street, Glasgow G1 1XW, Scotland, United Kingdom.
J Biol Chem. 2010 Mar 26;285(13):9749-9761. doi: 10.1074/jbc.M109.043117. Epub 2010 Jan 21.
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.
MAPK 和 Akt 通路是许多神经元系统营养信号的主要介质。在血管活性肠肽/分泌素/胰高血糖素相关肽家族中，垂体腺苷酸环化酶激活肽（PACAP）与特定的 PAC(1)受体亚型结合，可以通过尚未完全了解的机制，参与多种信号通路并促进神经保护。使用原代交感神经元系统，目前的研究表明，PACAP 激活 PAC(1)HOP1 受体，通过一个整合的程序，在生长因子撤出后促进神经元存活，从而参与 MAPK 和 Akt 神经营养途径。PACAP 不仅刺激生存 ERK1/2 和 ERK5 的激活，而且还平行地废除 SAPK/JNK 和 p38 MAPK 信号。与 PACAP 在 ERK1/2 磷酸化中的强大和快速作用相反，PACAP 刺激 PAC(1)HOP1 受体信号晚期的 Akt 磷酸化。从抑制剂和免疫沉淀分析来看，PACAP/PAC(1)HOP1 受体介导的 Akt 反应不代表转激活机制，而是似乎依赖于 G alpha(q)/磷酸肌醇 3-激酶γ活性和囊泡内化途径。磷酸肌醇 3-激酶γ选择性抑制剂阻断了原代神经元培养物和 PAC(1)HOP1 过表达细胞系中 PACAP 刺激的 Akt 磷酸化；受体效应器的 RNA 干扰介导的敲低减弱了 PACAP 介导的 Akt 激活。同样，内吞途径的干扰也阻断了 Akt 磷酸化。在 ERK 和 Akt 通路之间，PACAP 刺激的 Akt 信号是在生长因子撤出后减轻培养神经元凋亡的主要级联。PACAP 介导的 Akt 信号在内涵体中的分区可能是导致生存途径所需的信号转导高时空特异性的关键机制。
