mAKAP-orchestrated phosphorylation events: regulation of PDE4D3

描述(申请人提供)：cAMP是一种重要的第二信使，调节心脏的几个生理事件，包括收缩、新陈代谢和基因转录。最近的一些研究表明，磷酸二酯酶(PDE)不仅对心脏基础cAMP水平的控制具有重要意义，而且还由于PDE的细胞位置而调节cAMP的局部变化。因此，确定控制PDE定位和活性的分子决定因素，以及每个PDE所涉及的生物学过程，将有助于我们进一步了解心脏中的cAMP信号。我们之前已经描述了一种支架蛋白，它将磷酸二酯酶PDE4D3隔离到分化的心肌细胞的核膜上。A-激酶锚定蛋白mAKAP由cAMP依赖的蛋白激酶PDE4D3、Map Kinase ERK5、鸟嘌呤核苷酸交换因子EPAC、蛋白磷酸酶2A和Ryanodine受体组成的复合体。先前的数据表明，mAKAP协调了PDE4D3的ERK5和PKA调控。这些磷酸化诱导的PDE4D3活性变化将反过来调节复合体周围cAMP的浓度，最终调节复合体中的所有cAMP效应物，即PKA、PDE4D3和EPAC。这一建议的三个具体目的将试图1)阐明调节PDE4D3磷酸化的生理事件调节cAMP浓度和Ryanodine受体的磷酸化状态2)确定PDE4D3磷酸化对EPAC介导的ERK5活性和ERK5介导的心肌肥大的功能后果，以及3)确定调控PDE去磷酸化的复合体中的磷酸酶。心脏病是美国的头号死因。心脏肥大是心脏对持续增加的心输出量需求做出反应的主要代偿机制。最终，心肌肥厚会导致心脏病和心力衰竭的进展。然而，一些研究表明，抑制心肌肥厚可以降低死亡和进展为心力衰竭的风险。这项研究将进一步加深我们对心肌肥厚分子机制的理解，并有助于为药物设计寻找新的靶点，以帮助治疗肥厚。

DESCRIPTION (provided by applicant): cAMP is an important second messenger that regulates several physiological events in the heart including contraction, metabolism and gene transcription. Several recent studies have illustrated not only the importance of phosphodiesterases (PDE) for the control of basal cAMP levels in the heart, but also in the regulation of localized changes of cAMP due to the cellular location of PDEs. Therefore, identifying the molecular determinants governing PDE localization and activity, as well as the biological processes attributed to each PDE, will further our knowledge of cAMP signaling in the heart. We have previously described a scaffolding protein that sequesters the phosphodiesterase PDE4D3 to the nuclear envelope in differentiated cardiac myocytes. The A-Kinase Anchoring Protein mAKAP maintains a complex consisting of the cAMP-dependent protein kinase, PDE4D3, the Map Kinase ERK5, the guanine nucleotide exchange factor Epac, the protein phosphatase 2A, and the Ryanodine Receptor. Previous data has shown mAKAP orchestrated both ERK5 and PKA regulation of PDE4D3. These phosphorylation-induced changes in PDE4D3 activity will in turn modulate the concentration of cAMP surrounding the complex, ultimately regulating all cAMP effectors in the complex, namely PKA, PDE4D3 and Epac. The three Specific Aims of this proposal will try to 1) elucidate the physiological events that regulate PDE4D3 phosphorylation regulate cAMP concentration and the phosphorylation state of the Ryanodine Receptor 2) determine the functional consequence of PDE4D3 phosphorylation on Epac-mediated ERK5 activity and ERK5-mediated cardiac hypertrophy, and 3) identify the phosphatase in the complex that governs dephosphorylation of the PDE. Heart disease is the number one cause of death in the United States. Cardiac hypertrophy is the major compensatory mechanism by which the heart responds to a continued, increased demand for cardiac output. Ultimately, cardiac hypertrophy leads to progression into cardiac disease and to heart failure. However, several studies have shown that inhibition of cardiac hypertrophy lowers the risk of death and progression into heart failure. This study will further our understanding of the molecular mechanism of cardiac hypertrophy and help to identify novel targets for drug design to aid in the treatment of hypertrophy.