The function of AKAP-dependent protein-protein interactions in the regulation of vasopressin-mediated water reabsorption and cardiac myocyte contractility

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A-kinase anchoring proteins (AKAPs) comprise a family of scaffolding proteins that target protein kinase A (PKA) and other signaling proteins to cellular compartments and thereby confine the activities of the associated proteins to defined regions within cells. The arginine-vasopressin (AVP)-induced redistribution of aquaporin-2 (AQP2) from intracellular vesicles into the plasma membrane of renal principal cells constitutes the molecular basis of AVP-mediated water reabsorption. The process depends on interactions of AKAPs with PKA. AKAP-dependent protein-protein interactions also facilitate ß-adrenoceptor-induced increases in cardiac myocyte contractility. Dysregulation of these processes is associated with diseases, including nephrogenic diabetes insipidus and chronic heart failure. We have identified direct interactions of AKAP18δ with PKA, phosphodiesterase (PDE)4D3 and phospholamban (PLB) and have shown that they play key roles in the regulation of AVP-mediated water reabsorption and ß-adrenoceptor-induced increases in cardiac myocyte contractility. In addition, we have identified other new AKAP18δ interacting proteins, and discovered small molecules disrupting AKAP-PKA interactions. By using these molecules we have revealed a negative feedback loop which depends on AKAP-PKA interactions and terminates ß-adrenoceptor-induced cAMP synthesis in cardiac myocytes. However, the molecular details underlying AKAP-based compartmentalized signaling which controls AVP-mediated water reabsorption and cardiac myocyte contractility are largely unknown. The aim of the proposed project is to gain mechanistic insight into the molecular mechanisms controlling AVP-mediated water reabsorption and cardiac myocyte contractility. To achieve this goal, we will define the functions of the new AKAP18δ protein interactions, and we will identify and characterize the roles of new AKAPs and their interactions in the two processes. In addition, we aim to elucidate the molecular mechanisms underlying the negative feedback regulation limiting ß-adrenoceptor-induced cAMP synthesis in cardiac myocytes. An important goal of the project is to define the functions of the new AKAP-dependent protein-protein interactions by pharmacological interference with already available and novel small molecules. Chemical compounds modulating AKAP functions and altering compartmentalized cellular signaling may open new avenues for the treatment of diseases (e.g. renal diseases and chronic heart failure).