Novel Regulation of Adenylyl Cyclases by Direct Protein-Protein Interactions: Insights from Snapin and Ric8a

Adenosine 3',5'-cyclic mononucleotide (cAMP) is one of the most important second messengers which govern cellular signal transductions. Adenylyl cyclases (ACs), which are cAMP-synthesizing enzymes, are responsible for cAMP production during extracellular stimulation or intracellular metabolic alteration. In mammals, 9 transmembrane ACs and 1 soluble AC have been identified and characterized. In the past 2 decades, the biochemical properties of these ACs have been extensively studied. Genetic knockout and transgenic overexpression mouse models of at least 6 ACs have been produced, revealing their specific in vivo functions. An awareness of the importance of microdomains and cellular compartmentation for selective AC regulation has also been fostered. Most intriguingly, a handful of novel AC-binding proteins have recently been reported. Selective binding of ACs to their binding partners allows the precise compartmentalization of ACs and permits unique regulation. Based on recent studies on AC-interacting proteins (particularly Snapin and Ric8a), this review focuses on the importance and possible involvement of AC-interacting proteins in (1) the association of the cAMP signaling pathway with various cellular machineries and (2) the coordination of tightly regulated cAMP signaling by other signaling molecules.