Antidiabetic Sulfonylureas and cAMP Cooperatively Activate Epac2A

Identification of the binding site of Epac2A for an antidiabetic drug may enable the development of improved therapies. Cooperation Between cAMP and Antidiabetic Drugs A class of drugs called sulfonylureas increase insulin secretion from pancreatic β cells in patients with type 2 diabetes. One sulfonylurea mechanism for enhancing insulin secretion is through stimulation of the guanine nucleotide exchange factor Epac2A. Takahashi et al. used molecular docking simulation to predict the sulfonylurea binding site on Epac2A and verified in cells with site-directed mutants that sulfonylureas bound to one of two cyclic nucleotide–binding domains and cooperated with the endogenous Epac activator cyclic adenosine monophosphate to promote Epac2A function and stimulate the Epac target Rap1. The identification of specific amino acids in Epac2A that mediate interactions with sulfonylureas could help to develop drugs for treating diabetes. Sulfonylureas are widely used drugs for treating insulin deficiency in patients with type 2 diabetes. Sulfonylureas bind to the regulatory subunit of the pancreatic β cell potassium channel that controls insulin secretion. Sulfonylureas also bind to and activate Epac2A, a member of the Epac family of cyclic adenosine monophosphate (cAMP)–binding proteins that promote insulin secretion through activation of the Ras-like guanosine triphosphatase Rap1. Using molecular docking simulation, we identified amino acid residues in one of two cyclic nucleotide–binding domains, cNBD-A, in Epac2A predicted to mediate the interaction with sulfonylureas. We confirmed the importance of the identified residues by site-directed mutagenesis and analysis of the response of the mutants to sulfonylureas using two assays: changes in fluorescence resonance energy transfer (FRET) of an Epac2A-FRET biosensor and direct sulfonylurea-binding experiments. These residues were also required for the sulfonylurea-dependent Rap1 activation by Epac2A. Binding of sulfonylureas to Epac2A depended on the concentration of cAMP and the structures of the drugs. Sulfonylureas and cAMP cooperatively activated Epac2A through binding to cNBD-A and cNBD-B, respectively. Our data suggest that sulfonylureas stabilize Epac2A in its open, active state and provide insight for the development of drugs that target Epac2A.

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