Exchange Protein Directly Activated by Cyclic AMP Isoform 2 Is Not a Direct Target of Sulfonylurea Drugs

It has been reported by Zhang et al. that antidiabetic sulfonylurea drugs promote insulin secretion by directly binding to exchange protein directly activated by cyclic AMP isoform 2 (Epac2) and activating its down-stream effector Rap1. However, a critical link for an unambiguous validation of a direct interaction between Epac2 and sulfonylurea using purified individual components is missing. Our in vitro analyses using purified full-length Epac2 and Rap1 suggest that sulfonylureas are not able to directly bind to Epac2, nor are they capable of triggering Epac2-dependent Rap1 activation.