The sequence and orientation of the insert was checked by restriction enzyme digest, and subsequently a QIAGEN Plasmid Maxi Kit (QIAGEN, Manchester, UK) was used to purify transfection grade DNA. HEK293, MIN6 (44), 1.1B4 (41), and EndoC-βH1 (54) cells were transfected using Lipofectamine 2000 (Invitrogen, Paisley, UK) in 48-well plates using 250 ng of each reporter construct and 1 ng of Renilla control vector. Each condition was repeated in six separate wells. Dual-Luciferase Reporter Assay (Promega, Southampton, UK) was used to measure Luciferase normalized against Renilla. All experiments were done in triplicate. The following cloning primers were used: CCA ACA AAT AGT AAG CAT TAT TAC C (rs7163757, forward) and CAA ATA GTT GTA GAT ATG TGG CAT T (rs7163757, reverse).