Identification of a glucose response element in the promoter of the rat glucagon receptor gene

We cloned the 5' upstream region of the rat glucagon receptor gene, demonst rating that the 5' noncoding domain of the glucagon receptor mRNA contained two untranslated exons of 131 and 166 nucleotides (nt), respectively, sepa rated by two introns of 0.6 and 3.2 kilobase pairs. We also observed an alt ernative splicing involving the 166-base pair exon, Cloning of up to 2 kilo base pairs of the newly identified genomic domain and transfection of vario us constructs driving a reporter gene, in pancreatic islet cell line INS-I, uncovered a strong glucose regulation of the promoter activity of plasmids containing up to nucleotide -868, or more, upstream from the transcription al start point. This promoter activity displayed threshold-like behavior, w ith low activity of the promoter below 5 mM glucose, and maximal activation as of 10 mM glucose. This glucose regulation was mapped to a highly palind romic 19-nucleotide region between nt -545 and -527, Indeed, deletion or mu tation of this sequence abolished the glucose regulation. This domain conta ined two palindromic "E-boxes" CACGTG and CAGCTG separated by 3 nt, a featu re similar to the "L4 box" found in the pyruvate kinase L gene promoter. Th is is the first description of a G protein-coupled receptor gene promoter r egulated by glucose.