Characterization of the mouse sulfonylurea receptor 1 promoter and its regulation

The ATP-sensitive potassium channels (K-ATP(+) channels) are heteromultimer ic structures formed by a member of the sulfonylurea receptor (SUR) family and a member of the inwardly rectifying potassium channel family (Kir6.x), The K+,, channels play an essential role in nutrient-induced insulin secret ion from the pancreatic beta-cell, We have cloned and characterized the pro moter region of the mouse SUR1 gene, and have shown that it lacks CAAT and TATA boxes or an initiator element. Studies of transcription initiation in several tissues showed that there is a common SUR1 promoter in brain, heart , and pancreas and in the pancreatic beta-cell line, PTC3, The SUR1 gene us es multiple transcription start sites with the major site located 54 base p airs 5'-upstream of the translation initiation site. Transient transfection experiments in pancreatic p-cell lines showed that the proximal promoter f ragment -84/+54 is sufficient for significant transcriptional activity. The proximal promoter region contains multiple SP1-binding sites, and cotransf ection experiments of the SUR1 promoter-luciferase vector with SP1 expressi on Vector in Drosophila SL2 cells demonstrated a stimulatory effect of SP1 on SUR1 transcriptional activity. The mobility shift assays confirmed the i nteraction of the SP1 transcription factor with the proximal promoter regio n of the SUR1 gene. Together, these results indicate that SP1 may mediate t ranscription initiation of the SUR1 gene. In addition, we have described th e coordinate regulation of the gene expression of both K-ATP(+),, channel s ubunits by glucocorticoids. SUR1 and Kir6,2 mRNA levels are down-regulated by similar to 40-50% in response to glucocorticoid treatment. Interestingly , the extent of the inhibitory effect as well as the kinetics and sensitivi ty are very similar for both mRNAs, Studies of mRNA turnover demonstrate th at glucocorticoids most likely decrease the transcriptional activity of bot h SUR1 and Kir6,2 genes since glucocorticoids failed to affect the stabilit y of each mRNA, Likewise, the reduction in mRNA levels was correlated with a decrease in SUR1 and Kir6,2 protein levels.