Cyclic adenosine 3 ',5 '-monophosphate increases pancreatic glucokinase activity and gene expression

Comparison of the pancreatic and hepatic glucokinase gene transcripts revea ls tissue-specific control of expression and the existence of two distinct promoters in a single glucokinase gene. The existence of alternate promoter s suggests that separate factors regulate glucokinase transcription in the two tissues. Hepatic glucokinase expression has been shown to be repressed by cAMP; however, in the pancreatic p-cell it is unlikely that cAMP repress es glucokinase activity, as cAMP is known to positively affect glucose-indu ced insulin secretion, a process that in mature islets requires pancreatic glucokinase activity. In this work we demonstrate that cAMP indeed has a st imulatory effect on pancreatic glucokinase. The cyclic nucleotide stimulate s pancreatic glucokinase activity after 3-h incubation, and maximal effects are observed after 6 and 12 h of treatment, Using the bDNA assay, a sensit ive signal amplification technique, we detected relative increases in gluco kinase messenger RNA levels of 40.5 +/- 7.5% after 3-h incubation with cAMP . This stimulatory effect was increased to 106.3 +/- 22% after 6-h incubati on and sustained up to 12 h of incubation. Inhibition of gene transcription by actinomycin D abolishes cAMP-induced glucokinase activity. In transfect ed fetal islets, cAMP increased the activity of the - 1000 bp rat glucokina se promoter by 60 +/- 6%. These data demonstrate that cAMP has a stimulator y effect on pancreatic glucokinase gene expression and that the nucleotide has opposite effects on pancreatic and hepatic glucokinase, supporting the concept that glucokinase transcription in the liver and that in the p-cell differ.