Calcium-Mobilizing Insulin Secretagogues Stimulate Transcription That Is Directed by the Cyclic Adenosine 3′,5′-Monophosphate/Calcium Response Element in a Pancreatic Islet β-Cell Line

In pancreatic β-cells, calcium is required for insulin secretion, but can also stimulate gene transcription. High potassium-induced membrane depolarization and calcium influx have previously been shown to activate kinases that phosphorylate and thereby activate the transcription factor cAMP response element (CRE)-binding protein (CREB) binding to CREs. It is unknown, however, whether hormones and neurotransmitters can activate this mechanism. Arginine vasopressin (AVP), bombesin, and acetylcholine potentiate glucose-induced insulin secretion and are known to raise cytosolic calcium levels through binding to cell surface receptors that activate phospholipase C. The effect of AVP on CRE-directed transcription was examined in the β-cell line HIT. AVP (0.1-100 nM) stimulated gene transcription after transient transfection of a reporter gene that was placed under the transcriptional control of a CRE. This effect was inhibited by a vasopressin V₁ receptor antagonist and depended on calcium influx and calcineurin phosphatase activity. By immunoblots with antiphospho-CREB antibodies and by using a Ga14-CREB fusion protein, it was shown that AVP induces the phosphorylation and activation of CREB. Like AVP, bombesin (100 nM) and the muscarinic agonist carbachol (200 μM) stimulated CRE-mediated transcription. These results show that calcium-mobilizing insulin secretagogues can activate CREB/CRE-directed transcription in HIT cells, offering a mechanism by which these secretagogues could produce long term effects on β-cell function, changing the pattern of gene expression.