Abstract
Cyclic AMP potentiates glucose-stimulated insulin release and mediates the stimulatory effects of hormones such as glucagon-like peptide 1 (GLP-1) on pancreatic beta-cells. By inhibition of cAMP-degrading phosphodiesterase (PDE) and, in particular, selective inhibition of PDE3 activity, stimulatory effects on insulin secretion have been observed. Molecular and functional information on beta-cell PDE3 is, however, scarce. To provide such information, we have studied the specific effects of the PDE3B isoform by adenovirus-mediated overexpression. In rat islets and rat insulinoma cells, approximate 10-fold overexpression of PDE3B was accompanied by a 6-8-fold increase in membrane-associated PDE3B activity. The cAMP concentration was significantly lowered in transduced cells (INS-1(832/13)), and insulin secretion in response to stimulation with high glucose (11.1 mm) was reduced by 40% (islets) and 50% (INS-1). Further, the ability of GLP-1 (100 nm) to augment glucose-stimulated insulin secretion was inhibited by approximately 30% (islets) and 70% (INS-1). Accordingly, when stimulating with cAMP, a substantial decrease (65%) in exocytotic capacity was demonstrated in patch-clamped single beta-cells. In untransduced insulinoma cells, application of the PDE3-selective inhibitor OPC3911 (10 microm) was shown to increase glucose-stimulated insulin release as well as cAMP-enhanced exocytosis. The findings suggest a significant role of PDE3B as an important regulator of insulin secretory processes.
Highlights
Cyclic AMP potentiates glucose-stimulated insulin release and mediates the stimulatory effects of hormones such as glucagon-like peptide 1 (GLP-1) on pancreatic -cells
By employing reverse transcriptase-PCR using total RNA isolated from rat islets and INS-1 cells, the presence of mRNA encoding PDE3A is demonstrated in islets, whereas it is absent in the INS-1 cells (Fig. 1C)
Because GLP-1 is a promising candidate for treatment of type 2 diabetes [3], we found it relevant to assess whether PDE3B is involved in the regulation of cAMP elevated by this hormone
Summary
Vol 277, No 40, Issue of October 4, pp. 37446 –37455, 2002 Printed in U.S.A. Important Role of Phosphodiesterase 3B for the Stimulatory Action of cAMP on Pancreatic -Cell Exocytosis and Release of Insulin*. Cyclic AMP potentiates glucose-stimulated insulin release and mediates the stimulatory effects of hormones such as glucagon-like peptide 1 (GLP-1) on pancreatic -cells. Molecular and functional information on -cell PDE3 is, scarce To provide such information, we have studied the specific effects of the PDE3B isoform by adenovirus-mediated overexpression. Treatment with adenylyl cyclase activators, e.g. forskolin, results in a potentiation of glucose-induced insulin release [1], as does stimulation with hormones and neurotransmitters known to act as stimulatory G-protein agonists [2]. The enhancing effect of general inhibitors of PDE, such as isobutylmethylxanthine, on glucosestimulated insulin release has been known for decades [10] and has contributed to the concept that cAMP and/or cGMP are functionally important in -cells. Using the patch-clamp technique, we were able to demonstrate a substantial decrease in cAMP-potentiated exocytosis in single -cells overexpressing PDE3B
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