Desensitization of islet cells to bombesin involves both receptor down- modulation and inhibition of receptor function

SL Swope and A Schonbrunn

Department of Pharmacology, Harvard Medical School, Boston, Massachusetts.

The neuropeptide bombesin has a powerful but transient stimulatory effect on insulin secretion in the pancreatic islet cell line HIT-T15. We have previously shown that pretreatment of HIT-T15 cells with a saturating concentration of bombesin (100 nM) for 1.5-2 hr abolishes their secretory response to a second challenge with peptide and decreases [125I-Tyr4]bombesin binding by over 90%. In this study we examined the mechanisms involved in desensitization to bombesin. To determine whether receptor modulation was responsible, we compared the effect of bombesin pretreatment on [125I-Tyr4]bombesin binding and on the ability of bombesin to stimulate insulin release. Both effects occurred very rapidly and were maximal by 10 min. Although pretreatment of cells for 90 min with a subsaturating concentration of bombesin did not affect either the ED50 for bombesin-stimulated secretion or the apparent Kd for bombesin binding, it decreased both the maximum secretory response to a subsequent challenge with the peptide and bombesin receptor number. However, the extent of desensitization was greater than the extent of receptor down-regulation at all times examined during pretreatment and recovery. Furthermore, bombesin was 3 times more potent at inducing desensitization (ED50 = 0.35 +/- 0.08 nM) than down-regulation (ED50 = 1.1 +/- 0.4 nM). These results suggest that desensitization was not due solely to a reduction in receptor number. Because bombesin stimulates diacylglycerol production in HIT- T15 cells, we used the phorbol ester 12-O-tetradecanoylphorbol-13- acetate (TPA) to determine whether protein kinase C also played a role in desensitization to the peptide. Pretreatment of cells with TPA did not affect either [125I-Tyr4]bombesin binding or the dose dependence for bombesin-stimulated hormone release. However, TPA pretreatment did decrease the maximum secretory response to bombesin by 40% and caused a 50% reduction in bombesin-induced accumulation of inositol triphosphates and elevation of intracellular free calcium. Conversely, bombesin pretreatment reduced the secretory response to TPA by 40%. These studies indicate that the mechanism for desensitization to bombesin is a complex process that involves down-regulation of the bombesin receptor, inhibition of intracellular second messenger production, and reduction of protein kinase C-stimulated secretion.

Volume 37, Issue 5, pp. 758-766, 05/01/1990
Copyright © 1990 by American Society for Pharmacology and Experimental Therapeutics

This article has been cited by other articles:

				R. T. Jensen, J. F. Battey, E. R. Spindel, and R. V. Benya International Union of Pharmacology. LXVIII. Mammalian Bombesin Receptors: Nomenclature, Distribution, Pharmacology, Signaling, and Functions in Normal and Disease States Pharmacol. Rev., March 1, 2008; 60(1): 1 - 42. [Abstract] [Full Text] [PDF]

				R. V. Benya, T. Kusui, T. Katsuno, T. Tsuda, S. A. Mantey, J. F. Battey, and R. T. Jensen Glycosylation of the Gastrin-Releasing Peptide Receptor and Its Effect on Expression, G Protein Coupling, and Receptor Modulatory Processes Mol. Pharmacol., April 13, 2001; 58(6): 1490 - 1501. [Abstract] [Full Text]

				B. Y. Williams, S. B. Dion, and A. Schonbrunn Role of Receptor and Protein Kinase C Activation in the Internalization of the Gastrin-Releasing Peptide Receptor Mol. Pharmacol., November 1, 1998; 54(5): 889 - 898. [Abstract] [Full Text]

				S. Cvejic, N. Trapaidze, C. Cyr, and L. A. Devi Thr[IMAGE], Located within the COOH-terminal Tail of the [IMAGE] Opiate Receptor, Is Involved in Receptor Down-regulation J. Biol. Chem., February 23, 1996; 271(8): 4073 - 4076. [Abstract] [Full Text] [PDF]

				G. S. Kroog, E. Sainz, P. J. Worland, M. A. Akeson, R. V. Benya, R. T. Jensen, and J. F. Battey The Gastrin-releasing Peptide Receptor Is Rapidly Phosphorylated by a Kinase Other Than Protein Kinase C After Exposure to Agonist J. Biol. Chem., April 7, 1995; 270(14): 8217 - 8224. [Abstract] [Full Text] [PDF]

				R. V. Benya, T. Kusui, J. F. Battey, and R. T. Jensen Chronic Desensitization and Down-regulation of the Gastrin-releasing Peptide Receptor Are Mediated by a Protein Kinase C-dependent Mechanism J. Biol. Chem., February 17, 1995; 270(7): 3346 - 3352. [Abstract] [Full Text] [PDF]