Bombesin Receptor Subtype-3 (BRS-3) Regulates Glucose-Stimulated Insulin Secretion in Pancreatic Islets across Multiple Species

Abstract

Bombesin receptor subtype-3 (BRS-3) regulates energy homeostasis, and BRS-3 agonism is being explored as a possible therapy for obesity. Here we study the role of BRS-3 in the regulation of glucose-stimulated insulin secretion (GSIS) and glucose homeostasis. We quantified BRS-3 mRNA in pancreatic islets from multiple species and examined the acute effects of Bag-1, a selective BRS-3 agonist, on GSIS in mouse, rat, and human islets, and on oral glucose tolerance in mice. BRS-3 is highly expressed in human, mouse, rhesus, and dog (but not rat) pancreatic islets and in rodent insulinoma cell lines (INS-1 832/3 and MIN6). Silencing BRS-3 with small interfering RNA or pharmacological blockade with a BRS-3 antagonist, Bantag-1, reduced GSIS in 832/3 cells. In contrast, the BRS-3 agonist (Bag-1) increased GSIS in 832/3 and MIN6 cells. The augmentation of GSIS by Bag-1 was completely blocked by U73122, a phospholipase C inhibitor. Bag-1 also enhanced GSIS in islets isolated from wild-type, but not Brs3 knockout mice. In vivo, Bag-1 reduced glucose levels during oral glucose tolerance test in a BRS-3-dependent manner. BRS-3 agonists also increased GSIS in human islets. These results identify a potential role for BRS-3 in islet physiology, with agonism directly promoting GSIS. Thus, in addition to its potential role in the treatment of obesity, BRS-3 may also regulate blood glucose levels and have a role in the treatment of diabetes mellitus.

Comparative Pharmacology of Bombesin Receptor Subtype-3, Nonpeptide Agonist MK-5046, a Universal Peptide Agonist, and Peptide Antagonist Bantag-1 for Human Bombesin Receptors

“…In this study, we compared the ability of the naturally occurring Bn-related peptides GRP and NMB and the universal Bn-receptor agonist ligand peptide #1 (Mantey et al, 1997;Pradhan et al, 1998) to interact with and activate the three human Bnreceptor subtypes-hGRP-R, hNMB-R, and hBRS-3 -with that of MK-5046, a recently reported Sebhat et al, 2011) BRS-3-receptor selective nonpeptide agonist, and Bantag-1, a BRS-3 selective peptide antagonist (Guan et al, 2010;Feng et al, 2011). To be certain the results were reflective of the pharmacology of these peptides, two different Bn-receptor-containing cells were used to assess the results with each human Bn-receptor subtype.…”

“…Even though it is an orphan receptor, it is classified as a mammalian bombesin (Bn) receptor because of its homology (47-51% amino acid identities) with the two mammalian Bn receptors, gastrin-releasing peptide receptor (GRP-R) and neuromedin B receptor (NMB-R) . BRS-3 is putatively involved in a broad range of physiologic and pathophysiological processes (Ohki-Hamazaki et al, 1997;Jensen et al, 2008;Majumdar and Weber, 2012a,b;Sayegh, 2013), including energy homeostasis (Ohki-Hamazaki et al, 1997;Ladenheim et al, 2008;Guan et al, 2010Guan et al, , 2011Metzger et al, 2010;Feng et al, 2011), feeding behavior (Maekawa et al, 2004;Ladenheim et al, 2008;Majumdar and Weber, 2012a;Sayegh, 2013), glucose metabolism (Ohki-Hamazaki et al, 1997;Nakamichi et al, 2004;Jensen et al, 2008;Feng et al, 2011;Majumdar and Weber, 2012a), gastrointestinal motility , and lung cancer development and injury (Shan et al, 2004;Tan et al, 2006). However, exploration of the role of BRS-3 in physiological and pathophysiologic processes had been limited because the natural ligand is unknown, and, in contrast to the other Bn receptors, no selective agonists and antagonists are available (Heinz-Erian et al, 1987;von Schrenck et al, 1990;Wang et al, 1990a,b;Jensen and Coy, 1991;Jensen et al, 2008;Majumdar and Weber, 2012b).…”

“…Recent studies have reported that the nonpeptide MK-5046 [(2S)-1,1,1-trifluoro-2-[4-(1H-pyrazol-1-yl)phenyl]-3-(4-{[1-(trifluoromethyl)cyclopropyl]methyl}-1H-imidazol-2-yl)propan-2-ol] is an orally active, potent, and selective BRS-3 agonist (Sebhat et al, 2011;Guan et al, 2011;Reitman et al, 2012), with activity in mice, rats, dogs , and humans (Reitman et al, 2012). Furthermore, recently a selective peptide antagonist Bantag-1 [Boc-Phe-His-4-amino-5-cyclohexyl-2,4,5-trideoxypentonyl-Leu-(3-dimethylamino) benzylamide N-methylammonium trifluoroacetate] also has been reported (Guan et al, 2010;Feng et al, 2011). There are limited data on the pharmacologic characteristics of these compounds (Guan et al, 2010Feng et al, 2011;Sebhat et al, 2011).…”

“…Furthermore, recently a selective peptide antagonist Bantag-1 [Boc-Phe-His-4-amino-5-cyclohexyl-2,4,5-trideoxypentonyl-Leu-(3-dimethylamino) benzylamide N-methylammonium trifluoroacetate] also has been reported (Guan et al, 2010;Feng et al, 2011). There are limited data on the pharmacologic characteristics of these compounds (Guan et al, 2010Feng et al, 2011;Sebhat et al, 2011). In addition, for the Bn-receptor family, similar to other gastrointestinal hormone/neurotransmitter G protein-coupled receptors, nonpeptide-agonists are uncommon (Freidinger, 1993;Jensen et al, 2008;Uehara et al, 2011); in fact, MK-5046 is the first high-affinity, widely used nonpeptide agonist for any member of the Bn family of receptors.…”

“…We also compared the pharmacology of these two agonists with the peptide Bantag-1, which has been described as a selective and potent antagonist of BRS-3 (Guan et al, 2010;Feng et al, 2011).…”