Bombesin Receptor Subtype-3 in Human Diseases

Dynamic Phosphoproteomics of BRS3 Activation Reveals the Hippo Signaling Pathway for Cell Migration

Bombesin receptor subtype-3 (BRS3) is an orphan G-protein coupled receptor (GPCR) that is involved in a variety of pathological and physiological processes, while its biological functions and underlying regulatory mechanisms remain largely unknown. In this study, a quantitative phosphoproteomics approach was employed to comprehensively decipher the signal transductions that occurred upon intracellular BRS3 activation. The lung cancer cell line H1299-BRS3 was treated with MK-5046, an agonist of BRS3, for different durations. Harvested cellular proteins were digested and phosphopeptides were enriched by immobilized titanium (IV) ion affinity chromatography (Ti⁴⁺-IMAC) for label-free quantification (LFQ) analysis. A total of 11,938 phosphopeptides were identified, corresponding to 3,430 phosphoproteins and 10,820 phosphosites. Data analysis revealed that 27 phosphopeptides corresponding to six proteins were involved in the Hippo signaling pathway, which was significantly regulated by BRS3 activation. Verification experiments demonstrated that downregulation of the Hippo signaling pathway caused by BRS3 activation could induce the dephosphorylation and nucleus localization of the Yes-associated protein (YAP), and its association with cell migration was further confirmed by kinase inhibition. Our data collectively demonstrate that BRS3 activation contributes to cell migration through downregulation of the Hippo signaling pathway.

Neuromedin B excites central lateral amygdala neurons and reduces cardiovascular output and fear-potentiated startle

Neuromedin B (NMB) and gastrin-releasing peptide (GRP) are the two mammalian analogs in the bombesin peptide family that exert a variety of actions including emotional processing, appetitive behaviors, cognition, and tumor growth. The bombesin-like peptides interact with three receptors: the NMB-preferring bombesin 1 (BB1) receptors, the GRP-preferring bombesin 2 (BB2) receptors and the orphan bombesin 3 (BB3) receptors. Whereas, injection of bombesin into the central amygdala reduces satiety and modulates blood pressure, the underlying cellular and molecular mechanisms have not been determined. As administration of bombesin induces the expression of Fos in the lateral nucleus of the central amygdala (CeL) which expresses BB1 receptors, we probed the effects of NMB on CeL neurons using in vitro and in vivo approaches. We showed that activation of the BB1 receptors increased action potential firing frequency recorded from CeL neurons via inhibition of the inwardly rectifying K+ (Kir) channels. Activities of phospholipase Cβ and protein kinase C were required, whereas intracellular Ca2+ release was unnecessary for BB1 receptor-elicited potentiation of neuronal excitability. Application of NMB directly into the CeA reduced blood pressure and heart rate and significantly reduced fear-potentiated startle. We may provide a cellular and molecular mechanism whereby bombesin-like peptides modulate anxiety and fear responses in the amygdala.

Two novel bombesin-like neuropeptides from the skin secretion of Pelophylax kl. esculentus: Ex vivo pharmacological characterization on rat smooth muscle types

Mammalian bombesin-like neuropeptides (BLPs) play an important role in regulation of physiological and pathophysiological processes. Frog skin-derived BLPs, of smaller size and diverse lengths and sequences at their N-terminus, have attracted the attention of many researchers. However, these N-terminal variants and the receptors modulating their pharmacological actions are poorly studied and less understood. In this study, two BLPs, namely, [Asn³, Lys⁶, Thr¹⁰, Phe¹³]3–14-bombesin and [Asn³, Lys⁶, Phe¹³]3–14-bombesin with primary structures NLGKQWATGHFM and NLGKQWAVGHFM were isolated from the skin secretion of hybrid Pelophylax kl. esculentus. Both BLPs share a similar primary structure with only a single amino acid substitution at the eighth position (threonine to valine), while they have quite different myotropic potencies with EC₅₀ values in the range of 22.64 ± 9.7 nM (N = 8) to 83.93 ± 46.9 nM (N = 8). The potency of [Asn³, Lys⁶, Thr¹⁰, Phe¹³]3–14-bombesin was approximately 3-fold higher than that of [Asn³, Lys⁶, Phe¹³]3–14-bombesin. Through the investigation of receptor selectivity using a canonical bombesin receptor antagonist, it was found that [Asn³, Lys⁶, Thr¹⁰, Phe¹³]3–14-bombesin and [Asn³, Lys⁶, Phe¹³]3–14-bombesin had an affinity to both BB1 and BB2 receptors. Their contractile functions are mainly modulated by both BB1 and BB2 receptors on rat urinary bladder and BB2 alone on rat uterus smooth muscle preparations. These data may provide new insights into the design of potent and selective ligands for bombesin receptors. Moreover, [Asn³, Lys⁶, Thr¹⁰, Phe¹³]3–14-bombesin and [Asn³, Lys⁶, Phe¹³]3–14-bombesin did not induce significant hemolysis and toxicity in normal human cells, suggesting that these two natural novel BLPs have great potential for development into new drug candidates.

The Nonpeptide Agonist MK-5046 Functions As an Allosteric Agonist for the Bombesin Receptor Subtype-3

Allosteric ligands of various G-protein-coupled receptors are being increasingly described and are providing important advances in the development of ligands with novel selectivity and efficacy. These unusual properties allow expanded opportunities for pharmacologic studies and treatment. Unfortunately, no allosteric ligands are yet described for the bombesin receptor family (BnRs), which are proposed to be involved in numerous physiologic/pathophysiological processes in both the central nervous system and peripheral tissues. In this study, we investigate the possibility that the bombesin receptor subtype-3 (BRS-3) specific nonpeptide receptor agonist 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] functions as a BRS-3 allosteric receptor ligand. We find that in BRS-3 cells, MK-5046 only partially inhibits iodine-125 radionuclide (125I)-Bantag-1 [Boc-Phe-His-4-amino-5-cyclohexyl-2,4,5-trideoxypentonyl-Leu-(3-dimethylamino) benzylamide N-methylammonium trifluoroacetate] binding and that both peptide-1 (a universal BnR-agonist) and MK-5046 activate phospholipase C; however, the specific BRS-3 peptide antagonist Bantag-1 inhibits the action of peptide-1 competitively, whereas for MK-5046 the inhibition is noncompetitive and yields a curvilinear Schild plot. Furthermore, MK-5046 shows other allosteric behaviors, including slowing dissociation of the BRS-3 receptor ligand 125I-Bantag-1, dose-inhibition curves being markedly affected by increasing ligand concentration, and MK-5046 leftward shifting the peptide-1 agonist dose-response curve. Lastly, receptor chimeric studies and site-directed mutagenesis provide evidence that MK-5046 and Bantag-1 have different binding sites determining their receptor high affinity/selectivity. These results provide evidence that MK-5046 is functioning as an allosteric agonist at the BRS-3 receptor, which is the first allosteric ligand described for this family of receptors. SIGNIFICANCE STATEMENT: G-protein-coupled receptor allosteric ligands providing higher selectivity, selective efficacy, and safety that cannot be obtained using usual orthosteric receptor-based strategies are being increasingly described, resulting in enhanced usefulness in exploring receptor function and in treatment. No allosteric ligands exist for any of the mammalian bombesin receptor (BnR) family. Here we provide evidence for the first such example of a BnR allosteric ligand by showing that MK-5046, a nonpeptide agonist for bombesin receptor subtype-3, is functioning as an allosteric agonist.

Homomultimer strategy for improvement of radiolabeled peptides and antibody fragments in tumor targeting

A homomultimeric radioligand is composed of multiple identical ligands connected to the linker and radionuclide to detect a variety of overexpressed receptors on cancer cells. Multimer strategy holds great potential for introducing new radiotracers based on peptide and monoclonal antibody (mAb) derivatives in molecular imaging and therapy. It offers a reliable procedure for the preparation of biological-based targeting with diverse affinities and pharmacokinetics. In this context, we provide a useful summary and interpretation of the main results by a comprehensive look at multimeric radiopharmaceuticals in nuclear oncology. Therefore, there will be explanations for the strategy mechanisms and the main variables affecting the biodistribution results. The discussion is followed by highlights of recent work in the targeting of various types of receptors. The consequences are expressed based on comparing some parameters between monomer and multimer counterparts in each relevant section.

Agonist-induced extracellular vesicles contribute to the transfer of functional bombesin receptor-subtype 3 to recipient cells

Extracellular vesicles (EVs) are important carriers for biomolecules in the microenvironment that greatly promote intercellular and extracellular communications. However, it is unclear whether bombesin receptor-subtype 3 (BRS-3), an orphan G-protein coupled receptor, can be packed into EVs and functionally transferred to recipient cells. In this study, we applied the synthetic agonist and antagonist to activate and inhibit the BRS-3 in HEK293-BRS-3 cells, whose EVs release was BRS-3 activation dependent. The presence of BRS-3 in harvested EVs was further confirmed by an enhanced green fluorescent protein tag. After recipient cells were co-cultured with these EVs, the presence of BRS-3 in the recipient cells was discovered, whose function was experimentally validated. Quantitative proteomics approach was utilized to decipher the proteome of the EVs derived from HEK293-BRS-3 cells after different stimulations. More than 900 proteins were identified, including 51 systematically dysregulated EVs proteins. The Ingenuity Pathway Analysis (IPA) revealed that RhoA signaling pathway was as an essential player for the secretion of EVs. Selective inhibition of RhoA signaling pathway after BRS-3 activation dramatically reversed the increased secretion of EVs. Our data, collectively, demonstrated that EVs contributed to the transfer of functional BRS-3 to the recipient cells, whose secretion was partially regulated by RhoA signaling pathway.

Regulatory Peptides in Asthma

Numerous regulatory peptides play a critical role in the pathogenesis of airway inflammation, airflow obstruction and hyperresponsiveness, which are hallmarks of asthma. Some of them exacerbate asthma symptoms, such as neuropeptide Y and tachykinins, while others have ameliorating properties, such as nociception, neurotensin or β-defensin 2. Interacting with peptide receptors located in the lungs or on immune cells opens up new therapeutic possibilities for the treatment of asthma, especially when it is resistant to available therapies. This article provides a concise review of the most important and current findings regarding the involvement of regulatory peptides in asthma pathology.

Hemorphins Targeting G Protein-Coupled Receptors

Hemorphins are short peptides produced by the proteolysis of the beta subunit of hemoglobin. These peptides have diverse physiological effects especially in the nervous and the renin-angiotensin systems. Such effects occur through the modulation of a diverse range of proteins including enzymes and receptors. In this review, we focus on pharmacological and functional targeting of G protein-coupled receptors (GPCRs) by hemorphins and their implication in physiology and pathophysiology. Among GPCRs, the opioid receptors constitute the first set of targets of hemorphins with implication in analgesia. Subsequently, several other GPCRs have been reported to be directly or indirectly involved in hemorphins’ action. This includes the receptors for angiotensin II, oxytocin, bombesin, and bradykinin, as well as the human MAS-related G protein-coupled receptor X1. Interestingly, both orthosteric activation and allosteric modulation of GPCRs by hemorphins have been reported. This review links hemorphins with GPCR pharmacology and signaling, supporting the implication of GPCRs in hemorphins’ effects. Thus, this aids a better understanding of the molecular basis of the action of hemorphins and further demonstrates that hemorphin-GPCR axis constitutes a valid target for therapeutic intervention in different systems.