Distinguishing bombesin receptor subtypes using the oocyte assay

The Role of a Natural Amphibian Skin-Based Peptide, Ranatensin, in Pancreatic Cancers Expressing Dopamine D2 Receptors

Despite the progress in early diagnostic and available treatments, pancreatic cancer remains one of the deadliest cancers. Therefore, there is an urgent need for novel anticancer agents with a good safety profile, particularly in terms of possible side-effects. Recently dopaminergic receptors have been widely studied as they were proven to play an important role in cancer progression. Although various synthetic compounds are known for their interactions with the dopaminergic system, peptides have recently made a great comeback. This is because peptides are relatively safe, easy to correct in terms of the improvement of their physicochemical and biological properties, and easy to predict. This paper aims to evaluate the anticancer activity of a naturally existing peptide-ranatensin, toward three different pancreatic cancer cell lines. Additionally, since there is no sufficient information confirming the exact character of the interaction between ranatensin and dopaminergic receptors, we provide, for the first time, binding properties of the compound to such receptors.

Different types of bombesin receptors on neurons in the dorsal raphe nucleus and the rostral hypothalamus in rat brain slices in vitro

The actions of the peptides bombesin (BN), gastrin releasing peptide (GRP), neuromedin C (NMC), litorin and neuromedin B (NMB) were studied on neurons in slices of rat brain maintained in vitro to determine the BN receptor type present in different brain areas. Intracellular and extracellular recordings were made from hypothalamic neurons on the border of the periventricular nucleus (PVN) and suprachiasmatic nucleus (SCN) and from mesencephalic 5-HT sensitive neurons in the dorsal raphe nucleus. In the region of the brain containing the SCN and PVN, BN and the BN-related peptides excited 31 out of 77 neurons on which they were tested. There was little difference in the potency of the BN-related peptides as excitants of neurons, the EC50 being about 10 nM. The response to the peptides usually lasted between 5 and 15 min with little sign of desensitization. Using NMC, GRP and NMB as agonists, the equilibrium constant for the GRP receptor antagonist [D-Phe6]-BN-(6-13)-ethylamide was approximately 10 nM. The response to the peptides fully recovered on washout of the antagonist. The CCKB/gastrin receptor antagonist CI-988 (1 microM) had no effect on either GRP- or NMC-mediated excitation. In the dorsal nucleus 40 of 75 neurons were sensitive to the BN-related peptides. BN, [Tyr4]-BN, NMB and litorin, were 10-20 times more potent than GRP and NMC. The responses to the BN-related peptides were not blocked by the selective GRP receptor antagonists [D-Phe6]-BN-(6-13)-methylester, [DF5Phe6][D-Ala11]-BN-(6-13)-methylester and [D-Phe6]-BN-(6-13)- ethylamide.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuromedin B receptor, expressed in Xenopus laevis oocytes, selectively couples to G alpha q and not G alpha 11

G-proteins of the q family have been implicated as mediators of bombesin receptors action. We cloned Xenopus G alpha q and G alpha 11 and specifically disrupted the synthesis of either protein with selective antisense oligonucleotides. G alpha q antisense inhibited responses mediated by neuromedin B receptor (NMB-R) by 74%, though not by gastrin-releasing peptide receptor (GRP-R). G alpha 11 antisense had little effect on either GRP-R- or NMB-R-mediated responses. This suggests that NMB-R couples to G alpha q, and that GRP-R and NMB-R show distinct G-protein coupling preferences in the Xenopus oocyte.

Bombesin/GRP-preferring and neuromedin B-preferring receptors in the rat urogenital system

Bombesin binding sites were localized in the rat urogenital system by autoradiography of 125I-Tyr4-bombesin binding to frozen tissue sections. Saturable binding was observed in the bladder, seminal vesicle, uterus, and oviduct. In all organs, the binding sites corresponded to layers of smooth muscle. Radioligand binding studies were performed on homogenized membrane preparations from bladder, uterus, and seminal vesicle. Membrane binding was saturable, reversible, time- and temperature-dependent, and specific for bombesin and related peptides. Analysis of saturable equilibrium binding from all three organs yielded a best fit to a one-site model of high affinity binding with apparent KdS of 720 pM for bladder, 470 pM for uterus, and 700 pM for seminal vesicle. Neuromedin B was potent in displacing saturable 125I-Tyr4-bombesin binding from bladder and seminal vesicle but not uterus membranes. In order to characterize these binding sites further, the ability of these membranes to interact with a specific bombesin receptor antagonist, [Leu13-psi-CH2NH-Leu14]-bombesin, and with GTP-gamma-S was determined. [Leu13-psi-CH2NH-Leu14]-bombesin was much more potent in displacing saturable 125I-Tyr4-bombesin binding from uterus than from bladder and seminal vesicle membranes, further supporting the distinction between the uterus and the bladder/seminal vesicle binding sites as bombesin receptor subtypes. GTP-gamma-S inhibited saturable 125I-Tyr4-bombesin binding to membranes from all three organs, indicating that both receptor subtypes are linked to GTP-binding proteins. We conclude that smooth muscle in the rat urogenital system expresses bombesin receptors and that endogenous GRP and neuromedin B may regulate some reproductive and excretory functions. The bladder and seminal vesicle express the neuromedin B-preferring subtype and the uterus expresses the bombesin/GRP-preferring subtype of bombesin receptor.

Molecular cloning of a new bombesin receptor subtype expressed in uterus during pregnancy

The homology screening approach has been used to clone a new member of the guanine-nucleotide-binding-protein-coupled receptor superfamily from guinea pig uterus. The cloned cDNA encodes a 399-amino-acid protein and shows the highest amino acid similarity to members of the bombesin receptor family; 52% and 47% similarity to the gastrin-releasing-peptide (GRP) receptor and the neuromedin-B receptor, respectively. Binding experiments with the stably transfected LLC-PK1 cell line expressing the new receptor protein confirmed the bombesin-like nature of the cloned receptor. The relative order of ligand affinity, GRP = neuromedin C much greater than neuromedin B, suggests that the cloned cDNA represents the GRP subtype rather than the neuromedin-B subtype of bombesin receptors. Northern-blot analysis of mRNA species from several guinea-pig tissues showed that the mRNA for the new bombesin receptor subtype is expressed mainly in uteri of pregnant animals.

Purification, molecular cloning, and functional expression of the cholecystokinin receptor from rat pancreas

The cholecystokinin (CCK) family of peptides and their receptors are widely distributed throughout the gastrointestinal and central nervous systems where they regulate secretion, motility, growth, anxiety, and satiety. The CCK receptors can be subdivided into at least two subtypes, CCKA and CCKB on the basis of pharmacological studies. We report here the purification of the CCKA receptor to homogeneity from rat pancreas by using ion-exchange and multiple affinity chromatographic separations. This allowed partial peptide sequencing after chemical/enzymatic cleavage and synthesis of degenerate oligonucleotide primers. These primers were used for initial cloning of the cDNA from rat pancreas by PCR. The predicted protein sequence of the cDNA clone contained the five partial peptide sequences obtained from the purified protein. Seven putative transmembrane domains suggest its membership in the guanine nucleotide-binding regulatory protein-coupled receptor superfamily. In vitro transcripts of the cDNA clone were functionally expressed in Xenopus oocytes and displayed the expected agonist and antagonist specificity.