Molecular cloning of the human brain and gastric cholecystokinin receptor: structure, functional expression and chromosomal localization

A new CCK-B/gastrin receptor antagonist acts as an agonist on the rat pancreas

The new CCK-B/gastrin receptor antagonist PD 136450 is of potential value in treating neurologic and psychiatric disorders. We investigated possible side effects on the rat pancreas using acute and chronic administration schedules. In chronic experiments, four groups of rats were given either PD 136450, the proton pump inhibitor BY 308 (in order to induce hypergastrinemia), a combination of both, or control solutions over 14 d. Pancreatic growth, DNA, and protein content were significantly increased in rats given PD 136450 irrespective of circulating gastrin levels. Furthermore, an anticoordinate shift in pancreatic enzyme content in favor of trypsin and chymotrypsin at the expense of amylase and lipase was observed. Plasma CCK levels remained unchanged in this group making a role of circulating hormone unlikely. In order to investigate a possible direct agonist effect of the CCK-B/gastrin receptor antagonist, we studied amylase release from isolated rat pancreatic acini in response to PD 136450 and sulfated CCK8 alone and in combination with the specific CCK-A receptor antagonist MK 329. Increasing concentrations of PD 136450 caused a monophasic dose-response curve in contrast to the well-known biphasic amylase release in response to CCK8. Addition of increasing doses of PD 136450 to a concentration of CCK causing maximal stimulation of amylase release (0.1 nM) further enhanced amylase release from pancreatic acini. The specific CCK-A receptor antagonist MK 329 dose-dependently inhibited CCK8- and PD 136450-induced amylase release. In conclusion, the new CCK-B/gastrin receptor antagonist PD 136450 exhibited profound agonist actions on the rat pancreas mediated via CCK-A receptors.

Gastrin13 and the C-terminal octapeptide of cholecystokinin are differently coupled to G-proteins in guinea-pig brain membranes

In the course of our study concerning gastrin and cholecystokinin (CCK) receptors, we synthesized and characterized a labelled gastrin ligand, [125I]BH[Leu15]gastrin-(5-17) (3-(3-[125I]iodo-4-hydroxyphenyl)propionyl[Leu15]gastrin-(5-17)). On isolated canine fundic mucosal cells and human Jurkat lymphoblastic cell line, known to express CCKB/gastrin receptors, the binding experiments performed indicate that [125I]BH[Leu15]gastrin-(5-17) provides a convenient biologically active ligand for cholecystokinin/gastrin receptor studies. We showed in this study that, on guinea-pig brain membranes known to possess CCKB and CCKA receptors, [125I]BH[Leu15]gastrin-(5-17) binds to a single class of high-affinity binding sites in a saturable and specific manner. [125I]BH[Leu15]gastrin-(5-17) interacts with guinea-pig brain membranes with a maximal binding capacity that is about three-fold lower than that of [125I]BHCCK8 (CCK8, the C-terminal octapeptide of cholecystokinin). The apparent affinities of CCK analogues and selective CCK receptor antagonists L-365,260 and MK-329 for the sites labelled by both probes were in accordance with a CCKB-like profile. Association-dissociation kinetics of [125I]BH[Leu15]gastrin-(5-17) and [125I]BHCCK8 were performed and compared. They showed that [125I]BHCCK8 equilibrated more slowly than [125I]BH[Leu15]gastrin-(5-17). The effects of pH, monovalent and divalent cations on binding of both probes were investigated. The results obtained did not indicate strong differences between [125I]BH[Leu15]gastrin-(5-17) and [125I]BHCCK8 binding. Binding experiments in the presence of stable analogues of GTP showed a different behavior between [125I]BH[Leu15]gastrin-(5-17) and [125I]BHCCK8. GTP gamma S strongly decreased [125I]BH[Leu15]gastrin-(5-17) binding whereas it weakly affected [125I]BHCCK8 binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of cloned human cholecystokinin-B receptor as a gastrin receptor

The cholecystokinin (CCK)-B receptor cloned from human brain was characterized as a gastrin receptor by using heterologous expression systems of COS-7 cells and Xenopus oocytes. 125I-gastrin binding to human CCK-B receptor expressed in COS-7 was time-dependent, saturable and also specific, as well as 125-I-CCK-8. The binding of 125I-gastrin was inhibited by CCK-8 about 10-fold more potently than by gastrin. The rank order of potency of several antagonists to 125I-gastrin binding was YM022 > CI-988 > L-365,260 > L-364,718. Addition of GTP gamma S, a nonhydrolysable analog of GTP, dose-dependently inhibited 125I-gastrin binding, and lowered the gastrin binding affinity, Gastrin (10(-9)-10(-7) M) also evoked a Ca(2+)-dependent Cl- current in Xenopus oocytes expressing CCK-B receptors. These results suggest that the pharmacological profile of the cloned human CCK-B receptor using 125I-gastrin is closely parallel to that reported in gastric mucosa, and that the receptor transduces cellular signals of gastrin as well as those of CCK-8.

Characterisation of CCKB receptors on GH3 pituitary cells: receptor activation is linked to Ca2+ mobilisation

Cholecystokinin receptors on GH3 rat anterior pituitary cells have been characterised using radioligand binding and Ca2+ mobilisation. [125I]Bolton Hunter CCK-8s (BHCCK) bound dose dependently to GH3 cells (Kd 85 pM, Bmax 23 fmol/mg protein). Competition curves with CCK-8s (IC50 2.4 nM), pentagastrin (IC50 25 nM) and devazepide (IC50 820 nM), were consistent with a population predominantly of CCKB receptors. Binding of [125I]BHCCK to lysed cells was inhibited by 10 microM GTP-gamma-S and 10 microM GppNHp, suggesting the receptor was linked to a guanine nucleotide binding protein. Intracellular Ca2+ mobilisation was a functional consequence of CCKB receptor activation in GH3 cells using the fluorescent dye fura-2. CCK-8s (0.1 nM-1 microM) and the selective CCKB receptor agonist, pentagastrin, (0.1 nM-100 microM) dose dependently increased intracellular Ca2+ with a similar maximal increase of 2.85-fold and 2.77-fold respectively. Response to a submaximal dose of the CCKB receptor agonist pentagastrin (100 nM) was dose dependently blocked by the CCKB receptor antagonist L-365,260. GH3 cells may therefore provide a useful model to study CCKB receptor coupling in a pituitary cell line.

Isolation and partial amino acid sequence of a 78 kDa porcine gastrin-binding protein

1. A 78 kDa protein (p78) has been partially purified from washed membranes isolated from the corpus of porcine gastric mucosa. The purification was monitored by covalent cross-linking of iodinated [Nle15]-gastrin. 2. A single N-terminal sequence extending for 33 amino acids was obtained from the p78 preparation. Partial sequences totalling 192 amino acids were also obtained from 14 tryptic and 3 Staphylococcal V8 peptides. 3. 10 peptides plus the N-terminal sequence were derived from a previously unsequenced protein which was distantly related to the product of the E. coli fadB gene (Baldwin G. S. (1993) Comp. Biochem. Physiol. 104B, 55-61). The remaining 7 peptides were derived from the beta-subunit of the gastric H+/K(+)-ATPase. 4. The gastrin-binding activity remained in association with p78, and could be separated from the beta-subunit of the gastric H+/K(+)-ATPase, during chromatography on tomato lectin-Sepharose. 5. We conclude that p78 binds gastrin, and is a novel member of the enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase family of enzymes.

Molecular cloning, functional expression, and chromosomal localization of the human cholecystokinin type A receptor

The results presented here describe for the first time the molecular cloning of the human CCKA-R. Expression of the recombinant receptor shows the expected subtype pharmacology and coupling to phosphoinositide hydrolysis reported for the native human CCKA-R. This knowledge will enhance our understanding of its distribution, pharmacology, and structure and will improve our understanding of its physiological role in the gastrointestinal and nervous systems in humans. Ultimately, this should hasten the understanding and therapy of gastrointestinal and neuropsychiatric disorders.

Cholecystokinin receptor family. Molecular cloning, structure, and functional expression in rat, guinea pig, and human

A review of the literature encompassing numerous pharmacological, physiological, and biochemical studies indicates the presence of at least four CCK receptor types, CCKA, CCKB, gastrin, and CG-4 receptors. Multiple subtypes of the CCKAR have been postulated to account for the differences in pharmacology or affinity cross-linking of CCKARs between pancreas and gallbladder and the presence of high and low affinity CCKARs on pancreatic acini. Multiple subtypes of the CCKBR have been postulated to explain the differences in pharmacology and physiology between gastric and gallbladder smooth muscle CCKBRs. We recently cloned and functionally expressed both the CCKAR and the CCKBR from rat, guinea pig, and human. The CCKAR and CCKBR are 48% homologous and constitute a family of receptors within the guanine nucleotide-binding regulatory protein-coupled superfamily of receptors. Each receptor is highly conserved between species. A single cDNA encoding a single protein is present in both pancreas and gallbladder and can account for both high and low affinity CCKARs found on pancreatic acini when transfected into COS-7 cells. A single cDNA encoding a single CCKBR protein is present in both the central nervous system and the periphery including the gastrointestinal system. Therefore, the gastrin receptor is actually a CCKBR present on parietal cells. Genomic and cDNA library hybridization as well as Northern and Southern hybridization studies among rat, guinea pig, and human species identifies only two members of the CCK receptor family, CCKAR and CCKBR. Although these studies do not identify other closely related members of the CCK receptor family, they do not rule out the existence of other less closely related members. Furthermore, differences in tissue and species-specific posttranslational processing, receptor coupling, and associated membrane protein and lipid heterogeneity may be among some of the other factors that may account for the phenotypic expression of more receptor subtypes than molecular studies would predict.

Biological actions of cholecystokinin

Cholecystokinin (CCK) has emerged as an important mammalian neuropeptide, localized in peripheral organs and in the central nervous system. This review presents an overview of the molecular aspects of CCK peptides and CCK receptors, the anatomical distribution of CCK, the neurophysiological actions of CCK, release of CCK and effects of CCK on release of other neurotransmitters, and the actions of CCK on digestion, feeding, cardiovascular function, respiratory function, neurotoxicity and seizures, cancer cell proliferation, analgesia, sleep, sexual and reproductive behaviors, memory, anxiety, and dopamine-mediated exploratory and rewarded behaviors. Human clinical studies of CCK in feeding disorders and panic disorders are described. New findings are presented on potent, nonpeptide CCK antagonists, selective for the two CCK receptor subtypes, which demonstrate that endogenous CCK has biologically important effects on physiology and behavior.

Guinea pig gallbladder and pancreas possess identical CCK-A receptor subtypes: receptor cloning and expression

Cholecystokinin (CCK) receptors mediate pancreatic acinar secretion and gallbladder contraction. Pharmacological and functional studies in pancreas and gallbladder demonstrate a CCK-A receptor subtype in both tissues. However, some pharmacological studies and affinity cross-linking studies of CCK receptors on pancreatic acini and gallbladder suggest that these two tissues possess two different subtypes of the CCK-A receptor. We cloned these receptors in guinea pig using a cDNA clone of the CCK-A receptor from rat pancreas. The guinea pig gallbladder CCK-A receptor was cloned by hybridization screening of a gallbladder cDNA library using a cDNA probe from the rat CCK-A receptor coding region. The guinea pig pancreas CCK-A receptor cDNA was cloned via the polymerase chain reaction using primers corresponding to the guinea pig gallbladder CCK-A receptor 5'- and 3'-noncoding regions. CCK-A receptor clones from guinea pig pancreas and gallbladder had identical nucleotide sequences, which were 80% homologous to the rat CCK-A receptor cDNA sequence. The deduced amino acid sequence from guinea pig CCK-A receptors was 89% homologous to the rat CCK-A receptor sequence. Dose-inhibition binding studies of transiently expressed receptors by CCK agonists and antagonists exhibited a CCK-A receptor pharmacologically similar to the rat CCK-A receptor. These studies indicate that the CCK-A receptors in guinea pig pancreas and gallbladder are identical and do not support previous proposals that they may represent different receptor subtypes.

Marked increase in cholecystokinin B receptor messenger RNA levels in rat dorsal root ganglia after peripheral axotomy

It is now well established that the expression of peptides in rat primary sensory neurons is dramatically changed in response to peripheral nerve injury. Thus, as first shown by Jessell et al. peripheral axotomy causes a decrease in substance P levels in the dorsal horn of the corresponding spinal cord segments, and this is due to down-regulation of peptide synthesis in dorsal root ganglion neurons. In contrast, other peptides such as vasoactive intestinal polypeptide and peptide histidine isoleucine, galanin and neuropeptide Y are all markedly upregulated in the rat L4 and L5 dorsal root ganglia after sciatic nerve sectioning. The levels of another peptide, cholecystokinin and its messenger RNA are normally very low or undectable in rat primary sensory neurons, but after peripheral axotomy approximately 30% of the ganglion neurons express cholecystokinin messenger RNA. During the last few years a number of peptide receptors have been cloned, and they all belong to the family of G-protein coupled receptors with seven membrane spanning segments, among them the two cholecystokinin receptors cholecystokininA and cholecystokininB. Ghilardi et al. have recently described presence of cholecystokininB binding sites in rat dorsal root ganglia neurons. In the present study we report that the messenger RNA for the cholecystokininB receptor is present at very low levels in normal dorsal root ganglia of the rat, but axotomy causes a very marked increase in the number of sensory neurons of all sizes expressing cholecystokininB receptor messenger RNA, suggesting an increased sensitivity to cholecystokinin for many primary sensory neurons of different modalities after lesion.

The human gastrin/cholecystokinin type B receptor gene: alternative splice donor site in exon 4 generates two variant mRNAs

Gastrin and its carboxyl-terminal homolog cholecystokinin (CCK) exert a variety of biological actions in the brain and gastrointestinal tract that are mediated in part through one or more G protein-coupled receptors which exhibit similar affinity for both peptides. Genomic clones encoding a human gastrin/CCKB receptor were isolated by screening a human EMBL phage library with a partial-length DNA fragment which was based on the nucleotide sequence of the canine gastrin receptor. The gene contained a 1356-bp open reading frame consisting of five exons interrupted by 4 introns and was assigned to human chromosome 11p15.4. A region of exon 4, which encodes a portion of the putative third intracellular loop, appears to be alternatively spliced to yield two different mRNAs, one containing (452 amino acids; long isoform) and the other lacking (447 amino acids; short isoform) the pentapeptide sequence Gly-Gly-Ala-Gly-Pro. The two receptor isoforms may contribute to functional differences in gastrin- and CCK-mediated signal transduction.

Species specificity of pharmacological characteristics of CCK-B receptors

Novel CCK-B receptor antagonists, tetronothiodin and L-156,586, showed different affinities for CCK-B receptors in brain membranes from human, rat, guinea pig and mouse. [125I]CCK-8 bound to these membranes with a similar affinity. However, tetronothiodin was most potent in rat (IC50 = 3.6 nM), followed by guinea pig (96 nM), human (210 nM) and mouse (280 nM). L-156,586 bound with highest affinity to membranes from guinea pig (11 nM), and with lowest affinity to membranes from mouse (220 nM). These results suggest the existence of species specificity of CCK-B receptors, and that these two compounds are useful tools for discrimination between these receptors.

Neurobiological investigations into the role of cholecystokinin in panic disorder

Cholecystokinin (CCK) is a neurotransmitter found in high density in the brains of mammals. Microiontophoretic studies showing that benzodiazepines selectively antagonized CCK-induced excitation of rat hippocampal neurons have led to the hypothesis that CCK is an anxiogenic peptide. The hypothesis was supported by demonstrations that CCK-tetrapeptide (CCK4) induces panic attacks in humans. This paper reviews phases of investigations which studied the validity of CCK4 as a panicogenic agent and research strategies for the study of panic disorder using CCK4 as an investigative tool.