FRINK Linked Data Fragments server

Matches in SemOpenAlex for { <https://semopenalex.org/work/W2034999710> ?p ?o ?g. }

• W2034999710 endingPage "28784" @default.
• W2034999710 startingPage "28779" @default.
• W2034999710 abstract "The enteroendocrine hormone, gastrin, exerts trophic effects on the gastric mucosa through the CCK-B/gastrin receptor (CCK-BR). To varying degrees in different species, excess circulating gastrin leads to proliferation of enterochromaffin-like cells and to the development of gastric carcinoid tumors. The African rodent, Mastomys natalensis, is distinguished from other mammals by its propensity toward CCK-BR-mediated growth even in the absence of hypergastrinemia. Here, we report that theMastomys CCK-BR, when expressed in COS-7 cells, differs from the respective human, canine, and rat receptor homologs by its ability to trigger ligand-independent (i.e., constitutive) inositol phosphate formation. To define the molecular basis of this observation, a series of Mastomys-human chimeric receptors was investigated. Functional characterization of these constructs revealed that a limited segment of the Mastomys CCK-BR, transmembrane domain VI through the C-terminal end, is sufficient to confer constitutive activity to the human protein. Mutagenesis studies within this CCK-BR region defined a combination of threeMastomys amino acids that, when introduced into the human receptor, together conferred a level of ligand-independent signaling comparable with the Mastomys CCK-BR. Complementing prior observations that single point mutations can lead to ligand-independent signaling, our findings suggest that multiple naturally occurring amino acid polymorphisms and/or mutations may together result in an enhanced basal level of receptor activity. The enteroendocrine hormone, gastrin, exerts trophic effects on the gastric mucosa through the CCK-B/gastrin receptor (CCK-BR). To varying degrees in different species, excess circulating gastrin leads to proliferation of enterochromaffin-like cells and to the development of gastric carcinoid tumors. The African rodent, Mastomys natalensis, is distinguished from other mammals by its propensity toward CCK-BR-mediated growth even in the absence of hypergastrinemia. Here, we report that theMastomys CCK-BR, when expressed in COS-7 cells, differs from the respective human, canine, and rat receptor homologs by its ability to trigger ligand-independent (i.e., constitutive) inositol phosphate formation. To define the molecular basis of this observation, a series of Mastomys-human chimeric receptors was investigated. Functional characterization of these constructs revealed that a limited segment of the Mastomys CCK-BR, transmembrane domain VI through the C-terminal end, is sufficient to confer constitutive activity to the human protein. Mutagenesis studies within this CCK-BR region defined a combination of threeMastomys amino acids that, when introduced into the human receptor, together conferred a level of ligand-independent signaling comparable with the Mastomys CCK-BR. Complementing prior observations that single point mutations can lead to ligand-independent signaling, our findings suggest that multiple naturally occurring amino acid polymorphisms and/or mutations may together result in an enhanced basal level of receptor activity. cholecystokinin-B/gastrin receptor enterochromaffin-like inositol phosphate transmembrane domain. The cholecystokinin-B/gastrin receptor (CCK-BR)1 is a seven transmembrane domain G protein-coupled receptor that is widely expressed in the gastrointestinal tract and in the central nervous system (1Walsh J.H. Gut Peptides. 1st Ed. Raven Press, New York1994Crossref Google Scholar). Stimulation of the CCK-BR by either of the endogenous peptides, CCK-8 or gastrin, triggers phospholipase C-mediated conversion of membrane phospholipids to inositol phosphates and diacylglycerol, which in turn initiates a series of downstream signaling events (1Walsh J.H. Gut Peptides. 1st Ed. Raven Press, New York1994Crossref Google Scholar). In the CNS, the CCK-BR is postulated to modulate anxiety as well as the perception of pain (2Ravard S. Dourish C.T. Trends Pharmacol. Sci. 1990; 11: 271-273Abstract Full Text PDF PubMed Scopus (170) Google Scholar, 3Wiertelak E.P. Maier S.F. Watkins L.R. Science. 1992; 256: 830-833Crossref PubMed Scopus (120) Google Scholar). In the stomach, it is well established that activation of this receptor subtype stimulates acid secretion as well as mucosal growth (1Walsh J.H. Gut Peptides. 1st Ed. Raven Press, New York1994Crossref Google Scholar). Recent studies in which CCK-BR-deficient mice were generated by targeted gene disruption revealed that absence of the CCK-BR results in thinning of the gastric mucosa and a reduced density of both gastric enterochromaffin-like (ECL) and parietal cells (4Langhans N. Rindi G. Chiu M. Rehfeld J.F. Ardman B. Beinborn M. Kopin A.S. Gastroenterology. 1997; 112: 280-286Abstract Full Text PDF PubMed Scopus (185) Google Scholar, 5Nagata A. Ito M. Iwata N. Kuno J. Takano H. Minowa O. Chihara K. Matsui T. Noda T. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 11825-11830Crossref PubMed Scopus (219) Google Scholar). Conversely, receptor overactivity in rodents, induced by hypergastrinemia, leads to gastric mucosal hypertrophy marked by increased synthesis of DNA, RNA, and protein (6Johnson L.R. Physiology of the Gastrointestinal Tract. Raven Press, New York1987Google Scholar). Long-term stimulation of the CCK-BR by elevated circulating gastrin may ultimately result in the development of ECL cell carcinoid tumors (7Modlin I.M. Tang L.H. Gastroenterology. 1996; 111: 783-810Abstract Full Text Full Text PDF PubMed Scopus (126) Google Scholar). Among mammals, there is a broad spectrum of susceptibility to gastrin-induced proliferation and tumor formation, with the highest sensitivity observed in the African rodent, Mastomys natalensis. During its normal course of aging, Mastomysmay develop gastric carcinoid tumors even with normal circulating gastrin levels. In this animal, hypergastrinemia potentiates the enhanced rate of gastric ECL cell tumor development (7Modlin I.M. Tang L.H. Gastroenterology. 1996; 111: 783-810Abstract Full Text Full Text PDF PubMed Scopus (126) Google Scholar). The increased susceptibility of Mastomys to ECL cell growth, even in the absence of elevated circulating gastrin, led us to speculate that this receptor homolog was functionally different from the CCK-BR in other species. There is ample precedent that species-dependent differences in the amino acid sequence of the CCK-BR can lead to alterations in the pharmacologic properties of the receptor. We have previously shown that interspecies polymorphisms markedly alter CCK-BR interactions with synthetic ligands, i.e., a single amino acid difference between the canine and human CCK-BRs results in a reversal of the affinity rank order for non-peptide antagonists (8Beinborn M. Lee Y.M. McBride E.W. Quinn S.M. Kopin A.S. Nature. 1993; 362: 348-350Crossref PubMed Scopus (194) Google Scholar). In a subsequent study, we demonstrated that single and double amino acid differences between the mouse, human, and dog receptors led to marked alterations in drug-induced inositol phosphate formation, the primary second messenger generated in response to activation of the CCK-BR (9Kopin A.S. McBride E.W. Gordon M.C. Quinn S.M. Beinborn M. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 11043-11048Crossref PubMed Scopus (29) Google Scholar). In this study, recombinant CCK-BRs from different species were expressed in COS-7 cells and functionally compared. Only theMastomys receptor had a significant level of ligand-independent (i.e., constitutive) signaling activity. To understand the molecular basis of this finding, we utilized a series of human/Mastomys CCK-BR chimeric receptors to map the limited domain that confers ligand-independent signaling. Point mutations were then introduced within this region of the protein to identify residues that underlie the species-dependent constitutive activity. Restriction endonucleases and T4 DNA ligase were purchased from New England Biolabs Inc. Iodinated cholecystokinin octapeptide (125I CCK-8; specific activity, 2200 Ci/mmol) and [3H]myoinositol (specific activity 40–60 Ci/mmol) were obtained from NEN Life Science Products. Unlabeled CCK-8 was purchased from Peninsula Laboratories (Belmont, CA). TheMastomys CCK-BR cDNA (generously provided by Dr. T. Chiba) was subcloned into the expression vector pcDNA I (Invitrogen) and sequenced. Two differences in translated amino acid sequence from the originally published version (10Nakata H. Matsui T. Ito M. Taniguchi T. Naribayashi Y. Arima N. Nakamura A. Kinoshita Y. Chihara K. Hosoda S. Chiba T. Biochem. Biophys. Res. Commun. 1992; 187: 1151-1157Crossref PubMed Scopus (116) Google Scholar) were noted:317GPGLASANQA326 (old)versus 317GPGPGPRPNQA327(revised) and 359C (old) versus 360R (revised). Of note, the 320PGPRP revision results in the introduction of an additional amino acid, thus increasing the numbering by “1” of residues C-terminal to proline 324. The revisedMastomys cDNA has been submitted to GenBank. Naturally occurring PstI sites, in the same relative position of the human (11Lee Y.M. Beinborn M. McBride E.W. Lu M. Kolakowski Jr., L.F. Kopin A.S. J. Biol. Chem. 1993; 268: 8164-8169Abstract Full Text PDF PubMed Google Scholar) and the Mastomys (10Nakata H. Matsui T. Ito M. Taniguchi T. Naribayashi Y. Arima N. Nakamura A. Kinoshita Y. Chihara K. Hosoda S. Chiba T. Biochem. Biophys. Res. Commun. 1992; 187: 1151-1157Crossref PubMed Scopus (116) Google Scholar) CCK-BR (corresponding to human cDNA nucleotides 607–612), were used to generate thePstI chimeras. Oligonucleotide-directed mutagenesis was used to introduce XhoI and MluI sites (corresponding to human cDNA nucleotides 910–915 and 986–992) into the respective receptor cDNAs from each species (12Kopin A.S. McBride E.W. Quinn S.M. Kolakowski Jr., L.F. Beinborn M. J. Biol. Chem. 1995; 270: 5019-5023Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar). TheXhoI and MluI chimeric receptor cDNAs were constructed by replacing segments of the human CCK-BR cDNA with the corresponding Mastomys sequence. Mutant receptors, in which 1–3 amino acids were replaced, were generated using oligonucleotide-directed mutagenesis (12Kopin A.S. McBride E.W. Quinn S.M. Kolakowski Jr., L.F. Beinborn M. J. Biol. Chem. 1995; 270: 5019-5023Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar). All chimeric and mutant receptor cDNA constructs were confirmed using the Applied Biosystems 373 DNA sequencer. COS-7 cells were grown in Dulbecco's modified Eagle's medium supplemented with 10% fetal calf serum and gentamicin (100 μg/ml). The cells were maintained at 37 °C in a 5% CO2 atmosphere. Utilizing the DEAE-dextran method (13Kopin A.S. Lee Y.M. McBride E.W. Miller L.J. Lu M. Lin H.Y. Kolakowski Jr., L.F. Beinborn M. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 3605-3609Crossref PubMed Scopus (473) Google Scholar), cells (106/10-cm dish) were transiently transfected with 5 μg of either the expression vector, pcDNA I, or the relevant CCK-BR cDNA construct. In control experiments (see Fig. 4), the amount of transfected DNA was adjusted (1–5 μg/10-cm dish) to obtain comparable receptor expression levels of the human and Mastomys CCK-BR. 24 h after transfection, cells were trypsinized and divided into 24-well plates (5 × 103 cells/well). The following day, competition binding experiments were performed in Hank's balanced salt solution supplemented with 25 mm HEPES, pH 7.3, 0.2% bovine serum albumin, and 0.15 mm phenylmethylsulfonyl fluoride. 20 pm of 125I-CCK-8 (NEN Life Science Products) was used as the radioligand in the absence or presence of increasing concentrations of unlabeled CCK-8 (0–0.3 μm). After incubation for 80 min at 37 °C, cells were washed three times with Hank's balanced salt solution and hydrolyzed in 1 n NaOH. Bound radioactivity was quantified, and receptor expression levels were calculated using computerized nonlinear curve fitting (MacLigand). In all experiments, the human wild-type CCK-BR was included as a control. Transfected COS-7 cells were cultured overnight in serum-free medium containing 3 μCi of [3H]myoinositol/ml. Ligand-independent and agonist (0.3 μm CCK-8)-stimulated [3H]inositol phosphate production were assessed at 37 °C in the presence of 10 mm LiCl. After incubation of the cells for either 0.5 or 1 h (see text), inositol metabolites were extracted with methanol/chloroform, and the upper phase was analyzed for inositol phosphates by strong anion exchange chromatography. The production of inositol phosphates was expressed as a fraction of the total cellular tritium content. To determine the receptor-mediated component of IP production, all measurements were corrected by the amount of IP formation in COS-7 cells expressing pcDNA I (the expression vector) alone. Second messenger signaling by COS-7 cells expressing the human (11Lee Y.M. Beinborn M. McBride E.W. Lu M. Kolakowski Jr., L.F. Kopin A.S. J. Biol. Chem. 1993; 268: 8164-8169Abstract Full Text PDF PubMed Google Scholar, 14Pisegna J.R. de Weerth A. Huppi K. Wank S.A. Biochem. Biophys. Res. Commun. 1992; 189: 296-303Crossref PubMed Scopus (216) Google Scholar, 15Ito M. Matsui T. Taniguchi T. Tsukamoto T. Murayama T. Arima N. Nakata H. Chiba T. Chihara K. J. Biol. Chem. 1993; 268: 18300-18305Abstract Full Text PDF PubMed Google Scholar), canine (13Kopin A.S. Lee Y.M. McBride E.W. Miller L.J. Lu M. Lin H.Y. Kolakowski Jr., L.F. Beinborn M. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 3605-3609Crossref PubMed Scopus (473) Google Scholar), rat (16Wank S.A. Harkins R. Jensen R.T. Shapira H. de Weerth A. Slattery T. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 3125-3129Crossref PubMed Scopus (400) Google Scholar), or Mastomys (10Nakata H. Matsui T. Ito M. Taniguchi T. Naribayashi Y. Arima N. Nakamura A. Kinoshita Y. Chihara K. Hosoda S. Chiba T. Biochem. Biophys. Res. Commun. 1992; 187: 1151-1157Crossref PubMed Scopus (116) Google Scholar) CCK-B receptors was assessed in the presence and in the absence of cholecystokinin octapeptide (CCK-8). With agonist stimulation, each receptor led to comparable levels of IP production (Fig. 1 A). In contrast, only theMastomys protein triggered ligand-independent IP formation that was significantly higher than the level observed in cells transfected with the expression vector, pcDNA I (Fig. 1 B). Increased expression of a constitutively active receptor will result in a parallel increase in both agonist-induced and ligand-independent second messenger signaling (17Samama P. Cotecchia S. Costa T. Lefkowitz R.J. J. Biol. Chem. 1993; 268: 4625-4636Abstract Full Text PDF PubMed Google Scholar). Consistent with this expectation, a positive correlation was observed between CCK-8-stimulated and ligand-independent signaling in COS-7 cells expressing theMastomys CCK-BR (Fig. 2). In contrast, signaling by the human CCK-BR in the absence of ligand was always close to zero regardless of the level of CCK-8-induced IP formation. These observations confirm that the MastomysCCK-BR is constitutively active, whereas the human homolog is not. A comparison of IP production after 0.5 and 1 h provided additional support that only the Mastomys CCK-BR is constitutively active. As shown in Fig. 3 A, a time-dependent increase in basal IP production is observed in cells expressing the Mastomys CCK-BR, whereas this is not the case in cells expressing the human receptor. As a control, the maximal level of CCK-8-induced signaling was also compared at 0.5- and 1-h incubation times. Consistent with expectation, agonist-induced IP production by either the Mastomys or the human CCK-BR increased to a similar extent independent of the respective basal level of signaling (Fig. 3 B). It has been recently established that constitutive activity of G protein-coupled receptors can be attenuated by a novel class of ligands, inverse agonists (18Barker E.L. Westphal R.S. Schmidt D. Sanders-Bush E. J. Biol. Chem. 1994; 269: 11687-11690Abstract Full Text PDF PubMed Google Scholar, 19Beinborn M. Quinn S.M. Kopin A.S. J. Biol. Chem. 1998; 273: 14146-14151Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar). The availability of such a compound for the CCK-BR, L-740,093 (R enantiomer), enabled us to provide additional confirmation of constitutive signaling by theMastomys CCK-BR. L-740,093 R attenuated ligand-independent IP production by the Mastomys receptor but had no effect on the basal activity of the human CCK-BR (Fig. 4 A). Half-maximal inhibition of ligand-independent signaling by L-740,093 R in cells expressing the Mastomys receptor was achieved at a concentration of 1.73 nm (Fig. 4 B). The marked difference in ligand-independent second messenger signaling by the Mastomys and human CCK-BR homologs was observed despite 92% amino acid identity between the two proteins. In an attempt to define a minimal domain of the Mastomys receptor, which conferred ligand-independent activity, a series of chimeric receptors was constructed with varying N-terminal portions of human sequence linked to complementary C-terminal portions of theMastomys protein (PstI, XhoI, and MluI chimeras, see Fig. 5). When functionally assessed in COS-7 cells, each of these chimeric receptors had a level of constitutive activity approaching that of theMastomys wild-type CCK-BR. Constitutive activity of the MluI chimera suggested that transfer of a small segment of the Mastomys receptor was sufficient to confer constitutive activity to the human protein. Sequence comparison between the Mastomys and human receptors within this limited domain, which spans transmembrane domain VI through the C terminus (see Fig. 5), revealed four candidate amino acids that could potentially confer constitutive signaling activity (Fig. 6 A). Many previously reported examples of constitutively active G protein-coupled receptors are the result of single amino acid substitutions (20Parma J. Duprez L. Van Sande J. Cochaux P. Gervy C. Mockel J. Dumont J. Vassart G. Nature. 1993; 365: 649-651Crossref PubMed Scopus (851) Google Scholar, 21Shenker A. Laue L. Kosugi S. Merendino Jr., J.J. Minegishi T. Cutler Jr., G.B. Nature. 1993; 365: 652-654Crossref PubMed Scopus (653) Google Scholar, 22Parent J.-L. LeGouill C. de Brum-Fernandes A.J. Rola-Pleszczynski M. Stankova J. J. Biol. Chem. 1996; 271: 7949-7955Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar). Based on this precedent, a series of four mutant human CCK-BRs was generated. In each receptor, one of the four human amino acids was replaced with the corresponding Mastomys residue. None of the single point mutations in the human CCK-BR was sufficient to significantly increase ligand-independent signaling relative to the human wild-type value (data not shown). The absence of ligand-independent signaling with single amino acid substitutions suggests that a combination of severalMastomys residues is required to confer constitutive signaling activity. To determine which of the four candidate Mastomys amino acids contributed to constitutive activity, an alternative strategy was utilized. With the cDNA encoding the human/Mastomys MluI chimera as a template for mutagenesis, each residue unique to theMastomys receptor (Leu344, Ile353, Asp407, Pro423) was sequentially replaced with its corresponding human homolog (Val340, Val349, Glu403, Ala419). A second series of four mutant human receptors was thus generated, each including a different combination of three Mastomys amino acids (Fig. 6 B). A decrease in constitutive signaling with replacement of the respective Mastomys amino acid indicated that the corresponding residue participated in ligand-independent signaling. Mutants 1, 2, and 3 had a significantly lower level of constitutive activity than the Mastomys wild-type receptor, suggesting that each of the Mastomys amino acids (Leu344, Ile353, Asp407), which had been substituted with the corresponding human residue, contributed to ligand-independent signaling (Fig. 6 B). In contrast, triple mutant 4 maintained constitutive activity comparable with the level of the Mastomys protein, despite substitution of Pro423 by an alanine residue. The latter finding suggests that the residue at position 423 played no appreciable role in conferring constitutive activity to the Mastomys CCK-BR. Comparison of the recombinant canine, rat, Mastomys, and human CCK-BRs expressed in COS-7 cells revealed that only theMastomys receptor triggered ligand-independent IP formation. Constitutive signaling activity of the Mastomys protein was confirmed by three additional observations: (i) the level of ligand-independent signaling correlated with respective levels of CCK-8-induced signaling, (ii) ligand-independent [3H]inositol phosphate formation increased with extended incubation time, and (iii) ligand-independent signaling could be inhibited in a concentration-dependent manner by the inverse agonist, L-740,093 R. Of note, none of these criteria applied to the human CCK-BR, which was tested in parallel. Together, these findings establish that the Mastomysreceptor is constitutively active as a consequence of interspecies variability in the CCK-BR. Since the Mastomys cDNA utilized in this study was isolated from an enterochromaffin-like cell carcinoid (10Nakata H. Matsui T. Ito M. Taniguchi T. Naribayashi Y. Arima N. Nakamura A. Kinoshita Y. Chihara K. Hosoda S. Chiba T. Biochem. Biophys. Res. Commun. 1992; 187: 1151-1157Crossref PubMed Scopus (116) Google Scholar), it was important to consider whether the corresponding protein resulted from a somatic mutation in the tumor. This possibility is unlikely based on sequence identity between the cDNA used in our experiments and CCK-BR cDNAs isolated from a number of normal Mastomystissues, including isolated gastric parietal cells and cerebral cortical tissue (7Modlin I.M. Tang L.H. Gastroenterology. 1996; 111: 783-810Abstract Full Text Full Text PDF PubMed Scopus (126) Google Scholar). The observation that species-dependent polymorphisms can result in constitutive activation of a G protein-coupled receptor suggests an important mechanism by which ligand-independent signaling can occur in nature. As such, our observation complements two previous reports which revealed that constitutive activity may be a distinguishing feature of certain G protein-coupled receptor subtypes (23Tiberi M. Caron M.G. J. Biol. Chem. 1994; 269: 27925-27931Abstract Full Text PDF PubMed Google Scholar) or splice variants (24Hasegawa H. Negishi M. Ichikawa A. J. Biol. Chem. 1996; 271: 1857-1860Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar). Study of both human and rat dopamine receptors indicated that the D1B subtype is constitutively active, whereas the D1A subtype is not (23Tiberi M. Caron M.G. J. Biol. Chem. 1994; 269: 27925-27931Abstract Full Text PDF PubMed Google Scholar). In the mouse, it has been found that alternative splicing of the prostaglandin E3 receptor results in a constitutively active isoform of this receptor (24Hasegawa H. Negishi M. Ichikawa A. J. Biol. Chem. 1996; 271: 1857-1860Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar). For both the D1 and the mouse prostaglandin E3 receptor, ligand-independent signaling is a property of naturally occurring receptor variants within a given species rather than a species-dependent phenomenon as observed with the Mastomys CCK-BR. The vast majority of naturally occurring constitutively active receptors reported in the literature can be attributed to single amino acid mutations. These point mutations have been identified in extracellular (25Paschke R. Ludgate M. N. Engl. J. Med. 1997; 337: 1675-1681Crossref PubMed Scopus (214) Google Scholar), transmembrane domain (21Shenker A. Laue L. Kosugi S. Merendino Jr., J.J. Minegishi T. Cutler Jr., G.B. Nature. 1993; 365: 652-654Crossref PubMed Scopus (653) Google Scholar, 26Robbins L.S. Nadeau J.H. Johnson K.R. Kelly M.A. Roselli-Rehfuss L. Baack E. Mountjoy K.G. Cone R.D. Cell. 1993; 72: 827-834Abstract Full Text PDF PubMed Scopus (774) Google Scholar, 27Konopka J.B. Margarit S.M. Dube P. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 6764-6769Crossref PubMed Scopus (106) Google Scholar, 28Blueml K. Mutschler E. Wess J. J. Biol. Chem. 1994; 269: 18870-18876Abstract Full Text PDF PubMed Google Scholar), and intracytoplasmic segments (20Parma J. Duprez L. Van Sande J. Cochaux P. Gervy C. Mockel J. Dumont J. Vassart G. Nature. 1993; 365: 649-651Crossref PubMed Scopus (851) Google Scholar, 22Parent J.-L. LeGouill C. de Brum-Fernandes A.J. Rola-Pleszczynski M. Stankova J. J. Biol. Chem. 1996; 271: 7949-7955Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar, 29Schipani E. Kruse K. Juppner H. Science. 1995; 268: 98-100Crossref PubMed Scopus (567) Google Scholar, 30Kjelsberg M.A. Cotecchia S. Ostrowski J. Caron M.G. Lefkowitz R.J. J. Biol. Chem. 1992; 267: 1430-1433Abstract Full Text PDF PubMed Google Scholar) of the corresponding G protein-coupled receptors. In contrast to this precedent, it is of note that three amino acids act in concert to confer constitutive activity to the Mastomys CCK-BR. Two of these residues (Leu344, Ile353) are located in transmembrane domain VI of the Mastomys CCK-BR, consistent with reports indicating a role of TMD VI in receptor activation. Studies with the photoreceptor rhodopsin, another member of the seven transmembrane domain receptor superfamily, suggest that movement of TMD VI is required for G protein activation (31Farrens D.L. Altenbach C. Yang K. Hubbell W.L. Khorana H.G. Science. 1996; 274: 768-770Crossref PubMed Scopus (1112) Google Scholar). In addition, rotation of TMD VI has been demonstrated with either ligand or mutation-induced activation of the β2 adrenergic receptor (32Gether U. Lin S. Ghanouni P. Ballesteros J.A. Weinstein H. Kobilka B.K. EMBO J. 1997; 16: 6737-6747Crossref PubMed Google Scholar, 33Javitch J.A. Fu D. Liapakis G. Chen J. J. Biol. Chem. 1997; 272: 18546-18549Abstract Full Text Full Text PDF PubMed Scopus (184) Google Scholar). Complementing these prior observations, the occurrence of activating polymorphisms in TMD VI of the CCK-BR further illustrates that this portion of the protein may be an important regulator of receptor-mediated signaling. The third activating polymorphism in the Mastomys CCK-BR (Asp407 versus Glu403 in the human receptor) is found in the carboxyl terminus. This region of G protein-coupled receptors has been hypothesized to play a role in constraining the protein through palmitoylated cysteine residues that are believed to be anchored in the cell membrane. Truncations of the carboxyl terminus can result in constitutive activity as shown for the PGE3 receptor (24Hasegawa H. Negishi M. Ichikawa A. J. Biol. Chem. 1996; 271: 1857-1860Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar) and the thyrotropin-releasing hormone receptor (34Matus-Leibovitch N. Nussenzveig D.R. Gershengorn M.C. Oron Y. J. Biol. Chem. 1995; 270: 1041-1047Abstract Full Text Full Text PDF PubMed Scopus (38) Google Scholar). Alternately, deletion or truncation of the carboxyl terminus may leave the signaling properties of a G protein-coupled receptor unchanged (35Thomas W.G. Thekkumkara T.J. Motel T.J. Baker K.M. J. Biol. Chem. 1995; 270: 207-213Abstract Full Text Full Text PDF PubMed Scopus (127) Google Scholar). The variable consequences of carboxyl-terminal truncations may indicate that this domain may act in concert with other regions of the receptor to define the basal level of signaling. Consistent with this possibility, our results suggest that a combination of transmembrane domain VI and carboxyl terminus amino acids together confer constitutive activity to the Mastomys CCK-BR. Several naturally occurring constitutively active G protein-coupled receptors, each the result of single amino acid mutations, cause alterations of physiologic function both in animals as well as in humans. Constitutively active melanocyte-stimulating hormone receptor isoforms result in darkening of fur and skin color in mice (26Robbins L.S. Nadeau J.H. Johnson K.R. Kelly M.A. Roselli-Rehfuss L. Baack E. Mountjoy K.G. Cone R.D. Cell. 1993; 72: 827-834Abstract Full Text PDF PubMed Scopus (774) Google Scholar). Activating mutations in the luteinizing hormone receptor lead to precocious puberty (21Shenker A. Laue L. Kosugi S. Merendino Jr., J.J. Minegishi T. Cutler Jr., G.B. Nature. 1993; 365: 652-654Crossref PubMed Scopus (653) Google Scholar), whereas constitutively active parathyroid hormone receptors result in Jansen-type metaphyseal chondrodysplasia (29Schipani E. Kruse K. Juppner H. Science. 1995; 268: 98-100Crossref PubMed Scopus (567) Google Scholar). Constitutively active mutants of the thyroid-stimulating hormone receptor have been identified in patients with thyroid adenomas (20Parma J. Duprez L. Van Sande J. Cochaux P. Gervy C. Mockel J. Dumont J. Vassart G. Nature. 1993; 365: 649-651Crossref PubMed Scopus (851) Google Scholar). In contrast to constitutively active receptors that arise from single point mutations (discussed above), ligand-independent signaling by theMastomys CCK-BR results from a triple amino acid alteration. The observation that multiple naturally occurring residue changes can lead to constitutive receptor activity introduces a new consideration in the search for receptor abnormalities underlying physiologic alterations. In the case of the Mastomys CCK-BR, thein vivo consequences of receptor overactivity remain to be determined. Based on precedent with constitutively active G protein-coupled receptors resulting in tumor formation (20Parma J. Duprez L. Van Sande J. Cochaux P. Gervy C. Mockel J. Dumont J. Vassart G. Nature. 1993; 365: 649-651Crossref PubMed Scopus (851) Google Scholar, 36Allen L.F. Lefkowitz R.J. Caron M.G. Cotecchia S. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 11354-11358Crossref PubMed Scopus (292) Google Scholar), it is intriguing to speculate that the ligand-independent signaling by theMastomys CCK-BR may in part explain the increased susceptibility of this species to the development of ECL cell hyperplasia as well as ECL cell-derived carcinoid tumors. We thank Wyeth-Lederle for providing L- 740,093 R, Dr. T. Chiba for providing theMastomys CCK-BR cDNA, and Dr. S. A. Wank for providing the rat CCK-BR cDNA. We are grateful to Drs. M. Bläker, Y. Ren, A. Leiter, and A. Kane for critical reading of the manuscript and to B. Desai, C. Chen, and L. Sundararajan for technical assistance." @default.
• W2034999710 created "2016-06-24" @default.
• W2034999710 creator A5008402391 @default.
• W2034999710 creator A5019236825 @default.
• W2034999710 creator A5065818430 @default.
• W2034999710 creator A5082620506 @default.
• W2034999710 date "1998-11-01" @default.
• W2034999710 modified "2023-10-18" @default.
• W2034999710 title "Interspecies Polymorphisms Confer Constitutive Activity to theMastomys Cholecystokinin-B/Gastrin Receptor" @default.
• W2034999710 cites W1489775551 @default.
• W2034999710 cites W1517156830 @default.
• W2034999710 cites W1536524213 @default.
• W2034999710 cites W1541533178 @default.
• W2034999710 cites W1641874896 @default.
• W2034999710 cites W1677997440 @default.
• W2034999710 cites W196234132 @default.
• W2034999710 cites W1977579738 @default.
• W2034999710 cites W1979100850 @default.
• W2034999710 cites W1982527304 @default.
• W2034999710 cites W1989535966 @default.
• W2034999710 cites W1990109135 @default.
• W2034999710 cites W1999767086 @default.
• W2034999710 cites W2007311397 @default.
• W2034999710 cites W2009191433 @default.
• W2034999710 cites W2019742616 @default.
• W2034999710 cites W2024476894 @default.
• W2034999710 cites W2025013212 @default.
• W2034999710 cites W2053174683 @default.
• W2034999710 cites W2054009022 @default.
• W2034999710 cites W2062207135 @default.
• W2034999710 cites W2065125656 @default.
• W2034999710 cites W2067157370 @default.
• W2034999710 cites W2068176708 @default.
• W2034999710 cites W2068477597 @default.
• W2034999710 cites W2070304988 @default.
• W2034999710 cites W207069409 @default.
• W2034999710 cites W2071587854 @default.
• W2034999710 cites W2072915505 @default.
• W2034999710 cites W2093094352 @default.
• W2034999710 cites W2097836571 @default.
• W2034999710 cites W2138566752 @default.
• W2034999710 cites W2321550529 @default.
• W2034999710 cites W4253910242 @default.
• W2034999710 doi "https://doi.org/10.1074/jbc.273.44.28779" @default.
• W2034999710 hasPubMedId "https://pubmed.ncbi.nlm.nih.gov/9786876" @default.
• W2034999710 hasPublicationYear "1998" @default.
• W2034999710 type Work @default.
• W2034999710 sameAs 2034999710 @default.
• W2034999710 citedByCount "31" @default.
• W2034999710 countsByYear W20349997102012 @default.
• W2034999710 countsByYear W20349997102013 @default.
• W2034999710 countsByYear W20349997102014 @default.
• W2034999710 countsByYear W20349997102016 @default.
• W2034999710 countsByYear W20349997102018 @default.
• W2034999710 countsByYear W20349997102019 @default.
• W2034999710 countsByYear W20349997102020 @default.
• W2034999710 crossrefType "journal-article" @default.
• W2034999710 hasAuthorship W2034999710A5008402391 @default.
• W2034999710 hasAuthorship W2034999710A5019236825 @default.
• W2034999710 hasAuthorship W2034999710A5065818430 @default.
• W2034999710 hasAuthorship W2034999710A5082620506 @default.
• W2034999710 hasBestOaLocation W20349997101 @default.
• W2034999710 hasConcept C107539642 @default.
• W2034999710 hasConcept C126322002 @default.
• W2034999710 hasConcept C134018914 @default.
• W2034999710 hasConcept C170493617 @default.
• W2034999710 hasConcept C2776986829 @default.
• W2034999710 hasConcept C2777593968 @default.
• W2034999710 hasConcept C2777951760 @default.
• W2034999710 hasConcept C32110497 @default.
• W2034999710 hasConcept C49039625 @default.
• W2034999710 hasConcept C54355233 @default.
• W2034999710 hasConcept C56191518 @default.
• W2034999710 hasConcept C71924100 @default.
• W2034999710 hasConcept C86803240 @default.
• W2034999710 hasConceptScore W2034999710C107539642 @default.
• W2034999710 hasConceptScore W2034999710C126322002 @default.
• W2034999710 hasConceptScore W2034999710C134018914 @default.
• W2034999710 hasConceptScore W2034999710C170493617 @default.
• W2034999710 hasConceptScore W2034999710C2776986829 @default.
• W2034999710 hasConceptScore W2034999710C2777593968 @default.
• W2034999710 hasConceptScore W2034999710C2777951760 @default.
• W2034999710 hasConceptScore W2034999710C32110497 @default.
• W2034999710 hasConceptScore W2034999710C49039625 @default.
• W2034999710 hasConceptScore W2034999710C54355233 @default.
• W2034999710 hasConceptScore W2034999710C56191518 @default.
• W2034999710 hasConceptScore W2034999710C71924100 @default.
• W2034999710 hasConceptScore W2034999710C86803240 @default.
• W2034999710 hasIssue "44" @default.
• W2034999710 hasLocation W20349997101 @default.
• W2034999710 hasOpenAccess W2034999710 @default.
• W2034999710 hasPrimaryLocation W20349997101 @default.
• W2034999710 hasRelatedWork W1020341931 @default.
• W2034999710 hasRelatedWork W1970378675 @default.
• W2034999710 hasRelatedWork W1982594208 @default.
• W2034999710 hasRelatedWork W2031272904 @default.
• W2034999710 hasRelatedWork W2034906614 @default.
• W2034999710 hasRelatedWork W2042209138 @default.

• next