Gastrin Expression Research Articles

Ileal expression of gastrin and cholecystokinin: In search of a related hormone

Antibodies against the common active site of cholecystokinin (CCK) and gastrin stain three endocrine celltypes in the gut: G-cells (that synthesize gastrin) I-cells (that synthesize CCK), and TG-cells (whose product is unknown). In order to examine whether TG-cells either process progastrin or proCCK in a specific manner, or express a novel gastrin-CCK related hormone, we studied the distal porcine ileum, which have far more TGthan G- and I-cells. Ileal CCK and gastrin mRNA corresponded to those of the antroduodenal mucosa. Gel, ion-exchange and reversed-phase chromatography monitored with sequence-specific immunoassays showed that the ileal mucosa on average contain 0.3 and 7.6 pmol g progastrin and proCCK, respectively; 1.1 and 13.5 pmol g glycine-extended intermediates; and 1.1 and 24.8 pmol g of bioactive carboxyamidated gastrin and CCK, respectively. Gastrin was present only as non-sulfated gastrin-34, whereas CCK occurred in forms similar to those of the proximal intestine. Although ileal progastrin processing is tissue specific, the amounts of gastrin and CCK are too small to explain the TG-cells. Moreover, since the ileal extracts were without traces of other peptides having the C-terminus common to gastrin and CCK, the results suggest that TG-cells produce a peptide, which is only weakly related to gastrin and CCK.

Spasmolytic polypeptide: A trefoil peptide secreted by rat gastric mucous cells

Background/Aims: Spasmolytic polypeptide (SP) is a trefoil peptide expressed in the digestive tract. This study aimed to determine the structure and distribution of SP expression in the rat gastrointestinal tract. Methods: The structure of rat SP was determined from the sequence of complementary DNAs isolated from antral RNA. SP gene expression was localized by Northern blotting and in situ hybridization in the adult and fetal rat digestive tract. Expression of the SP peptide was localized by immunocytochemistry and Western blot analysis. Results: SP messenger (m)RNA was found predominantly in the stomach with highest expression in the antrum. High levels of SP mRNA were expressed in the fetal stomach before gastrin and somatostatin expression. Surprisingly, SP mRNA and peptide did not colocalize in the gastric mucosa, SP mRNA being superficial to SP peptide immunoreactivity throughout the gastric mucosa. Abundant SP immunoreactivity was seen in the lumen of the gastric glands and the mucus layer adherent to the gastric mucosa, indicating luminal secretion. Conclusions:In the rat, SP is a peptide secreted predominantly from antral mucous cell. The high concentrations of SP in the adherent gastric mucus layer (approximately 10 μmol/L) suggest that SP functions as a structural peptide rather than a regulatory peptide.

Novel expression of gastrin (CCK-B) receptors in pancreatic carcinomas and dysplastic pancreas from transgenic mice

Transgenic mice bearing the elastase I promoter—SV40 T-antigen fusion gene (ELSV) develop pancreatic acinar cell carcinomas by 3 to 6 months of age. The purpose of the study was to determine if pancreatic carcinomas and dysplastic pancreas from the Tg (Ela-1, SV40E + Ela-1, neo) Bril9 strain of ELSV transgenic mice express gastrin (CCK-B) receptors. To accomplish this, we utilized iodine 125 ( 125I) -gastrin binding studies, reverse transcription-polymerase chain reaction (RTPCR), and Southern blot analysis to examine pancreatic carcinomas from 26-week-old male ELSV transgenic mice, dysplastic pancreas from 8-weekold male ELSV transgenic mice, and normal pancreas from 30-week-old nontransgenic male mice (SJL/J) and from 8-week-old nontransgenic male mice (B6SJLF 1/J). No saturable gastrin binding to normal nontransgenic mouse pancreas was found. In contrast, saturable gastrin binding was detected at pH 6.5, 22 °C, in 9 of 13 pancreatic carcinomas and all 5 dysplastic pancreata. Competitive inhibition 125I-gastrin binding assays showed gastrin bound to a single class of high-affinity receptors (receptor binding affinity [K d] 0.11 ± 0.02 nM, binding capacities ranging from 1 to 60 fmol/mg protein for pancreatic carcinomas; K d: 0.15 ± 0.04 nM, binding capacities ranging from 1 to 9 fmol/mg protein for dysplastic pancreas). RT-PCR and Southern blot analysis confirmed 125I-gastrin binding studies by demonstrating gastrin (CCK-B) receptor mRNA expression in pancreatic carcinomas and dysplastic pancreas but an absence of mRNA expression in normal nontransgenic mouse pancreas. In conclusion, pancreatic carcinomas and dysplastic pancreas in ELSV transgenic mice novelly express gastrin (CCK-B) receptors. This expression may provide a growth advantage to acinar cells as part of the multistage process of carcinogenesis.

The Tumor Biology Of Gastrin And Cholecystokinin

Publisher Summary This chapter discusses the tumor biology of gastrin and cholecystokinin (CCK) by giving a description of the normal biology of the gastrin and CCK systems followed by a discussion of the expression and growth stimulation of gastrin and CCK peptides in carcinomas, sarcomas, and benign tumors. The novel methods for the measurement of gastrin and CCK expression in experimental and clinical oncology have been mentioned. The single most important aspect in gastrin and CCK tumor biology is the possible involvement of gastrin in the development of several common carcinomas. Expression of the gastrin gene has been found not only in colorectal carcinomas, but also in bronchial, ovarian, pancreatic, and apparently some gastric carcinomas. Specific aspects of the association between gastrin or CCK, and cancer have been reviewed. However, because the emphasis has been on clinical correlations, a more comprehensive review including the basic aspects is needed.

Activation of gastrin transcription in pancreatic insulinoma cells by a CACC promoter element and a 70-kDa sequence-specific DNA-binding protein.

Gastrin gene expression in the pancreatic islets is developmentally regulated and occurs largely during fetal life. Deletional analysis of transiently transfected rat insulinoma cells with gastrin 5'-flanking sequences in luciferase reporter genes demonstrated that the gastrin promoter sequence proximal to -111 base pairs (bp) contains the cis-regulatory elements necessary for maximal transcription. Mutational analysis identified the sequence CCCCACCCCA (-109 to -100 bp) as a positive cis-regulatory element (CACC) located 5' to a previously described negative element (-100 to -90 bp) and E-box positive element at -82 bp. Multimers of the CACC element in a heterologous promoter activated transcription independent of the other cis-regulatory elements. CACC binding proteins were purified from insulinoma cell nuclear extracts by cation exchange and affinity chromatography. Southwestern blot of nuclear extracts identified a 70-kDa CACC-binding protein. Mutational analysis of the CACC element showed a close correlation between DNA binding of this protein and transcriptional activation. Transcriptional activation by multimers of the CACC element in a heterologous promoter was detected in a variety of cell lines but was strongest in those of islet lineage. Likewise, the presence of the 70-kDa CACC-binding protein was found in many cell lines but was most abundant in the insulinoma cells. The CACC-binding protein has not been previously identified among the known pancreatic regulatory factors and may have an important role in the developmental expression of gastrin.

Expression of the gastric H+/K(+)-ATPase and histidine decarboxylase during omeprazole treatment.

The gastric proton pump H+/K(+)-ATPase in the parietal cell is central to acid secretion into the stomach. We performed the following experiment to examine the pattern of expression of the alpha- and beta-subunits of the H+/K(+)-ATPase at the transcriptional level during 7 days' application of the proton pump inhibitor omeprazole, in relation to the expression of gastrin and histamine, two stimuli of gastric acid secretion. Serum gastrin concentrations and mRNA levels of antral gastrin, fundic histidine decarboxylase (HDC) and H+/K(+)-ATPase alpha- and beta-subunits were determined after 8 h, 1, 3 and 7 days. Omeprazole treatment rapidly caused an increase in the serum gastrin concentration and the antral gastrin mRNA level after 3 days. HDC mRNA expression showed a steady increase with a 5-fold induction after 1 week. However, mRNA levels of the alpha- and beta-subunits of the H+/K(+)-ATPase were unchanged during the course of omeprazole treatment. These results suggest that omeprazole inhibition of the gastric proton pump does not result in feedback activation of H+/K(+)-ATPase gene expression despite adaptive changes of the endocrine stomach.

Developmental expression of pancreatic gastrin and somatostatin in the sheep

The nature and developmental profile of pancreatic gastrin and somatostatin were determined in the ovine fetus, a model considered relevant to human development. Gastrin and somatostatin peptide and mRNA were examined in the pancreas of fetal sheep at 80, 105, 125 and 140 days gestation (term: 145 days), 15-day-old lambs and adult sheep. Highest concentrations of gastrin (both amidated and the glycine-extended precursor) were observed in the lamb pancreas with gastrin mRNA levels highest at 140 days gestation. Amidated gastrin was present almost entirely as sulphated gastrin-17 while glycine-extended gastrin was mostly present as a high molecular weight form. Only glycine-extended gastrin was detected in the adult pancreas, indicating attenuated processing in mature adult pancreas. Up to 140 days gestation, gastrin mRNA correlated better with glycine-extended gastrin than with the amidated form, suggesting that amidation was a rate-limiting factor in the production of bioactive gastrin. Somatostatin mRNA and peptide reached a higher concentration and peaked before that of gastrin. Gastrin is a normal product of the fetal and adult pancreas although, when compared to the antrum, the levels are low and the processing to amidated forms is substantially reduced. Unlike in the stomach, the developmental profile of pancreatic gastrin and somatostatin does not appear to be linked.

Initiation of gastrin expression during the development of the mouse pancreas

Gastrin expression occurs in the pancreas in only two situations: (1) in cases of gastrinoma and (2) in the embryonic/fetal pancreas. The initiation of gastrin expression in the embryonic pancreas may be recapitulated during gastrinoma tumorigenesis. For this reason, we have tried to identify the point of onset of gastrin expression in the developing pancreas. Previously, determining the point of onset for genes in embryonic tissues has been difficult because of low expression levels and small tissue samples. Using the sensitive polymerase chain reaction assay, we were able to determine, with a sensitivity of 10 molecules of mRNA, the earliest expression of gastrin in the developing pancreas. This expression occurred at 30 somites, or at a gestation of 9.5 to 10 days.

Detection of gastrin mRNA by in situ hybridization using radioactive‐ and digoxigenin‐labelled probes: a comparative study

The hormone gastrin is mainly produced by the G cells of the antral mucosa and plays a major role in the regulation of digestive mucosal growth. Since it permits identification of cell types containing mRNA, in situ hybridization (ISH) appears to be an interesting method for studying gastrin-producing tissues. In this study, in situ detection of gastrin mRNA has been carried out on frozen sections of four human normal antral mucosa samples and of six colonic carcinomas removed from patients with high levels of plasma gastrin, using a gastrin oligonucleotidic DNA probe. We have compared the results provided respectively by the [35s] labelling and the digoxigenin labelling of the synthetic probe. Positive cells were found in each normal sample analysed with radioactive- as well as digoxigenin-labelled antisense probes. The total number of cells expressing gastrin mRNA appeared slightly higher with the [35s]-labelled probe, while the digoxigenin-labelled probe gave a better definition of positive signals. In contrast, neither radioactive nor cold probes gave positive signals in the six colonic carcinoma samples, although gastrin expression had been demonstrated in these tumours using a reverse transcriptase-PCR method. These results show that, although ISH does not seem sensitive enough to allow the detection of very low levels of gastrin expression, it would appear to be a reliable method for visualizing gastrin mRNA in human antral mucosa.

20. Initiation of gastrin expression during development of the mouse pancreas

20. Initiation of gastrin expression during development of the mouse pancreas

Gastrin and Cancer

Publisher Summary This chapter describes the biology of the gastrin system and the involvement of gastrin in the development of various forms of cancer. The chapter presents new analytical methods for the measurement of gastrin in clinical oncology. Gastrin is a well-studied hormone that is discovered as a gastric acid-stimulating factor in extracts of antral mucosa. The elaborate biosynthetic pathway of gastrin in its main site of synthesis—the antral G cells—is now well described (B12, H5, 52, SIO). The pathway explains the molecular heterogeneity of gastrin in tissue and in circulation (52, R11, Y1). The active site homology of gastrin with cholecystokinin (CCK) poses large analytical problems because the active site is strongly immunogenic and both CCK and gastrin receptors may bind peptides having common sequences. Consequently, evaluation of antibody and receptor binding of gastrin and studies of the carcinogenic effects of gastrin require due consideration of possible interactions and cross-reactivity with CCK peptides. In normal mammalian organisms, gastrin is generally produced by the antral G cells (L1 and R2). The chapter concludes with a discussion of the expression and synthesis of antral and extra-antral gastrin.

Expression and post-translational processing of gastrin in heterologous endocrine cells.

The biosynthesis of gastrin involves a complex series of post-translational processing reactions that result in the formation of a biologically active secretory product. To study the mechanisms for two specific reactions in gastrin processing, namely dibasic cleavage and amidation, we infected AtT-20, GH3, and Rin5-f cells with the retroviral expression vector, pZip-NeoSV(X), containing human gastrin cDNA. We detected gastrin and its glycine extended post-translational processing intermediates (G-gly) in the media and cell extracts of successfully infected cells. Characterization of the molecular forms of gastrin in these cell lines revealed that GH3 and Rin5-f processed gastrin in a manner similar to antral G-cells but the cleavage of the Lys74-Lys75 bond that converts G34 to G17 appeared to be suppressed in AtT-20 cells. Even after conversion of this site to Arg74-Arg75 via site-directed mutagenesis, the At-20 cells synthesized G34 predominantly. All of the infected cells amidated gastrin but the gastrin/G-gly ratio, a reflection of amidation within the cells, was enhanced in GH3 and Rin5-f cells but diminished in AtT-20 cells upon treatment with dexamethasone (10(-4) M) for 3 days. The dibasic cleavage of gastrin was uneffected by dexamethasone. Our data suggest that the activities of post-translational processing reactions responsible for the synthesis of biologically active gastrin exhibit considerable tissue and substrate specificity.

Pulmonary blastoma with neuroendocrine differentiation in cell morules resembling neuroepithelial bodies

Pulmonary blastoma is an infrequent malignant neoplasm, so called because of its resemblance to fetal lung. The original description outlined the components as variable mixtures of epithelial and stromal elements. More recently, a variant displaying almost exclusively epithelial differentiation has been described. We report our findings in a case of pulmonary blastoma with predominance of epithelial cells, forming tubular structures and large morules. The architectural arrangement of the morules was remarkably similar to normal bronchial neuroepithelial bodies. Moreover, their immunohistochemical profiles were also very similar, including the expression of cytokeratins, chromogranin, neuron-specific enolase, synaptophysin, gastrin, calcitonin, bombesin, somatostatin and serotonin.

Gastrin in Non-Neoplastic Pancreatic Tissue from Patients with and without Gastrinomas

Processing-independent radioimmunoanalysis for progastrin showed that extracts of normal pancreatic tissue from normal subjects (n = 5) and from patients with adenocarcinoma of the papilla of Vater (n = 4) contain progastrin and its products. The concentrations varied from 0.1 to 5.8 pmol/g tissue, of which carboxyamidated bioactive gastrins constituted 0.03-1.9 pmol/g. In histologically normal and nonneoplastic pancreatic tissue from patients with duodenal (n = 3) and pancreatic (n = 2) gastrinomas the expression of gastrin was significantly higher-14.5 pmol/g (median), of which 28% was bioactive amidated gastrins. Gastrin-17 was the main bioactive product, but its immediate precursor, glycine-extended gastrin-17, constituted the predominant part of the preprogastrin product in pancreatic tissue. Proper gastrinoma tissue contained several precursor forms, including intact unprocessed progastrin. Progastrins were also found in high concentrations in plasma from the gastrinoma patients. The results raise the possibility that increased expression of progastrin and its products in non-neoplastic pancreatic tissue is a primary defect predisposing to neoplasia.

Gastrin gene expression and regulation in rat islet cell lines.

Gastrin gene expression was observed in two permanent rat insulinoma (RIN) cell lines derived from a rat insulinoma. Gastrin expression was selective; highest expression was seen in a cell line which did not express other islet cell hormones. Gastrin mRNA transcription initiated from the same promoter as antral gastrin mRNA. DNA transfection studies with a gastrin chloramphenicol acetyltransferase chimeric gene showed higher expression in gastrin-expressing RIN cells than non-gastrin-expressing islet cells. This implies that gastrin-expressing RIN cells selectively express a trans-acting transcriptional activator which binds to cis-acting regulatory sequences within the 5'-flanking DNA sequence and first exon of the gastrin gene. The gastrin peptide precursor synthesized in these RIN cell lines is subject to the same repertoire of posttranslational modifications within the cell's secretory apparatus (endoproteolytic cleavage, tyrosine sulfation, and C-terminal amidation) as seen in antral G cells. Gastrin mRNA levels in these RIN cells were selectively increased by increasing the extracellular calcium concentration. Membrane depolarization also stimulated gastrin mRNA levels, probably through activation of voltage-sensitive calcium channels. Thus, these gastrin-expressing RIN cell lines provide permanent cell lines useful in analyzing the cellular regulation of gastrin gene expression.

Differential gastrin gene expression in rat gastrointestinal tract and pancreas during neonatal development.

Gastrin gene expression exhibits a complex pattern of tissue-specific expression during the neonatal development of the gastrointestinal tract and pancreas. In the rat fetus, the pancreas is the major site of gastrin expression; very little gastrin is found in the antrum which is the major site of adult expression. Pancreatic gastrin mRNA is identical to the antral species having the same transcriptional initiation site. The post-translational processing of the pancreatic gastrin peptide, however, differs in being fully tyrosine sulfated, and thus it resembles gastrin's homologue, cholecystokinin. Pancreatic gastrin is maximally expressed during late fetal gestation before the marked rise in somatostatin, insulin, and glucagon mRNA levels which occurs during the last 4 days of gestation. After birth, gastrin mRNA levels rapidly disappear as the other islet mRNAs achieve stable maximal levels. Unlike the pancreas, gastrin gene expression in the duodenum and antrum is similar to the development profiles of somatostatin and glucagon gene expression. In the duodenum, however, expression of cholecystokinin differs from the common developmental pattern in being expressed only after birth. Thus, pancreatic gastrin gene expression shows a reciprocal relationship to the developmental expression of cholecystokinin in the duodenum.

Concordant expression of gastrin releasing peptide (GRP) and GRP gene associated peptides (GGAPs) in primary and metastatic human small cell lung cancers (SCLCs): An immunohistochemical analysis

Concordant expression of gastrin releasing peptide (GRP) and GRP gene associated peptides (GGAPs) in primary and metastatic human small cell lung cancers (SCLCs): An immunohistochemical analysis