Caerulein and gastrin(2-17 ds) regulate differently synthesis of secretory enzymes, mRNA levels and cell proliferation in pancreatic acinar cells (AR4-2J)

By modulating α2β1 integrin signalling, gastrin increases adhesion oF AGS-GR gastric cancer cells

Peritoneal metastasis is a major cause of recurrence of gastric cancer and integrins are key molecules involved in gastric cancer cells attachment to the peritoneum. The peptide hormone, gastrin, initially identified for its role in gastric acid secretion is also a growth factor for gastric mucosa. Gastrin has also been shown to contribute to gastric cancers progression. Here, we provide the first evidence that gastrin increases the adhesion of gastric cancer cells. Gastrin treatment induces the expression of α2 integrin subunit through a mechanism that involves the ERK pathway. We also observed in response to gastrin an increase in the amount of α2 integrin associated with β1subunit. In addition, gastrin-stimulated cell adhesion was blocked with an anti-α2β1 integrin neutralizing antibody. We also show that gastrin activates the integrin pathway via the phosphorylation of β1 integrin by a Src family kinase. This mechanism may contribute to the enhancement of cell adhesion observed in response to gastrin since we found an inhibition of gastrin-mediated cell adhesion when cells were treated with a Src inhibitor. By regulating one of the key step of the metastatic process gastrin might contribute to increase the aggressive behaviour of human gastric tumours.

Hereditary pancreatitis of 3 Chinese children: Case report and literature review

BACKGROUND

Hereditary pancreatitis (HP) is quite rare and is distinguished by incomplete penetrance presentation as early-onset relapsing pancreatitis, usually beginning in childhood. HP is now known to be commonly relevant to mutations in the PRSS1 (gene-encoding cationic trypsinogen), SPINK1 (serine protease inhibitor, Kazal type 1), CFTR (cystic fibrosis), carboxypeptidase A1 (CPA1), and chymotrypsin C (CTRC) genes as reported in some Caucasian studies. HP has a variable spectrum of severity and may develop complications.

METHODS & RESULTS

We describe the clinical course of 3 preschool children, hospitalized with postprandial abdominal pain, whose laboratory tests showed high serum amylase. Similar episodes of abdominal pain led to readmission, and the patients recovered quickly after using symptomatic therapy. The condition of the first boy, who developed a pancreatic tail pseudocyst and splenic infarction, was especially complicated. The boy underwent 2 endoscopic retrograde cholangiopancreatographies and stenting, along with a surgical procedure that completely relieved his symptoms for 3 months. The 3 patients and their parents were given genetic testing. All of the patients carried 1 or more gene mutations inherited from their mothers, fathers, or both parents; however, none of the parents were affected.

CONCLUSION

For children with repeated pancreatitis, clinicians should consider HP in the differential diagnosis. It is reliable to perform gene sequencing on suspicious patients and their parents. Multidisciplinary and comprehensive treatment should be recommended to manage HP and its complications. Cholangiopancreatography and stenting is a relatively minimally invasive approach when compared with surgery and can be tried as an early intervention. Surgical procedures should be reserved for patients with complications.

Pentagastrin-induced protein synthesis in the parotid gland of the anaesthetized rat, and its dependence on CCK-A and -B receptors and nitric oxide generation

In parotid glands of pentobarbitone-anaesthetized rats, the incorporation of [3H]leucine into trichloroacetic acid-insoluble materials, reflecting protein synthesis, increased by 17% (compared to saline-treated rats) in response to infusion of pentagastrin (20 microg kg(-1), i.v. for 1 h) under muscarinic and alpha- and beta-adrenoceptor blockade. Both the CCK-A receptor antagonist lorglumide (48 mg kg(-1), i.v.) and the CCK-B receptor antagonist itriglumide (5.5 mg kg(-1), i.v.), given separately, prevented the expected increase in pentagastrin and, in addition, reduced the glandular protein synthesis by 16 and 12%, respectively, below the level of saline-treated rats. In rats treated with saline only, the glandular protein synthesis was reduced by 22% by the CCK-A receptor antagonist and by 17% by the CCK-B receptor antagonist; combined, the two antagonists caused no further reduction (20%). There was no increase in the glandular protein synthesis of pentagastrin-treated rats compared to that of the saline-treated rats when both groups of rats were exposed to a combination of the two types of CCK receptor antagonists. In pentagastrin-treated rats, the protein synthesis in the parotid glands was 23% less in the presence of the non-selective nitric oxide (NO) synthase inhibitor L-NAME (30 mg kg(-1), i.v.) than in its absence; the result was the same (23%) when the neuronal NO synthase inhibitor Nomega-propyl-L-arginine (N-PLA; 30 mg kg(-1), i.v.) replaced L-NAME. The protein synthesis in rats treated with saline only was not reduced by L-NAME; nor was the protein synthesis of saline-treated rats different from that of pentagastrin- and L-NAME-treated rats. Thus, under 'basal' conditions, a portion of the glandular protein synthesis, as well as the whole increase in synthesis in response to administration of pentagastrin, engaged both types of CCK receptors. Furthermore, NO generation, owing to neuronal NO synthase activity, was required for the increase to occur in response to pentagastrin, whereas a non-NO-dependent pathway was responsible for the protein synthesis under 'basal' conditions.

Transient agonist-induced regulation of the cholecystokinin-A and cholecystokinin-B receptor mRNA levels in rat pancreatic acinar AR42J cells

BACKGROUND

CCK-8 and gastrin exert multiple effects in the gastrointestinal tract and the nervous system. Their actions are mediated via the G-protein coupled CCK-A and CCK-B receptors.

METHODS

Rat pancreatic acinar tumor AR42J cells express both CCK receptor subtypes. This cell line was used to characterize the agonist-dependent regulation of CCK-A and CCK-B receptor gene expression.

RESULTS

CCK-8 (10 nM) or gastrin (10 nM) reduced CCK-A receptor mRNA expression to 56% and 53%, respectively 2 h after hormonal exposure. In contrast, the level of CCK-B receptor gene expression was upregulated to 157% and 153%, respectively. These effects are most probably linked to the CCK-B receptor in AR42J cells. The phorbolester PMA (100 nM), a protein kinase C activator, downregulated CCK-A receptor expression but did not affect CCK-B receptor gene transcription. Activation of protein kinase A by forskolin (10 microM) or Bt(2)cAMP (100 microM) is not involved in the transient regulation of CCK receptor mRNA expression. Both elevated CCK-B and decreased CCK-A receptor mRNA expression returned to basal levels 6 h after continuous stimulation.

CONCLUSION

These results demonstrate that CCK-A and CCK-B receptor mRNA levels are differentially regulated by their agonists via distinct signal transduction mechanisms in AR42J cells.

Effect of hypergastrinemia on pancreatic carcinogenesis

BACKGROUND

Previous studies in our laboratory demonstrated that pancreatic carcinomas in rodents express receptors for the peptide hormone gastrin that are not present in normal adult pancreas. In view of an abundant literature suggesting that gastrin may promote growth of various gastrointestinal tissues and tumors, the effect of hypergastrinemia on the process of pancreatic carcinogenesis was evaluated.

METHODS

Rats received subcutaneous injections of the pancreatic carcinogen azaserine at 19 and 26 days of age. Starting at 12 months of age, animals were randomized to treatment with the proton pump inhibitor lansoprazole or vehicle by gavage for 6 months. At autopsy, pancreatic wet weight normalized to body weight was recorded, as well as the number of benign and malignant pancreatic lesions.

RESULTS

Serum gastrin levels were determined by radioimmunoassay and showed a greater than two-fold increase in lansoprazole-treated animals. Pancreatic wet weight in hypergastrinemic rats was increased compared to controls (p <0.05). Premalignant lesions such as acidophilic atypical acinar cell foci, adenomas, heterogeneous phenotypic populations of nodules within nodules, and carcinoma-in-situ were not increased in the hypergastrinemic group. Likewise, there was no difference in the incidence of invasive carcinoma in hypergastrinemic animals (10%) compared to controls (5.7%).

CONCLUSION

Hypergastrinemia stimulated an increase in pancreatic weight, but did not stimulate development of premalignant lesions or progression to cancer in the azaserine model of rat pancreatic acinar cell carcinoma.

Gastrin stimulates beta-cell neogenesis and increases islet mass from transdifferentiated but not from normal exocrine pancreas tissue

It is still unclear which factors regulate pancreatic regeneration and beta-cell neogenesis and which precursor cells are involved. We evaluated the role of intravenously infused gastrin in regenerating pancreas of duct-ligated rats. The ligation of exocrine ducts draining the splenic half of the pancreas resulted in acinoductal transdifferentiation within the ligated part but not in the unligated part. We found that infusion of gastrin from day 7 to 10 postligation resulted in a doubling of the beta-cell mass in the ligated part as measured by morphometry. This increase in insulin-expressing cells was not associated with increased proliferation, hypertrophy, or reduced cell death of the beta-cells. Furthermore, we found an increased percentage of single, extra-insular beta-cells and small beta-cell clusters induced by gastrin infusion. These changes occurred only in the ligated part of the pancreas, where transdifferentiation of the exocrine acinar cells to ductlike cells (metaplasia) had occurred, and was not found in the normal unaffected pancreatic tissue. In conclusion, we demonstrate that administration of gastrin stimulates beta-cell neogenesis and expansion of the beta-cell mass from transdifferentiated exocrine pancreas.

Mitogenic effect of gastrin and expression of gastrin receptors in duct-like cells of rat pancreas

BACKGROUND & AIMS

Ductular metaplastic cells are observed during pancreas injury. Growth control by gastrin and expression of gastrin/cholecystokinin (CCK) B receptors were evaluated in these cells.

METHODS

Acinoductal transdifferentiation was induced in vitro by culturing of acinar cells, and ductular metaplasia was obtained in vivo by ligation of the pancreatic ducts. Mitogenic effects of gastrin I on ductal complexes in vivo and of tetragastrin, pentagastrin, and gastrin I and II, with or without the CCK-B receptor antagonist L-365,260, on duct-like cells in vitro were analyzed by 5-bromo-2'-deoxyuridine labeling. Immunocytochemistry, Western blotting, and reverse-transcription polymerase chain reaction were applied for detection of the CCK-B receptor.

RESULTS

Gastrin analogues induced a mitogenic stimulus in the duct-like cells in vitro and in ductal complexes in duct-ligated rat pancreas. Immunocytochemistry showed expression of CCK-B receptors in these models and in fetal but not normal adult exocrine pancreas. Additionally, up-regulation of CCK-B receptors during ductular metaplasia was shown by Western blotting and reverse-transcription polymerase chain reaction.

CONCLUSIONS

Duct-like pancreatic epithelial cells in vitro and ductal complexes in vivo express gastrin/CCK-B receptors and proliferate in response to gastrin.

FGF-2 isoforms of 18 and 22.5 kDa differentially modulate t-PA and PAI-1 expressions on the pancreatic carcinoma cells AR4-2J: consequences on cell spreading and invasion

Pancreatic tumors overexpress FGF-2 and t-PA, but the implication of the growth factor in t-PA synthesis and t-PA-dependent tumor invasion remains unknown. FGF-2 is present in different isoforms: The 18 kDa FGF-2 is secreted, while the 22.5 kDa one is nuclearized and exerts intracrine regulations bypassing cell-surface FGF receptors. Rat pancreatic carcinoma AR4-2J cells producing either the 18 or the 22.5 kDa FGF-2 after transfection with FGF-2 cDNAs have been used to analyze the role of FGF-2 in t-PA expression and t-PA-related cell spreading. The 22.5 kDa FGF-2 reduced t-PA and PAI-1 synthesis 2-fold. Addition of recombinant 18 kDa FGF-2 (rFGF-2) to cell cultures resulted in increased t-PA and decreased PAI-1 expression. By contrast, rFGF-2 did not significantly modify t-PA synthesis in cells producing the 22.5 kDa FGF-2. Cell spreading was t-PA-dependent. Furthermore, cells producing the 22.5 kDa FGF-2 migrated less than control cells and cells producing the 18 kDa FGF-2. Overall, our data show that secretory FGF-2 is involved in t-PA synthesis by pancreatic cancer cells and facilitates cell spreading. The 22.5 kDa FGF-2 exerts opposite effects by decreasing t-PA expression in basal conditions and during rFGF-2 stimulation. Since the expression of the 22.5 kDa FGF-2 is under specific controls, its up-regulation might have the potential to reduce spreading of pancreatic cancer cells.

Divergent proliferative responses to a gastrin receptor ligand in synchronized and unsynchronized rat pancreatic AR42J tumour cells

Depending upon experimental model, the CCK-B/gastrin receptor ligand CI-988 exhibits either agonist or antagonist activity. To confirm that CI-988 behaves as an antagonist toward gastrin-stimulated growth, its effects on cell proliferation were investigated in unsynchronized and synchronized AR42J rat pancreatic tumour cells. In unsynchronized cultures CI-988 alone had no effect, but inhibited gastrin-stimulated cell proliferation. In contrast, in synchronized cultures, CI-988 stimulated cell proliferation. Similarly, CI-988 inhibited gastrin-stimulated cAMP production in unsynchronized cells, but stimulated cAMP formation in synchronized cultures. Therefore, CI-988 stimulation of cAMP production and proliferation in AR42J cell cultures appears to be cell cycle-dependent. CI-988 inhibited gastrin-stimulated intracellular calcium ([Ca2+]i) mobilization in both populations and thus acted as an antagonist toward this pathway. Because CCK receptor densities and affinities were similar in both cell populations, the data suggest that CI-988's divergent effects on cell proliferation are governed by postreceptor signalling events which vary with cell cycle.

The CCKB/gastrin receptor is coupled to the regulation of enzyme secretion, protein synthesis and p70 S6 kinase activity in acinar cells from ElasCCKB transgenic mice

In order to determine which physiological functions can be regulated by the pancreatic CCKB/gastrin receptor, studies were carried out on pancreatic acini from mice expressing transgenic CCKB/gastrin receptors in the exocrine pancreas (ElasCCKB mice). Acini were stimulated by sulfated gastrin in the presence of SR 27897 (1.8 microM), blocking endogenous CCKA receptors. After 30 min incubation with gastrin, the secretion of chymotrypsinogen and amylase showed superimposable monophasic dose-response curves. Enzyme secretion was detectable and maximal at 100 pM and 1 nM of gastrin, respectively. No increase in chymotrypsinogen and amylase mRNAs was detected for doses of gastrin which specifically occupy the CCKB/gastrin receptor. In contrast, gastrin stimulated total protein synthesis in isolated acini from ElasCCKB mice. [35S]Methionine incorporation into total proteins was increased dose-dependently to a maximum for 30 pM gastrin and inhibited with higher doses (> 300 pM). Gastrin stimulated p70 S6 kinase activity for concentrations ranging from 10 pM to 1 nM. Gastrin-stimulated p70 S6 kinase activity and protein synthesis were blocked by rapamycin and wortmannin. Therefore, in ElasCCKB mice acinar cells, the CCKB/gastrin receptor mediates enzyme release and protein synthesis. However, a more efficient coupling of the CCKB/gastrin receptor to protein synthesis than to enzyme secretion was demonstrated. CCKB/gastrin receptor-stimulated protein synthesis likely results from an enhancement of mRNA translation and involves phosphatidyl inositol 3-kinase and p70 S6 kinase.

AR4-2J cells: a model to study polypeptide hormone receptors

The AR4-2J cell line is derived from a transplantable tumour of the exocrine rat pancreas. Acinar in origin, this cell line contains significant amounts of amylase and can be grown in continuous culture. Many in vitro studies have been done using these cells; these studies were often complemented with in vivo experiments on animals. Particularly, many polypeptide hormones interacting with specific receptors located on the cell membrane have been analysed. The accurate knowledge of the hormone-receptor interactions has allowed to design interesting analogs of these hormones. In several cases, these compounds are powerful antagonists and are able to control cell proliferation induced by the corresponding polypeptide hormones. Other cell lines are useful to understand human pancreatic cancer. These human cell lines (Capan 1, Panc-1 for example) are of ductal origin and differ from AR4-2J cells, especially regarding the distribution of several polypeptide hormone and growth factor receptors. Both models are important for basic studies of neuropeptides, gastrointestinal peptides and their receptors, as well as for a better understanding of the underlying mechanisms of human pancreatic cancer.

Cells retrovirally transfected with fibroblast growth factor-2 isoforms exhibit altered adenylate cyclase activity and G-protein functionality

Basic fibroblast growth factor (FGF-2) is synthesized as different molecular mass isoforms all lacking the signal-peptide sequence. The high molecular-mass isoforms (21-24 kDa) possess a signal sequence directing their nuclear translocation. The role of each isoform is still poorly understood, however, modifications in intracellular signalling pathways could explain some effects of these peptides. In order to evaluate the role of FGF-2 isoforms on the adenylate cyclase (AC) signalling pathway, we retrovirally infected a rat pancreatic cell line (AR4-2J) with point-mutated FGF-2 cDNAs, allowing the expression of the 18 (A5 cells) or 22.5 kDa isoform (A3 cells) at a low level. In membrane preparations of A3 cells, unscheduled expression of the 22.5 kDa FGF-2 isoform induced a 2-fold decrease in both basal and forskolin-stimulated AC activity. Studies carried out on intact cells also showed decreased accumulation of cAMP in A3 cells in the presence of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine. Both FGF-2 peptides also induced functional modifications of G-proteins without affecting their levels. The 22.5 kDa peptide led to enhanced ADP-ribosylation of both alpha(s)-subunits in vitro, whereas the expression of the low molecular-mass 18 kDa peptide resulted in a 2-fold increase in alpha12 and alpha0 ADP-ribosylations. Furthermore, control CAT cells (AR4-2J cells transfected with the retrovirus containing the chloramphenicol acetyltransferase gene) and A5 cells were growth-inhibited by 8-Br-cAMP, in contrast to A3 cells. These data provide evidence that the expression of FGF-2 peptides could play a role in cell functions by modifying the AC signalling pathway. FGF-2 peptides are able to modulate both AC activity and the regulatory G-proteins. Finally FGF-2 expression may interfere with cAMP-regulated cell proliferation.

Gastrin does not stimulate growth of the rat pancreas

BACKGROUND

Gastrin is thought to stimulate growth of the pancreas via gastrin/cholecystokinin (CCK)-B-type receptors. The aim of the present study was to examine the trophic response of the pancreas to exogenous gastrin or to hypergastrinemia of endogenous origin and to hypogastrinemia with or without concomitant hyperCCKemia.

METHODS

Hypergastrinemia was induced in male Sprague-Dawley rats by continuous infusion of human Leu15-gastrin-17 (5 nmol/kg/h, subcutaneously), by removal of the acid-producing part of the stomach (fundectomy), or by treatment with omeprazole (400 mumol/ kg/day, orally). Hypogastrinemia was induced by antrectomy or by gastrectomy. HyperCCKemia was induced by pancreaticobiliary diversion (PBD). The rats were killed 10 days or 8 weeks after the operations or treatments. The concentrations of circulating gastrin and CCK were measured by radioimmunoassay. The pancreatic weight and DNA content were determined.

RESULTS

Gastrin infusion, omeprazole treatment, and fundectomy greatly increased the serum gastrin concentration. The resulting levels were very similar in the three groups and probably represent the maximum attainable physiologic serum gastrin concentration. Whereas gastrin infusion or omeprazole treatment (hypergastrinemia) and antrectomy (hypogastrinemia) were without effect on the weight and DNA content of the pancreas, gastrectomy (hypogastrinemia) and fundectomy (hypergastrinemia) increased the weight and DNA content. PBD (hyperCCKemia) greatly increased the weight and DNA content of the pancreas. PBD plus fundectomy, PBD plus gastrectomy, PBD plus antrectomy, and PBD plus omeprazole increased the weight and DNA content of the pancreas, as did PBD alone.

CONCLUSION

CCK is a physiologically important trophic stimulus for the rat pancreas, but gastrin is not. The increase in pancreatic weight and DNA content after fundectomy and gastrectomy cannot be explained by means of either gastrin or CCK.

Differential regulation of fibroblast growth factor (FGF) receptor-1 mRNA and protein by two molecular forms of basic FGF. Modulation of FGFR-1 mRNA stability

To evaluate possible functional differences between basic fibroblast growth factor (FGF) 2 isoforms we analyzed the effects of the 18-kDa FGF-2 which mainly localizes in the cytosol and that of the nuclear-targeted 22.5-kDa form on FGF receptors (FGFR) expression. These peptides were expressed at low amounts through a retroviral-infection system. Point mutated FGF-2 cDNAs under the control of the beta-actin promoter were used to infect a pancreatic cell line (AR4 2J) which does not produce FGF-2. Saturation and competition binding studies with 125I-FGF-2 revealed a 3-fold increase in both high and low affinity receptors in cells expressing the 22.5-kDa form and a 2-fold increase only in the high affinity receptors in cells producing the 18-kDa form. Kd values and molecular weights of the high affinity receptors were unaffected. Increasing cell densities or cell treatment with exogenous FGF-2 resulted in FGFR down-regulation as in control cells. Neutralizing anti-FGF-2 antibodies and suramin did not affect receptor density in control and in cells producing the 22.5-kDa form but further increased by 60 and 80%, respectively, the receptor level in cells synthesizing the 18-kDa form. These data suggest the involvement of the intracellular stored FGF-2 in FGFR up-regulation. Although all cells expressed FGFR-1, -2, and -3 mRNA only the FGFR-1 transcript was found increased, 6-fold in 22.5-kDa expressing cells and 3-fold in cell producing the shortest secreted isoform. The increase in FGFR-1 mRNA levels in the 22.5-kDa expressing cells was due to enhanced stability of the transcript. Confocal microscopy detected the presence of FGFR-1 at the cell surface whereas secretory isoforms of the receptor were not observed. Reverse transcriptase-polymerase chain reaction did not reveal significant differences in the expression of FGFR-1 variants. In the 22.5-kDa expressing cells exogenous FGF-2 evoked a stronger translocation of the calcium-phospholipid-dependent PKC. These results indicate that the transfected FGF-2 isoforms up-regulated FGFR-1 mRNA and protein. The 22.5-kDa form acted by increasing FGFR-1 mRNA stability enhancing cell responses to exogenous FGF-2.

Epidermal growth factor induces the differential release of GP2 and amylase from AR4-2J cells

Epidermal growth factor (EGF) stimulates secretion of glycoprotein 2 (GP2) in a time-and concentration-dependent manner from the AR4-2J pancreatoma cell line. Cell differentiation induced by dexamethasone treatment for 3 d, however, did not significantly alter either basal or EGF-stimulated GP2 release. Basal and EGF-stimulated GP2 release were similarly unaffected by caerulein, which promotes amylase secretion by a regulated route. A brief exposure to cycloheximide profoundly blocked EGF-evoked GP2 secretion. Furthermore, EGF-stimulated GP2 release was not accompanied by significant alterations in intracellular ionic calcium levels, in contrast to the stimulatory actions of caerulein. We conclude that EGF-stimulated release of GP2 occurs via a novel secretory pathway that is neither regulated nor constitutive as currently defined.

The role of gastrin and cholecystokinin in normal and neoplastic gastrointestinal growth

Gastrin and cholecystokinin (CCK) act as growth factors for the gastric mucosa and the pancreas, respectively. CCK is also responsible, via the CCK-A receptor, for the pancreatic hyperplasia observed following the feeding of protease inhibitors or pancreaticobiliary diversion. Hypergastrinaemia does not increase the incidence of spontaneous gastrointestinal carcinoma, but does stimulate the proliferation of gastric enterochromaffin-like cells via the gastrin/CCK-B receptor, with a consequent increase in the incidence of gastric carcinoids. Whether gastrin influences mutagen-induced gastrointestinal carcinogenesis is still controversial, but CCK clearly enhances the induction by carcinogens of acinar tumours in the pancreas. While gastrin increases xenograft growth of 50% of gastrointestinal tumours tested, effects on the proliferation of gastrointestinal tumour cell lines in vitro have been more difficult to demonstrate, perhaps because many cell lines are already maximally stimulated by autocrine gastrin. Gastrin mRNA and progastrin, but not mature amidated gastrin, have been detected in all gastrointestinal cell lines tested. Although cell proliferation is inhibited by gastrin/CCK receptor antagonists, the spectrum of antagonist affinities is not consistent with binding to either CCK-A or gastrin/CCK-B receptors. Definition of the molecular structure of the receptor involved in the autocrine loop may lead to novel therapies for gastrointestinal cancer.