Gastrin stimulates the formation of a p60Src/p125FAK complex upstream of the phosphatidylinositol 3-kinase signaling pathway

C-Src is Activated by the EGF Receptor in a Pathway that Mediates JNK and ERK Activation by Gonadotropin-Releasing Hormone in COS7 Cells

The key participants in G-protein-coupled receptor (GPCR) signaling are the mitogen-activated protein kinase (MAPK) signaling cascades. The mechanisms involved in the activation of the above cascades by GPCRs are not fully elucidated. The prototypical GPCR is the receptor for gonadotropin-releasing hormone (GnRHR), which serves as a key regulator of the reproductive system. Here, we expressed GnRHR in COS7 cells and found that GnRHR transmits its signals to MAPKs mainly via Gαi and the EGF receptor, without the involvement of Hb-EGF or PKCs. The main pathway that leads to JNK activation downstream of the EGF receptor involves a sequential activation of c-Src and PI3K. ERK activation by GnRHR is mediated by the EGF receptor, which activates Ras either directly or via c-Src. Beside the main pathway, the dissociated Gβγ and β-arrestin may initiate additional (albeit minor) pathways that lead to MAPK activation in the transfected COS7 cells. The pathways detected are significantly different from those in other GnRHR-bearing cells, indicating that GnRH can utilize various signaling mechanisms for MAPK activation. The unique pathway elucidated here, in which c-Src and PI3K are sequentially activated downstream of the EGF receptor, may serve as a prototype of signaling mechanisms by GnRHR and additional GPCRs in various cell types.

Does the Use of Proton Pump Inhibitors Increase the Risk of Pancreatic Cancer? A Systematic Review and Meta-Analysis of Epidemiologic Studies

Background: One of the most frequently used medications for treating gastrointestinal disorders is proton pump inhibitor (PPI), which reportedly has potential adverse effects. Although the relationship between the use of PPIs and the risk of pancreatic cancer has been extensively investigated, the results remain inconsistent. Hence, this meta-analysis aimed to evaluate such relationship. Methods: We searched for literature and subsequently included 10 studies (seven case–control and three cohort studies; 948,782 individuals). The pooled odds ratio (OR) and 95% confidence intervals (CI) for pancreatic cancer were estimated using a random-effects model. We also conducted sensitivity analysis and subgroup analysis. Results: The pooled OR of the meta-analysis was 1.698 (95% CI: 1.200–2.402, p = 0.003), with a substantial heterogeneity (I² = 98.75%, p < 0.001). Even when studies were excluded one by one, the pooled OR remained statistically significant. According to the stratified subgroup analyses, PPI use, and pancreatic cancer incidence were positively associated, regardless of the study design, quality of study, country, and PPI type. Conclusion: PPI use may be associated with the increased risk of pancreatic cancer. Hence, caution is needed when using PPIs among patients with a high risk of pancreatic cancer.

Endogenous Gastrin Collaborates With Mutant KRAS in Pancreatic Carcinogenesis

OBJECTIVE

The KRAS gene is the most frequently mutated gene in pancreatic cancer, and no successful anti-Ras therapy has been developed. Gastrin has been shown to stimulate pancreatic cancer in an autocrine fashion. We hypothesized that reactivation of the peptide gastrin collaborates with KRAS during pancreatic carcinogenesis.

METHODS

LSL-Kras; P48-Cre (KC) mutant KRAS transgenic mice were crossed with gastrin-KO (GKO) mice to develop GKO/KC mice. Pancreata were examined for 8 months for stage of pancreatic intraepithelial neoplasia lesions, inflammation, fibrosis, gastrin peptide, and microRNA expression. Pancreatic intraepithelial neoplasias from mice were collected by laser capture microdissection and subjected to reverse-phase protein microarray, for gastrin and protein kinases associated with signal transduction. Gastrin mRNA was measured by RNAseq in human pancreatic cancer tissues and compared to that in normal pancreas.

RESULTS

In the absence of gastrin, PanIN progression, inflammation, and fibrosis were significantly decreased and signal transduction was reversed to the canonical pathway with decreased KRAS. Gastrin re-expression in the PanINs was mediated by miR-27a. Gastrin mRNA expression was significantly increased in human pancreatic cancer samples compared to normal human pancreas controls.

CONCLUSIONS

This study supports the mitogenic role of gastrin in activation of KRAS during pancreatic carcinogenesis.

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.

Immunohistochemical examination of cholecystokinin and gastrin receptors (CCK-2/gastrin-R) expression in normal and exocrine cancerous human pancreatic tissues

OBJECTIVE

Evaluating tissue samples of normal and exocrine cancerous human pancreas on the expression of CCK2/gastrin receptor. We performed an immunohistochemical protocol that allows efficient detection of this receptor in formalin-fixed, paraffin-embedded human tissues.

METHODS

Twenty (20) paraffin blocks of pancreatic tissue sections were collected from the Departments of pathology, Central University Hospital of Sidi-bel-Abbes City (Western Algeria) for the period 2004-2013; ten (10) of them were normal pancreatic samples; and ten (10) cancerous pancreatic sections. The samples were studied using an immunohistochemical protocol for CCK-2/gastrin receptors.

RESULTS

Our immunohistochemical analysis revealed that CCK-2/gastrin receptors were expressed in both normal and malignant pancreatic cells but with different immunoreactivity levels and different immunostaining intensity i.e., CCK-2/gastrin receptors were highly expressed within the cytoplasmic area of cancerous cells; 40% of the samples had an immunoreactivity (IR) of (+++) and 60% (++++); the immunostaining was as well very intense since we reported a dark brown staining of the malignant cells. However; in normal pancreatic tissues; CCK-2/gastrin receptors IR levels were very low; 80% of the samples had an IR of (+); and 20% had (++) and the immunostaining was less intense; we noted a light brown staining of few normal pancreatic cells.

CONCLUSION

The gastrointestinal peptides CCK could be very interesting targets for exocrine pancreatic cancer therapies; thus further surveys such as western blotting and RTPCR could indentify CCK-2/gastrin receptors as a helpful biomarker for exocrine pancreatic cancer diagnosis and treatment.

Anti-Gastrins Antiserum Combined with Lowered Dosage Cytotoxic Drugs to Inhibit the Growth of Human Gastric Cancer SGC7901 Cells in Nude Mice

The objective of this study was to determine the effect of anti-gastrin antiserum in combination with varied dosages of cytotoxic drugs (5-Fluorouracil (5FU) + Cisplatin (CDDP)) in vivo growth of the human gastric cancer cell-line, SGC-7901, which expressed cholecystokininB/gastrin receptors and secreted gastrin. The anti-gastrin antiserum was obtained by immunizing rabbits using a novel immunogen vaccine, which was composed of the common amino-terminal portion of human carboxy-amidated gastrin-17 (G17) and glycine-extended gastrin-17 (gly-G17) and the common carboxy-terminal portion of progastrin (in a 50:50 mixture) all covalently linked to tetanus toxoid (TT) by specific peptide spacers. The antiserum neutralized both G17 and gly-G17 by enzyme-linked immunosorbent assay (ELISA), and a synthetic progastrin peptide, as well, using an E. coli expressed his-tagged progastrin.

The tumor was implanted subcutaneously into the backside of BALB/c nude mice, and the combination antibody-drug treatment using low dose combination chemotherapy had significantly reduced median tumor volumes (62% reduction; p =0.0018) and tumor weights (53% reduction; p =0.0062) when compared to the conventional high dose chemotherapy treated control mice that had a corresponding similar reductive effect, using just the two standard cytotoxic drugs alone; namely by reducing the tumor volumes (65%; p =0.0016) and tumor weights (59% reduction; p=0.0033). Importantly, the immunological treatment had little of the toxicities and side-effects of the full chemotherapy doses alone, which was effected by using a significant decrease in the dosage of chemotherapeutic drugs, while maintaining the same level of efficacy at reduction of tumor growth.

Demonstration and biological significance of a gastrin-P21-activated kinase 1 feedback loop in colorectal cancer cells

Gastrins, including amidated gastrin17 and glycine-extended gastrin17, are important growth factors in colorectal cancer (CRC). The p21-activated kinase 1 (PAK1) plays key roles in cellular processes including proliferation, survival, and motility, and in cell transformation and tumor progression. PAK1 expression increases with the progression of CRC, and knockdown of PAK1 blocks CRC cell growth and metastasis both in vitro and in vivo. The aim of this study was to determine the interaction between PAK1 and gastrins in CRC cells. PAK1 expression and activation were assayed by Western blots, and concentrations of gastrin mRNA and peptides by real-time PCR and radioimmunoassay, respectively. Proliferation of CRC cells was measured by (3)H-thymidine incorporation, and vascular endothelial growth factor : VEGF) secretion was measured by ELISA. Gastrins activated PAK1 via PI3K-dependent pathways. Activated PAK1 in turn mediated gastrin-stimulated activation of β-catenin and VEGF secretion in CRC cells, as knockdown of PAK1 blocked stimulation of these cellular processes by gastrins. Downregulation of gastrin reduced the expression and activity of PAK1, but in contrast there was a compensatory increase in gastrins either when PAK1 was downregulated, or after treatment with a PAK inhibitor. Our results indicate that PAK1 is required for the stimulation of CRC cells by gastrins, and suggest the existence of an inhibitory feedback loop by which PAK1 downregulates gastrin production in CRC cells.

The duration of gastrin treatment affects global gene expression and molecular responses involved in ER stress and anti-apoptosis

Background

How cells decipher the duration of an external signal into different transcriptional outcomes is poorly understood. The hormone gastrin can promote a variety of cellular responses including proliferation, differentiation, migration and anti-apoptosis. While gastrin in normal concentrations has important physiological functions in the gastrointestine, prolonged high levels of gastrin (hypergastrinemia) is related to pathophysiological processes.

Results

We have used genome-wide microarray time series analysis and molecular studies to identify genes that are affected by the duration of gastrin treatment in adenocarcinoma cells. Among 403 genes differentially regulated in transiently (gastrin removed after 1 h) versus sustained (gastrin present for 14 h) treated cells, 259 genes upregulated by sustained gastrin treatment compared to untreated controls were expressed at lower levels in the transient mode. The difference was subtle for early genes like Junb and c-Fos, but substantial for delayed and late genes. Inhibition of protein synthesis by cycloheximide was used to distinguish between primary and secondary gastrin regulated genes. The majority of gastrin upregulated genes lower expressed in transiently treated cells were primary genes induced independently of de novo protein synthesis. This indicates that the duration effect of gastrin treatment is mainly mediated via post-translational signalling events, while a smaller fraction of the differentially expressed genes are regulated downstream of primary transcriptional events. Indeed, sustained gastrin treatment specifically induced prolonged ERK1/2 activation and elevated levels of the AP-1 subunit protein JUNB. Enrichment analyses of the differentially expressed genes suggested that endoplasmic reticulum (ER) stress and survival is affected by the duration of gastrin treatment. Sustained treatment exerted an anti-apoptotic effect on serum starvation-induced apoptosis via a PKC-dependent mechanism. In accordance with this, only sustained treatment induced anti-apoptotic genes like Clu, Selm and Mcl1, while the pro-apoptotic gene Casp2 was more highly expressed in transiently treated cells. Knockdown studies showed that JUNB is involved in sustained gastrin induced expression of the UPR/ER stress related genes Atf4, Herpud1 and Chac1.

Conclusion

The duration of gastrin treatment affects both intracellular signalling mechanisms and gene expression, and ERK1/2 and AP-1 seem to play a role in converting different durations of gastrin treatment into distinct cellular responses.

The Src kinase Yes is activated in pancreatic acinar cells by gastrointestinal hormones/neurotransmitters, but not pancreatic growth factors, which stimulate its association with numerous other signaling molecules

For growth factors, cytokines, G-protein-coupled receptors and numerous other stimuli, the Src Family of kinases (SFK) play a central signaling role. SFKs also play an important role in pancreatic acinar cell function including metabolism, secretion, endocytosis, growth and cytoskeletal integrity, although the specific SFKs involved are not fully known. In the present study we used specific antibodies for the SFK, Yes, to determine its presence, activation by pancreatic secretagogues or growth factors, and interaction with cellular signaling cascades mediated by CCK in which Yes participates in to cause acinar cell responses. Yes was identified in acini and secretagogues known to activate phospholipase C (PLC) [CCK, carbachol, bombesin] as well as post-receptor stimulants activating PKC [TPA] or mobilizing cellular calcium [thapsigargin/calcium ionophore (A23187)] each activated Yes. Secretin, which activates adenylate cyclase did not stimulate Yes, nor did pancreatic growth factors. CCK activation of Yes required both high- and low-affinity CCK(1)-receptor states. TPA-/CCK-stimulated Yes activation was completely inhibited by thapsigargin and the PKC inhibitor, GF109203X. CCK/TPA stimulated the association of Yes with focal adhesion kinases (Pyk2, FAK) and its autophosphorylated forms (pY397FAK, pY402Pyk2). Moreover, CCK/TPA stimulated Yes interacted with a number of other signaling proteins, including Shc, PKD, p130(Cas), PI3K and PTEN. This study demonstrates that in rat pancreatic acini, the SFK member Yes is expressed and activated by CCK and other gastrointestinal hormones/neurotransmitters. Because its activation results in the direct activation of many cellular signaling cascades that have been shown to mediate CCK's effect in acinar cell function our results suggest that it is one of the important pancreatic SFKs mediating these effects.

Somatic mutations in CCK2R alter receptor activity that promote oncogenic phenotypes

The roles of cholecystokinin 2 receptor (CCK2R) in numerous physiologic processes in the gastrointestinal tract and central nervous system are well documented. There has been some evidence that CCK2R alterations play a role in cancers, but the functional significance of these alterations for tumorigenesis is unknown. We have identified six mutations in CCK2R among a panel of 140 colorectal cancers and 44 gastric cancers. We show that these mutations increase receptor activity, activate multiple downstream signaling pathways, increase cell migration, and promote angiogenesis. Our findings suggest that somatic mutations in CCK2R may promote tumorigenesis through deregulated receptor activity and highlight the importance of evaluating CCK2R inhibitors to block both the normal and mutant forms of the receptor.

The role of Sonic Hedgehog as a regulator of gastric function and differentiation

The Hedgehog (Hh) genes play a key role in the regulation of embryonic development and govern processes such as cell differentiation, cell proliferation, and tissue patterning. In vertebrate embryos, Hh gene expression regulates correct formation of limbs, skeleton, muscles, and organs including stomach. In the adult, the Hh pathway functions in tissue repair and regeneration, along with maintenance of stem cells. Sonic Hedgehog (Shh) signaling has been extensively studied for its role in developmental and cancer biology. Recent advances in the field of gastroenterology show that in the stomach, Shh is responsible for proper differentiation of the gastric glands. The aberrant activity of the Shh signaling pathway leads to an altered gastric differentiation program and loss of gastric acid secretion that is the predominant function of the stomach. In this chapter, we review the most recent findings that reveal the role of Shh as a regulator of gastric function and differentiation and how this signaling is dysregulated during the development of gastric cancer in response bacterial infection.

αV integrin: A new gastrin target in human pancreatic cancer cells

AIM: To analyse α_V integrin expression induced by gastrin in pancreatic cancer models.

METHODS: α_V integrin mRNA expression in human pancreatic cancer cells was analysed using a “cancer genes” array and confirmed by real-time reverse transcription-polymerase chain reaction (PCR). Western blotting and semi-quantitative immunohistochemistry were used to examine protein levels in human pancreatic cancer cell lines and pancreatic tissues, respectively. The role of α_V integrin on gastrin-induced cell adhesion was examined using blocking anti-α_V integrin monoclonal antibodies. Adherent cells were quantified by staining with crystal violet.

RESULTS: Using a “cancer genes” array we identified α_V integrin as a new gastrin target gene in human pancreatic cancer cells. A quantitative real-time PCR approach was used to confirm α_V integrin gene expression. We also demonstrate that Src family kinases and the PI 3-kinase, two signalling pathways specifically activated by the CCK-2 receptor (CCK2R), are involved in gastrin-mediated α_V integrin expression. In contrast, inhibition of the ERK pathway was without any effect on α_V integrin expression induced by gastrin. Our results also show that gastrin modulates cell adhesion viaα_V integrins. Indeed, in vitro adhesion assays performed on fibronectin show that gastrin significantly increases adhesion of pancreatic cancer cells. The use of blocking anti-α_V integrin monoclonal antibodies completely reversed the increase in cell-substrate adhesion induced by gastrin. In addition, we showed in vivo that the targeted CCK2R expression in the pancreas of Elas-CCK2 mice, leads to the overexpression of α_V integrin. This process may contribute to pancreatic tumour development observed in these transgenic animals.

CONCLUSION: α_V integrin is a new gastrin target in pancreatic cancer models and contributes to gastrin effects on cell adhesion.

Cholecystokinin and gastrin receptors

Cholecystokinin and gastrin receptors (CCK1R and CCK2R) are G protein-coupled receptors that have been the subject of intensive research in the last 10 years with corresponding advances in the understanding of their functioning and physiology. In this review, we first describe general properties of the receptors, such as the different signaling pathways used to exert short- and long-term effects and the structural data that explain their binding properties, activation, and regulation. We then focus on peripheral cholecystokinin receptors by describing their tissue distribution and physiological actions. Finally, pathophysiological peripheral actions of cholecystokinin receptors and their relevance in clinical disorders are reviewed.

Mechanism for Src activation by the CCK2 receptor: Patho-physiological functions of this receptor in pancreas

AIM: To investigate in vivo, whether CCK2 receptors (CCK2R) regulate proteins known to play a crucial role in cell proliferation and cancer development and analyse in vitro the molecular mechanisms that lead to Src activation; in particular, to identify the domains within the CCK2R sequence that are implicated in this activation.

METHODS: The expression and activation of Src and ERK were studied in vivo using immuno-fluorescence and western-blot techniques. We used pancreatic tissues derived from wild type or Elas-CCK2 mice that expressed the CCK2R in pancreatic acini, displayed an increased pancreatic growth and developed preneoplastic lesions. The pancreatic tumor cell line AR4-2J expressing the endogenous CCK2R or COS-7 cells transiently transfected with wild type or mutant CCK2R were used as in vitro models to study the mechanism of Src activation. Src activation was measured by in vitro kinase assays, ERK activation by western blot using anti-phospho-ERK antibodies and the involvement of Src in gastrin-induced cell proliferation by MTT test.

RESULTS: We showed in vivo that the targeted CCK2R expression in the pancreas of Elas-CCK2 mice, led to the activation of Src and the ERK pathway. Src was activated upstream of the ERK pathway by the CCK2R in pancreatic tumoral cells and contributed to the proliferative effects mediated by this receptor. In vitro results demonstrated that activation of the Src/ERK pathway by the CCK2R required the NPXXY motif, located within the CCK2R sequence at the end of the 7^th transmembrane domain, and suggested the putative role of Gq in this mechanism.

CONCLUSION: Deregulation of the Src/ERK pathway by the CCK2R might represent an early step that contributes to cell proliferation, formation of preneoplastic lesions and pancreatic tumor development.

Cholecystokinin-2 receptor modulates cell adhesion through beta 1-integrin in human pancreatic cancer cells

Several lines of evidence suggest that gastrin and the CCK-2 receptor (CCK2R) could contribute to pancreatic carcinogenesis by modulating processes such as proliferation, cell adhesion or migration. In the current study, we used a 'cancer gene array' and identified beta1-integrin subunit as a new gastrin-regulated gene in human pancreatic cancer cells. We also demonstrated that Src family kinases and the phosphatidylinositol-3-kinase (PI-3-kinase) pathway play a crucial role in the expression of beta1-integrin induced by gastrin. Our results also showed that gastrin modulates cell-substrate adhesion via beta1-integrin. Indeed, using blocking anti-beta1-integrin monoclonal antibodies, we completely reversed the increase in cell-substrate adhesion induced by gastrin. In addition, we observed that in response to gastrin, beta1-integrin is tyrosine phosphorylated by Src family kinases and associates with paxillin, a scaffold protein involved in focal adhesion and integrin signalling. This mechanism might be involved in gastrin-induced cell adhesion. Moreover, we showed in vivo that targeted CCK2R expression in the pancreas of Elas-CCK2 mice leads to the overexpression of beta1-integrin. This process may contribute to pancreatic tumour development observed in these transgenic animals.

Gastrin exerts pleiotropic effects on human melanoma cell biology

The effects of gastrin (G17) on the growth and migration factors of four human melanoma cell lines (HT-144, C32, G-361, and SKMEL-28) were investigated. The expression patterns of cholecystokinin (CCK)(A), CCK(B), and CCK(C) gastrin receptors were investigated in these cells and in seven clinical samples by means of reverse transcription polymerase chain reaction. Melanoma cells appear to express mRNA for CCK(C) receptors, but not for CCK(A) or CCK(B) receptors. Although gastrin does not significantly modify the growth characteristics of the cell lines under study, it significantly modifies their cell migration characteristics. These modifications occur at adhesion level by modifying the expression levels of alpha(v) and beta3 integrins, at motility level by modifying the organization of the actin cytoskeleton, and at invasion level by modifying the expression levels of matrix metalloproteinase 14. We recently demonstrated the presence of CCK(B) receptors in mouse endothelial cells involved in glioblastoma neoangiogenesis. Chronic in vivo administration of a selective CCK(B) receptor antagonist to mice bearing xenografts of human C32 melanoma cells significantly decreased levels of neoangiogenesis, resulting in considerable delays in the growth of these C32 xenografts. In conclusion, our study identifies the pleiotropic effects of gastrin on melanoma cell biology.

Integrin activates receptor-like protein tyrosine phosphatase alpha, Src, and Rho to increase prolactin gene expression through a final phosphatidylinositol 3-kinase/cytoskeletal pathway that is additive with insulin

We previously showed that receptor-like protein tyrosine phosphatase (RPTP)-alpha inhibited insulin-increased prolactin gene transcription. Others suggested that RPTPalpha was a key intermediary between integrins and activation of Src. We present evidence that inhibition of insulin-increased prolactin gene transcription was secondary to RPTPalpha activation of Src, reflecting its role as mediator of integrin responses. Src kinase activity was increased in GH4 cells transiently or stably expressing RPTPalpha and cells plated on the integrin-alpha5beta1 ligand fibronectin. C-terminal Src kinase inactivated Src and blocked RPTPalpha inhibition of insulin-increased prolactin gene transcription. Expression of dominant-negative Src also prevented the RPTPalpha-mediated inhibition of insulin-increased prolactin gene expression. Low levels of a constitutively active Src mutant (SrcY/F) stimulated whereas higher expression levels of Src Y/F inhibited prolactin gene expression. Src-increased prolactin gene transcription was inhibited by expression of a blocking Rho-mutant (RhoN19), suggesting that Src acted through or required active Rho. Experiments with an activated Rho-mutant (RhoL63) demonstrated a biphasic activation/repression of prolactin gene transcription that was similar to the effect of Src. The effects of both Src and Rho were phosphatidylinositol 3-kinase dependent. Expression of SrcY/F or RhoL63 altered the actin cytoskeleton and morphology of GH4 cells. Taken together, these data suggest a physiological pathway from the cell matrix to increased prolactin gene transcription mediated by RPTPalpha/Src/Rho/phosphatidylinositol 3-kinase and cytoskeletal change that is additive with effects of insulin. Over activation of this pathway, however, caused extreme alteration of the cytoskeleton that blocked activation of the prolactin gene.

Gastrin and cancer: a review

In 1905, a Cambridge physiologist, John Sydney Edkins, initially identified a hormone responsible of gastric acid secretion, which he called gastric secretin, or gastrin. While gastrin's role in acid secretion is now well defined, more recent studies have implicated the various isoforms of gastrin in cancer. Important advances in the last decade have included the recognition of biological activity for processing intermediates such as progastrin and the glycine-extended gastrin. Here, we give an overview of the roles of these peptides in cancer, highlighted by molecular, cellular and integrated studies on animal models for progastrin-derived peptides and their receptors.

Mechanism of the Vascular Angiotensin II/α2-Adrenoceptor Interaction

alpha(2)-Adrenoceptors potentiate vascular responses to angiotensin II. The goal of this study was to test the hypothesis that the phospholipase C (PLC)/protein kinase C (PKC)/c-src/phosphatidylinositol 3-kinase (PI3K) pathway contributes to the vascular angiotensin II/alpha(2)-adrenoceptor interaction. In rats in vivo, intrarenal infusions of angiotensin II (10 ng/kg/min) increased renal vascular resistance by 5.8 +/- 0.5 units, and this response was enhanced (p < 0.05) to 9.1 +/- 1.2 units by UK-14,304 [5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine; 3 microg/kg/min; alpha(2)-adrenoceptor agonist]. Intrarenal infusions of U-73122 [1-[6-[[(17beta)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]-hexyl]-1H-pyrrole-2,5-dione; 3 microg/min; PLC inhibitor], GF109203X [bisindolylmaleimide I; 10 microg/min; PKC inhibitor], CGP77675 [1-(2-{4-[4-amino-5-(3-methoxyphenyl)pyrrolo[2,3-d]pyrimidin-7-yl]phenyl}ethyl)piperidin-4-ol; 5 microg/min; c-src inhibitor], and wortmannin (1 microg/min; PI3K inhibitor) abolished the angiotensin II/alpha(2)-adrenoceptor interaction. In isolated perfused rat kidneys, angiotensin II (0.3, 1, and 3 nM) increased perfusion pressure (by 15 +/- 8, 39 +/- 4, and 93 +/- 9 mm Hg, respectively), and UK-14,304 (1 microM) potentiated these responses (to 36 +/- 4, 67 +/- 7, and 135 +/- 17 mm Hg, respectively). This angiotensin II/alpha(2)-adrenoceptor interaction was abolished by U-73122 (10 microM), GF109203X (3 microM), CGP77675 (5 microM), and wortmannin (0.2 microM). Preglomerular microvascular smooth muscle cells expressed phospholipase (PLC)-beta(2), PLC-beta(3), c-src, phospho(tyrosine 416)-c-src, and PI3K. In these cells, angiotensin II (0.1 microM) and UK-14,304 (1 microM) per se did not increase phospho-c-src; however, the combination of angiotensin II plus UK-14,304 doubled phospho-c-src, and this interaction was abolished by U-73122 (10 microM) and GF109203X (3 microM). In conclusion, the PLC/PKC/c-src/PI3K pathway may contribute importantly to the interaction between alpha(2)-adrenoceptors and angiotensin II on renal vascular resistance.

Expression of cholecystokinin-2/gastrin receptor in the murine pancreas modulates cell adhesion and cell differentiation in vivo

The presence of gastrin and cholecystokinin-2 (CCK2) receptors in human preneoplastic and neoplastic gastrointestinal lesions suggests a role in cancer development. In addition to the growth-promoting action of gastrin, recently a role of the cholecystokinin-2/gastrin receptor (CCK2-R) modulating cellular morphology in cultured epithelial cells has been shown. Here, we have investigated in transgenic (ElasCCK2) mice whether ectopic expression of human CCK2-R in the exocrine pancreas affected epithelial differentiation. Cellular localization of cell adhesion molecules, differentiation markers, and transcription factors was determined using immunofluorescence techniques. Before tumor formation, expression and subcellular localization of proteins of the adherens junction complex, differentiation markers, and transcription factors were altered in ElasCCK2 exocrine pancreas, indicating an evolution from an acinar to a ductal phenotype. Loss of cell polarity, defective secretion, and loss of intercellular adhesion in acini of ElasCCK2 mice was confirmed by ultrastructural analysis. Finally, expression of the transgene in mice treated with the carcinogen azaserine resulted in enhanced size of preneoplastic lesions as well as an increased degree of acinar-ductal transdifferentiation. Thus, these data represent the first evidence for the CCK2-R modulating intercellular adhesion and cell fate in vivo and show that these alterations may contribute to enhanced sensitivity of ElasCCK2 pancreas to chemical carcinogens.

Transgenic expression of CCK2 receptors sensitizes murine pancreatic acinar cells to carcinogen-induced preneoplastic lesions formation

In humans, initial events of pancreatic carcinogenesis remain unknown, and the question of whether this cancer, which has a ductal phenotype, exclusively arises from duct cells has been raised. Previous studies have demonstrated that transgenic expression of the CCK2 receptor in acinar cells of ElasCCK2 mice plays a role in the development of pancreatic neoplasia. The aim of our study was to examine initial steps of carcinogenesis in ElasCCK2 mice, adding a supplementary defect by using a chemical carcinogen, azaserine. Results of posttreatment sequential immunohistochemical examinations and quantifications demonstrate that mice responded to azaserine. Transition of acinar cells into duct-like cells expressing Pdx1 and gastrin, as well as proliferation of acinar cells, were transiently observed in both transgenic and control mice. The carcinogen also induced formation of preneoplastic lesions, adenomas, exhibiting properties of autonomous growth. Importantly, expression of the CCK2 receptor increased the susceptibility of pancreas to azaserine. Indeed, treated ElasCCK2 mice exhibited larger areas of pancreatic acinar-ductal transition, increased cellular proliferation as well as larger adenomas areas vs. control mice. These amplified responses may be related to auto/paracrine stimulation of CCK2 receptor by gastrin expressed in newly formed duct-like cells. Our results demonstrate that activation of CCK2 receptor and azaserine result in cumulative effects to favor the emergence of a risk situation that is a potential site for initiation of carcinogenesis.

The biological and therapeutic importance of gastrin gene expression in pancreatic adenocarcinomas

The gastrin gene is expressed widely in pancreatic adenocarcinomas and the study aimed to assess its role in both the resistance of cancer cells to apoptosis and the sensitivity of cells to chemotherapeutic agents. Two human pancreatic cell lines, PAN1 and BXPC3, expressed gastrin at both the RNA and protein levels and are shown to be representative of human pancreatic adenocarcinomas in terms of gastrin expression. Inhibition of endogenous gastrin production by tumor cells was achieved with neutralizing gastrin antiserum and transfection with a gastrin antisense plasmid. Gastrin antiserum synergized with both taxotere and gemcitabine in inhibiting the in vitro growth of the PAN1 cell line with the inhibitory effect of the antiserum increasing from 12.7% to 70.2% with taxotere (P < 0.05) and 28.6% with gemcitabine (P < 0.01) after controlling for the effects of the cytotoxics. Synergy was only achieved with taxotere in BXPC3 cells with the inhibitory effect of gastrin antiserum increasing from 22.9% to 50.0% (P < 0.005). Cells transfected with gastrin antisense had reduced in vitro growth in low serum conditions and were poorly tumorigenic in nude mice at an orthotopic site. Gastrin antisense-transfected PAN1 cells had increased sensitivity to the antiproliferative effects of both gemcitabine (IC50 of > 100 microg/ml reduced to 0.1 microg/ml) and taxotere (IC50 of 20 microg/ml reduced to < 0.01 microg/ml) when compared with vector controls. The increased sensitivity of PAN1 antisense coincided with increased caspase-3 activity and reduced protein kinase B/Akt phosphorylation in response to both gemcitabine and taxotere. Gastrin gene circumvention may be an optimal adjunct to chemotherapeutic agents, such as taxotere and gemcitabine, in pancreatic adenocarcinoma.

Agonist-independent activation of Src tyrosine kinase by a cholecystokinin-2 (CCK2) receptor splice variant

Src activity is elevated in a majority of colonic and pancreatic cancers and is associated with late stage aggressive cancers. However, the mechanisms leading to its increased activity remain largely undefined. Agonist binding to the cholecystokinin-2 (CCK2)/gastrin receptor (CCK2R), a G-protein-coupled receptor, increases Src activity in a variety of normal and neoplastic cell lines. Recently, we and others (Hellmich, M. R., Rui, X. L., Hellmich, H. L., Fleming, R. Y., Evers, B. M., and Townsend, C. M., Jr. (2000) J. Biol. Chem. 275, 32122-32128; Ding, W. Q., Kuntz, S. M., and Miller, L. J. (2002) Cancer Res. 62, 947-952; Smith, J. P., Verderame, M. F., McLaughlin, P., Martenis, M., Ballard, E., and Zagon, I. S. (2002) Int. J. Mol. Med. 10, 689-694) have identified a splice variant of CCK2R, called CCK2i4svR, that is expressed in human colorectal and pancreatic cancers but not by cells of the adjacent nonmalignant tissue. Compared with CCK2R, CCK2i4svR contains an additional 69 amino acids within its third intracellular loop (3il) domain. Because CCK2i4svR is the only splice variant expressed in some human colon and pancreatic cancers, we questioned whether CCK2i4svR could regulate Src activity. Stably transfected HEK293 cells were used because, unlike many cancer-derived cells, they have a low level of basal Src activity. We report that, in contrast to CCK2R, CCK2i4svR activates Src kinase in the absence of agonist stimulation. In vitro kinase assay of immunoprecipitated receptor protein showed a 6-8-fold increase in Src kinase activity associated with CCK2i4svR compared with CCK2R. Expression of the 3il domain of the CCK2i4svR alone was sufficient to partially activate Src kinase. Together, these data support the hypothesis that the increased Src activity observed in some pancreatic and colorectal cancers is due, in part, to the co-expression of CCK2i4svR.

The role of protein tyrosine kinases in CYP1A1 induction by omeprazole and thiabendazole in rat hepatocytes

Benzimidazoles compounds like omeprazole (OME) and thiabendazole (TBZ) mediate CYP1A1 induction differently from classical aryl hydrocarbon receptor (AhR) ligands, 3-methylcholanthrene (3-MC) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). To clarify the involvement of an intracellular signal pathway in CYP1A1 induction by OME and TBZ, the TBZ, OME and 3-MC signal-transducing pathways were compared by using specific protein tyrosine kinase inhibitors in primary culture of rat hepatocytes. The effect of OME and TBZ (75-250 microM) on cytochrome P450 1A1 (CYP1A1) expression was therefore studied in primary cultures of rat hepatocytes after 24 h, 48 h and 72 h of exposure. Both compounds provoked a dose- and time-dependent increase in CYP1A1 (EROD activity, protein and mRNA levels), but OME was less effective at all the concentrations and times tested. The mechanism of benzimidazole-mediated induction of CYP1A1 was investigated by comparison with 3-MC, a prototypical AhR ligand. As expected, OME and TBZ were unable to displace [(3)H]-TCDD from its binding sites to the AhR in competitive binding studies. Moreover, classic tyrosine kinase inhibitor herbimycin A (HA) inhibited the two benzimidazoles-mediated CYP1A1 inductions, but only partially inhibited the 3-MC-mediated one. Another two tyrosine kinase inhibitors, Lavendustin A (LA) and genistein (GEN), had no effect on CYP1A1 induction by benzimidazoles and 3-MC. These results are consistent with the implication of a tyrosine kinase, most probably the Src tyrosine kinase, in the mechanism of CYP1A1 induction in rat hepatocytes.

c-Src is activated by the epidermal growth factor receptor in a pathway that mediates JNK and ERK activation by gonadotropin-releasing hormone in COS7 cells

Key participants in G protein-coupled receptor (GPCR) signaling are the mitogen-activated protein kinase (MAPK) signaling cascades. The mechanisms involved in the activation of the above cascades by GPCRs are not fully elucidated. A prototypic GPCR that has been widely used to study these signaling mechanisms is the receptor for gonadotropin-releasing hormone (GnRHR), which serves as a key regulator of the reproductive system. Here we expressed GnRHR in COS7 cells and found that GnRHR transmits its signals to MAPKs mainly via G alpha i, EGF receptor without the involvement of Hb-EGF, and c-Src, but independently of PKCs. The main pathway that leads to JNK activation downstream of the EGF receptor involves a sequential activation of c-Src and phosphatidylinositol 3-kinase (PI3K). ERK activation by GnRHR is mediated by the EGF receptor, which activates Ras either directly or via c-Src. Besides the main pathway, the dissociated G beta gamma and beta-arrestin may initiate additional, albeit minor, pathways that lead to MAPK activation in the transfected COS7 cells. The pathways detected are significantly different from those in other cell lines bearing GnRHR, indicating that GnRH can utilize various signaling mechanisms for the activation of MAPK cascades. The unique pathway elucidated here in which c-Src and PI3K are sequentially activated downstream of the EGF receptor may serve as a prototype of signaling mechanisms by GnRHR and by additional GPCRs in various cell types.

pp60c-Src Kinase mediates growth effects of the full-length precursor progastrin1-80 peptide on rat intestinal epithelial cells, in vitro

Growth factor effects of precursor forms of gastrins have become evident in recent years. However, intracellular pathways that mediate growth effects of the precursor molecules are not known. In previous studies, we reported an increase in Tyr phosphorylation of pp60(c-Src) in intestinal epithelial cells (IEC) in response to the fully processed form of gastrin [gastrin(1-17) (G17)]. We have now examined whether c-Src kinase is similarly phosphorylated and activated in response to the full-length precursor molecule, progastrin (PG)(1-80), (recombinant human PG) in IEC cells. We found a significant increase in pp60(c-Src) kinase activity in response to both G17 and PG (0.1-1.0 nM), suggesting that growth effects of both the precursor and fully processed gastrin molecules may be mediated via similar pathways. On the other hand, pp62(c-Yes) was not phosphorylated or activated in response to either G17 or PG. To examine whether c-Src kinase mediates proliferative effects of PG, IEC cells were microinjected with anti-Src-IgG and (3)H-thymidine ((3)H-Tdr) uptake of the cells measured. Control cells received nonimmune IgG. The (3)H-Tdr uptake of cells stimulated with 1.0 nM PG was significantly reduced in cells microinjected with anti-c-Src-IgG; control IgG had no effect. In cells stimulated with 1.0% fetal calf serum, microinjection with c-Src-IgG had no effect on (3)H-Tdr uptake. The specificity of the effect was further confirmed by blocking the inhibitory effect of anti-c-Src-IgG with antigenic Src peptide. These results suggest that activation of c-Src kinase likely represents a critical step in mediating proliferative effects of both the precursor and fully processed forms of gastrins on IEC.

Gastrin mediated cholecystokinin-2 receptor activation induces loss of cell adhesion and scattering in epithelial MDCK cells

The presence of gastrin and CCK-2/gastrin receptors in human preneoplastic and neoplastic lesions of pancreas and colon suggests a role in cancer development. Gastrin's growth-promoting action has been established, but a role in cellular morphogenetic processes promoting tumor invasion has been elusive. Our aim was (i) to investigate whether activation of the CCK-2R affects cellular morphology, intercellular adhesion and motility, as crucial parameters of epithelial differentiation, and (ii) to identify the signaling pathways and mechanisms implicated. Madin-Darby Canine Kidney (MDCK) cells were chosen to generate an epithelial non-tumorigenic model system expressing human CCK-2R. Epithelial differentiation and motility were analysed upon CCK-2R activation using immunocytochemistry and invasion assays. The functionality of adhesion complexes and activity of signaling proteins was determined with biochemical techniques. CCK-2R activation induced cell dissociation and enhanced invasion, preceded by decreased membrane localization of adherens junction molecules and nuclear accumulation of beta-catenin. Concomitantly, and requiring the activation of several signaling pathways, catenins were shifted from the cytoskeletal to the cytoplasmic fraction, suggesting the detachment of the cytoskeleton from the adherens complex. These data represent the first evidence for the CCK-2R, regulating cell-cell and cell-substrate adhesion and support a role for CCK-2R in the progression of carcinoma.

Receptor biology and intracellular regulatory mechanisms in pancreatic acinar cells

Continuing progress is being made in understanding the regulation of pancreatic acinar cell function by receptor-activated intracellular signaling mechanisms. Knowledge of how ligands interact at the molecular level with their receptors and activate heterotrimeric G proteins is increasing. In addition to inositol trisphosphate, intracellular messengers include cyclic ADP ribose, nicotinic acid adenine dinucleotide phosphate, arachidonic acid, and diacylglycerol. Ca signaling involves the interaction of inositol trisphosphate, cyclic ADP ribose, and nicotinic acid adenine dinucleotide phosphate with distinct subcellular Ca stores. Ca signals ultimately induce exocytosis of zymogen granules and identification of the proteins involved on the granule and plasma membrane, and understanding of their roles is continuing. Other receptor-activated signaling pathways primarily regulate nonsecretory events. Considerable progress has been made in understanding how the mammalian target of rapamycin pathway regulates protein synthesis through translation factors and ribosomal proteins. Other pathways in acinar cells include the mitogen-activated protein kinases, the tyrosine kinases, and the transforming growth factor-beta-Smad pathways.

Lysophosphatidylcholine enhances superoxide anions production via endothelial NADH/NADPH oxidase

Reactive oxygen species (ROS) including superoxide anions (O2(-)) play a key role in atherogenesis, and endothelial cells have the ability to generate ROS. To investigate the enzymatic sources of ROS and the effects of lysophosphatidylcholine (LPC), an atherogenic lipid, we measured ROS production in cultured bovine aortic endothelial cells (BAECs) by the lucigenin-enhanced chemiluminescence (CL) method and electron spin resonance (ESR). BAEC homogenates had the enzymatic activity of NADH/NADPH oxidase. BAECs cultured on microcarrier beads generated O2(-) under basal conditions. The inhibition of NADH/ NADPH oxidase by diphenylene iodonium (DPI) significantly attenuated O2(-) production, whereas no inhibitors of other oxidases suppressed it. Although LPC enhanced O2(-) production approximately 3.1-fold, its action was suppressed by DPI. Tyrosine kinase inhibitors significantly attenuated LPC-induced O2(-) production. ESR with DMPO demonstrated that LPC increased the formation of the DMPO-hydroxyl adduct in dose- and time-dependent manners. These data suggest that the basal production of O2(-) in endothelial cells is mainly mediated by the NADH/NADPH oxidase system and that LPC activates this oxidase to enhance O2(-) production through a tyrosine kinase-dependent pathway. The enhancement of ROS production by LPC is probably involved in its atherogenic property.

Shear stress regulates endothelial nitric oxide synthase expression through c-Src by divergent signaling pathways

In this study, we defined the signaling cascade responsible for increased eNOS mRNA expression in response to laminar shear stress. This pathway depends on the tyrosine kinase c-Src because shear induction of eNOS mRNA is blocked by the c-Src inhibitors PP1 and PP2, as well as an adenovirus encoding kinase inactive c-Src. After activation of c-Src, this pathway diverges. One arm is responsible for the short-term (6 hour) increase in eNOS mRNA. This involves a transient, 1-hour increase in eNOS transcription, as detected by nuclear run-on, that is dependent on activation of Ras and is blocked by adenoviral infection with dominant negative Ras. Downstream of Ras, MEK1/2 and ERK1/2 are important in this pathway, as 2 inhibitors of MEK1/2, PD98059 and UO126, completely prevented this early increase in eNOS mRNA. ERK1/2 was rapidly phosphorylated in response to shear, and this was prevented by c-Src and Ras inhibition. Further, Raf is phosphorylated in response to shear stress, and this is prevented by c-Src inhibition, suggesting that Raf may transduce the signal between Ras and ERK1/2. The second arm of the pathway linking activation of c-Src to eNOS expression involves stabilization of eNOS mRNA by shear stress. This response to shear is completely abrogated by the c-Src inhibitor PP1 but not altered by Ras or MEK1/2 inhibition. Thus, c-Src plays a central role in modulation of eNOS expression in response to shear stress via divergent pathways involving a short-term increase in eNOS transcription and a longer-term stabilization of eNOS mRNA.

Involvement of phosphatidylinositol 3-kinase and mitogen-activated protein kinases in glycine-extended gastrin-induced dissociation and migration of gastric epithelial cells

The various molecular forms of gastrin can act as promoters of proliferation and differentiation in different regions of the gastrointestinal tract. We report a novel stimulatory effect of glycine-extended gastrin(17) only on cell/cell dissociation and cell migration in a non-tumorigenic mouse gastric epithelial cell line (IMGE-5). In contrast, both amidated and glycine-extended gastrin(17) stimulated proliferation of IMGE-5 cells via distinct receptors. Glycine-extended gastrin(17)-induced dissociation preceded migration and was blocked by selective inhibitors of phosphatidylinositol 3-kinase (PI3-kinase) but did not require mitogen-activated protein (MAP) kinase activation. Furthermore, glycine-extended gastrin(17) induced a PI3-kinase-mediated tyrosine phosphorylation of the adherens junction protein beta-catenin, partial dissociation of the complex between beta-catenin and the transmembrane protein E-cadherin, and delocalization of beta-catenin into the cytoplasm. Long lasting activation of MAP kinases by glycine-extended gastrin(17) was specifically required for the migratory response, in contrast to the involvement of a rapid and transient MAP kinase activation in the proliferative response to both amidated and glycine-extended gastrin(17). Therefore, the time course of MAP kinase activation appears to be a critical determinant of the biological effects mediated by this pathway. Together with the involvement of PI3-kinase in the dissociation of adherens junctions, long term activation of MAP kinases seems responsible for the selectivity of this novel effect of G(17)-Gly on the adhesion and migration of gastric epithelial cells.

Gastrin, CCK, signaling, and cancer

Gastrin, produced by G cells in the gastric antrum, has been identified as the circulating hormone responsible for stimulation of acid secretion from the parietal cell. Gastrin also acts as a potent cell-growth factor that has been implicated in a variety of normal and abnormal biological processes including maintenance of the gastric mucosa, proliferation of enterochromaffin-like cells, and neoplastic transformation. Here, we review the models used to study the effects of gastrin on cell proliferation in vivo and in vitro with respect to mechanisms by which this hormone might influence normal and cancerous cell growth. Specifically, human and animal models of hypergastrinemia and hypogastrinemia have been described in vivo, and several cells that express cholecystokinin (CCK)B/gastrin receptors have been used for analysis of intracellular signaling pathways initiated by biologically active amidated gastrins. The binding of gastrin or CCK to their common cognate receptor triggers the activation of multiple signal transduction pathways that relay the mitogenic signal to the nucleus and promote cell proliferation. A rapid increase in the synthesis of lipid-derived second messengers with subsequent activation of protein phosphorylation cascades, including mitogen-activated protein kinase, is an important early response to these signaling peptides. Gastrin and CCK also induce rapid Rho-dependent actin remodeling and coordinate tyrosine phosphorylation of cellular proteins including the non-receptor tyrosine kinases p125fak and Src and the adaptor proteins p130cas and paxillin. This article reviews recent advances in defining the role of gastrin and CCK in the control of cell proliferation in normal and cancer cells and in dissecting the signal transduction pathways that mediate the proliferative responses induced by these hormonal GI peptides in a variety of normal and cancer cell model systems.