Gastrin and phorbol 12-myristate 13-acetate regulate the human histidine decarboxylase promoter through Raf-dependent activation of extracellular signal-regulated kinase-related signaling pathways in gastric cancer cells

Hypergastrinemia Expands Gastric ECL Cells Through CCK2R+ Progenitor Cells via ERK Activation

BACKGROUND & AIMS

Enterochromaffin-like (ECL) cells in the stomach express gastrin/cholecystokinin 2 receptor CCK2R and are known to expand under hypergastrinemia, but whether this results from expansion of existing ECL cells or increased production from progenitors has not been clarified.

METHODS

We used mice with green fluorescent protein fluorescent reporter expression in ECL cells (histidine decarboxylase [Hdc]-green fluorescent protein), as well as Cck2r- and Hdc-driven Tamoxifen inducible recombinase Cre (Cck2r-CreERT2, Hdc-CreERT2) mice combined with Rosa26Sor-tdTomato (R26-tdTomato) mice, and studied their expression and cell fate in the gastric corpus by using models of hypergastrinemia (gastrin infusion, omeprazole treatment).

RESULTS

Hdc-GFP marked the majority of ECL cells, located in the lower third of the gastric glands. Hypergastrinemia led to expansion of ECL cells that was not restricted to the gland base, and promoted cellular proliferation (Ki67) in the gastric isthmus but not in basal ECL cells. Cck2r-CreERT2 mice marked most ECL cells, as well as scattered cell types located higher up in the glands, whose number was increased during hypergastrinemia. Cck2r-CreERT2⁺ isthmus progenitors, but not Hdc⁺ mature ECL cells, were the source of ECL cell hyperplasia during hypergastrinemia and could grow as 3-dimensional spheroids in vitro. Moreover, gastrin treatment in vitro promoted sphere formation from sorted Cck2r⁺Hdc^- cells, and increased chromogranin A and phosphorylated- extracellular signal-regulated kinase expression in CCK2R-derived organoids. Gastrin activates extracellular signal-regulated kinase pathways in vivo and in vitro, and treatment with the Mitogen-activated protein kinase kinase 1 inhibitor U0126 blocked hypergastrinemia-mediated changes, including CCK2R-derived ECL cell hyperplasia in vivo as well as sphere formation and chromogranin A expression in vitro.

CONCLUSIONS

We show here that hypergastrinemia induces ECL cell hyperplasia that is derived primarily from CCK2R⁺ progenitors in the corpus. Gastrin-dependent function of CCK2R⁺ progenitors is regulated by the extracellular signal-regulated kinase pathway.

Analysis of histamine receptor knockout mice in models of inflammation

The diverse functions of histamine are mediated by four specific histamine receptor subtypes, which belong to the family of G-protein-coupled receptors. Here, we summarize data obtained with histamine-deficient L-histidine decarboxylase knockout and histamine receptor subtype knockout mice in inflammation models. Advantages and disadvantages of the knockout approaches compared with pharmacologic approaches are discussed critically. Due to many controversial data it is very difficult to draw clear-cut conclusions from the data provided in the literature. Thus, the published studies highlight the complexity of histamine function in inflammation and the need for much more systematic experimental work.

Gastric acid, calcium absorption, and their impact on bone health

Calcium balance is essential for a multitude of physiological processes, ranging from cell signaling to maintenance of bone health. Adequate intestinal absorption of calcium is a major factor for maintaining systemic calcium homeostasis. Recent observations indicate that a reduction of gastric acidity may impair effective calcium uptake through the intestine. This article reviews the physiology of gastric acid secretion, intestinal calcium absorption, and their respective neuroendocrine regulation and explores the physiological basis of a potential link between these individual systems.

[Helicobacter pylori in human stomach: can it be called mutualism or a disease?]

Helicobacter pylori (H. pylori) has been a major concern as a gastric pathogen with unique features since discovered in the end of the 20th century. Recent data on comparative genome study have revealed that H. pylori has successfully survived with its host though over 58,000 years of evolution and migration from continent to continent. To maintain the symbiotic relationship with human, H. pylori has come up with ways to induce host tolerance as well as exert harmful injuries. Studies about H. pylori have accumulated the knowledge about how the cellular and molecular interactions are controlled and regulated to decide whether the symbiotic relationship is directed to diseases or peaceful mutualism. We reviewed recent literatures and research outcomes about the H. pylori and host interaction in molecular and cellular basis.

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.

Gastrin stimulates expression of plasminogen activator inhibitor-1 in gastric epithelial cells

Plasminogen activator inhibitor (PAI)-1 is associated with cancer progression, fibrosis and thrombosis. It is expressed in the stomach but the mechanisms controlling its expression there, and its biological role, are uncertain. We sought to define the role of gastrin in regulating PAI-1 expression and to determine the relevance for gastrin-stimulated cell migration and invasion. In gastric biopsies from subjects with elevated plasma gastrin, the abundances of PAI-1, urokinase plasminogen activator (uPA), and uPA receptor (uPAR) mRNAs measured by quantitative PCR were increased compared with subjects with plasma concentrations in the reference range. In patients with hypergastrinemia due to autoimmune chronic atrophic gastritis, there was increased abundance of PAI-1, uPA, and uPAR mRNAs that was reduced by octreotide or antrectomy. Immunohistochemistry revealed localization of PAI-1 to parietal cells and enterochromaffin-like cells in micronodular neuroendocrine tumors in hypergastrinemic subjects. Transcriptional mechanisms were studied by using a PAI-1-luciferase promoter-reporter construct transfected into AGS-G(R) cells. There was time- and concentration-dependent increase of PAI-1-luciferase expression in response to gastrin that was reversed by inhibitors of the PKC and MAPK pathways. In Boyden chamber assays, recombinant PAI-1 inhibited gastrin-stimulated AGS-G(R) cell migration and invasion, and small interfering RNA treatment increased responses to gastrin. We conclude that elevated plasma gastrin concentrations are associated with increased expression of gastric PAI-1, which may act to restrain gastrin-stimulated cell migration and invasion.

Histamine synthesis and lessons learned from histidine decarboxylase deficient mice

This chapter summarizes the information about the transcriptional regulation of histidine decarboxylase (HDC), which is the catabolic enzyme of histamine synthesis, and the activity of histamine in vivo as clarified using HDC gene deficient mice (HDC-KO). The research of the regulatory mechanism of histamine synthesis has been focused on transcriptional and posttranslational aspects. The generation ofHDC-KO mice clarified several new pathophysiological functions of histamine. It is now recognized that the activity of histamine is not limited to allergic, peptic and neurological functions as in the old paradigm, but extends to other fields such as cardiology, immunology and infectious diseases. Therefore, this chapter will focus on these newly revealed functions of histamine. For example, histamine was known to be involved in the effector phase of allergic responses, but a role has now been shown in the sensitization phases and in innate immunity. In the allergic bronchial asthma model using HDC-KO mice it was found that histamine positively controls eosinophilia, but not bronchial hypersensitivity. The effect on eosinophils was afterwards shown to be mediated through the activity of the histamine H4 receptor. The recent advances in the understanding of histamine synthesis and the activity of HDC have dramatically expanded our understanding of the scope of histamine function.

The production and role of gastrin-17 and gastrin-17-gly in gastrointestinal cancers

The gastrointestinal peptide hormone gastrin is responsible for initiating the release of gastric acid in the stomach in response to the presence of food and/or humoral factors such as gastrin releasing peptide. However, it has a role in the growth and maintenance of the gastric epithelium, and has been implicated in the formation and growth of gastric cancers. Hypergastrinemia resulting from atrophic gastritis and pernicious anemia leads to hyperplasia and carcinoid formation in rats, and contributes to tumor formation in humans. Additionally, gastrin has been suspected to play a role in the formation and growth of cancers of the colon, but recent studies have instead implicated gastrin processing intermediates, such as gastrin-17-Gly, acting upon a putative, non-cholecystokinin receptor. This review summarizes the production and chemical structures of gastrin and of the processing intermediate gastrin-17-Gly, as well as their activities in the gastrointestinal tract, particularly the promotion of colon cancers.

Polyamines affect histamine synthesis during early stages of IL-3-induced bone marrow cell differentiation

Mast cells synthesize and store histamine, a key immunomodulatory mediator. Polyamines are essential for every living cell. Previously, we detected an antagonistic relationship between the metabolisms of these amines in established mast cell and basophilic cell lines. Here, we used the IL-3-driven mouse bone marrow-derived mast cell (BMMC) culture system to further investigate this antagonism in a mast cell model of deeper physiological significance. Polyamines and histamine levels followed opposite profiles along the bone marrow cell cultures leading to BMMCs. alpha-Difluoromethylornithine (DFMO)-induced polyamine depletion resulted in an upregulation of histidine decarboxylase (HDC, the histamine-synthesizing enzyme) expression and activity, accompanied by increased histamine levels, specifically during early stages of these cell cultures, where an active histamine synthesis process occurs. In contrast, DFMO did not induce any effect in either HDC activity or histamine levels of differentiated BMMCs or C57.1 mast cells, that exhibit a nearly inactive histamine synthesis rate. Sequence-specific DNA methylation analysis revealed that the DFMO-induced HDC mRNA upregulation observed in early bone marrow cell cultures is not attributable to a demethylation of the gene promoter caused by the pharmacological polyamine depletion. Taken together, the results support an inverse relationship between histamine and polyamine metabolisms during the bone marrow cell cultures leading to BMMCs and, moreover, suggest that the regulation of the histamine synthesis occurring during the early stages of these cultures depends on the concentrations of polyamines.

Gastrin-mediated interleukin-8 and cyclooxygenase-2 gene expression: differential transcriptional and posttranscriptional mechanisms

BACKGROUND & AIMS

Gastrin induces the expression of cyclooxygenase (COX)-2 and interleukin (IL)-8; however, the mechanism(s), especially in gastric epithelial cells, is not well understood. Here, we have determined the intracellular mechanisms mediating gastrin-dependent gene expression.

METHODS

AGS-E human gastric cancer cell line stably expressing cholecystokinin-2 receptor was treated with amidated gastrin-17. Real-time polymerase chain reaction, Western blot, and enzyme-linked immunosorbent assay were performed to determine COX-2 and IL-8 expression and Akt, Erk, and p38 phosphorylation. Gene promoter activity was determined by luciferase assay. Electrophoretic mobility shift assay analysis was performed for nuclear factor kappaB (NF-kappaB) and activator protein-1 activity. RNA stability was determined after actinomycin D treatment. HuR localization was determined by immunocytochemistry.

RESULTS

Gastrin induced COX-2 and IL-8 expression in AGS-E cells, which was inhibited by phosphatidylinositol 3' kinase (PI3K) and p38 inhibitors. Gastrin-mediated Akt activation was observed to be downstream of p38. IL-8 expression was dependent on COX-2-mediated prostaglandin E(2) synthesis. In the presence of an NF-kappaB inhibitor MG132, IL-8 transcription was inhibited, but not that of COX-2. This was confirmed after knockdown of the p65 RelA subunit of NF-kappaB. Further studies showed that COX-2 gene transcription is regulated by activator protein-1. Gastrin increased the stability of both COX-2 and IL-8 messenger RNA (mRNA) in a p38-dependent manner, the half-life increasing from 31 minutes to 8 hours and approximately 4 hours, respectively. Gastrin, through p38 activity, also enhanced HuR expression, nucleocytoplasmic translocation, and enhanced COX-2 mRNA binding.

CONCLUSIONS

Gastrin differentially induces COX-2 and IL-8 expression at the transcriptional and posttranscriptional levels by PI3K and p38 mitogen-activated protein kinase pathways, respectively.

Regulation of mammalian gastrin/CCK receptor (CCK2R) expression in vitro and in vivo

The gastrin/CCK receptor (CCK2R) mediates the physiological functions of gastrin in the stomach, including stimulation of acid secretion and cellular proliferation and migration, but little is known about the factors that regulate its expression. We identified endogenous CCK2R expression in several cell lines and used luciferase promoter-reporter constructs to define the minimal promoter required for transcription in human gastric adenocarcinoma, AGS, and rat gastric mucosa, RGM1, cells. Consensus binding sites for SP1, C/EBP and GATA were essential for activity. Following serum withdrawal from RGM1 and AR42J cells, endogenous CCK2R mRNA abundance and the activity of a CCK2R promoter-reporter construct were significantly elevated. Transcription of CCK2R was also increased in AGS-G(R) and RGM1 cells by gastrin through mechanisms partly dependent upon protein kinase C (PKC) and mitogen/extracellular signal-regulated kinase (MEK). Gastrin significantly increased endogenous CCK2R expression in RGM1 cells, and CCK2R protein expression was elevated in the stomach of hypergastrinaemic animals. In mice with cryoulcers in the acid-secreting mucosa, CCK2R expression increased progressively in the regenerating mucosa adjacent to the ulcer repair margin, evident at 6 days postinjury and maximal at 13 days. De novo expression of CCK2R was observed in the submucosa beneath the repairing ulcer crater 6-9 days postinjury. Many of the cells in mucosa and submucosa that expressed CCK2R in response to cryoinjury were identified as myofibroblasts, since they coexpressed vimentin and smooth muscle alpha-actin but not desmin. The data suggest that increased CCK2R expression might influence the outcome of epithelial inflammation or injury and that the response may be mediated in part by myofibroblasts.

The Helicobacter pylori's protein VacA has direct effects on the regulation of cell cycle and apoptosis in gastric epithelial cells

In this study, we have evaluated the effects on cell cycle regulation of VacA alone and in combination with other two Helicobacter pylori proteins, cytotoxin-associated protein (CagA) and HspB, using the human gastric epithelial cells (AGS). Our results indicate that VacA alone was able to inhibit the G1 to S progression of the cell cycle. The VacA capacity of inhibiting cell progression from G1 to S phase was also observed when cells were co-transfected with CagA or HspB. Moreover, VacA over-expression caused apoptosis in AGS cells through activation of caspase 8 and even more of caspase 9, thus indicating an involvement of both the receptor-mediated and the mitochondrial pathways of apoptosis. Indeed, the two pathways probably can co-operate to execute cell death with a prevalence of the mitochondrial pathways. Our data taken together provide additional information to further enhance our understanding of the molecular mechanism by which H. pylori proteins alter the growth status of human gastric epithelial cells.

An upstream CRE-E-box element is essential for gastrin-dependent activation of the cyclooxygenase-2 gene in human colon cancer cells

Cyclooxygenase-2, the inducible enzyme of arachidonic acid metabolism and prostaglandin synthesis, is over expressed in colorectal cancer. Inhibition of COX-1/-2 by non-steroidal anti-inflammatory drugs is associated with a decreased risk for these malignancies, whereas high serum gastrin levels elevate this risk. As gastrin exhibits trophical effects on colonic epithelium we sought to explore whether it is capable to induce COX-2 expression in a human colon cancer cell line. The aim of this study is the description of the gastrin evoked effects on the transcriptional activity of the COX-2 gene in colorectal cancer cells and the identification of regulatory promoter elements. Reporter gene assays were performed with the gastrin-stimulated human colorectal cancer cell-line Colo-320, which was stable transfected with the human cholecystokinin-B/gastrin receptor cDNA and COX-2-promoter-luciferase constructs containing different segments of the 5'-region of the COX-2 gene or with mutated promoter constructs. Transcription factors were characterized with electrophoretic mobility shift assays. Gastrin-dependent induction of COX-2 mRNA was shown using "real-time" PCR. Resulting elevated Prostaglandin E2-levels were measured using ELISA. Gastrin stimulated the PGE2-generation and COX-2-mRNA expression in human Colo-320-B cells potently, obviously by transactivating the COX-2-promoter using a region between - 68 bp and + 70 bp. Further examinations identified a CRE-E-box element between - 56 bp and - 48 bp mediating the gastrin-effects on the COX-2 gene. Transcription factors binding to this promoter element were USF-1 und -2. These results show the necessity to perform succeeding studies, which could describe possible mechanisms in which gastrin and COX-2 contribute to the induction of colorectal carcinomas.

Gastrin transactivates the chromogranin A gene through MEK-1/ERK- and PKC-dependent phosphorylation of Sp1 and CREB

Our previous work revealed that gastrin regulates chromogranin A (CgA) transcription through enhanced binding of Sp1, CREB and Egr-1 to a proximal gastrin-responsive promoter element (Gas-RE). Here, we provide a detailed characterization of the signalling pathways transmitting the effect of gastrin on the CgA promoter. Gastrin treatment of gastric AGS-B cells potently stimulated MEK-1 as well as MAP kinases ERK-1/-2, JNK and p38 in a time-dependent manner. Interruption of ERK-1/-2/MEK-1 pathways abolished the transactivating effect of gastrin, whereas blockade of JNK or p38 activity was without effect. Functional promoter analysis revealed that the minimal element CgA-85/-64 was sufficient and necessary to confer MEK-1/ERK responsiveness. Analysis of proximal signalling pathways showed that activation of the MEK-1/ERK-1/2 module by gastrin does not require Ras, PI3-kinase or intracellular calcium signals, but depends on activation of kinases of the PKC family. This report demonstrates that a pathway comprising PKCs>Raf-1>MEK-1>ERK-1/-2 mediates the effect of gastrin on the CgA promoter, and strongly suggests that enhanced phosphorylation of Sp1 and CREB is crucial for CgA transactivation through the G protein-coupled CCK-B/gastrin receptor.

Involvement of MAP kinases in lipopolysaccharide-induced histamine production in RAW 264 cells

Roles of mitogen-activated protein (MAP) kinases in lipopolysaccharide (LPS)-induced production of histamine in the mouse macrophage-like cell line RAW 264 were analyzed. Incubation of RAW 264 cells in the presence of LPS increased histamine levels in the conditioned medium in a concentration- and time-dependent manner. The levels of histidine decarboxylase (HDC) mRNA and the 74-kDa HDC protein were also increased at 4 to 8 h and 8 to 12 h, respectively. LPS elicited the phosphorylation of p44/42 MAP kinase, p38 MAP kinase, and c-Jun N-terminal kinase (JNK). The MAP kinase-Erk kinase 1 inhibitor U0126 (0.1-10 microM) suppressed the LPS-induced phosphorylation of p44/42 MAP kinase, and inhibited the LPS-induced production of histamine and expression of the HDC mRNA and 74-kDa HDC protein in a concentration-dependent manner. The JNK inhibitor SP600125 (3-30 microM) suppressed the LPS-induced phosphorylation of c-Jun, and inhibited the LPS-induced production of histamine and expression of the HDC mRNA and 74-kDa protein in a concentration-dependent manner. Combined treatment with U0126 (0.3 microM) and SP600125 (10 microM) inhibited the LPS-induced production of histamine additively. The p38 MAP kinase inhibitor SB203580 (0.1-10 microM) partially inhibited the LPS-induced production of histamine. These findings suggest that LPS increases histamine production in RAW 264 cells by inducing the expression of the 74-kDa HDC protein, and that the LPS-induced expression of HDC is up-regulated at the transcriptional level by MAP kinases, especially p44 MAP kinase and JNK.

Histamine-cytokine connection in immunity and hematopoiesis

A number of recent studies have led to a reappraisal of the functional capacities of histamine in immunity and hematopoiesis. This change of perspective was provided by the following findings: (1) the evidence for multiple cellular sources of histamine, differing from mature basophils and mast cells by their ability to newly synthesize and liberate the mediator without prior storage, (2) the discovery of a novel histamine receptor (H4R), preferentially expressed on hematopoietic and immunocompetent cells, (3) the potential intracellular activity of histamine through cytochrome P450 and (4) the demonstration of a histamine-cytokine cross-talk. Indeed, cytokines not only modulate the degranulation process of histamine but also control its neosynthesis by the histamine-forming enzyme, histidine decarboxylase (HDC), at transcriptional and post-transcriptional levels. In turn, histamine intervenes in the intricate cytokine network, regulating cytokine production by immune cells through distinct receptors signaling distinct biological effects. This type of regulation is particularly relevant in the context of TH1/TH2 differentiation, autoimmunity and tumor immunotherapy.

Molecular biology of gastric cancer: Helicobacter infection and gastric adenocarcinoma: bacterial and host factors responsible for altered growth signaling

Gastric cancer remains the second most common cause of cancer-related mortality worldwide. The single most common cause of gastric cancer is chronic infection with the gram-negative microaerophilic spiral bacterium: Helicobacter pylori. Recent advances in this field have identified host factors which predispose to gastric cancer formation via modulation of the host immune response. In addition, recent work has explored bacterial virulence factors which may directly cause tissue damage, and lead to gastric carcinogenesis, as well as factors responsible for enhanced immune response. Environmental factors, long associated with a predilection for gastric cancer, are recognized as modifiers of key growth signalling pathways within the gastric mucosa and as such lead to growth alterations. This review focuses on exploring new advances in our understanding of bacterial factors, host genetic polymorphisms and the interaction between the bacterium and host at the level of the immune response and the regulation of proliferative and apoptotic signal transduction cascades. Modulation of the pivotal balance between cell growth and cell death leads to the formation of gastric adenocarcinoma.

Gastrin stimulates receptor-mediated proliferation of human esophageal adenocarcinoma cells

The prevalence of esophageal adenocarcinoma in the setting of Barrett's metaplasia continues to increase in Western nations at a rate greater than any other cancer. The trophic properties of gastrin have been documented in gastric, pancreatic and colon cancer cell lines, suggesting a potential role for this regulatory peptide in the growth of these malignancies. The aims of these studies were to identify and characterize the presence of functional cholecystokinin type-2 (gastrin) receptors on the membranes of human esophageal adenocarcinoma cells. Reverse transcriptase-polymerase chain reaction (RT-PCR) demonstrated the presence of cholecystokinin type-2 receptor transcripts in human esophageal adenocarcinoma cell lines. Competitive binding assays revealed specific binding of gastrin in SEG-1 cells (IC50 of 2.4 x 10(-8) M). This finding was confirmed by laser scanning confocal microscopy through internalization of rhodamine green labeled gastrin heptapeptide in SEG-1 cells. Gastrin caused a dose-dependent increase in proliferation of SEG-1 cells when compared to controls. This effect was abolished by co-incubation with L365,260, a CCK-2-specific receptor antagonist. Gastrin-induced phosphorylation of the p44 and p42 mitogen-activated protein kinases was demonstrated by Western blot analysis. In conclusion, the studied human esophageal adenocarcinoma cell lines possess cholecystokinin type-2 (gastrin) receptors. Receptors bind gastrin, resulting in increased proliferation in SEG-1 cells.

Role of macrophage-derived histamine in atherosclerosis-- chronic participation in the inflammatory response --

The atherosclerotic intimal lesion contains endothelial cells, smooth muscle cells, monocytes/macrophages and T lymphocytes, which constitute a histamine-cytokine network that participates in chronic inflammatory responses. Monocytes/macrophages and T lymphocytes express the histamine-producing enzyme histidine decarboxylase (HDC), and specific histamine receptors (HHR), which are switched from HH2R to HHR1 during macrophage differentiation. Endothelial and smooth muscle cells also express HHR in response to histamine. The effects of histamine on these cells include a regulation of atherosclerosis-related events such as cell proliferation, expression of matrix metalloproteinase, adhesion molecules and cytokines. Furthermore, recent studies have indicated that histamine and the activation of its specific receptors modulate the Th1/Th2 balance in inflammatory lesions through the regulation of cytokine production from inflammatory cells. The histamine-cytokine network in the atherosclerotic intima could regulate inflammatory and immune responses, including Th1/Th2 balance, and contribute to atherogenesis.

Role of small GTP binding proteins in the growth-promoting and antiapoptotic actions of gastrin

G17 has growth promoting and antiapoptotic effects on the AR4-2J pancreatic acinar cell line. We previously reported that whereas MAPK regulates G17-stimulation of AR4-2J cell proliferation, Akt mediates the antiapoptotic action of G17. We examined the signal-transduction pathways mediating G17 stimulation of AR4-2J cell growth and survival. G17 activated the small GTP binding proteins Ras, Rac, Rho, and Cdc42. Transduction of the cells with adenoviral vectors expressing dominant negative Akt, Ras, Rho, and Cdc42 but not dominant negative Rac inhibited AR4-2J cell proliferation and survival. Both exoenzyme C3 from Clostridium botulinum (C3), a toxin known to inactivate Rho, and PD98059, a MAPK inhibitor, reversed G17 inhibition of AR4-2J cell apoptosis. G17 induction of Akt activation was reduced by >60% by both dominant negative Ras and Rho and by 30% by dominant negative Cdc42. In contrast, G17-stimulated MAPK activation was blocked by >80% by dominant negative Ras but not by dominant negative Rho and Cdc42. Similar results were observed in the presence of C3. Dominant negative Rac failed to affect G17 induction of both Akt and MAPK, whereas it inhibited sorbitol by almost 50% but not G17-stimulated activation of p38 kinase. Thus G17 promotes AR4-2J cell growth and survival through the activation of multiple GTP binding proteins, which, in turn, regulate different protein kinase cascades. Whereas Ras activates Akt and MAPK, Rho and Cdc42 appear to regulate Akt and possibly other as yet unidentified kinases mediating the growth-stimulatory actions of G17.

Molecular mechanisms of gastrin-dependent gene regulation

The peptide hormone gastrin is the key regulator of gastric acid secretion. Gastrin exerts its effects as acid secretagogue through functional activation of gastric enterochromaffin-like (ECL) cells, which control acid secretion through biosynthesis and release of histamine. In ECL cells, concerted activation of histidine decarboxylase (HDC), vesicular monoamine transporter 2 (VMAT2), and chromogranin A (CgA) genes by gastrin is a prerequisite for proper acid control. To elucidate the molecular pathways underlying gastrin-dependent control of ECL cell genes, we recently analyzed the signaling cascades, regulatory promoter elements, and transcription factors mediating the transcriptional effects of gastrin. Our studies identified the Raf>MEK1>ERK 1/-2 kinase module as the common signaling pathway mediating gastrin-dependent ECL cell gene transcription. In contrast to this uniform signaling cascade, pronounced heterogeneity was detected between cis- and trans-activating regulatory factors conferring gastrin responsiveness. The molecular diversity of transcription factors and regulatory enhancer elements transmitting gastrin-triggered gene transcription offers the molecular basis for synergistic, but differential, regulation of HDC, VMAT2, and CgA genes during a secretory challenge of ECL cells by gastrin and possibly other acid secretagogues.

Signal transduction events involved in TPA downregulation of SP-A gene expression

Surfactant protein A (SP-A), the most abundant pulmonary surfactant protein, plays a role in innate host defense and blocks the inhibitory effects of serum proteins on surfactant surface tension-lowering properties. SP-A mRNA and protein are downregulated by phorbol esters (TPA) via inhibition of gene transcription. We evaluated the TPA signaling pathways involved in SP-A inhibition in a lung cell line, H441 cells. TPA caused sustained phosphorylation of p44/42 mitogen-activated protein kinase (MAPK), p38 MAPK, and c-Jun-NH2-terminal kinase. An inhibitor of conventional and novel isoforms of protein kinase C (PKC) and two inhibitors of p44/42 MAPK kinase partially or completely blocked the inhibitory effects of TPA on SP-A mRNA levels. In contrast, inhibitors of conventional PKC-α and -β, stress-activated protein kinases, protein phosphatases, protein kinase A, and the phosphatidylinositol 3-kinase pathway had no effect on the TPA-mediated inhibition of SP-A mRNA. TPA also stimulated the synthesis of c-Jun mRNA and protein in a time-dependent manner. Inhibitors of the p44/42 MAPK signaling pathway and PKC blocked the TPA-mediated phosphorylation of p44/42 MAPK and the increase in c-Jun mRNA. We conclude that TPA inhibits SP-A gene expression via novel isoforms of PKC, the p44/42 MAPK pathway, and the activator protein-1 complex.

Helicobacter pylori stimulates host cyclooxygenase-2 gene transcription: critical importance of MEK/ERK-dependent activation of USF1/-2 and CREB transcription factors

Cyclooxygenase-2 (COX-2) represents the inducible key enzyme of arachidonic acid metabolism and contributes to the pathogenesis of gastroduodenal ulcers and gastric cancer. Helicobacter pylori infection is associated with elevated gastric COX-2 levels, but the mechanisms underlying H. pylori-dependent cox-2 gene expression are unclear. H. pylori stimulated cox-2 mRNA and protein abundance in gastric epithelial cells in vitro and in vivo, and functional analysis of the cox-2 gene promoter mapped its H. pylori-responsive region to a proximal CRE/Ebox element at -56 to -48. Moreover, USF1/-2 and CREB transcription factors binding to this site were identified to transmit H. pylori-dependent cox-2 transcription. Activation of MEK/ERK1/-2 signalling by bacterial virulence factors located outside the H. pylori cag pathogenicity island (cagPAI) was found to mediate bacterial effects on the cox-2 promoter. Our study provides a detailed description of the molecular pathways underlying H. pylori-dependent cox-2 gene expression in gastric epithelial cells, and may thus contribute to a better understanding of mechanisms underlying H. pylori pathogenicity.

The cholecystokinin2-receptor mediates calcitonin secretion, gene expression, and proliferation in the human medullary thyroid carcinoma cell line, TT

Gastrin-induced release of calcitonin from medullary thyroid carcinomas (MTC) is based on the expression of the cholecystokinin(2)-receptor (CCK(2)R) in these tumors. Recently, we have shown that the CCK(2)R is expressed not only in MTC but also in C-cells within the normal thyroid gland. The functions of the CCK(2)R in MTC and C-cells are largely unknown. We therefore explored the effects of gastrin-induced CCK(2)R stimulation in the highly differentiated MTC cell line, TT. CCK(2)R expression in TT-cells is detectable by RT-PCR as well as immunocytochemistry. Stimulation of the CCK(2)R by gastrin induces immediate release of calcitonin from TT-cells. Moreover, quantitative (LightCycler) RT-PCR demonstrates that gastrin stimulates transcription of the calcitonin and chromogranin A genes in TT-cells. TT-cell proliferation, assessed by counting of viable cells and (3)H-thymidine uptake, is markedly increased by gastrin. This effect is inhibited by the CCK(2)R-specific antagonist L-365,260. Our findings suggest physiological functions for the CCK(2)R in calcitonin-secretion and gene expression as well as a pathophysiological role in MTC proliferation. CCK(2)R antagonists might have therapeutic potential in these tumors.

PACAP and gastrin regulate the histidine decarboxylase promoter via distinct mechanisms

The enterochromaffin-like (ECL) cell controls gastric acid secretion via histamine, generated by l-histidine decarboxylase (HDC). HDC expression is regulated by gastrin. However, gastrin is not alone in controlling ECL cell function. For example, the neural peptide pituitary adenylate cyclase-activating polypeptide (PACAP) also increases ECL cell proliferation. To investigate a potential role of PACAP in regulating HDC expression, we generated a series of HDC promoter-luciferase reporter constructs and transiently transfected them into PC12 cells (stably expressing the gastrin-CCK-2 receptor). We found that PACAP regulates HDC promoter activity. This is temporally biphasic, involving both adenyl cyclase and phospholipase C-dependent pathways. Deletional analysis, block mutation, and EMSA demonstrated a PACAP-response element at -177 to -170, wholly necessary for the effects of PACAP and discrete from known gastrin-responsive elements. Discrete neural and endocrine pathways regulate ECL cells through different patterns of postreceptor signaling and promoter activation, which may be appropriate to their functions in vivo.

Effects ofHelicobacter pylori infection on cell cycle progression and the expression of cell cycle regulatory proteins

Helicobacter pylori lives in the stomach lumen adhering and specifically interacting with gastric epithelial cells. H. pylori infection can cause a broad range of diseases. Although most infected individuals only develop a chronic inflammation of the stomach, some patients progress to chronic gastritis, duodenal ulceration, or, rarely, cancer. H. pylori is able to send and to receive signals from the gastric epithelium, allowing host and bacteria to become linked in a dynamic equilibrium. Several studies have demonstrated that H. pylori infection induces morphological changes of gastric epithelial cells other than cell proliferation, increase of mitosis and mutations. It has also been demonstrated that H. pylori may predispose to cancer by altering gastric epithelial cell turnover acting specifically on transcription factors. Although H. pylori is able to induce several host responses, it specifically perturbs the delicate balance of those factors that usually help to maintain cell homeostasis. The study of mechanisms of interaction between the bacterium and gastric cells will surely help to prevent the increase and diffusion of malignancies all over the world.

Kruppel-like factor 4 (KLF4) represses histidine decarboxylase gene expression through an upstream Sp1 site and downstream gastrin responsive elements

Histidine decarboxylase (HDC) is the enzyme that catalyzes the conversion of histidine to histamine, a bioamine that plays an important role in allergic responses, inflammation, neurotransmission, and gastric acid secretion. Previously, we demonstrated that gastrin activates HDC promoter activity in a gastric cancer (AGS-E) cell line through three overlapping downstream promoter elements. In the current study, we used the yeast one-hybrid strategy to identify nuclear factors that bind to these three elements. Among eight positives from the one-hybrid screen, we identified Kruppel-like factor 4 (KLF4) (previously known as gut-enriched Kruppel-like factor (GKLF)) as one factor that binds to the gastrin responsive elements in the HDC promoter. Electrophoretic mobility shift assays confirmed that KLF4 is able to bind all three gastrin responsive elements. In addition, transient cotransfection experiments showed that overexpression of KLF4 dose dependently and specifically inhibited HDC promoter activity. Regulation of HDC transcription by KLF4 was confirmed by changes in the endogenous HDC messenger RNA by KLF4 small interfering RNA and KLF4 overexpression. We further showed that KLF4 inhibits HDC promoter activity by competing with Sp1 at the upstream GC box and also independently by binding the three downstream gastrin responsive elements. Taken together, these results indicate that KLF4 can act to repress HDC gene expression by Sp1-dependent and -independent mechanisms.

Transcriptional regulation of the human trefoil factor, TFF1, by gastrin

BACKGROUND & AIMS

This study aimed to identify gastrin-sensitive genes that may mediate the effects of this hormone on gastric epithelial architecture.

METHODS

Gastrin-sensitive genes were identified by messenger RNA (mRNA) differential display of the gastric fundus from gastrin-deficient (GAS-KO) or wild-type mice. Gastrin-stimulated expression of the trefoil peptide TFF1 in mouse fundus and in the gastric cancer cell line AGS-G(R) was determined by Northern blot and real-time polymerase chain reaction. Transcriptional regulation of TFF1 in AGS-G(R) cells was studied using promoter-reporter assays and electrophoretic mobility shift assay. Expression of TFF1 and the cholecystokinin(B) receptor in response to gastric mucosal injury was determined by immunohistochemistry.

RESULTS

mRNA differential display identified TFF1 as a gastrin-regulated gene. TFF1 mRNA was reversibly reduced in GAS-KO mice and increased in a hypergastrinemic transgenic strain versus respective background strains. TFF1 mRNA expression was rapidly and potently induced by gastrin in a gastric cancer cell line that expresses the gastrin/cholecystokinin(B) receptor. Gastrin responsiveness of the human TFF1 promoter mapped to a G-C rich region 300 base pairs upstream of the transcriptional start site. This region bound the transcription factors SP3 and MAZ. Gastrin activated transcription through a Raf-, Mek- and Erk-dependent but Ras-independent pathway. TFF1 expression was induced both directly and by transactivation between neighboring cells. Neither direct nor indirect gastrin-induced TFF1 expression required activation of the epidermal growth factor receptor.

CONCLUSIONS

Gastrin exerts tonic control of TFF1 expression but also has the potential for rapid up-regulation of this trefoil factor. TFF1 is a potential candidate to counterbalance the proliferative effects of gastrin.

Stimulatory effects of nitric oxide donors on histamine release in isolated rat gastric mucosal cells

We previously reported stimulatory effects of endogenous and exogenous nitric oxide (NO) on gastric acid secretion. In the present study, we investigated effects of NO donors on release of histamine, which is related to acid secretion, in isolated rat gastric mucosal cells. NO donors such as (+/-)-(E)-4-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexanamide (NOR 1) and sodium nitroprusside significantly augmented the histamine release. It was inhibited by 2-(4-carboxyphenyl)-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-amide (carboxy-PTIO), a NO scavenger, and 6-(phenylamino)-5,8-quinolinedione (LY83583), a soluble guanylate cyclase inhibitor. Dibutyryl cyclic GMP also stimulated histamine release. These results suggest that NO donors act on cyclic GMP pathway in isolated gastric mucosal cells, resulting in facilitation of histamine release. NO may stimulate gastric acid secretion through histamine release from the histamine-containing cells, possibly enterochromaffin-like cells.

Long-term Treatment with Sterigmatocystin, a Fungus Toxin, Enhances the Development of Intestinal Metaplasia of Gastric Mucosa in Helicobacter pylori-infected Mongolian Gerbils

BACKGROUND

Helicobacter pylori is a human gastric carcinogen. Sterigmatocystin (ST), a fungus toxin, is a risk factor of gastric cancer. Cytotoxin-vacuolation toxin A (VacA) present in supernatants of H. pylori suspensions can cause gastritis and ulcer. The aim of this study was to examine the effects of H. pylori, ST and VacA in Mongolian gerbils.

METHODS

Male Mongolian gerbils (n = 196) were treated with H. pylori supernatants (10 ml/1000 mg) mixed with diet or inoculated intragastrically with H. pylori alone or with ST (100 or 1000 ppb), and then killed 27 months later. Gastric tissue sections were stained with haematoxylin and eosin (H&E), periodic acid-Schiff (PAS), Alcian blue (AB, pH 2.5) and with immunostaining for PCNA and p53 expression.

RESULTS

In H. pylori-infected gerbils, the normal mucosa was replaced by hyperplastic epithelium. Severe gastritis, cystic dilatation of gastric glands, hyperplastic polyps and intestinal metaplasia were observed. In H. pylori + ST (1000 ppb) gerbils, intestinal metaplasia was significantly more frequent than in H. pylori alone animals. No pathological changes were observed in the H. pylori supernatant group. Osseous metaplasia was observed in the H. pylori + ST (100 ppb) group. Serum gastrin levels of the H. pylori + ST (1000 ppb) group were significantly higher than those of the other groups. PCNA labelling index and p53 index of infected gerbils were significantly higher than those of uninfected groups.

CONCLUSION

H. pylori causes gastritis, ulcer and intestinal metaplasia. ST enhances the development of intestinal metaplasia and increases gastrin levels in H. pylori-infected Mongolian gerbils.

Gastrin stimulates cyclooxygenase-2 expression in intestinal epithelial cells through multiple signaling pathways. Evidence for involvement of ERK5 kinase and transactivation of the epidermal growth factor receptor

Gastrin is a hormone produced by G-cells in the normal gastric antrum. However, colorectal carcinoma cells may aberrantly produce gastrin and exhibit increased expression of cholecystokinin B (CCK-B)/gastrin receptors. Gastrin is trophic for the normal gastric oxyntic mucosa and exerts a growth-promoting action on gastrointestinal malignancy. Thus, gastrin may act as an autocrine/paracrine or endocrine factor in the initiation and progression of colorectal carcinoma. The molecular mechanisms involved have not been elucidated. Hypergastrinemia induced by Helicobacter pylori infection is associated with increased cyclooxygenase-2 (COX-2) expression in gastric and colorectal tissues, suggesting the possibility that gastrin up-regulates COX-2 expression in these tissues; this has not been confirmed. We report here that gastrin significantly increases the expression of COX-2 mRNA and protein, the activity of the COX-2 promoter, and the release of prostaglandin E(2) from a rat intestinal epithelial cell line transfected with the CCK-B receptor. These actions were dependent upon the activation of multiple MAPK signal pathways, including ERK5 kinase; transactivation of the epidermal growth factor receptor; and the increased expression and activities of transcription factors ELK-1, activating transcription factor-2, c-Fos, c-Jun, activator protein-1, and myocyte enhancer factor-2. Thus, our findings identify the signaling pathways coupling the CCK-B receptor with up-regulation of COX-2 expression. This effect may contribute to this hormone-dependent gastrointestinal carcinogenesis, especially in the colon.

Interaction of early growth response protein 1 (Egr-1), specificity protein 1 (Sp1), and cyclic adenosine 3'5'-monophosphate response element binding protein (CREB) at a proximal response element is critical for gastrin-dependent activation of the chromogranin A promoter

Recently, binding of specific protein 1 (Sp1) and cAMP response element binding protein (CREB) to a GC-rich element at -92/-62 has been identified as a critical step in gastrin-dependent regulation of the chromogranin A (CgA) gene in gastric epithelial cells. Here we demonstrate that binding of early growth response protein 1 (Egr-1) to the distal part of the -92/-62 site is also required for gastrin-dependent CgA transactivation. Gastrin elevated cellular and nuclear Egr-1 levels in a time-dependent manner and also increased Egr-1 binding to the CgA -92/-73 region. Disruption of this site reduced gastrin responsiveness without influencing basal promoter activity, while loss of Sp1 and/or CREB binding sites diminished basal and gastrin-stimulated CgA promoter activity. Ectopic Egr-1 overexpression potently stimulated the CgA promoter, whereas coexpression of Egr-1 with Sp1 and/or CREB resulted in additive effects. Functional analysis of Sp1-, Egr-1-, or CREB-specific promoter mutations in transfection studies confirmed the tripartite organization of the CgA -92/-62 element. Signaling studies revealed that MAPK kinase 1 (MEK1)/ERK1/2 cascades are critical for gastrin-dependent Egr-1 protein accumulation as well as Egr-1 binding to the CgA promoter. Our studies for the first time identify Egr-1 as a nuclear target of gastrin and show that functional interplay of Egr-1, Sp1, and CREB is indispensable for gastrin-dependent CgA transactivation in gastric epithelial cells.

Identification and characterization of a third gastrin response element (GAS-RE3) in the human histidine decarboxylase gene promoter

In human gastric cancer cells the human histidine decarboxylase gene is regulated by gastrin through two overlapping cis-acting elements known as gastrin response elements 1&2 (GAS-RE1, GAS-RE2) [J. Biol. Chem. 274 (1999) 20961]. Here, we report the identification and characterization of a third element GAS-RE3 that was localized to a region +28 to +48 downstream of the transcriptional start site (+1). Gastrin stimulation induced a rapid increase in binding to the element of a novel nuclear factor named gastrin response element-binding protein 3 (GAS-REBP3). Block mutations in the GAS-RE3 sequence (+38GTGCG(+42) to +38TAAGT(+42)) led to reduced promoter activity and decreased binding in EMSA. UV cross-linking studies and Southwestern blot analysis with wildtype and mutant GAS-RE3 showed that GAS-REBP3 was a approximately 110kDa protein. Thus, gastrin-mediated regulation of HDC gene expression appears to be mediated by a complex cis-acting element, which binds at least three distinct nuclear factors.

Gastrin-stimulated gastric epithelial cell invasion: the role and mechanism of increased matrix metalloproteinase 9 expression

The gastric hormone gastrin regulates the organization of the gastric epithelium, but the cellular control mechanisms are yet unknown. Epithelial remodelling typically involves extracellular proteolysis mediated by the matrix metalloproteinases (MMPs). Since a gene-array analysis of the gastric cancer cell line AGS-G(R) suggested that gastrin increased MMP-9 expression, we examined the control of MMP-9 expression by gastrin. Gelatin zymography confirmed gastrin induction of MMP-9 in AGS-G(R) cells, but showed a small inhibition of MMP-2. Immunocytochemical studies showed that MMP-9 was localized to vesicles that appeared to traffic along the processes that were extended in response to gastrin. Gastrin stimulated the invasion of AGS-G(R) cells through artificial basement membrane, which was reduced by an inhibitor of MMP-2/-9. There was also an increase in MMP-9 in the stomach of patients with elevated plasma gastrin and multiple-endocrine neoplasia type 1 (MEN-1) syndrome, suggesting in vivo regulation of MMP-9 expression by gastrin. Finally, we showed that the expression of 1.9 kb of human MMP-9 gene promoter coupled with luciferase (MMP-9-luc) was increased 7.65+/-1.2-fold by gastrin, via a pathway which includes stimulation of protein kinase C, and activation of Raf and the mitogen-activated protein (MAP) kinase pathway. The tumour suppressor menin (which is mutated in MEN-1 syndrome) inhibited the expression of MMP-9-luc by gastrin. These results suggest that gastrin increases MMP-9 expression, which is associated with increased invasion, and this is a putative mechanism regulating remodelling of the gastric epithelium.

Mechanism of activation of protein kinase D2(PKD2) by the CCK(B)/gastrin receptor

Recently, we cloned a novel serine/threonine kinase termed protein kinase D2 (PKD2). PKD2 can be activated by phorbol esters both in vivo and in vitro but also by gastrin via the cholecystokinin/CCK(B) receptor in human gastric cancer cells stably transfected with the CCK(B)/gastrin receptor (AGS-B cells). Here we identify the mechanisms of gastrin-induced PKD2 activation in AGS-B cells. PKD2 phosphorylation in response to gastrin was rapid, reaching a maximum after 10 min of incubation. Our data demonstrate that gastrin-stimulated PKD2 activation involves a heterotrimeric G alpha(q) protein as well as the activation of phospholipase C. Furthermore, we show that PKD2 can be activated by classical and novel members of the protein kinase C (PKC) family such as PKC alpha, PKC epsilon, and PKC eta. These PKCs are activated by gastrin in AGS-B cells. Thus, PKD2 is likely to be a novel downstream target of specific PKCs upon the stimulation of AGS-B cells with gastrin. Our data suggest a two-step mechanism of activation of PKD2 via endogenously produced diacylglycerol and the activation of PKCs.

Gastrin-stimulated gastric epithelial cell invasion: the role and mechanism of increased matrix metalloproteinase 9 expression

The gastric hormone gastrin regulates the organization of the gastric epithelium, but the cellular control mechanisms are yet unknown. Epithelial remodelling typically involves extracellular proteolysis mediated by the matrix metalloproteinases (MMPs). Since a gene-array analysis of the gastric cancer cell line AGS-G(R) suggested that gastrin increased MMP-9 expression, we examined the control of MMP-9 expression by gastrin. Gelatin zymography confirmed gastrin induction of MMP-9 in AGS-G(R) cells, but showed a small inhibition of MMP-2. Immunocytochemical studies showed that MMP-9 was localized to vesicles that appeared to traffic along the processes that were extended in response to gastrin. Gastrin stimulated the invasion of AGS-G(R) cells through artificial basement membrane, which was reduced by an inhibitor of MMP-2/-9. There was also an increase in MMP-9 in the stomach of patients with elevated plasma gastrin and multiple-endocrine neoplasia type 1 (MEN-1) syndrome, suggesting in vivo regulation of MMP-9 expression by gastrin. Finally, we showed that the expression of 1.9 kb of human MMP-9 gene promoter coupled with luciferase (MMP-9-luc) was increased 7.65+/-1.2-fold by gastrin, via a pathway which includes stimulation of protein kinase C, and activation of Raf and the mitogen-activated protein (MAP) kinase pathway. The tumour suppressor menin (which is mutated in MEN-1 syndrome) inhibited the expression of MMP-9-luc by gastrin. These results suggest that gastrin increases MMP-9 expression, which is associated with increased invasion, and this is a putative mechanism regulating remodelling of the gastric epithelium.

GATA proteins are potential negative regulators of HDC gene expression in the gastric epithelium

In this study, we used the gastric epithelial cell line AGS-G(R) to investigate the role of GATA transcription factors in the regulation of both basal and gastrin-stimulated L-histidine decarboxylase (HDC) gene transcription. Using reporter gene technology, we compared the transcriptional activity of a construct, hHDC503, which contained the 5'-flanking region of the human HDC gene with that of similar constructs lacking selected GATA consensus sequences. We demonstrated the expression of GATA-4 and GATA-6 proteins within the AGS-G(R) cells and found evidence that these transcription factors can negatively regulate HDC gene expression.

B-Raf/Rap1 signaling, but not c-Raf-1/Ras, induces the histidine decarboxylase promoter in Helicobacter pylori infection

Histidine decarboxylase (HDC) is the key enzyme for gastric histamine synthesis, and enhanced HDC expression is critically involved in the pathogenesis of gastric disorders, including gastroduodenal ulcer disease. We characterized the pathogenicity mechanism underlying activation of the HDC promoter in H. pylori-infected gastric epithelial cells and performed a detailed analysis of the participating signaling elements. We found that H. pylori infection of gastric epithelial cells activated the MEK1-2/ERK1-2 cascade through cAMP-dependent stimulation of Rap1 and B-Raf, but not Ras/c-Raf-1, leading to potent transactivation of the human HDC promoter. H. pylori-triggered elevation of adenylate cyclase activity was directed by GalphaS-subunits of heterotrimeric G proteins. Stimulation of this signaling cascade was triggered independent of bacterial-cell contact by a small molecular- weight component(s) (approximately 1 kDa) released by H. pylori and did not require a functional type IV secretion system. Thus, our studies demonstrate for the first time to our knowledge that the GalphaS-->cAMP-->Rap1--->B-Raf-->MEK1/2-->ERK1/2 pathway is critical for H. pylori-dependent epithelial gene regulation, which can be induced via a bioactive component(s) apart from the site of bacterial colonization. These results further elucidate the molecular mechanisms underlying interaction of H. pylori with gastric epithelial cells and help to define potential molecular targets for therapeutic interventions in the context of H. pylori-related gastric diseases.

Helicobacter pylori strain-specific modulation of gastric mucosal cellular turnover: implications for carcinogenesis

Helicobacter pylori colonization induces inflammation in essentially all hosts, a persistent process that increases the risk of developing distal gastric adenocarcinoma. However, only a small percentage of persons carrying H. pylori develop neoplasia; enhanced risk may be related to differences in expression of specific bacterial products, differences in the host response to the bacteria, or the interaction between host and microbe. H. pylori strains that have the cag pathogenicity island are associated with further increased risk for developing distal gastric cancer; however, host responses to H. pylori, such as altered epithelial cell proliferation and apoptosis, also may be important in lowering the threshold for carcinogenesis. H. pylori cag+ strains selectively enhance proliferation and attenuate apoptosis in human mucosa compared to cag- strains. However, cag+ strains also induce more severe gastritis, suggesting that host inflammatory mediators such as cytokines, prostaglandins, and hormones may modulate H. pylori-induced alterations in cellular turnover. In the Mongolian gerbil model of gastric carcinogenesis, apoptosis increases early and transiently following H. pylori infection, but scores progressively decline despite worsening gastric inflammation. Epithelial cell proliferation peaks later and is significantly related to increased gastrin levels, suggesting that epithelial cell growth in H. pylori-colonized mucosa may be mediated by gastrin-dependent mechanisms. An emerging model invoked by these data is one in which H. pylori cag+ strains, in conjunction with host mediators, enhance gastric epithelial cell proliferation but not apoptosis in vivo. The combination of increased proliferation without a concordant increase in apoptosis may therefore contribute to the heightened retention of mutagenized cells, which over decades may increase the subsequent risk for gastric cancer.

Helicobacter pylori and gastrointestinal tract adenocarcinomas

Although gastric adenocarcinoma is associated with the presence of Helicobacter pylori in the stomach, only a small fraction of colonized individuals develop this common malignancy. H. pylori strain and host genotypes probably influence the risk of carcinogenesis by differentially affecting host inflammatory responses and epithelial-cell physiology. Understanding the host-microbial interactions that lead to neoplasia will improve cancer-targeted therapeutics and diagnostics, and provide mechanistic insights into other malignancies that arise within the context of microbially initiated inflammatory states.

L-histidine decarboxylase decreases its own transcription through downregulation of ERK activity

A poorly defined negative feedback loop decreases transcription of the L-histidine decarboxylase (HDC) gene. To help understand this regulation, we have studied the effect of HDC protein expression on HDC gene transcription in transfected AGS-B cells. Expression of the rat HDC protein inhibited HDC promoter activity in a dose-dependent fashion. The region of the HDC promoter mediating this inhibitory effect corresponded to a previously defined gastrin and extracellular signal-related kinase (ERK)-1 response element. Overexpression of the HDC protein reduced nuclear factor binding in this region. Experiments employing specific histamine receptor agonists indicated that the inhibitory effect was not dependent on histamine production, and studies with the HDC inhibitor alpha-fluoromethylhistidine revealed that inhibition was unrelated to enzyme activity. Instead, an enzymatically inactive region at the amino terminal of the HDC enzyme (residues 1-271) was shown to mediate inhibition. Fluorescent chimeras containing this domain were not targeted to the nucleus, arguing against specific inhibition of the HDC transcription machinery. Instead, we found that overexpression of HDC protein decreased ERK protein levels and ERK activity and that the inhibitory effect of HDC protein could be overcome by overexpression of ERK1. These data suggest a novel feedback-inhibitory role for amino terminal sequences of the HDC protein.

Gastrin induces expression and promoter activity of the vesicular monoamine transporter subtype 2

Gastric enterochromaffin-like cells produce histamine in response to the antral hormone gastrin and accumulate the biogenic amine in secretory organelles via vesicular monoamine transporter subtype 2. The putative effects of gastrin on vesicular monoamine transporter subtype 2 expression and promoter activity are poorly understood. In the present study we used highly enriched rat enterochromaffin-like cells (purity, >90%) and rat pheochromocytoma cells stably transfected with a gastrin/cholecystokinin B receptor to investigate the expression and transcriptional regulation of vesicular monoamine transporter subtype 2. Stimulation of vesicular monoamine transporter subtype 2 mRNA and protein expression was observed in isolated enterochromaffin-like cells after 3- to 7-h incubation with gastrin (10(-7) M), forskolin (10(-5) M), or ionomycin (10(-5) M). Deletion analysis of the rat vesicular monoamine transporter subtype 2 promoter defined the minimal promoter sequence necessary for full basal activity as a -121 bp segment upstream of exon 1 containing two Sp1 sites (-97 to -88 bp and -68 to -59 bp) and a cAMP-responsive element (-44 to -35 bp). Gastrin (10(-7) M) stimulated extracellular signal related kinase1/2 phosphorylation, activated Sp1 and cAMP-responsive element-binding protein, and further induced activity of the complete rat vesicular monoamine transporter subtype 2 promoter (-800 bp) in gastrin/cholecystokinin B receptor cells. The -121-bp fragment was able to confer full gastrin responsiveness, and site-directed mutagenesis of the Sp1 and cAMP-responsive element motifs demonstrated their crucial importance for basal and inducible activities. Comparison of promoter activity of histidine decarboxylase, chromogranin A, or vesicular monoamine transporter subtype 2 in transfected cell lines revealed significant differences in basal and gastrin-stimulated activities. Our current study provides the first evidence that gastrin directly stimulates the expression and promoter activity of vesicular monoamine transporter subtype 2. Sp1 and cAMP-responsive element-binding protein recognition motifs located within 121 bp upstream of exon 1 appear to be indispensable for full basal and inducible promoter activities. Diverging effects of gastrin on histidine decarboxylase, chromogranin A, and vesicular monoamine transporter subtype 2 promoter may account for the coordinated synthesis and storage of histamine in this neuroendocrine cell type.

Expression of hepatocyte growth factor, transforming growth factor alpha, apoptosis related proteins Bax and Bcl-2, and gastrin in human gastric cancer

BACKGROUND

Gastric cancer is one of the most frequent neoplasms and a leading cause of the death world-wide. In recent years, epidemiological and animal studies demonstrated a link between gastric cancer and chronic infection with H. pylori. The exact mechanism responsible for the development of gastric cancer in H. pylori-infected patients still remains unclear. There is evidence that the up-regulation of certain growth factors could play an important role in the promotion of the gastric carcinogenesis.

AIMS

The present study was designed to determine the gene expression of major known growth factors such as transforming growth factor alpha (TGFalpha), hepatocyte growth factor (HGF) and gastrin in the gastric cancer tissue, the surrounding mucosa and, for comparison, in the normal gastric mucosa. Furthermore, the luminal and plasma levels of gastrin in patients with gastric cancer were determined. In addition, the gene and protein expressions of apoptosis-related proteins such as Bax and Bcl-2 were investigated by reverse transcription-polymerase chain reaction and Western blot. Twenty-five gastric cancer patients and 40 age- and gender-matched control subjects hospitalized with non-ulcer dyspepsia were included into this study.

RESULTS

An overall H. pylori-seropositivity among gastric cancer patients was about 72% and was significantly higher than in the controls (56%). The prevalence of CagA-positive strains was also significantly higher among gastric cancer patients than in controls (56% vs. 32%). The gene expression of HGF and TGFalpha was detected more frequently in gastric cancer tissue samples than in normal gastric mucosa (52% vs. 12% for HGF and 48% vs. 24% for TGFalpha). The extent of protein expression in Western blotting analysis for HGF and TGFalpha correlated with the mRNA expression of these factors. Gene expression of gastrin was detected in the antrum of all tested patients and in the majority (84%) of gastric cancer patients. The median plasma and luminal concentrations of gastrin in gastric cancer patients were significantly higher than in controls. The gene expression of bcl-2 was detected in all (100%) and that of proapoptotic bax only in 56% of gastric cancer samples. In comparison to the surrounding non-tumorous tisssue, the gene expression of bax was significantly down-regulated and the gene expression of bcl-2 was up-regulated in gastric cancer tissue. At the protein level, Bax was not detectable and Bcl-2 was seen in 80% of gastric cancer samples.

CONCLUSIONS

It is concluded that the patients infected with H. pylori, especially with CagA-positive strains, are at a higher risk of developing a gastric cancer. An increased production and release of gastrin, as well as an over-expression of growth factors such as HGF and TGFalpha, might contribute to the gastric carcinogenesis. In addition, a dysregulation of the Bax/Bcl-2 system with significant up-regulation of Bcl-2 is observed in gastric cancer.

[Regulation of histamine production in macrophages]

Stimulating cells of the mouse macrophage-like cell line RAW 264.7 with the Ca(2+)-ATPase inhibitor thapsigargin increased histamine production. Thapsigargin increased the levels of histidine decarboxylase (HDC) mRNA at 4 h and the expression of 74-kDa HDC protein at 8 h. PD98059, a specific inhibitor of MEK-1 which phosphorylates p44/p42 MAP kinase, strongly suppressed the thapsigargin-induced histamine production, the increase in HDC mRNA level and 74-kDa HDC protein expression. In contrast, SB203580, an inhibitor of p38 MAP kinase, showed only a partial inhibition of histamine production. TPA and LPS also induced histamine production in RAW 264.7 cells, and the histamine production induced by TPA or LPS was also inhibited by PD98059, but the effect of SB203580 was partial. The synthetic glucocorticoid dexamethasone inhibited thapsigargin-induced histamine production, 74-kDa HDC protein expression and the activation of p44/p42 MAP kinases. In conclusion, the increase in histamine production in macrophages stimulated with inflammatory stimulants is due to the increased expression of 74-kDa HDC, which is positively regulated by activated p44/p42 MAP kinases. Dexamethasone inhibits thapsigargin-induced HDC protein expression and histamine production by inhibiting the MAP kinase activation.

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.

The gastrins: their production and biological activities

Gastric epithelial organization and function are controlled and maintained by a variety of endocrine and paracrine mediators. Peptides encoded by the gastrin gene are an important part of this system because targeted deletion of the gene, or of the gastrin-CCKB receptor gene, leads to decreased numbers of parietal cells and decreased gastric acid secretion. Recent studies indicate that the gastrin precursor, preprogastrin, gives rise to a variety of products, each with a distinctive spectrum of biological activity. The conversion of progastrin to smaller peptides is regulated by multiple mechanisms including prohormone phosphorylation and secretory vesicle pH. Progastrin itself stimulates colonic epithelial proliferation; biosynthetic intermediates (Gly-gastrins) stimulate colonic epithelial proliferation and gastric epithelial differentiation; and C-terminally amidated gastrins stimulate colonic proliferation, gastric epithelial proliferation and differentiation, and acid secretion. The effects of progastrin-derived peptides on gastric epithelial function are mediated in part by release of paracrine factors that include histamine, epidermal growth factor (EGF)-receptor ligands, and Reg. The importance of the appropriate regulation of this system is shown by the observation that prolonged moderate hypergastrinemia in transgenic mice leads to remodelling of the gastric epithelium, and in the presence of Helicobacter, to gastric cancer.