Progastrin expression predisposes mice to colon carcinomas and adenomas in response to a chemical carcinogen

Deficiency in mammalian STN1 promotes colon cancer development via inhibiting DNA repair

Despite the high lethality of colorectal cancers (CRCs), only a limited number of genetic risk factors are identified. The mammalian ssDNA-binding protein complex CTC1-STN1-TEN1 protects genome stability, yet its role in tumorigenesis is unknown. Here, we show that attenuated CTC1/STN1 expression is common in CRCs. We generated an inducible STN1 knockout mouse model and found that STN1 deficiency in young adult mice increased CRC incidence, tumor size, and tumor load. CRC tumors exhibited enhanced proliferation, reduced apoptosis, and elevated DNA damage and replication stress. We found that STN1 deficiency down-regulated multiple DNA glycosylases, resulting in defective base excision repair (BER) and accumulation of oxidative damage. Collectively, this study identifies STN1 deficiency as a risk factor for CRC and implicates the previously unknown STN1-BER axis in protecting colon tissues from oxidative damage, therefore providing insights into the CRC tumor-suppressing mechanism.

Molecular pathogenesis, targeted therapies, and future perspectives for gastric cancer

Gastric cancer is a major source of global cancer mortality with limited treatment options and poor patient survival. As our molecular understanding of gastric cancer improves, we are now beginning to recognize that these cancers are a heterogeneous group of diseases with incredibly unique pathogeneses and active oncogenic pathways. It is this molecular diversity and oftentimes lack of common oncogenic driver mutations that bestow the poor treatment responses that oncologists often face when treating gastric cancer. In this review, we will examine the treatments for gastric cancer including up-to-date molecularly targeted therapies and immunotherapies. We will then review the molecular subtypes of gastric cancer to highlight the diversity seen in this disease. We will then shift our discussion to basic science and gastric cancer mouse models as tools to study gastric cancer molecular heterogeneity. Furthermore, we will elaborate on a molecular process termed paligenosis and the cyclical hit model as key events during gastric cancer initiation that impart nondividing mature differentiated cells the ability to re-enter the cell cycle and accumulate disparate genomic mutations during years of chronic inflammation and injury. As our basic science understanding of gastric cancer advances, so too must our translational and clinical efforts. We will end with a discussion regarding single-cell molecular analyses and cancer organoid technologies as future translational avenues to advance our understanding of gastric cancer heterogeneity and to design precision-based gastric cancer treatments. Elucidation of interpatient and intratumor heterogeneity is the only way to advance future cancer prevention, diagnoses and treatment.

Progastrin production transitions from Bmi1+/Prox1+ to Lgr5high cells during early intestinal tumorigenesis

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Secretion of progastrin is a signature event of early malignant transformation in the colon.

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In the healthy epithelium, progastrin is produced by a subset of enteroendocrine cells expressing both Bmi1 and Prox1.

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LGR5-high intestinal stem cells are a primary source of progastrin production in early mouse and human intestinal adenomas.

Progastrin is an unprocessed soluble peptide precursor with a well-described tumor-promoting role in colorectal cancer. It is expressed at small levels in the healthy intestinal mucosa, and its expression is enhanced at early stages of intestinal tumor development, with high levels of this peptide in hyperplastic intestinal polyps being associated with poor neoplasm-free survival in patients. Yet, the precise type of progastrin-producing cells in the healthy intestinal mucosa and in early adenomas remains unclear. Here, we used a combination of immunostaining, RNAscope labelling and retrospective analysis of single cell RNAseq results to demonstrate that progastrin is produced within intestinal crypts by a subset of Bmi1⁺/Prox1⁺/LGR5^low endocrine cells, previously shown to act as replacement stem cells in case of mucosal injury. In contrast, our findings indicate that intestinal stem cells, specified by expression of the Wnt signaling target LGR5, become the main source of progastrin production in early mouse and human intestinal adenomas. Collectively our results suggest that the previously identified feed-forward mechanisms between progastrin and Wnt signaling is a hallmark of early neoplastic transformation in mouse and human colonic adenomas.

The application of transgenic and gene knockout mice in the study of gastric precancerous lesions

Gastric intestinal metaplasia is a precursor for gastric dysplasia, which is in turn, a risk factor for gastric adenocarcinoma. Gastric metaplasia and dysplasia are known as gastric precancerous lesions (GPLs), which are essential stages in the progression from normal gastric mucosa to gastric cancer (GC) or gastric adenocarcinoma. Genetically-engineered mice have become essential tools in various aspects of GC research, including mechanistic studies and drug discovery. Studies in mouse models have contributed significantly to our understanding of the pathogenesis and molecular mechanisms underlying GPLs and GC. With the development and improvement of gene transfer technology, investigators have created a variety of transgenic and gene knockout mouse models for GPLs, such as H/K-ATPase transgenic and knockout mutant mice and gastrin gene knockout mice. Combined with Helicobacter infection, and treatment with chemical carcinogens, these mice develop GPLs or GC and thus provide models for studying the molecular biology of GC, which may lead to the discovery and development of novel drugs. In this review, we discuss recent progress in the use of genetically-engineered mouse models for GPL research, with particular emphasis on the importance of examining the gastric mucosa at the histological level to investigate morphological changes of GPL and GC and associated protein and gene expression.

Clinical Significance of Serum Gastrin Levels in Patients with Colorectal Cancer

Aims

An association between elevated serum gastrin levels and the presence of human colorectal cancer has been reported, and gastrin has been shown to stimulate the growth of experimentally induced colon neoplasia. The aim of this study was to determine the preoperative and postoperative concentrations of serum gastrin in 53 patients with colorectal cancer and to assess the correlation between gastrin levels and tumor characteristics and prognosis.

Materials and Methods

A prospective study was performed over a six-year period during which 53 patients received potentially curative surgery for colorectal cancer. The prognostic variables used for the analysis included age, sex, tumor site, stage and degree of differentiation, preoperative and postoperative serum values of carcinoembryonic antigen (CEA) and gastrin, cancer-related mortality, and survival. CEA and gastrin serum values were determined using radioimmunological methods. Follow-up was carried out with clinical and radiological tests.

Results

The mean preoperative gastrin concentration was 51.2 ± 27.4 pg/mL (range 12–146). Significantly increased serum gastrin concentrations, which returned to normal after surgery, were detected only in patients with well-differentiated cancer (74.2 ± 28.3 pg/mL; moderately differentiated, 52.1 ± 23.8; poorly differentiated, 29.9 ± 12.3, p=0.02). The prognosis was unrelated to serum gastrin level; instead, tumor stage, preoperative CEA value, and degree of differentiation affected patient survival.

Conclusions

This study showed that the serum gastrin concentration is not an appropriate clinical oncogenic factor. Although occurring only in well-differentiated tumors, serum gastrin is unrelated to the prognosis of patients with colorectal cancer.

A novel antibody against cancer stem cell biomarker, DCLK1-S, is potentially useful for assessing colon cancer risk after screening colonoscopy

DCLK1 expression is critically required for maintaining growth of human colon cancer cells (hCCCs). Human colorectal tumors (CRCs) and hCCCs express a novel short isoform of DCLK1 (DCLK1-S; isoform 2) from β-promoter of hDCLK1 gene, while normal colons express long isoform (DCLK1-L; isoform 1) from 5'(α)-promoter, suggesting that DCLK1-S, and not DCLK1-L, marks cancer stem cells (CSCs). Even though DCLK1-S differs from DCLK1-L by only six amino acids, we succeeded in generating a monospecific DCLK1-S-Antibody (PS41014), which does not cross-react with DCLK1-L, and specifically detects CSCs. Subcellular localization of S/L-isoforms was examined by immune-electron-microscopy (IEM). Surprisingly, besides plasma membrane and cytosolic fractions, S/L also localized to nuclear/mitochondrial fractions, with pronounced localization of S-isoform in the nuclei and mitochondria. Sporadic CRCs develop from adenomas. Screening colonoscopy is used for detection/resection of growths, and morphological/pathological criteria are used for risk assessment and recommendations for follow-up colonoscopy. But, these features are not precise and majority of the patients will never develop cancer. We hypothesized that antibody-based assay(s), which identify CSCs, will significantly improve prognostic value of morphological/pathological criteria. We conducted a pilot retrospective study with PS41014-Ab, by staining archived adenoma specimens from patients who developed (high-risk), or did not develop (low-risk) adenocarcinomas within 10-15 years. PS41014-Ab stained adenomas from initial and follow-up colonoscopies of high-risk patients, at significantly higher levels (three to fivefold) than adenomas from low-risk patients, suggesting that PS41014-Ab could be used as an additional tool for assessing CRC risk. CRC patients, with high DCLK1-S-expressing tumors (by qRT-PCR), were reported to have worse overall survival than low expressers. We now report that DCLK1-S-specific Ab may help to identify high-risk patients at the time of index/screening colonoscopy.

Targeting progastrin enhances radiosensitization of colorectal cancer cells

A high percentage of advanced rectal cancers are resistant to radiation. Therefore, increasing the efficacy of radiotherapy by targeting factors involved in radioresistance seems to be an attractive strategy. Here we demonstrated that the pro-hormone progastrin (PG), known to be over-expressed in CRC, and recognized as a pro-oncogenic factor, is a radioresistance factor that can be targeted to sensitize resistant rectal cancers to radiations. First, we observed an increase in PG mRNA expression under irradiation. Our results also demonstrated that down-regulating PG mRNA expression using a shRNA strategy, significantly increases the sensitivity to irradiation (IR) in a clonogenic assay of different colorectal cancer cell lines. We also showed that the combination of PG gene down-regulation and IR strongly inhibits tumours progression in vivo. Then, we demonstrated that targeting PG gene radiosensitizes cancer cells by increasing radio-induced apoptosis shown by an increase in annexin V positive cells, caspases activation and PARP cleavage. We also observed the up-regulation of the pro-apoptotic pathway, JNK and the induction of the expression of pro-apoptotic factors such as BIM. In addition, we demonstrated in this study that inhibition of PG gene expression enhances radiation-induced DNA damage. Our data also suggest that, in addition to increase radio-induced apoptosis, targeting PG gene also leads to the inhibition of the survival pathways, AKT and ERK induced by IR. Taken together, our results highlight the role of PG in radioresistance and provide a preclinical proof of concept that PG represents an attractive target for sensitizing resistant rectal tumours to irradiation. .

Epigenetic regulation of human DCLK-1 gene during colon-carcinogenesis: clinical and mechanistic implications

Colorectal carcinogenesis is a multi-step process. While ~25% of colorectal cancers (CRCs) arise in patients with a family history (genetic predisposition), ~75% of CRCs are due to age-associated accumulation of epigenetic alterations which can result in the suppression of key tumor suppressor genes leading to mutations and activation of oncogenic pathways. Sporadic colon-carcinogenesis is facilitated by many molecular pathways of genomic instability which include chromosomal instability (CIN), micro-satellite instability (MSI) and CpG island methylator phenotype (CIMP), leading towards loss of homeostasis and onset of neoplastic transformation. The unopposed activation of Wnt/β-catenin pathways, either due to loss of APC function or up-regulation of related stimulatory pathways, results in unopposed hyperproliferation of colonic crypts, considered the single most important risk factor for colon carcinogenesis. Hypermethylation of CpG islands within the promoters of specific genes can potentially inactivate DNA repair genes and/or critical tumor suppressor genes. Recently, CpG methylation of the 5' promoter of human (h) DCLK1 gene was reported in many human epithelial cancers, including colorectal cancers (CRCs), resulting in the loss of expression of the canonical long isoform of DCLK1 (DCLK1-L) in hCRCs. Instead, a shorter isoform of DCLK1 (DCLK1-S) was discovered to be expressed in hCRCs, from an alternate β promoter of DCLKL1-gene; the clinical and biological implications of these novel findings, in relation to recent publications is discussed.

Epigenetic changes and alternate promoter usage by human colon cancers for expressing DCLK1-isoforms: Clinical Implications

DCLK1 specifically marks colon/pancreatic cancers in mice, and is expressed by human colon adenocarcinomas (hCRCs). Down-regulation of DCLK1 results in loss of cancer-stem-cells (CSCs), and inhibits spheroidal/xenograft growths from hCRC-cells. The 5'-promoter of DCLK1-gene is reportedly hypermethylated in hCRCs, resulting in loss of expression of DCLK1-transcripts, originating from 5'(α)-promoter (termed DCLK1-L, in here). However, in mouse colon-tumors, 5'-promoter of DCLK1-gene remains unchanged, and DCLK1-L, originating from 5'(α)-promoter, is expressed. We hypothesized that elevated levels of DCLK1-protein in hCRC-cells, may be transcribed/translated from an alternate-promoter. Several in silico and molecular biology approaches were used to test our hypothesis. We report for the first time that majority of hCRCs express short-transcripts of DCLK1 (termed DCLK1-S, in here) from an alternate β-promoter in IntronV of the gene, while normal-colons mainly express DCLK1-L from 5'(α)-promoter. We additionally report an important role of β-catenin and TCF4/LEF binding-sites for activating (α)-promoter, while activated NF-κBp65 (bound to NF-κB-cis-element), activates (β)-promoter in cancer-cells. DCLK1-S expression was examined in a cohort of 92 CRC patients; high-expressors had significantly worse overall-survival compared to low-expressors. Our novel findings' regarding usage of alternate (β)-promoter by hCRCs, suggests that DCLK1-S may represent an important target for preventing/inhibiting colon-cancers, and for eliminating colon-CSCs.

CCK2R identifies and regulates gastric antral stem cell states and carcinogenesis

OBJECTIVE

Progastrin is the incompletely cleaved precursor of gastrin that is secreted by G-cells in the gastric antrum. Both gastrin and progastrin bind to the CCK2 receptor (Cckbr or CCK2R) expressed on a subset of gastric epithelial cells. Little is known about how gastrin peptides and CCK2R regulate gastric stem cells and carcinogenesis. Interconversion among progenitors in the intestine is documented, but the mechanisms by which this occurs are poorly defined.

DESIGN

We generated CCK2R-CreERT mice and performed inducible lineage tracing experiments. CCK2R+ antral cells and Lgr5+ antral stem cells were cultured in a three-dimensional in vitro system. We crossed progastrin-overexpressing mice with Lgr5-GFP-CreERT mice and examined the role of progastrin and CCK2R in Lgr5+ stem cells during MNU-induced carcinogenesis.

RESULTS

Through lineage tracing experiments, we found that CCK2R defines antral stem cells at position +4, which overlapped with an Lgr5(neg or low) cell population but was distinct from typical antral Lgr5(high) stem cells. Treatment with progastrin interconverts Lgr5(neg or low) CCK2R+ cells into Lgr5(high) cells, increases CCK2R+ cell numbers and promotes gland fission and carcinogenesis in response to the chemical carcinogen MNU. Pharmacological inhibition or genetic ablation of CCK2R attenuated progastrin-dependent stem cell expansion and carcinogenesis.

CONCLUSIONS

CCK2R labels +4 antral stem cells that can be activated and expanded by progastrin, thus identifying one hormonal trigger for gastric stem cell interconversion and a potential target for gastric cancer chemoprevention and therapy.

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.

Circulating gastrin concentrations in patients at increased risk of developing colorectal carcinoma

BACKGROUND AND AIM

An increase in circulating concentrations of gastrin or gastrin precursors such as progastrin and glycine-extended gastrin has been proposed to promote the development of colorectal carcinomas (CRC). The aim of this study was to investigate whether or not circulating gastrin concentrations were increased in patients with an increased risk of developing CRC.

METHOD

Patients were divided according to their risk into the five following groups: familial adenomatous polyposis (n = 20), hereditary non-polyposis colorectal cancer (n = 53), cluster of common colorectal cancers (n = 13), personal history and/or family history of adenomatous polyps or CRC (n = 150) and controls (n = 42). Radioimmunoassay with four region-specific gastrin antisera was used to measure progastrin, glycine-extended gastrin (gastrin-gly), amidated gastrin (gastrin-amide), and total gastrin in peripheral blood taken at the time of colonoscopy.

RESULTS

Compared with the control group, familial adenomatous polyposis patients had significantly higher median values of total gastrin (29.8 pM vs 16.9 pM, P = 0.003) and gastrin-amide (17.1 pM vs 12.0 pM, P = 0.015). Patients with a personal or family history of adenomatous polyps or CRC also had higher circulating concentrations of total gastrin (21.8 pM) compared with controls (P < 0.05), while patients from all groups who presented with an adenomatous polyp on the day of colonoscopy had higher concentrations of total gastrin, progastrin, and gastrin-amide than patients without polyps.

CONCLUSION

Concentrations of gastrin precursors are increased in particular groups with an increased risk of developing CRC.

Deletion of glutathione peroxidase-2 inhibits azoxymethane-induced colon cancer development

The selenoprotein glutathione peroxidase-2 (GPx2) appears to have a dual role in carcinogenesis. While it protected mice from colon cancer in a model of inflammation-triggered carcinogenesis (azoxymethane and dextran sodium sulfate treatment), it promoted growth of xenografted tumor cells. Therefore, we analyzed the effect of GPx2 in a mouse model mimicking sporadic colorectal cancer (azoxymethane-treatment only). GPx2-knockout (KO) and wild-type (WT) mice were adjusted to an either marginally deficient (−Se), adequate (+Se), or supranutritional (++Se) selenium status and were treated six times with azoxymethane (AOM) to induce tumor development. In the −Se and ++Se groups, the number of tumors was significantly lower in GPx2-KO than in respective WT mice. On the +Se diet, the number of dysplastic crypts was reduced in GPx2-KO mice. This may be explained by more basal and AOM-induced apoptotic cell death in GPx2-KO mice that eliminates damaged or pre-malignant epithelial cells. In WT dysplastic crypts GPx2 was up-regulated in comparison to normal crypts which might be an attempt to suppress apoptosis. In contrast, in the +Se groups tumor numbers were similar in both genotypes but tumor size was larger in GPx2-KO mice. The latter was associated with an inflammatory and tumor-promoting environment as obvious from infiltrated inflammatory cells in the intestinal mucosa of GPx2-KO mice even without any treatment and characterized as low-grade inflammation. In WT mice the number of tumors tended to be lowest in +Se compared to −Se and ++Se feeding indicating that selenium might delay tumorigenesis only in the adequate status. In conclusion, the role of GPx2 and presumably also of selenium depends on the cancer stage and obviously on the involvement of inflammation.

Progastrin-induced secretion of insulin-like growth factor 2 from colonic myofibroblasts stimulates colonic epithelial proliferation in mice

BACKGROUND & AIMS

Many colon cancers produce the hormone progastrin, which signals via autocrine and paracrine pathways to promote tumor growth. Transgenic mice that produce high circulating levels of progastrin (hGAS) have increased proliferation of colonic epithelial cells and are more susceptible to colon carcinogenesis than control mice. We investigated whether progastrin affects signaling between colonic epithelial and myofibroblast compartments to regulate tissue homeostasis and cancer susceptibility.

METHODS

Colonic myofibroblast numbers were assessed in hGAS and C57BL/6 mice by immunohistochemistry. Human CCD18Co myofibroblasts were incubated with recombinant human progastrin (rhPG)(1-80) for 18 hours, and proliferation was assessed in the presence of pharmacologic inhibitors. The proliferation of human HT29 colonic epithelial cells was assessed after addition of conditioned media from CCD18Co cells incubated with progastrin. The effects of the insulin-like growth factor (IGF)-I receptor antagonist AG1024 were investigated in cultured HT29 cells and on the colonic epithelium of hGAS mice compared with mice that did not express transgenic progastrin (controls).

RESULTS

The colonic mucosa of hGAS mice contained greater numbers of myofibroblasts that expressed α-smooth muscle actin and vimentin than controls. Incubation of CCD18Co myofibroblasts with 0.1 nmol/L rhPG(1-80) increased their proliferation, which required activation of protein kinase C and phosphatidylinositol-3 kinase. CCD18Co cells secreted IGF-II in response to rhPG(1-80), and conditioned media from CCD18Co cells that had been incubated with rhPG(1-80) increased the proliferation of HT29 cells. The colonic epithelial phenotype of hGAS mice (crypt hyperplasia, increased proliferation, and altered proportions of goblet and enteroendocrine cells) was inhibited by AG1024.

CONCLUSIONS

Progastrin stimulates colonic myofibroblasts to release IGF-II, which increases proliferation of colonic epithelial cells. Progastrin might therefore alter colonic epithelial cells via indirect mechanisms to promote neoplasia.

p-21-Activated kinase 1 mediates gastrin-stimulated proliferation in the colorectal mucosa via multiple signaling pathways

Gastrins, including amidated (Gamide) and glycine-extended (Ggly) forms, function as growth factors for the gastrointestinal mucosa. The p-21-activated kinase 1 (PAK1) plays important roles in growth factor signaling networks that control cell motility, proliferation, differentiation, and transformation. PAK1, activated by both Gamide and Ggly, mediates gastrin-stimulated proliferation and migration, and activation of β-catenin, in gastric epithelial cells. The aim of this study was to investigate the role of PAK1 in the regulation by gastrin of proliferation in the normal colorectal mucosa in vivo. Mucosal proliferation was measured in PAK1 knockout (PAK1 KO) mice by immunohistochemistry. The expression of phosphorylated and unphosphorylated forms of the signaling molecules PAK1, extracellular signal-regulated kinase (ERK), and protein kinase B (AKT), and the expression of β-catenin and its downstream targets c-Myc and cyclin D1, were measured in gastrin knockout (Gas KO) and PAK1 KO mice by Western blotting. The expression and activation of PAK1 are decreased in Gas KO mice, and these decreases are associated with reduced activation of ERK, AKT, and β-catenin. Proliferation in the colorectal mucosa of PAK1 KO mice is reduced, and the reduction is associated with reduced activation of ERK, AKT, and β-catenin. In compensation, antral gastrin mRNA and serum gastrin concentrations are increased in PAK1 KO mice. These results indicate that PAK1 mediates the stimulation of colorectal proliferation by gastrins via multiple signaling pathways involving activation of ERK, AKT, and β-catenin.

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.

Mouse models of gastric cancer

Animal models have greatly enriched our understanding of the molecular mechanisms of numerous types of cancers. Gastric cancer is one of the most common cancers worldwide, with a poor prognosis and high incidence of drug-resistance. However, most inbred strains of mice have proven resistant to gastric carcinogenesis. To establish useful models which mimic human gastric cancer phenotypes, investigators have utilized animals infected with Helicobacter species and treated with carcinogens. In addition, by exploiting genetic engineering, a variety of transgenic and knockout mouse models of gastric cancer have emerged, such as INS-GAS mice and TFF1 knockout mice. Investigators have used the combination of carcinogens and gene alteration to accelerate gastric cancer development, but rarely do mouse models show an aggressive and metastatic gastric cancer phenotype that could be relevant to preclinical studies, which may require more specific targeting of gastric progenitor cells. Here, we review current gastric carcinogenesis mouse models and provide our future perspectives on this field.

Progastrin Peptides Increase the Risk of Developing Colonic Tumors: Impact on Colonic Stem Cells

Pre-neoplastic lesions (ACF, aberrant-crypt-foci; Hp, hyperplastic/dysplastic polyps) are believed to be precursors of sporadic colorectal-tumors (Ad, adenomas; AdCA, adenocarcinomas). ACF/Hp likely originate due to abnormal growth of colonic-crypts in response to aberrant queues in the microenvironment of colonic-crypts. Thus identifying factors which regulate homeostatic vs aberrant proliferation/apoptosis of colonocytes, especially stem/progenitor cells, may lead to effective preventative/treatment strategies. Based on this philosophy, role of growth-factors/peptide-hormones, potentially available in the circulation/microenvironment of colonic-crypts is being examined extensively. Since the time gastrins were discovered as trophic (growth) factors for gastrointestinal-cells, the effect of gastrins on the growth of normal/cancer cells has been investigated, leading to many discoveries. Seminal discoveries made in the area of gastrins and colon-cancer, as it relates to molecular pathways associated with formation of colonic tumors will be reviewed, and possible impact on diagnostic/preventative/treatment strategies will be discussed.

Progastrin overexpression imparts tumorigenic/metastatic potential to embryonic epithelial cells: phenotypic differences between transformed and nontransformed stem cells

We recently reported that overexpression of progastrin (PG) in embryonic epithelial cells (HEKmGAS cells) increased proliferation of the cells compared to that of control HEKC cells. Here, we report the novel finding that tumorigenic and metastatic potential of HEKmGAS cells is also increased significantly compared to that of HEKC cells. Cell surface-associated annexinA2 (CS-ANXA2) binds PG and is overexpressed on cancer cells, allowing us to successfully use fluorescently labeled PG peptide for enumerating metastatic lesions of transformed/cancer cells in vivo. Next, we examined the hypothesis that increased tumorigenic/metastatic potential of isogenic HEKmGAS versus HEKC cells maybe due to transformed phenotype of stem cells. FACSorting/FACScanning of cells demonstrated significant increases in percent doublecortin-CAM-kinase-like1 (DCLK1)/Lgr5-positive stem cells, coexpressing cluster of differentiation44 (CD44)/CS-ANXA2, in HEKmGAS versus HEKC cells. Distinct differences were noted in the morphology of HEKC versus HEKmGAS spheroidal growths on nonadherent cultures (selective for stem cells). HEKC spheroids were rounded with distinct perimeters (e.g., basement membranes), whereas HEKmGAS spheroids were amorphous with no perimeters. Relative levels of DCLK1/Lgr5/CD44 and ANXA2/β-catenin/pNFκBp65/metalloproteinases were significantly increased in HEKmGAS versus HEKC cells, growing as monolayer cultures, 3D spheroids (in vitro), or xenografts (in vivo). Interestingly, HEKC cells enriched for CS-ANXA2 developed amorphous spheroids, whereas downregulation of ANXA2 in HEKmGAS clones resulted in loss of matrixmetalloproteinases (MMPs) and re-formation of rounded spheroids, suggesting that high levels of CS-ANXA2/MMPs may impact spheroid morphology. Downregulation of DCLK1 significantly attenuated activation of β-catenin, with loss of proliferation of HEKmGAS and HEKC cells, suggesting that DCLK1 is required for maintaining proliferation of cells. Our results suggest the novel possibility that transformed stem cells, unlike nontransformed stem cells, coexpress stem cell markers DCLK1 and CD44 with CS-ANXA2.

P53 gene mutation increases progastrin dependent colonic proliferation and colon cancer formation in mice

Transgenic mice overexpressing human progastrin (hGAS) show colonic crypt hyper-proliferation and elevated susceptibility to colon carcinogenesis. We aimed to investigate effects of p53 mutation on colon carcinogenesis in hGAS mice. We show that introducing a p53 gene mutation further increases progastrin dependent BrdU labeling and results in markedly elevated number of aberrant crypt foci (ACF) and colonic tumors. We demonstrate that hGAS/Lgr5-GFP mice have higher number of Lgr5+ colonic stem cells per crypt when compared to Lgr5-GFP mice indicating that progastrin changes crypt biology through increased stem cell numbers and additional p53 mutation leads to more aggressive phenotype in this murine colon cancer model.

Clathrin mediates endocytosis of progastrin and activates MAPKs: role of cell surface annexin A2

Cell-surface-associated annexin A2 (CS-ANXA2) is a nonconventional "receptor" for progastrin; expression levels of both are elevated in colon cancers, and downregulation of either reduces tumorigenic potential of cells. We recently reported internalization of progastrin in target cells. Here, mechanisms mediating internalization of progastrin were examined. Initially, we confirmed that cell-surface ANXA2 mediates binding and internalization of progastrin in intestinal cells. Progastrin, covalently linked to sepharose beads, failed to activate p38MAPK/ERKs, suggesting internalization of progastrin was required for eliciting biological effects; importantly annexin A2 expression and availability of CS-ANXA2 were required for internalization of progastrin. Clathrin expression and formation of clathrin-coated pits were critically required for endocytotic internalization of progastrin; in the absence of clathrin, progastrin failed to activate p38MAPK/ERKs. Downregulation of caveolin had no effect on binding or internalization of progastrin. We therefore demonstrate for the first time that progastrin binds CS-ANXA2 and is rapidly internalized via clathrin-mediated endocytotic pathway, resulting in activation of MAPKinases. Targeting clathrin-mediated endocytosis of progastrin may thus inhibit previously reported co-carcinogenic/tumorigenic effects of progastrin on intestinal cells.

A new biomarker that predicts colonic neoplasia outcome in patients with hyperplastic colonic polyps

The most frequently occurring lesions in the colon are the hyperplastic polyps. Hyperplastic polyps have long been considered as lesions with no malignant potential and colonoscopy for these patients is not recommended. However, recent works suggest that hyperplastic polyps may represent precursor lesions of some sporadic colorectal cancers. Until now, no biomarker allows to identify the subset of hyperplastic polyps that may have a malignant potential. Because the hormone precursor progastrin has been involved in colon carcinogenesis, we investigated whether its expression in hyperplastic polyps predicts the occurrence of colonic neoplasm after resection of hyperplastic polyps. We retrospectively analyzed progastrin expression in hyperplastic polyps from 74 patients without history of colorectal pathology. In our study, 41% of patients presenting an initial hyperplastic polyp subsequently developed adenomatous polyps, recognized as precursor lesions for colorectal adenocarcinomas. Progastrin was overexpressed in the hyperplastic polyps in 40% of the patients. We showed a significant association between progastrin overexpression and shortened neoplasm-free survival (P = 0.001). Patients with high overexpression of progastrin had a 5-year neoplasm-free survival rate of 38% as compared with 100% for the patients with low progastrin expression. In addition, we established a predictive test on the basis of progastrin staining and patients' age that predicts occurrence of neoplasm after developing a first hyperplastic polyp with a sensitivity of 100% [95% confidence interval (CI), 79%-100%] and a specificity of 74% (51%-90%). We show that progastrin expression evaluation in hyperplastic polyps is an efficient prognostic tool to determine patients with higher risk of metachronous neoplasms who could benefit from an adapted follow-up.

Gastrins, iron homeostasis and colorectal cancer

The peptide hormone gastrin has been identified as a major regulator of acid secretion and a potent mitogen for normal and malignant gastrointestinal cells. The importance of gastric acid in the absorption of dietary iron first became evident 50 years ago when iron deficiency anemia was recognized as a long-term consequence of partial gastrectomy. This review summarizes the connections between circulating gastrins, iron status and colorectal cancer. Gastrins bind two ferric ions with micromolar affinity and, in the case of non-amidated forms of the hormone, iron binding is essential for biological activity in vitro and in vivo. The demonstration of an interaction between gastrin and transferrin by biochemical techniques led to the proposal that gastrins catalyze the loading of transferrin with iron. Several lines of evidence, including the facts that the concentrations of circulating gastrins are increased in mice and humans with the iron overload disease hemochromatosis and that transferrin saturation positively correlates with circulating gastrin concentration, suggest the potential involvement of gastrins in iron homeostasis. Conversely, recognition that ferric ions play an unexpected role in the biological activity of gastrins may assist in the development of useful therapies for colorectal carcinoma and other disorders of mucosal proliferation in the gastrointestinal tract. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.

In vivo analysis of mouse gastrin gene regulation in enhanced GFP-BAC transgenic mice

Gastrin is secreted from a subset of neuroendocrine cells residing in the gastric antrum known as G cells, but low levels are also expressed in fetal pancreas and intestine and in many solid malignancies. Although past studies have suggested that antral gastrin is transcriptionally regulated by inflammation, gastric pH, somatostatin, and neoplastic transformation, the transcriptional regulation of gastrin has not previously been demonstrated in vivo. Here, we describe the creation of an enhanced green fluorescent protein reporter (mGAS-EGFP) mouse using a bacterial artificial chromosome that contains the entire mouse gastrin gene. Three founder lines expressed GFP signals in the gastric antrum and the transitional zone to the corpus. In addition, GFP(+) cells could be detected in the fetal pancreatic islets and small intestinal villi, but not in these organs of the adult mice. The administration of acid-suppressive reagents such as proton pump inhibitor omeprazole and gastrin/CCK-2 receptor antagonist YF476 significantly increased GFP signal intensity and GFP(+) cell numbers in the antrum, whereas these parameters were decreased by overnight fasting, octreotide (long-lasting somatostatin ortholog) infusion, and Helicobacter felis infection. GFP(+) cells were also detected in the anterior lobe of the pituitary gland and importantly in the colonic tumor cells induced by administration with azoxymethane and dextran sulfate sodium salt. This transgenic mouse provides a useful tool to study the regulation of mouse gastrin gene in vivo, thus contributing to our understanding of the mechanisms involved in transcriptional control of the gastrin gene.

Annexin A2 mediates up-regulation of NF-κB, β-catenin, and stem cell in response to progastrin in mice and HEK-293 cells

BACKGROUND & AIMS

Prograstrin induces proliferation in colon crypts by activating p65nuclear factor-κB (NF-κB) (p65) and β-catenin. We investigated whether Annexin A2 (AnxA2), a progastrin receptor, activates NF-κB and β-catenin in vivo.

METHODS

ANXA2-null (ANXA2(-/-)) and wild-type (ANXA2(+/+)) mice were studied, along with clones of progastrin-responsive HEK-293 cells that stably expressed full-length progastrin (HEK-mGAS) or an empty vector (HEK-C). Small interfering RNA was used to down-regulate AnxA2, p65NF-κB, and β-catenin in cells.

RESULTS

Proliferation and activation of p65 and β-catenin increased significantly in HEK-mGAS compared with HEK-C clones. HEK-mGAS cells had a 2- to 4-fold increase in relative levels of c-Myc, cyclooxygenase (COX)-2, CyclinD1, double cortin CAM kinase-like 1 (DCAMKL+1), and CD44, compared with HEK-C clones. Down-regulation of AnxA2 in HEK-mGAS clones reduced activation of NF-κB and β-catenin, as well as levels of DCAMKL+1. Surprisingly, down-regulation of β-catenin had no effect on activation of p65NF-κB, whereas down-regulation of p65 significantly reduced activation of β-catenin in HEK-mGAS clones. Loss of either p65 or β-catenin significantly reduced proliferation of HEK-mGAS clones, indicating that both factors are required for the proliferative effects of progastrin. Lengths of colon crypts and levels of p65, β-catenin, DCAMKL+1, and CD44 were significantly higher in ANXA2(+/+) mice compared with either ANXA2(-/-) mice given progastrin or ANXA2(+/+) and ANXA2(-/-) mice given saline.

CONCLUSIONS

AnxA2 expression is required for the biologic effects of progastrin in vivo and in vitro and mediates the stimulatory effect of progastrin on p65NF-κ, β-catenin, and the putative stem cell markers DCAMKL+1 and CD44. AnxA2 might therefore mediate the hyperproliferative and cocarcinogenic effects of progastrin.

Gastrin increases its own synthesis in gastrointestinal cancer cells via the CCK2 receptor

The involvement of the gastrointestinal hormone gastrin in the development of gastrointestinal cancer is highly controversial. Here we demonstrate a positive-feedback loop whereby gastrin, acting via the CCK2 receptor, increases its own expression. Such an autocrine loop has not previously been reported for any other gastrointestinal hormone. Gastrin promoter activation was dependent on the MAP kinase pathway and did not involve Sp1 binding sites or epidermal growth factor receptor transactivation. As the treatment of gastrointestinal cancer cells with amidated gastrin led to increased expression of non-amidated gastrins, the positive-feedback loop may contribute to the sustained increase in circulating gastrins observed in colorectal cancer patients.

Stimulation of proliferation in the colorectal mucosa by gastrin precursors is blocked by desferrioxamine

Precursors of the peptide hormone gastrin stimulate proliferation in the colorectal mucosa and promote the development of colorectal carcinoma. Gastrins bind two ferric ions selectively and with high affinity, and the biological activity of glycine-extended gastrin (Ggly) in vitro is dependent on the presence of ferric ions. The aim of the present study was to determine whether or not iron is required for biological activity of progastrin and Ggly in vivo. Rats that had undergone a colostomy were infused with Ggly, and proliferation was measured in the defunctioned rectal mucosa. Proliferation was also measured in the colonic mucosa of hGAS and MTI-Ggly mice, which, by definition, overexpress progastrin and Ggly, respectively. The requirement for iron was assessed by thrice-weekly injection of the chelating agent desferrioxamine (DFO). The proliferation index in the defunctioned rectal mucosa was significantly increased in the Ggly-infused rats, and the increase was significantly reduced after treatment with DFO. Treatment with DFO significantly reduced the crypt height and proliferation index in the colonic mucosa of hGAS and MTI-Ggly mice but had no effect on the same variables in wild-type mice. These observations are consistent with the hypothesis that the biological activity of progastrin and Ggly in vivo is dependent on the presence of ferric ions and further suggest that chelating agents may block the stimulatory effects of gastrin precursors in the development of colorectal carcinoma.

Insulin-like growth factors are more effective than progastrin in reversing proapoptotic effects of curcumin: critical role of p38MAPK

Progastrin and insulin-like growth factors (IGFs) stimulate hyperproliferation of intestinal epithelial cells (IECs) via endocrine/paracrine routes; hyperproliferation is a known risk factor for colon carcinogenesis. In the present study, inhibitory potency of curcumin in the presence or absence of progastrin and/or IGF-II was examined. Progastrin and IGF-II significantly increased proliferation of an immortalized IEC cell line, IEC-18, whereas curcumin decreased the proliferation in a dose-dependent manner. IGF-II was significantly more effective than progastrin in reversing antiproliferative effects of curcumin and reversed proapoptotic effects of curcumin by >80%; progastrin was relatively ineffective toward reversing proapoptotic effects of curcumin. IEC-18 clones were generated to overexpress either progastrin (IEC-PG) or hIGF-II (IEC-IGF). Proliferation of IEC-PG and IEC-IGF clones was increased, compared with that of control clones. Curcumin significantly reduced proliferation of IEC-PG, but not IEC-IGF, clones. Similarly, a human colon cancer cell line, Caco-2 (which expresses autocrine IGF-II), was relatively resistant to inhibitory effects of curcumin. However, Caco-2 cells treated with anti-IGF-II-antibodies were rendered sensitive to inhibitory effects of curcumin. Significant differences in inhibitory potency of curcumin against PG- vs. IGF-II-stimulated growth of IEC-18 cells were not reflected by differences in curcumin-mediated inhibition of activated (phosphorylated) ERKs/IKK(alpha/beta)/p65NF-kappaB and c-Src in wild-type (wt)IEC-18 cells, in response to the two growth factors. Surprisingly, curcumin was almost ineffective in reducing IGF-II-stimulated activation of p38MAPK but significantly reduced progastrin-stimulated phosphorylation of p38. Treatment with a p38MAPK inhibitor resulted in loss of protective effects of IGF-II against inhibitory effects of curcumin. These novel findings suggest that growth factor profile of patients and tumors may dictate inhibitory potency of curcumin and that combination of curcumin + p38MAPK inhibitor may be required for reducing hyperproliferative or tumorigenic response of IECs to endocrine and autocrine IGFs.

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.

Gastrin, cholecystokinin and gastrointestinal tract functions in mammals

The aim of the present review is to synthesise and summarise our recent knowledge on the involvement of cholecystokinin (CCK) and gastrin peptides and their receptors in the control of digestive functions and more generally their role in the field of nutrition in mammals. First, we examined the release of these peptides from the gut, focusing on their molecular forms, the factors regulating their release and the signalling pathways mediating their effects. Second, general physiological effects of CCK and gastrin peptides are described with regard to their specific receptors and the role of CCK on vagal mucosal afferent nerve activities. Local effects of CCK and gastrin in the gut are also reported, including gut development, gastrointestinal motility and control of pancreatic functions through vagal afferent pathways, including NO. Third, some examples of the intervention of the CCK and gastrin peptides are exposed in diseases, taking into account intervention of the classical receptor subtypes (CCK1 and CCK2 receptors) and their heterodimerisation as well as CCK-C receptor subtype. Finally, applications and future challenges are suggested in the nutritional field (performances) and in therapy with regards to the molecular forms or in relation with the type of receptor as well as new techniques to be utilised in detection or in therapy of disease. In conclusion, the present review underlines recent developments in this field: CCK and gastrin peptides and their receptors are the key factor of nutritional aspects; a better understanding of the mechanisms involved may increase the efficiency of the nutritional functions and the treatment of abnormalities under pathological conditions.

The structure of bioactive analogs of the N-terminal region of gastrin-17

Gastrin-17 (G17) processing intermediates bind to non-CCK receptors which mediate growth of the colonic mucosa but also the formation and development of colonic cancers. In previous studies, we removed the C-terminal region of G17 to form G17(1-12) and considerably shorter C-terminally amidated and non-amidated analogs. Peptides as short as G17(1-4) continued to bind to a single site on DLD-1 human colonic carcinoma cells, while only the G17(1-6)-NH(2) and G17(1-12) peptides retained the ability to activate the receptor and stimulate cell proliferation in vitro. In this report, we studied the structure of these analogs, using a combination of ECD and VCD spectroscopy and replica exchange molecular dynamics (REMD) simulations in water, TFE, and membrane-mimicking environments, in order to determine preferred conformations that may have importance in promoting the biological activities. Mostly random meander structures, punctuated by a beta-turn at residues 1-4, were found in most peptides by REMD simulations. G17(1-3)-NH(2), which cannot form a beta-turn, failed to bind the non-CCK receptor, suggesting the importance of this feature for binding. Additionally, the beta-turn appeared more frequently in longer sequences, possibly explaining the higher affinity of the non-CCK receptor for these peptides seen previously. Finally, C-terminally amidated peptides generally showed greater formation of turn structure than their non-amidated counterparts as shown by ECD spectra, suggesting the importance of peptide length in stabilizing turn structure in N-terminal sequences, and perhaps explaining the ability of G17(1-6)-NH(2) to activate the non-CCK receptor where as the non-amidated G17(1-6) and shorter peptides do not.

Bioactivity of analogs of the N-terminal region of gastrin-17

Gastrin-17-Gly (G17-Gly) has been shown to bind to non-CCK nanomolar and micromolar affinity sites on DLD-1 and HT-29 human colonic carcinoma cells and to stimulate cellular proliferation. However, in previous studies, we showed that C-terminal truncation of the gastrin-17 (G17) to the G17 analog G17(1-12) and then to G17(1-6)-NH(2) did not remove the ability to bind to DLD-1 cells or to activate proliferation. This implies that residues and/or structural motifs required for bioactivity at these receptors rest in the N-terminal region of G17. In this work, radioligand binding studies conducted with further C-terminally truncated analogs revealed that sequences as short as G17(1-4) still bind to a single receptor with micromolar affinity. Additionally, cell proliferation assays showed that G17(1-12) stimulates proliferation of DLD-1 cells, as of HT-29 cells, but the sequences shorter than G17(1-6)-NH(2), including non-amidated G17(1-6), were incapable of stimulating proliferation. These observations indicate that the tetrapeptide pGlu-Gly-Pro-Trp is the minimum N-terminal sequence for binding to the probable growth-promoting site on DLD-1 cells. Since analogs shorter than G17(1-6) are able to bind the receptor, these peptides may be of use for developing selective antagonists.

Inactivating cholecystokinin-2 receptor inhibits progastrin-dependent colonic crypt fission, proliferation, and colorectal cancer in mice

Hyperproliferation of the colonic epithelium, leading to expansion of colonic crypt progenitors, is a recognized risk factor for colorectal cancer. Overexpression of progastrin, a nonamidated and incompletely processed product of the gastrin gene, has been shown to induce colonic hyperproliferation and promote colorectal cancer in mice, but the mechanism of pathogenesis has not been defined. Cholecystokinin-2 receptor (CCK2R) is the primary receptor for cholecystokinin (CCK) and amidated gastrin. Here, we show that Cck2r was expressed in murine colonic crypts and upregulated in the transgenic mice that overexpress human progastrin. Murine deletion of Cck2r abrogated progastrin-dependent increases in colonic proliferation, mucosal thickness, and beta-catenin and CD44 expression in the colon tumor. In addition, either deletion or antagonism of Cck2r resulted in the inhibition of progastrin-dependent increases in progenitors expressing doublecortin and CaM kinase-like-1 (DCAMKL1), stem cells expressing leucine rich repeat-containing G protein-coupled receptor 5 (LgR5), and colonic crypt fission. Furthermore, in the azoxymethane mouse model of colorectal carcinogenesis, Cck2r deletion in human progastrin-overexpressing mice resulted in markedly decreased aberrant crypt foci formation and substantially reduced tumor size and multiplicity. Taken together, these observations indicate that progastrin induces proliferative effects, primarily in colonic progenitor cells, through a CCK2R-dependent pathway. Moreover, our data suggest that CCK2R may be a potential target in the treatment or prevention of colorectal cancer.

Functional cross-talk between beta-catenin and NFkappaB signaling pathways in colonic crypts of mice in response to progastrin

We recently reported a critical role of NFkappaB in mediating hyperproliferative and anti-apoptotic effects of progastrin on proximal colonic crypts of transgenic mice overexpressing progastrin (Fabp-PG mice). We now report activation of beta-catenin in colonic crypts of mice in response to chronic (Fabp-PG mice) and acute (wild type FVB/N mice) progastrin stimulation. Significant increases were measured in relative levels of cellular and nuclear beta-catenin and pbeta-cat45 in proximal colonic crypts of Fabp-PG mice compared with that in wild type littermates. Distal colonic crypts were less responsive. Interestingly, beta-catenin activation was downstream of IKKalpha,beta/NFkappaB, because treatment of Fabp-PG mice with the NFkappaB essential modulator (NEMO) peptide (inhibitor of IKKalpha,beta/NFkappaB activation) significantly blocked increases in cellular/nuclear levels of total beta-catenin/pbeta-cat45/and pbeta-cat552 in proximal colons. Cellular levels of pbeta-cat33,37,41, however, increased in proximal colons in response to NEMO, probably because of a significant increase in pGSK-3betaTyr216, facilitating degradation of beta-catenin. NEMO peptide significantly blocked increases in cyclin D1 expression, thereby, abrogating hyperplasia of proximal crypts. Goblet cell hyperplasia in colonic crypts of Fabp-PG mice was abrogated by NEMO treatment, suggesting a cross-talk between the NFkappaB/beta-catenin and Notch pathways. Cellular proliferation and crypt lengths increased significantly in proximal but not distal crypts of FVB/N mice injected with 1 nM progastrin associated with a significant increase in cellular/nuclear levels of total beta-catenin and cyclin D1. Thus, intracellular signals, activated in response to acute and chronic stimulation with progastrin, were similar and specific to proximal colons. Our studies suggest a novel possibility that activation of beta-catenin, downstream to the IKKalpha,beta/NFkappaB pathway, may be integral to the hyperproliferative effects of progastrin on proximal colonic crypts.

Importance of gastrin in the pathogenesis and treatment of gastric tumors

In addition to regulating acid secretion, the gastric antral hormone gastrin regulates several important cellular processes in the gastric epithelium including proliferation, apoptosis, migration, invasion, tissue remodelling and angiogenesis. Elevated serum concentrations of this hormone are caused by many conditions, particularly hypochlorhydria (as a result of autoimmune or Helicobacter pylori (H pylori)-induced chronic atrophic gastritis or acid suppressing drugs) and gastrin producing tumors (gastrinomas). There is now accumulating evidence that altered local and plasma concentrations of gastrin may play a role during the development of various gastric tumors. In the absence of H pylori infection, marked hypergastrinemia frequently results in the development of gastric enterochromaffin cell-like neuroendocrine tumors and surgery to remove the cause of hypergastrinemia may lead to tumor resolution in this condition. In animal models such as transgenic INS-GAS mice, hypergastrinemia has also been shown to act as a cofactor with Helicobacter infection during gastric adenocarcinoma development. However, it is currently unclear as to what extent gastrin also modulates human gastric adenocarcinoma development. Therapeutic approaches targeting hypergastrinemia, such as immunization with G17DT, have been evaluated for the treatment of gastric adenocarcinoma, with some promising results. Although the mild hypergastrinemia associated with proton pump inhibitor drug use has been shown to cause ECL-cell hyperplasia and to increase H pylori-induced gastric atrophy, there is currently no convincing evidence that this class of agents contributes towards the development of gastric neuroendocrine tumors or gastric adenocarcinomas in human subjects.

Interrelationships between circulating gastrin and iron status in mice and humans

The observations that the peptide hormone gastrin interacts with transferrin in vitro and that circulating gastrin concentrations are increased in the iron-loading disorder hemochromatosis suggest a possible link between gastrin and iron homeostasis. This study tested the hypothesis that gastrin and iron status are interrelated by measurement of iron homeostasis in mice and humans with abnormal circulating gastrin concentrations. Intestinal iron absorption was determined by (59)Fe uptake following oral gavage, and concentrations of duodenal divalent metal transporter-1 (DMT-1) and hepatic hepcidin mRNAs were determined by quantitative real-time PCR in agastrinemic (GasKO), hypergastrinemic cholecystokinin 2 receptor-deficient (CCK2RKO), or wild-type mice. Iron status was measured by standard methods in the same mice and in hypergastrinemic humans with multiple endocrine neoplasia type 1 (MEN-1). Iron absorption was increased sixfold and DMT-1 mRNA concentration fourfold, and transferrin saturation was reduced 0.8-fold and hepcidin mRNA expression 0.5-fold in juvenile GasKO mice compared with age-matched wild-type mice. In mature mice, few differences were observed between the strains. Juvenile CCK2RKO mice were hypergastrinemic and had a 5.4-fold higher DMT-1 mRNA concentration than wild-type mice without any increase in iron absorption. In contrast to juvenile GasKO mice, juvenile CCK2RKO mice had a 1.5-fold greater transferrin saturation, which was reflected in a twofold increase in liver iron deposition at maturity compared with wild-type mice. The correlation between transferrin saturation and circulating gastrin concentration observed in mutant mice was also observed in human patients with MEN, in whom hypergastrinemia correlated positively (P = 0.004) with an increased transferrin saturation. Our data indicate that, in juvenile animals when iron demand is high, circulating gastrin concentrations may alter iron status by a CCK2R-independent mechanism.

Activation of NF-kappaB is required for mediating proliferative and antiapoptotic effects of progastrin on proximal colonic crypts of mice, in vivo

Mice overexpressing progastrin (PG) in intestinal mucosa (fatty acid-binding protein (Fabp)-PG mice) are at an increased risk of proximal colon carcinogenesis in response to azoxymethane. Here, we report a significant increase in the length of proximal colonic crypts in Fabp-PG mice, associated with potent antiapoptotic effects of PG, which likely contributed to the previously reported increase in colon carcinogenesis in Fabp-PG mice. Phosphorylation of kinase of IkappaBalpha (IKKalpha/beta), inhibitor of kappaB (IkappaB)alpha and p65NF-kappaB was significantly elevated in proximal colonic crypts of Fabp-PG versus wild-type mice, which was associated with degradation of IkappaBalpha and nuclear translocation/activation of p65. Surprisingly, distal colonic crypt cells were not as responsive to elevated levels of PG in Fabp-PG mice. Annexin II, recently described as a high-affinity receptor for PG, strongly co-localized with PG intracellularly and on basolateral membranes of proximal crypt cells, providing evidence that annexin-II binds PG in situ in colonic crypt cells. Proliferative and antiapoptotic effects of PG on proximal crypts of Fabp-PG mice were attenuated to wild-type levels, on treatment with NEMO peptide (an inhibitor of nuclear factor-kappaB (NF-kappaB) activation), demonstrating for the first time a critical role of NF-kappaB in mediating hyperproliferative affects of PG on colonic crypts of Fabp-PG mice, in vivo. Thus, downregulation of NF-kappaB may significantly reduce the increased risk of colon carcinogenesis in response to PG.

Immunohistochemical examination of gastrin, gastrin precursors, and gastrin/CCK-2 receptor in human esophageal squamous cell carcinomas

A promoting effect of gastrin on stimulating Barrett's oesophagus proliferation has been demonstrated, but whether it plays a regulating role for esophageal squamous cell carcinoma (ESCC) to date has not been fully investigated. The aim of this study is to examine the expressions of gastrin, gastrin precursors and gastrin/CCK-2 receptor in ESCC. Tissue specimen sections from 38 patients with ESSC obtained from a high incidence area of north China were assessed using immunohistochemistry for amidated gastrin, gastrin precursors (progastrin and glycine-extended gastrin) and gastrin/CCK-2 receptors. Their clinical histopathological significance was also analyzed. Of 38 ESCC, the immunoreactivities of gastrin, glycine-extended gastrin and progastrin were observed in 13.2% (5/38), 7.9% (3/38) and 23.68% (9/38) cases. The expression of progastrin was obviously higher than other gastrins, though not significantly (P > 0.05). In positive cases for gastrin or glycine-extended gastrin, the scores of positive tumor cell numbers were at a lower density (<10/abundant-distributed field). However, the scores of progastrin positive tumor cell density in five of nine positive cases were over 10/abundant-distributed field. The immunoreactivity of gastrin/CCK-2 receptor was also observed in 15.8% (6/38) ESCC cases. There was not significant correlation regarding immunohistochemical results with known histomorphological parameters i.e. gender, tumor location and TNM stages. Based on our current results, ESCC tumor cells could be a possible cellular source of gastrin precursors, which has been postulated to play a role in regulating the growth in some human tumor cells.

Chronic hypergastrinemia: causes and consequences

The hormone gastrin plays 2 important roles in gastrointestinal physiology--1 as a major factor in meal-stimulated gastric acid secretion and the other as a trophic hormone for epithelial and enterochromaffin cells. These roles are exaggerated to the point of pathology under conditions of chronic hypergastrinemia as exemplified by the Zollinger-Ellison syndrome and pernicious anemia. More recently, the concern about the potential risk of chronic hypergastrinemia has risen because of the widespread use of proton pump inhibitors for maintenance therapy in reflux esophagitis. For this reason, we present a concise overview of the origin, causes, and potential risks of chronic hypergastrinemia.

Carcinogenic hypergastrinemia: signet-ring cell carcinoma in a patient with multiple endocrine neoplasia type 1 with Zollinger-Ellison's syndrome

CONTEXT

Gastric neuroendocrine tumors are rare neoplasms that originate from gastric enterochromaffin-like (ECL) cells in the oxyntic mucosa. Gastrin and its derivates have been reported to regulate epithelial cell proliferation, migration, and differentiation. Mutations in the epithelial cadherin (E-cadherin) gene have been shown to be associated with the occurrence of diffuse gastric carcinomas in affected families.

OBJECTIVE

In this study we investigated the histopathological and molecular findings in the gastrointestinal wall of a patient with multiple endocrine neoplasia type 1 with malignant duodenal gastrinoma and multiple gastric ECL cell tumors, who additionally developed a signet-ring cell carcinoma of the stomach.

DESIGN AND PATIENT

Biopsies from the gastrointestinal tract of a patient with multiple endocrine neoplasia type 1 were immunostained for vesicular monoamine transporter-2 and E-cadherin. Nonamidated gastrin products were measured in the serum of the patient using antibodies that react with progastrin, Gly-extended, and amidated gastrins. Genetic analyses were performed to exclude germ-line mutations within the E-cadherin gene.

RESULTS

Immunohistochemical studies of gastric ECL cell tumors showed a largely diminished E-cadherin expression in comparison to gastric surface mucosa cells and a loss of E-cadherin expression in the cells of the signet-ring carcinoma. Detailed biochemical measurements revealed progastrin concentrations that were approximately 20%, and Gly-gastrin concentrations that were approximately 10% the amidated gastrin concentrations in plasma. Molecular analyses revealed no E-cadherin germ-line mutation.

CONCLUSION

Our immunohistochemical studies might suggest that the gastrinoma-associated excessive progastrin tissue concentrations led to diminished expression of E-cadherin within the gastric mucosa and promoted tumor development of a signet-ring cell carcinoma.

Significant increase in the aggressive behavior of transgenic mice overexpressing peripheral progastrin peptides: associated changes in CCK2 and serotonin receptors in the CNS

The gastrin precursor peptide, progastrin (PG), is secreted from enteroendocrine cells in the intestine and increased in patients with hypergastrinemia and colorectal cancers. In recent years, we and others have demonstrated an important role of PG peptides in colorectal carcinogenesis, and were surprised to note significant changes in the behaviors of transgenic mice overexpressing PGs. In the present studies, we examined emotional behaviors of transgenic mice overexpressing PG in the intestinal and peripheral circulation. Aggression, locomotor activity and anxiety-like behaviors of the homozygous transgenic (Tg/Tg) mice and the wild-type (WT) littermates were examined by intruder/resident test, open field and elevated plus maze, respectively. A significant increase in the aggression, locomotor activity, and anxiety-like behaviors was detected in the Tg/Tg vs WT mice. As CCK, CCK(2) receptors (CCK(2)R), and 5-HT(1A) receptors (5-HT(1A)R) in the CNS play an important role in these behaviors, possible changes in the expression of CCK and CCK(2)R and the density of CCK(2)R and 5-HT(1A)R were determined by either real-time RT-PCR or autoradiography of ligand binding assays. The results suggest that the expressions of CCK and CCK(2)R were increased in the hypothalamus, and the density of CCK(2)R were increased in the hypothalamus and amygdala of Tg/Tg vs WT mice. Similarly, the density of 5-HT(1A)R was increased in the hypothalamus. Our results suggest that an upregulation of the CCK response system and 5-HT(1A)R in the hypothalamus of Tg/Tg mice may mediate the alterations in the observed behaviors of these mice.

Expression of gastrin receptor in tumors and its application as a molecular target for cancer diagnosis and therapy

Gastrin is widely distributed in gastrointestinal tract and pancreatic tissues, and it plays important roles in the modulation of physiological functions and pathogenic mechanism of some diseases. Recent studies showed that gastrin might promote the pathogenesis and growth of tumors, especially digestive tumors such as gastric cancer and colorectal cancer. The biological effect of gastrin is mainly mediated by cholecystokinin (CCK) receptors. Gastrin mRNA has been found in CCK-receptor positive small-cell lung carcinoma, breast cancer, ovarian cancer and cancer stem cells of various origins and it may serve as the indicator of self-secretive regulation. The tumors with over-expressed gastin receptor can be diagnosed and treated by radiolabelling or linking to the cytotoxic agents with gastin peptide and analogs, and scintigraphy was used to visualize the image in vivo.

Gastrointestinal regulatory peptides: an overview

PURPOSE OF REVIEW

This review is intended to provide an overview of this section on 'Gastrointestinal regulatory peptides' and to emphasize both similarities and differences between 'classic' hormones and those peptides synthesized within, and released from, the gastrointestinal tract. It will also discuss recent investigation involving these peptides and their physiological properties and pathologic potential.

RECENT FINDINGS

More recent investigation, much of which is discussed in this section, has looked at the central role of the gastrointestinal tract, and specifically gastrointestinal regulatory peptides, in nutrient homeostasis and in the pathogenesis of obesity and other nutritional disorders.

SUMMARY

Regulatory peptides are chemical messengers that provide a means of communication between two cells which are commonly located in different organ systems. The peptides interact via a shared aqueous environment; whereas this environment is endocrine in nature for classic hormones and gastrointestinal peptides, the latter also include those peptides that communicate more directly with their target via paracrine, neurocrine, and autocrine routes. The field of gastrointestinal regulatory peptides is in its infancy, and the coming decades will witness the development of these peptides, as well as analogues and antagonists, as potential new forms of therapy of obesity and other nutrition-related disorders, as well as other maladies.