Clonal analysis of glandular stomach carcinogenesis in C3H/HeN<==>BALB/c chimeric mice treated with N-methyl-N-nitrosourea

Stem cells and origins of cancer in the upper gastrointestinal tract

The esophagus and stomach, joined by a unique transitional zone, contain actively dividing epithelial stem cells required for organ homeostasis. Upon prolonged inflammation, epithelial cells in both organs can undergo a cell fate switch leading to intestinal metaplasia, predisposing to malignancy. Here we discuss the biology of gastroesophageal stem cells and their role as cells of origin in cancer. We summarize the interactions between the stromal niche and gastroesophageal stem cells in metaplasia and early expansion of mutated stem-cell-derived clones during carcinogenesis. Finally, we review new approaches under development to better study gastroesophageal stem cells and advance the field.

GPR30-Expressing Gastric Chief Cells Do Not Dedifferentiate But Are Eliminated via PDK-Dependent Cell Competition During Development of Metaplasia

BACKGROUND & AIMS

Gastric chief cells, a mature cell type that secretes digestive enzymes, have been proposed to be the origin of metaplasia and cancer through dedifferentiation or transdifferentiation. However, studies supporting this claim have had technical limitations, including issues with the specificity of chief cell markers and the toxicity of drugs used. We therefore sought to identify genes expressed specifically in chief cells and establish a model to trace these cells.

METHODS

We performed transcriptome analysis of Mist1-CreERT-traced cells, with or without chief cell depletion. Gpr30-rtTA mice were generated and crossed to TetO-Cre mice, and lineage tracing was performed after crosses to R26-TdTomato mice. Additional lineage tracing experiments were performed using Mist1-CreERT, Kitl-CreERT, Tff1-Cre, and Tff2-Cre mice crossed to reporter mice. Mice were given high-dose tamoxifen or DMP-777 or were infected with Helicobacter pylori to induce gastric metaplasia. We studied mice that expressed mutant forms of Ras in gastric cells, using TetO-Kras^G12D, LSL-Kras^G12D, and LSL-Hras^G12V mice. We analyzed stomach tissues from GPR30-knockout mice. Mice were given dichloroacetate to inhibit pyruvate dehydrogenase kinase (PDK)-dependent cell competition.

RESULTS

We identified GPR30, the G-protein-coupled form of the estrogen receptor, as a cell-specific marker of chief cells in gastric epithelium of mice. Gpr30-rtTA mice crossed to TetO-Cre;R26-TdTomato mice had specific expression of GPR30 in chief cells, with no expression noted in isthmus stem cells or lineage tracing of glands. Expression of mutant Kras in GPR30⁺ chief cells did not lead to the development of metaplasia or dysplasia but, instead, led to a reduction in labeled numbers of chief cells and a compensatory expansion of neck lineage, which was derived from upper Kitl⁺ clones. Administration of high-dose tamoxifen, DMP-777, or H pylori decreased the number of labeled chief cells. Chief cells were eliminated from epithelia via GPR30- and PDK-dependent cell competition after metaplastic stimuli, whereas loss of GRP30 or inhibition of PDK activity preserved chief cell numbers and attenuated neck lineage cell expansion.

CONCLUSIONS

In tracing studies of mice, we found that most chief cells are lost during metaplasia and therefore are unlikely to contribute to gastric carcinogenesis. Expansion of cells that coexpress neck and chief lineage markers, known as spasmolytic polypeptide-expressing metaplasia, does not occur via dedifferentiation from chief cells but, rather, through a compensatory response from neck progenitors to replace the eliminated chief cells.

Gastrointestinal organoids: How they gut it out

The gastrointestinal tract is characterized by a self-renewing epithelium fueled by adult stem cells residing at the bottom of the intestinal crypt and gastric glands. Their activity and proliferation is strongly dependent on complex signaling pathways involving other crypt/gland cells as well as surrounding stromal cells. In recent years organoids are becoming increasingly popular as a new and powerful tool to study developmental or other biological processes. Organoids retain morphological and molecular patterns of the tissue they are derived from, are self-organizing, relatively simple to handle and accessible to genetic engineering. This review focuses on the developmental processes and signaling molecules involved in epithelial homeostasis and how a profound knowledge of these mechanisms allowed the establishment of a three dimensional organoid culture derived from adult gastrointestinal stem cells.

Stomach development, stem cells and disease

The stomach, an organ derived from foregut endoderm, secretes acid and enzymes and plays a key role in digestion. During development, mesenchymal-epithelial interactions drive stomach specification, patterning, differentiation and growth through selected signaling pathways and transcription factors. After birth, the gastric epithelium is maintained by the activity of stem cells. Developmental signals are aberrantly activated and stem cell functions are disrupted in gastric cancer and other disorders. Therefore, a better understanding of stomach development and stem cells can inform approaches to treating these conditions. This Review highlights the molecular mechanisms of stomach development and discusses recent findings regarding stomach stem cells and organoid cultures, and their roles in investigating disease mechanisms.

Stomach Organ and Cell Lineage Differentiation: from Embryogenesis to Adult Homeostasis

Gastric diseases cause considerable worldwide burden. However, the stomach is still poorly understood in terms of the molecular-cellular processes that govern its development and homeostasis. In particular, the complex relationship between the differentiated cell types located within the stomach and the stem and progenitor cells that give rise to them is significantly understudied relative to other organs. In this review, we will highlight the current state of the literature relating to specification of gastric cell lineages from embryogenesis to adulthood. Special emphasis is placed on substantial gaps in knowledge about stomach specification that we think should be tackled to advance the field. For example, it has long been assumed that adult gastric units have a granule-free stem cell that gives rise to all differentiated lineages. Here we will point out that there are also other models that fit all extant data, such as long-lived lineage-committed progenitors that might serve as a source of new cells during homeostasis.

Tissue-resident adult stem cell populations of rapidly self-renewing organs

The epithelial lining of the intestine, stomach, and skin is continuously exposed to environmental assault, imposing a requirement for regular self-renewal. Resident adult stem cell populations drive this renewal, and much effort has been invested in revealing their identity. Reliable adult stem cell biomarkers would accelerate our understanding of stem cell roles in tissue homeostasis and cancer. Membrane-expressed markers would also facilitate isolation of these adult stem cell populations for exploitation of their regenerative potential. Here, we review recent advances in adult stem cell biology, highlighting the promise and pitfalls of the candidate biomarkers of the various stem cell populations.

Stem cells and cancer of the stomach and intestine

Cancer in the 21st century has become the number one cause of death in developed countries. Although much progress has been made in improving patient survival, tumour relapse is one of the important causes of cancer treatment failure. An early observation in the study of cancer was the heterogeneity of tumours. Traditionally, this was explained by a combination of genomic instability of tumours and micro environmental factors leading to diverse phenotypical characteristics. It was assumed that cells in a tumour have an equal capacity to propagate the cancer. This model is currently known as the stochastic model. Recently, the Cancer stem cell model has been proposed to explain the heterogeneity of a tumour and its progression. According to this model, the heterogeneity of tumours is the result of aberrant differentiation of tumour cells into the cells of the tissue the tumour originated from. Tumours were suggested to contain stem cell-like cells, the cancer stem cells or tumour-initiating cells, which are uniquely capable of propagating a tumour much like normal stem cells fuel proliferation and differentiation in normal tissue. In this review we discuss the normal stem cell biology of the stomach and intestine followed by both the stochastic and cancer stem cell models in light of recent findings in the gastric and intestinal systems. The molecular pathways underlying normal and tumourigenic growth have been well studied, and recently the stem cells of the stomach and intestine have been identified. Furthermore, intestinal stem cells were identified as the cells-of-origin of colon cancer upon loss of the tumour suppressor APC. Lastly, several studies have proposed the positive identification of a cancer stem cell of human colon cancer. At the end we compare the cancer stem cell model and the stochastic model. We conclude that clonal evolution of tumour cells resulting from genetic mutations underlies tumour initiation and progression in both cancer models. This implies that at any point during tumour development any tumour cell can revert to a cancer stem cell after having gained a clonal advantage over the original cancer stem cell. Therefore, these models represent two sides of the same coin.

Leucine-rich repeat-containing G-protein-coupled receptors as markers of adult stem cells

Molecular markers are used to characterize and track adult stem cells. Colon cancer research has led to the identification of 2 related receptors, leucine-rich repeat-containing, G-protein-coupled receptors (Lgr)5 and Lgr6, that are expressed by small populations of cells in a variety of adult organs. Genetic mouse models have allowed the visualization, isolation, and genetic marking of Lgr5(+ve) and Lgr6(+ve) cells and provided evidence that they are stem cells. The Lgr5(+ve) cells were found to occupy locations not commonly associated with stem cells in the stomach, small intestine, colon, and hair follicles. A multipotent population of skin stem cells express Lgr6. Single Lgr5(+ve) stem cells from the small intestine and the stomach can be cultured into long-lived organoids. Further studies of these markers might reveal adult stem cell populations in additional tissues. Identification of the ligands for Lgr5 and 6 will help elucidate stem cell functions and modes of intracellular signaling.

Lgr5(+ve) stem cells drive self-renewal in the stomach and build long-lived gastric units in vitro

The study of gastric epithelial homeostasis and cancer has been hampered by the lack of stem cell markers and in vitro culture methods. The Wnt target gene Lgr5 marks stem cells in the small intestine, colon, and hair follicle. Here, we investigated Lgr5 expression in the stomach and assessed the stem cell potential of the Lgr5(+ve) cells by using in vivo lineage tracing. In neonatal stomach, Lgr5 was expressed at the base of prospective corpus and pyloric glands, whereas expression in the adult was predominantly restricted to the base of mature pyloric glands. Lineage tracing revealed these Lgr5(+ve) cells to be self-renewing, multipotent stem cells responsible for the long-term renewal of the gastric epithelium. With an in vitro culture system, single Lgr5(+ve) cells efficiently generated long-lived organoids resembling mature pyloric epithelium. The Lgr5 stem cell marker and culture method described here will be invaluable tools for accelerating research into gastric epithelial renewal, inflammation/infection, and cancer.

Prospective identification of a multilineage progenitor in murine stomach epithelium

BACKGROUND & AIMS

Epithelial stem cells in the stomach are responsible for constant renewal of the epithelium through generation of multiple gastric cell lineages that populate the gastric glands. However, gastric stem or progenitor cells have not been well-characterized because of the lack of specific markers that permit their prospective recognition. We identified an intestinal promoter that is active in a rare subpopulation of gastric epithelial cells and investigated whether these cells possess multilineage potential.

METHODS

A marked allele of the endogenous mouse villin locus was used to visualize single beta-galactosidase-positive cells located in the lower third of antral glands. A 12.4-kb villin promoter/enhancer fragment drives several transgenes (EGFP, beta-galactosidase, and Cre recombinase) in these cells in a pattern similar to that of the marked villin allele. Reporter gene activity was used to track these cells during development and to examine cell number in the context of inflammatory challenge while Cre activity allowed lineage tracing in vivo.

RESULTS

We show that these rare epithelial cells are normally quiescent, but multiply in response to interferon gamma. Lineage tracing studies confirm that these cells give rise to all gastric lineages of the antral glands. In the embryo, these cells are located basally in the stomach epithelium before completion of gastric gland morphogenesis.

CONCLUSIONS

We have identified a rare subpopulation of gastric progenitors with multilineage potential. The ability to prospectively identify and manipulate such progenitors in situ represents a major step forward in gastric stem cell biology and has potential implications for gastric cancer.

Gastric-and-intestinal mixed-type intestinal metaplasia: aberrant expression of transcription factors and stem cell intestinalization

Helicobacter pylori plays a causative role in the development of chronic atrophic gastritis, intestinal metaplasia (IM), and stomach cancer. Although IM has long attracted attention as a putative preneoplastic lesion for stomach cancers, its clinicopathologic significance has yet to be clarified in detail. Using gastric and intestinal epithelial cell markers, IM was here divided into two major types: a gastric-and-intestinal (GI) mixed type and a solely intestinal (I) type. In the former, gastric and intestinal phenotypic markers appeared not only at the glandular but also at the cellular level. Furthermore, neuroendocrine cells also showed intestinalization along with their exocrine counterparts. In animal models, GI-type IM was found to appear first, followed by the solely I type. Summarizing these data, it was suggested that IM might be caused by the gradual intestinalization of stem cells from the GI to the I type. The molecular mechanisms of IM include the ectopic expression of CDX1, CDX2, OCT-1, and members of the Erk pathway. Suppression of the expression of gastric transcription factors such as SOX2, genes that are involved in the Sonic hedgehog pathway, and RUNX3, a tumor suppressor gene, could be additional relevant alterations. The expression of PDX1 may also be associated with pseudopyloric gland metaplasia and IM. Detailed analysis of gene regulation may shed light on the molecular bases of gastric lesions, leading to strategies for chemoprevention.

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From gene mutations to tumours--stem cells in gastrointestinal carcinogenesis

Stem cells share many properties with malignant cells, such as the ability to self-renew and proliferate. Cancer is believed to be a disease of stem cells. The gastrointestinal tract has high cancer prevalence partly because of rapid epithelial cell turnover and exposure to dietary toxins. The molecular pathways of carcinogenesis differ according to the tissue. Work on hereditary cancer syndromes including familial adenomatous polyposis (FAP) has led to advances in our understanding of the events that occur in tumour development from a gastrointestinal stem cell. The initial mutation involved in the adenoma-carcinoma sequence is in the 'gatekeeper' tumour-suppressor gene adenomatous polyposis coli (APC). Somatic hits in this gene are non-random in FAP, with the type of mutation selected for by the position of the germline mutation. In the stomach, a metaplasia-dysplasia sequence occurs and is often related to Helicobacter pylori infection. Clonal expansion of mutated cells occurs by niche succession. Further expansion of the aberrant clone then occurs by the longitudinal division of crypts into two daughter units--crypt fission. Two theories seek to explain the early development of adenomas--the 'top down' and 'bottom up' hypotheses. Initial studies suggested that colorectal tumours were monoclonal; however, later work on chimeric mice and a sex chromosome mixoploid patient with FAP suggested that up to 76% of early adenomas were polyclonal. Introduction of a homozygous resistance allele has reduced tumour multiplicity in the mouse and has been used to rule out random collision of polyps as the cause of these observations. It is likely that short-range interaction between adjacent initiated crypts is responsible for polyclonality.

Gastric and intestinal phenotypes and histogenesis of advanced glandular stomach cancers in carcinogen-treated, Helicobacter pylori-infected Mongolian gerbils

The Helicobacter pylori-infected Mongolian gerbil (MG) has been established as an appropriate animal model for studies of stomach cancer development. However, there have hitherto been no data on the phenotypic classification of glandular stomach cancers in H. pylori-infected and non-infected MG. We therefore examined the phenotypes of 50 and six advanced glandular stomach cancers in H. pylori-infected and non-infected MG, respectively, as well as adjacent non-neoplastic mucosa, using several gastrointestinal epithelial phenotypic markers. The lesions were divided phenotypically into 21 gastric, 24 gastric-and-intestinal mixed, four intestinal and one null types, with 90.0% of the lesions harboring gastric elements and 56.0% demonstrating intestinal phenotypic expression in H. pylori-infected MG. All six lesions were classified as gastric type in non-infected MG. There was no clear correlation with the presence of intestinal metaplasia in surrounding mucosa. In conclusion, our data suggest that most advanced adenocarcinomas retain a gastric cellular phenotype in the glandular MG stomach. Thus, it might be proposed that intestinal metaplasia is a paracancerous phenomenon rather than a premalignant condition. H. pylori infection may trigger intestinalization of both stomach cancers and non-neoplastic mucosa.

Stem cell relationships and the origin of gastrointestinal cancer

Gastrointestinal stem cells have the capacity for long-term self-replication and the ability to give rise to all other epithelial cell lineages. These properties make them essential since they maintain tissue homeostasis by regulating cell turnover depending on the current demand. However, they are also important players in the earliest stages of gastric and colonic cancer, as they form a target for mutations to accumulate and lead to the development of the malignant phenotype. Due to the lack of reliable markers, gastrointestinal stem cells are difficult to define and characterise. This limits the knowledge about their number and position within the gastric gland and the intestinal crypt, respectively, and consequently about the clonal structure of these units. Therefore, the morphological events of early gastrointestinal carcinoma formation and expansion are hotly debated. In this review we summarize the properties of gastrointestinal stem cells and illuminate their role in the development of the earliest lesions in the gastric and colonic mucosa. We also resume current opinions about the morphological pathways and the clonality of these neoplasias and the subsequent mechanism of spread within the adjacent tissues.

Susceptibility to colon carcinogenesis in C3H<-->C57BL/6 chimeric mice reflects both tissue microenvironment and genotype

Considerable rodent strain differences have been documented with regard to susceptibility to colon carcinogens. To clarify mechanisms, chimeras of susceptible strain C3H and relatively resistant strain C57BL/6N (B6) mice were exposed to a colonotropic carcinogen, 1,2-dimethylhydrazine (DMH) and tumor incidence and multiplicity were assessed. In the chimeras, incidence was as high as the C3H level. Multiplicity of lesions of B6 cells was also increased (P<0.001), but maintenance of the strain difference. When tumor localization was analyzed, tumors of B6 genotype in chimeras demonstrated a greater spread of distribution than in the parental case. The chimeric environment may thus stimulate tumor initiation but cell autonomous suppressive factors may be retained.

Expression of small intestinal and colonic phenotypes in complete intestinal metaplasia of the human stomach

The incomplete intestinal metaplasia (IM) that is reported to be a risk factor for gastric carcinogenesis in man usually features sulfomucin production and thus is considered of colonic type. To cast light on the underlying mechanisms, we here examined the proportions of colonic and small intestinal phenotypes in IM by immunohistochemistry and real-time reverse transcription-polymerase chain reaction at the single isolated gland level. Carbonic anhydrase 1 (CA1) is a specific marker of colonic epithelial cells, whereas sucrase is specific to absorptive cells of the small intestine. Totals of 139 (23.5%) and 452 (76.5%) IM glands were judged to be CA1 positive and CA1 negative, respectively, in resected pyloric mucosa from cancer patients. The average score for MUC5AC in CA1-positive IMs was significantly lower than in CA1-negative counterpart tissue (P<0.0001), whereas the opposite was the case for sucrase (P<0.0001). High iron diamine-Alcian blue staining revealed CA1 expression to coincide with type I complete IM. The expression of CA1 mRNA strongly correlated with that of sucrase-isomaltase, and inversely with that of MUC5AC in isolated IM glands. In conclusion, CA1 could be colocalized with small intestinal proteins such as sucrase, but only rarely with the gastric mucin, MUC5AC. Its expression warrants further study, with the focus on stimulation and/or suppression mechanisms by gastric and intestinal transcription factors.

Involvement of bone marrow-derived cells in healing of experimental colitis in rats

Bone marrow is reported to contain hematopoietic stem cells and other adult somatic stem cells that have phenotypes of cells composing tissues other than bone marrow. To explore the implication of bone marrow-derived cells in the treatment of inflammatory bowel diseases, experimental colitis was induced in wild-type rats after transplantation of bone marrow from transgenic rats expressing green fluorescence protein (GFP). Chronic colitis was induced 21 days later using 30 mg 2,4,6-trinitrobenzenesulfonic acid (TNBS). Control rats received saline. At 28, 56, and 224 days after TNBS administration, rats were euthanized, and tissues were removed and processed for paraffin-embedded sections. Cells derived from bone marrow were identified by immunohistochemistry using anti-GFP antibody. To identify the phenotypes of the cells expressing GFP, we conducted serial-section analysis and double-staining analysis using antibodies against cytokeratin (epithelial cells) or vimentin (interstitial cells). In the present study, GFP-positive, bone marrow-derived cells occupied 37.6% and 4.25% of the colonic epithelium at 28 days and 56 days after the induction of TNBS-colitis, respectively. Also, significant amounts of mucosal and submucosal interstitial cells were derived from the bone marrow. These findings showed that a large amount of bone marrow-derived cells were involved in regeneration of the colon after experimental colitis in rats.

Coexistence of gastric- and intestinal-type endocrine cells in gastric and intestinal mixed intestinal metaplasia of the human stomach

Intestinal metaplasia (IM) in the human stomach has previously been classified into a gastric and intestinal mixed (GI-IM) and a solely intestinal phenotype (I-IM). The phenotypes of mucous and endocrine cells were evaluated in 3034 glandular ducts associated with chronic gastritis. In the pyloric region, the relative expression of gastric endocrine cell markers, such as gastrin and somatostatin, decreased gradually from glandular ducts with only gastric mucous cell phenotype (G type) to GI-IM toward I-IM, while that of the intestinal endocrine cell markers, glicentin, gastric inhibitory polypeptide (GIP), and glucagon-like peptide-1 (GLP-1) was inversely correlated. In the fundic region, gastrin-positive cells emerged in the pseudo-pyloric and GI-IM glands, whereas I-IM glands did not possess any gastrin-positive cells, suggesting the presence of a distinct pathway of intestinalization. Double staining revealed coexistence of gastrin- and GLP-1-positive cells in the same gland and occasionally in the same cell in GI-IM glands. These results suggest that the phenotypes of endocrine cells are in line with those for mucous counterparts and support the concept that all of the different types of mucous and endocrine cells in normal and IM glands might be derived from a single progenitor cell in each gland.

Efficiency of bone marrow-derived cells in regeneration of the stomach after induction of ethanol-induced ulcers in rats

BACKGROUND

Bone marrow contains hematopoietic stem cells, nonhematopoietic mesenchymal stem cells, and several precursor cells for osteoblasts, chondrocytes, adipocytes, myocytes, hepatocytes, and even neural cells. Research findings indicate that multipotent stem cells in the adult body may be used to recover the lost functions of damaged tissues. This study examined the involvement of bone marrow-derived cells in the regeneration of the stomach after experimental gastric ulcers were produced in rats.

METHODS

We transplanted the bone marrow of transgenic rats that expressed green fluorescence protein (GFP) throughout the body. Twenty-one days after the bone marrow transplantation (BMT), gastric ulceration was induced, using absolute ethanol. Control animals received saline. After various observation periods, rats harboring GFP-positive bone marrow-derived cells were killed, and the tissues were removed and processed to prepare paraffin-embedded sections. Cells expressing GFP were identified by conventional immunohistochemistry, using anti-GFP antibody. To identify whether cells expressing GFP were epithelial cells or interstitial cells such as fibroblasts, serial sections were examined with anti-cytokeratin antibody or anti-vimentin antibody, respectively. Furthermore, to confirm that cells expressing GFP were epithelial cells or interstitial cells, we used double-staining analysis with anti-GFP antibody or anti-cytokeratin antibody, respectively.

RESULTS

GFP-positive, bone marrow-derived cells were found in the cytokeratin-positive gastrointestinal epithelium, as well as among vimentin-positive interstitial cells. Interestingly, the proportions of GFP-positive, cytokeratin-positive epithelial cells and vimentin-positive interstitial cells were significantly greater in the ethanol-treated damaged stomachs than in the saline-treated controls.

CONCLUSIONS

The present study clearly demonstrates that bone marrow-derived cells are involved in the regeneration of the stomach after ethanol-induced ulcers in rats.

Role of Helicobacter pylori in gastric carcinogenesis: the origin of gastric cancers and heterotopic proliferative glands in Mongolian gerbils

Helicobacter pylori infection is well accepted to be a very important factor for the development of gastric carcinogenesis in the human stomach. In Mongolian gerbils treated with chemical carcinogens, H. pylori infection enhances glandular stomach carcinogenesis, and eradication of infection and results in curtailment of enhancing effects, particularly at early stages of associated inflammation. A high-salt diet exacerbates the effects of H. pylori infection on gastric carcinogenesis, and these two factors act synergistically to promote the development of gastric cancers in this animal model. However, the bacterium exerts the greater effects. Early acquisition significantly increases gastric chemical carcinogenesis in Mongolian gerbils, as compared to later infection. While heterotopic proliferative glands, hyperplastic and dilated glands localized beneath the muscularis mucosae, frequently develop with H. pylori infection alone in this animal model, they obviously regress on eradication, suggesting a relation to severe gastritis, rather than a malignant character. Furthermore, endocrine cells, positive for chromogranin A, are observed in the heterotopic proliferative glands, in contrast to cancerous lesions which lack endocrine elements. In conclusion, H. pylori is not an initiator, but rather a strong promoter of gastric carcinogenesis, whose eradication, together with reduction in salt intake, might effectively prevent gastric cancer development.

Immunohistochemically detectable Cdx2 is present in intestinal phenotypic elements in early gastric cancers of both differentiated and undifferentiated types, with no correlation to non-neoplastic surrounding mucosa

It has previously been reported that Cdx2 is the useful prognostic and intestinal phenotypic marker in advanced gastric cancers (GC). In this study, Cdx2 expression and phenotype in early GC and non-neoplastic surrounding mucosa were examined. A total of 130 early GC (70 intramucosal and 60 submucosally invasive cancers) histologically and phenotypically were evaluated. The expression of Cdx2 was assessed by immunohistochemistry. The lesions were phenotypically divided into 44 gastric (G), 42 gastric and intestinal mixed (GI), 30 intestinal (I), and 14 null (N) types, independent of the histological classification. Most of the early GC were Cdx2-positive, nuclear staining being strongly associated with intestinal phenotypic expression. Early differentiated cancers tended to feature both Cdx2 and intestinal phenotypic expression, while their undifferentiated counterparts were more likely to demonstrate only gastric phenotypic expression (P < 0.05). The phenotypes of six intramucosal microcarcinomas did not correlate with those of adjacent normal glands. These data suggest that Cdx2 is expressed in the very early stage of gastric carcinogenesis in association with the shift from gastric to intestinal phenotypic expression. This appears to occur in differentiated cancers at an earlier stage than in undifferentiated ones, and may be linked to suppression of expansion of malignant cells.

The gastrointestinal stem cell

The longevity of adult stem cells, and their potential for vast tissue regeneration, makes them a focal point of current research and debate, with future aspirations for the use of stem cells in the treatment of a number of human pathological conditions. Due to the rapid rate of cell turnover in the gastrointestinal tract, the stem cells of this tissue are amongst the most assiduous in the body, although they remain unidentified to this day due to their immature, undifferentiated phenotype. However, our knowledge of the mechanisms regulating gastrointestinal stem cell function is evolving, with the identification of putative cellular markers and the elucidation of signalling pathways which regulate cell behaviour in the normal and neoplastic gastrointestinal tract. This review describes the fundamental properties of the gastrointestinal stem cell including: (i) their number, location and origins, (ii) their primary function of deriving gastrointestinal cell lineages and maintaining tissue homeostasis, (iii) the acquisition of gastrointestinal cell lineages from adult stem cells of extraneous tissues and the consequences of this in a therapeutic context, and (iv) the genetic and morphological phenomena surrounding neoplastic transformation in the gastrointestinal tract.

Expression of Cdx2 and the phenotype of advanced gastric cancers: relationship with prognosis

PURPOSE

The clinicopathologic significance of the phenotype and Cdx2 expression has hitherto remained unclear in gastric cancers. In the present study, we therefore examined the correlation between prognosis, phenotype, and Cdx2 expression in advanced cases.

METHODS

We evaluated 177 advanced gastric carcinomas histologically and phenotypically. The expression of Cdx2 was also assessed by immunohistochemistry.

RESULTS

The lesions were phenotypically divided into 32 gastric (G type), 36 gastric and intestinal mixed (GI type), 53 intestinal (I type), and 56 null (N type) types, independent of the histological classification. Cdx2 nuclear staining demonstrated a close relation to intestinal phenotypic expression, not with the histological classification. Kaplan-Meier analysis of Cdx2 expression and the phenotype showed that the Cdx2 positive groups had a significantly better outcome than the negative ones (P=0.0013), and the patients with GI type cancers had significant better survival than those with N type (P=0.0052).

CONCLUSIONS

Our results suggest that Cdx2 is a useful prognostic marker. In addition, advanced gastric cancers with both intestinal and gastric phenotypic expression have a relatively good prognosis. Combined evaluation of gastric and intestinal epithelial cell markers, including Cdx2, is clinically useful to predict outcome in patients with advanced neoplasm of the stomach.

Absence of either gastric or intestinal phenotype in microscopic differentiated gastric carcinomas

Differentiated gastric carcinoma (DGC) corresponds roughly to the intestinal type of gastric carcinoma described by Laurén. It has been suggested that DGCs arise from intestinalized gastric mucosa, but recent findings regarding their mucin expression do not support this hypothesis. To evaluate the histogenetic relationship between DGCs and intestinal metaplasia, lesions that are as small as possible should be examined. Twenty-five DGCs, ranging in their greatest dimension from 0.4 to 2.7 mm, were collected and divided into two groups by size. Group A consisted of 13 lesions less than 1.4 mm across, and group B of 12 lesions 1.4 mm or more. The presence of mucin and a brush border was assessed by immunostaining with antibodies against human gastric mucin, pyloric-gland-type mucin, Muc-2 glycoprotein, and CD10 antigen, and the lesions were classified as having the gastric phenotype (G-type), intestinal phenotype (I-type), mixed gastric and intestinal phenotype (M-type), or null phenotype (N-type). Thirteen (52%) of the 25 lesions were N-type, 5 (20%) lesions were G-type, 5 (20%) were I-type, and 2 (8%) were M-type. Group A had a larger proportion of N-type lesions than B (10/13, or 77%, vs. 3/12, or 25%; p = 0.027, chi-square test for proportions). Group B had a larger proportion of G-type lesions than A (5/12, or 42%, vs. 0/13, or 0%; p = 0.033). The phenotypes of the carcinomas and their surrounding mucosa were unrelated. Therefore, DGCs may arise from gastric mucosa affected by intestinal metaplasia or not, without having either the gastric or intestinal phenotype.

Mosaic analysis of small intestinal development using the spf(ash)-heterozygous female mouse

Mosaic analysis using the spf(ash)-heterozygous female mouse was performed to clarify the cell lineage and cell behavior during small intestinal development with special attention given to the villus and crypt formation. The spf(ash) mutation, located on the X-chromosome, causes ornithine transcarbamylase (OTC) deficiency, which leads to mosaic expression of this enzyme in the small intestine of the heterozygous female mouse. In the small intestine in heterozygous fetuses, very small patches, which were aggregates of OTC-positive cells or negative cells, with no definite orientation to the villus structures were observed. In the neonatal small intestine, the intervillus region (the presumptive crypts) was polyclonal, and the majority of crypts were comprised exclusively cells of either genotype in 2-week-old small intestine. These results suggest that extensive migration and cell mixing of small intestinal epithelial cells, which have no definite correlation with the villus formation, occur in fetal stages of development, and that the crypt morphogenesis commences after birth independently of the monoclonality of the epithelial cells. Our data with the mosaic mice also reconfirmed the monoclonality of the adult small intestinal crypts demonstrated in mouse aggregation chimeras.

Stem cells and gastric cancer: role of gastric and intestinal mixed intestinal metaplasia

All of the different types of stomach epithelial cells are known to be derived from a single progenitor cell in each gland. Similarly, cancers develop from single cells, based on data from clonality analysis in C3H/HeN<-->BALB/c chimeric mice. Using gastric and intestinal epithelial cell markers, intestinal metaplasia (IM) can be divided into two major types: a gastric and intestinal (GI) mixed type, and a solely intestinal (I) type. Ectopic expression of Cdx genes and down-regulation of Sox2 in isolated single GI mixed IM glands suggests abnormal differentiation of stem cells that can produce both gastric (G) and I type cells. Similarly, phenotypic expression of gastric cancer cells of each histological type can be clearly classified into G and I type epithelial cells. The heterogeneity of phenotypic expression of gastric cancer cells in individual cancers is assumed to reflect this intrinsic potential for differentiation in two directions. Gastric cancers at early stages, independent of the histological type, mainly consist of G type cells, and phenotypic shift from G to I type expression is clearly observed with progression. The data thus suggest IM may not be a preneoplastic change in gastric carcinoma, but rather that cells of the I type may appear independently in the gastric mucosa in IM and in gastric cancers. Intestinalization of gastric mucosa and cancer cells may represent a kind of homeotic transformation. Whether disturbance of the regulation of Sox2 and Cdx genes may be of importance to the biological behavior of gastric cancers should therefore be clarified in future studies.

Multipotential stem cells in adult mouse gastric epithelium

Previous studies of chimeric animals demonstrate that multipotential stem cells play a role in the development of the gastric epithelium; however, despite much effort, it is not clear whether they persist into adulthood. Here, chemical mutagenesis was used to label random epithelial cells by loss of transgene function in adult hemizygous ROSA26 mice, a mouse strain expressing the transgene lacZ in all tissues. Many clones derived from such cells contained all the major epithelial cell types, thereby demonstrating existence of functional multipotential stem cells in adult mouse gastric epithelium. We also observed clones containing only a single mature cell type, indicating the presence of long-lived committed progenitors in the gastric epithelium. Similar results were obtained in duodenum and colon, showing that this mouse model is suitable for lineage tracing in all regions of the gastrointestinal tract and likely useful for cell lineage studies in other adult renewing tissues.

Gastrointestinal stem cells

Turnover of the epithelial cell lineages within the gastrointestinal tract is a constant process, occurring every 2-7 days under normal homeostasis and increasing after damage. This process is regulated by multipotent stem cells, which give rise to all gastrointestinal epithelial cell lineages and can regenerate whole intestinal crypts and gastric glands. The stem cells of the gastrointestinal tract are as yet undefined, although it is generally agreed that they are located within a 'niche' in the intestinal crypts and gastric glands. Studies of allophenic tetraparental chimeric mice and targeted stem cell mutations suggest that a single stem cell undergoes asymmetrical division to produce an identical daughter cell, and thus replicate itself, and a committed progenitor cell which further differentiates into an adult epithelial cell type. The discovery of stem cell plasticity in many tissues, including the ability of transplanted bone marrow to transdifferentiate into intestinal subepithelial myofibroblasts, provides a potential use of bone marrow cells to deliver therapeutic genes to damaged tissues, for example, in treatment of mesenchymal diseases in the gastrointestinal tract, such as fibrosis and Crohn's disease. Studies are beginning to identify the molecular pathways that regulate stem cell proliferation and differentiation into adult gastrointestinal cell lineages, such as the Wnt and Notch/Delta signalling pathways, and the importance of mesenchymal-epithelial interactions in normal gastrointestinal epithelium and in development and disease.

Mouse strain susceptibility to diethylnitrosamine induced hepatocarcinogenesis is cell autonomous whereas sex-susceptibility Is due to the micro-environment: analysis with C3H <--> BALB / c sexually chimeric mice

In man, liver cancer is on the increase, especially in males. Sex differences also exist in rodent models. To elucidate the mechanisms, chimeric mice were produced by amalgamation of early embryos from high and low hepatocarcinogen-susceptible strains, C3H and BALB / c. Tumor formation was initiated with 10 mg / kg of diethylnitrosamine at the ages of 7 and 14 days and mice were sacrificed at 30 and 45 weeks. The chimeras were classified into XY <--> XY, XY <--> XX, XX <--> XY, and XX <--> XX in terms of sex chromosomes by means of polymerase chain reaction-simple sequence length polymorphism analysis (SSLP) using Y chromosome-specific Sry primers in combination with the D3Mit21 marker. Liver lesions were analyzed histopathologically, by immunostaining using a C3H strain-specific antibody and by DNA in situ hybridization with the Y chromosome-specific digoxigenin-labeled Y353 / B probe. Sex and strain genotyping by SSLP analysis matched histological observations, confirming the reliability of our system. The strain differences in liver tumor numbers of each strain type in XY <--> XY and XX <--> XX subtypes of C3H <--> BALB / c chimeras were retained well (P < 0. 0001 and P < 0.001, respectively), indicating a minimum influence of the C3H or BALB / c surrounding milieu on development of individual lesions. On the other hand, significant promotion of XX cell tumors was evident in phenotypically male sexually chimeric XY <--> XX and XX <--> XY chimeras for both C3H (P < 0.02) and BALB / c (P < 0.01) lesions compared to the XX <--> XX case. The results suggest the presence of hormonal or micro-environmental factors specific for males, which are not caused cell-autonomously. Basic strain differences, however, are determined by intrinsic genetic factors rather than the strain-dependent micro-environment.

The clonal origin and clonal evolution of epithelial tumours

While the origin of tumours, whether from one cell or many, has been a source of fascination for experimental oncologists for some time, in recent years there has been a veritable explosion of information about the clonal architecture of tumours and their antecedents, stimulated, in the main, by the ready accessibility of new molecular techniques. While most of these new results have apparently confirmed the monoclonal origin of human epithelial (and other) tumours, there are a significant number of studies in which this conclusion just cannot be made. Moreover, analysis of many articles show that the potential impact of such considerations as patch size and clonal evolution on determinations of clonality have largely been ignored, with the result that a number of these studies are confounded. However, the clonal architecture of preneoplastic lesions provide some interesting insights --many lesions which might have been hitherto regarded as hyperplasias are apparently clonal in derivation. If this is indeed true, it calls into some question our hopeful corollary that a monoclonal origin presages a neoplastic habitus. Finally, it is clear, for many reasons, that methods of analysis which involve the disaggregation of tissues, albeit microdissected, are far from ideal and we should be putting more effort into techniques where the clonal architecture of normal tissues, preneoplastic and preinvasive lesions and their derivative tumours can be directly visualized in situ.

Epithelial stem cell repertoire in the gut: clues to the origin of cell lineages, proliferative units and cancer

Gastrointestinal stem cells are shown to be pluripotential and to give rise to all cell lineages in the epithelium. After damage, gut stem cells produce reparative cell lineages that produce a wide range of peptides with important actions on cell proliferation and migration, and promote regeneration and healing. Increase in stem cell number is considered to induce crypt fission, and lead to increases in the number of crypts, even in the adult; it is also the mode of spread of mutated clones in the colorectal mucosa. Stem cell repertoire is defined by both intrinsic programming of the stem cell itself, but signalling from the mesenchyme is also vitally important for defining both stem cell progeny and proliferation. Carcinogenesis in the colon occurs through sequential mutations, possibly occurring in a single cell. A case is made for this being the stem cell, but recent studies indicate that several stem cells may need to be so involved, since early lesions appear to be polyclonal in derivation.

Cell proliferation in gastrointestinal mucosa

Gastrointestinal cell proliferation plays an important role in the maintenance of the integrity of the gastrointestinal system. The study of gastrointestinal proliferation kinetics allows a better understanding of the complexity of the system, and also has important implications for the study of gastrointestinal carcinogenesis. Gastrointestinal stem cells are shown to be pluripotential and to give rise to all cell lineages in the epithelium. Carcinogenesis in the colon occurs through sequential mutations, possibly occurring in a single cell--the stem cell.

Lineage and clonal development of gastric glands

Individual gastric glands of the stomach are composed of cells of different phenotypes. These are derived from multipotent progenitor stem cells located at the isthmus region of the gland. Previous cell lineage analyses suggest that gastric glands, as in the colon and small intestine, are invariably monoclonal by adult stages. However, little is known about the ontogenetic progression of glandular clonality in the stomach. To examine this issue, we employed an in situ cell lineage marker in female mice heterozygous for an X-linked transgene. We found that stomach glands commence development as polyclonal units, but by adulthood (6 weeks), the majority progressed to monoclonal units. Our analysis suggests that at least three progenitor cells are required to initiate the development of individual gastric glands if they are analyzed just after birth. Hence, unlike the colon and small intestine, stomachs showed a significant fraction (10-25%) of polyclonal glands at adult stages. We suggest that these glands persist from polyclonal glands present in the embryonic stomach and hypothesize that they represent a subpopulation of glands with larger numbers of self-renewing stem cells.

Clonal analysis of superficial depressed-type gastric carcinoma in humans

BACKGROUND

An important unanswered question concerning the histogenesis of superficial-type gastric carcinoma is whether it is monoclonal or multiclonal in origin. Therefore, the authors analyzed multiple areas of each cancer with a clonality assay based on trinucleotide repeat length polymorphism of the human androgen receptor gene (HUMARA) that was subject to random inactivation of X chromosomes.

METHODS

The HUMARA assay was applied to 15 gastric carcinomas, early and advanced stage, manifested in superficial, depressed lesions of various sizes and at least some signet ring cells. DNA was extracted from fresh frozen and formalin fixed tumor tissues that were microdissected from the mucosal lesions, and the HUMARA locus was amplified by polymerase chain reaction with and without prior digestion of nonmethylated DNA with Hpa II. The amplified DNA samples were loaded on polyacrylamide gels, electrophoresed, and visualized by a silver-staining method.

RESULTS

In the 15 cases examined, 9 cancers were informative (had features of the types sought in this study), and in these 9 cancers a total of 57 areas were analyzed. In 7 of the 9 cancers, the inactivated allele was common to all the informative areas of each tumor, irrespective of the macroscopic shape of the tumor or the degree of histologic heterogeneity within it. In one of the two remaining cancers, the inactivated allele of one of the areas examined was different from those in the other areas.

CONCLUSIONS

Most of the superficial depressed-type gastric carcinomas in this study were demonstrated to be of monoclonal origin. This finding supports a notion expressed previously in the literature that superficial-type carcinoma has a long natural history, and it indicates that efforts to detect gastric carcinomas in early stages to improve patients' survival should be encouraged.

Potential preventive effects of Chelidonium majis L. (Papaveraceae) herb extract on glandular stomach tumor development in rats treated with N-methyl-N'-nitro-N nitrosoguanidine (MNNG) and hypertonic sodium chloride

The modifying effects of Chelidonium majis L. (Papaveraceae) herb extract (CH), an analgesic traditionally prescribed for gastric and duodenal ulcer patients, on gastric tumor development were studied in rats given N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Sixty-four male 6-week-old Wistar rats were used. Group 1 rats were initially given MNNG (200 mg/kg b.w.) by gavage at days 0 and 14 as well as saturated sodium chloride solution (S-NaCl, 1 ml per rat) every 3 days during weeks 0-3 (six times), and then placed on basal diet containing 0.1 or 0.2% CH for 16 weeks from week 4. Rats of Group 2 and 3 were treated with MNNG together with S-NaCl or saline (0.9% NaCl, 1 ml per rat), respectively, timed as in Group 1 but without further treatment. All surviving animals were killed at week 20 and histopathologically investigated. In the glandular stomach, the number of preneoplastic pepsinogen 1 altered pyloric glands (PAPGs) in the MNNG + S-NaCl-->CH (0.1%) group (Group 1) was significantly smaller than in the MNNG + S-NaCl group (Group 2) (P < 0.02). The incidences of forestomach neoplastic lesions (papillomas and squamous cell carcinomas) also showed a tendency to decrease with the CH treatment. The results thus indicate that CH exerts inhibitory effects on glandular stomach carcinogenesis in the rat, so that it may have potential as a chemopreventive agent for stomach cancer in man.

Induction of invasive squamous cell carcinomas in the forestomach of (C3H x MSM)F1, MSM, and C3H mice by N-methyl-N-nitrosourea and mutational analysis of the H-ras and p53 genes

Genetic analysis of tumors developing in F1 hybrids between genetically separate strains of mice makes it possible to search for loss of heterozygosity (LOH), information on which provides clues to finding tumor-suppressor genes. For this purpose, however, reproducible carcinogenic conditions for the organ of interest need to be first determined. In the present study, a forestomach model of squamous cell carcinomas (SCCs), induced in (C3H x MSM)F1 mice by N-methyl-N-nitrosourea (MNU), was established and mutational changes in the H-ras and p53 genes were examined in tumors. Male (C3H x MSM)F1, MSM and C3H mice were given MNU by i.g. intubation once a week at a dose of 0.03 mg/g body weight for 10 weeks, then kept without further treatment. At experimental weeks 38-46, markedly invasive SCCs were observed in the forestomach at incidences of 9/14 (64.3%), 9/16 (56.3%), and 2/10 (20.0%), respectively. In the three strains of mice, DNA analysis of SCCs by PCR-SSCP analysis followed by direct DNA sequencing revealed low incidences of point mutations in the H-ras (4/20, 20%) and p53 (3/20, 15%) genes. The results demonstrate the usefulness of the present animal experimental protocol for induction of high grade SCC in the forestomach of (C3H x MSM)F1 mice, and suggest the possibility that point mutations in the H-ras or p53 genes may play some role in pathways leading to the development of such lesions.

Primary monoclonal and secondary polyclonal growth of colon neoplastic lesions in C3H/HeN<-->BALB/c chimeric mice treated with 1,2-dimethylhydrazine immunohistochemical detection of C3H strain-specific antigen and simple sequence length polymorphism analysis of DNA

To determine the clonality and cellular origin of colon pre-neoplastic and neoplastic lesions, C3H/HeN<-->BALB/c chimeric mice treated with 1,2-dimethylhydrazine (DMH) were investigated immunohistochemically using a specific antibody to C3H strain-specific antigen (CSA) enabling immunohistochemical discrimination of C3H cells in histological sections of chimeric mouse tissues. To confirm the results of immunostaining, simple sequence length polymorphism (SSLP) analysis was performed on DNA samples extracted from histological sections of adenocarcinomas. C3H/HeN<-->BALB/c chimeric mice were produced by an aggregation procedure and together with BALB/c and C3H/HeN animals were given weekly s.c. injections of 20 mg/kg body weight DMH for up to 20 weeks. At weeks 20 and 35 animals were killed and autopsied. In normal colonic mucosa of the chimeras, each gland was composed entirely of either CSA-positive or -negative cells and no mixed glands were found. Cells of all focal atypias in chimeric mice were, in each case, homogeneous for one or another of the parental types. Of 91 adenomas in chimeric mice, only one comprised both types of cell. Among 119 adenocarcinomas, 12 contained cells of both parental types. In these tumors, however, the 2 phenotypes were not mixed together at random but arranged in discrete areas, with intermingling limited to the junctions. SSLP analysis demonstrated DNAs extracted from CSA-positive and -negative tumors to exhibit the polymorphic patterns of C3H and BALB/c, respectively, while mixed CSA-positive and -negative tumors showed mixtures of both polymorphic DNA types.

Emerging issues in mouse liver carcinogenesis

The mouse liver is the primary target site for carcinogenesis of more than 200 chemicals (including pesticides, food additives, pharmaceuticals, and industrial intermediates) tested in long-term toxicity safety assessment assays. Mouse liver tumors develop through defined morphological stages (similar to those found in other species) whether their origin is of undetermined etiology (spontaneous) or induced by chemicals. The morphologic type of hepatocytes in the various stages of hepatocarcinogenesis is sometimes associated with the specific inducing agent. Liver tumors developing in toxic livers often have more benign appearances and may progress to carcinomas at a slower rate than tumors developing in histologically normal livers. Specific tumors, dependent on the inducing chemical, may regress under defined protocols. Genotoxic and nongenotoxic mouse hepatocarcinogens each may induce tumors of either high malignant or low malignant potential. Liver tumors with specific H-ras oncogene mutations may appear morphologically and biologically similar to those without proven ras mutations. Thus, distinguishing mechanism of carcinogenesis by liver tumor morphology and mutation spectra may be difficult. Additionally, the presence of liver tumors with a morphology and a ras oncogene mutation spectrum characteristic of spontaneous tumors in histologically normal livers of mice exposed to a nongenotoxic test chemical may indicate promotion of spontaneous hepatocarcinogenesis by one of several potential mechanisms. Further research into the mechanisms responsible for the increased incidences of liver tumors in mice exposed to test chemicals could enhance human cancer risk assessments.