Gastrointestinal Epithelial Cell Proliferation Research Articles

MAPKs and Signal Transduction in the Control of Gastrointestinal Epithelial Cell Proliferation and Differentiation

Mitogen-activated protein kinase (MAPK) pathways are activated by several stimuli and transduce the signal inside cells, generating diverse responses including cell proliferation, differentiation, migration and apoptosis. Each MAPK cascade comprises a series of molecules, and regulation takes place at different levels. They communicate with each other and with additional pathways, creating a signaling network that is important for cell fate determination. In this review, we focus on ERK, JNK, p38 and ERK5, the major MAPKs, and their interactions with PI3K-Akt, TGFβ/Smad and Wnt/β-catenin pathways. More importantly, we describe how MAPKs regulate cell proliferation and differentiation in the rapidly renewing epithelia that lines the gastrointestinal tract and, finally, we highlight the recent findings on nutritional aspects that affect MAPK transduction cascades.

Trans-Cellular Genetic Modification in Cancer

Gastric and colon cancers contribute to more than 1 million deaths per year worldwide. Many tumors harbor mutations in a gene called adenomatous polyposis coli ( APC ) that affect proliferation of gastrointestinal epithelial cells. Inactivation of APC results in nuclear accumulation of β-catenin, a downstream effector of the Wnt signaling pathway that controls cell proliferation. Mice with an inactivating mutation in multiple intestinal neoplasia ( Min ), the ortholog of APC , also exhibit intestinal tumors and up-regulated Wnt signaling. Perreault et al. found that if mice partially deficient for Min (harboring one inactive Min gene copy) were crossed with mice deficient in a transcription factor called Foxl1, intestinal tumor frequency increased sevenfold and additional tumors developed in the stomach. Additional loss of Foxl1 did not change the rate of apoptosis in epithelial cells. However, 90% of the tumors had lost the normal copy of the Min gene, a condition known as loss of heterozygosity (LOH). Foxl1 is a transcription factor expressed in mesenchymal cells adjacent to gastrointestinal epithelial cells, and although mice lacking just Foxl1 show increased β-catenin accumulation in epithelial cells, they do not develop cancer. However, additional deletion of Foxl1 did not enhance nuclear β-catenin accumulation in Min -deficient mice, pointing to LOH as the molecular basis for increased tumor development. The authors suggest that Foxl1 expressed in mesenchymal cells acts as a genetic modifier of the Min gene in gastroepithelial cells and that contribution of the stroma may play an important role in the initiation of gastrointestinal tumors in humans. N. Perreault, S. D. Sackett, J. P. Katz, E. E. Furth, K. H. Kaestner, Foxl1 is a mesenchymal Modifier of Min in carcinogenesis of stomach and colon. Genes Devel. 19 , 311-315 (2005). [Abstract] [Full Text]

The winged helix transcription factor foxa2 is required for the control of gastrointestinal epithelial cell proliferation

The winged helix transcription factor foxa2 is required for the control of gastrointestinal epithelial cell proliferation

Interleukin-1, interleukin-8, tumour necrosis factor alpha and interferon gamma stimulate DNA synthesis but have no effect on apoptosis in small-intestinal cell lines.

Cytokines stimulate lymphocyte cell proliferation and affect cell division in several other cell types. Helicobacter pylori-induced gastritis and coeliac disease are characterized by an increased cell proliferation in association with an increased production of proinflammatory cytokines, which could contribute to these cell kinetic changes. Our aim is to examine in vitro whether cytokines usually present in the gastrointestinal mucosa affect DNA synthesis and apoptosis in a rat and a human small-intestinal cell line. IEC-6 and FHs-74 cells were incubated for 24 h with 10(-13)-10(-9) M of tumour necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), interleukin-2 (IL-2), interleukin-6 (IL-6), interleukin-8 (IL-8), transforming growth factor-beta (TGF-beta) and interferon gamma (IFN-gamma). IEC-6 cells were also incubated with 10(-13)-10(-9) M of interleukin-1alpha (IL-1alpha) and 10(-8) M of interleukin-1 receptor antagonist (IL-1ra). The cells were labelled with 3H-methyl thymidine for the final 4 hours, and then processed for autoradiography. DNA synthesis was evaluated by the labelling index (LI%). Apoptosis was evaluated in IEC-6 cells by changes in membrane lipid asymmetry using annexin-V binding to externalized phosphatidylserine (flow cytometry) and by estimating the caspase activity. TNF-alpha, IL-1beta, IL-8 and IFN-gamma significantly and markedly increased the LI, even at low concentrations (P< 0.0001), in both IEC-6 and FHs-74 cells, as did IL-1alpha in IEC-6 cells. TGF-beta significantly reduced the LI in both cell lines (P< 0.0001), whereas IL-2, IL-6 and IL-1ra did not affect DNA synthesis significantly. None of IL-1beta, IL-8, TNF-alpha or IFN-gamma affected apoptosis in IEC-6 cells. TNF-alpha, IL-1alpha, IL-1beta, IL-8 and IFN-gamma stimulated DNA synthesis in a human and a rat small-intestinal cell line. The cytokines exert their mitogenic action directly on the intestinal cells via specific receptors. Our findings indicate that pro-inflammatory cytokines may participate in the regulation of the gastrointestinal epithelial cell proliferation in health and disease.

Substratum-Dependent and Region-Specific Control of Attachment and Proliferation of Gastrointestinal Epithelial Cells in Primary Serum-Free Culture

A system for the primary serum-free culture of fetal rat gastrointestinal epithelial cells was used to examine the role of the extracellular matrix (ECM) in the attachment and proliferation of these epithelial cells. Forestomach epithelial cells (FSEC) were able to attach to and proliferate on plastic dishes without a substratum, while glandular stomach epithelial cells (GSEC) and duodenal epithelial cells (DEC) were unable to do so. The presence of a substratum promoted the attachment and proliferation of these epithelial cells. The effects of various components of the ECM differed depending on the type of cell. FSEC attached most efficiently to a substratum of fibronectin, while GSEC did so to laminin. DEC attached more efficiently to type I collagen and fibronectin than to any other substratum. FSEC proliferated most rapidly on laminin, while GSEC and DEC did so on collagen gels. These substrata induced the most efficient attachment and proliferation of FSEC, and they were effective in promoting the attachment and proliferation of GSEC and DEC in decreasing order of efficiency, indicating the existence of a head-to-tail gradient in the response of epithelial cells to substrata. The expression of c-myc mRNA in these cells differed depending upon the substratum on which they were cultured and the mRNA level was well correlated with the extent of the cell proliferation, indicating that the cell proliferation is mediated by c-myc gene expression, which is regulated by cell–ECM interactions. The results of the present study demonstrate that proliferation of gastrointestinal epithelial cells is regulated region-specifically not only by soluble factors but also by insoluble components of the ECM.

Abnormal cell proliferation and p52/p35-CSK expression in the colons of aging rats.

In rodents and in humans, aging is associated with increased gastrointestinal epithelial cell proliferation and an expanded crypt proliferative compartment similar to that seen in the preneoplastic bowel. We have compared the distribution of a series of cytoskeletal antigens that are modified when colonic cancer cells differentiate in vitro in the colon of young (4-7 month) and aging (22-26 month) Fischer 344 rats. Two such proteins, p52 and p35, (that are increased in cultured senescent cells) differ in their position in the crypt axis and subcellular localization between young and aging rats. In young rats, immunoreactive p52 protein is present solely near the colonic crypt surface epithelium but in aging rats p52 expressing cells are found deeper in crypts. The intracellular localization of p35 also differs markedly in young and aging animals. The distribution of these proteins appears to be a reproducible biomarker of aging. Antigenic changes similar to those observed in aging colons also are seen in crypt cells of patients with ulcerative colitis and in the flat colonic mucosa of patients with adenomatous polyps and colon cancer. The combination of proliferative and differentiation changes suggest that the flat mucosa of the colon of aging rats has preneoplastic features.

Plasma and tissue hormones in the dog after administration of the prostaglandin analogue, misoprostol.

Dogs were given a prostaglandin analogue, misoprostol, at a dose that significantly increases gastrointestinal epithelial cell proliferation. Both basal and postprandial concentrations of gastrin were significantly higher in the misoprostol-treated dogs and more than doubled after the meal in both the controls and in the test group. Plasma enteroglucagon, cholecystokinin, insulin and glucose-dependent insulinotrophic peptide all increased postprandially, with no effect of misoprostol. Tissue concentrations of bombesin, gastrin and somatostatin were unaffected by misoprostol, but the fundic glucagon-like immunoreactivity was significantly increased. Thus high doses of misoprostol have only minor effects on gastrointestinal regulatory peptides, suggesting that the trophic effect of prostaglandins on the intestinal tract may be direct.

The Role of Gut-Glucagon-Like Immunoreactants in the Control of Gastrointestinal Epithelial Cell Renewal

In vitro and in vivo studies have provided considerable information on the possible physiologic function of circulating gastrointestinal hormones as well as locally acting regulatory peptides in the multifactorial control of adaptive gastrointestinal epithelial cell proliferation and cell renewal. It has been suggested by circumstantial evidences that enteroglucagon (EG; G-GLI I) may act as a trophic factor on the intestinal mucosa which may account for adaptive changes of the small intestine following various stimuli. However, we have shown that there are experimental conditions (germ-free rats after conventionalisation; jejunal self-filling blind loops) in which intestinal hyperplasia does not correspond to an increase in the concentrations of enteroglucagon in plasma or intestinal mucosa. Furthermore, despite a continuous immunoneutralisation of circulating endogenous enteroglucagon by monoclonal antibodies there was an adaptive, hyperplastic response of the ileal remnants after a 70% proximal small bowel resection which was of the same magnitude as in the control group but was even greater considering the increased number of mitoses per crypt. In order to gain additional insight into the putative role of enteroglucagon as an enterotrophic regulatory peptide, an in vitro model was used to investigate the effect of highly purified rat G-GLI I on the proliferative response of primary small intestinal epithelial cells of fetal rats. Whereas there was a well known growth-promoting action of EGF, the proliferation of rat fetal intestinal epithelial cells was inhibited by the addition of purified G-GLI I. These results indicate that enteroglucagon does not act as an enterotrophic factor but provide the first direct evidence consistent with an antitrophic role of enteroglucagon in the small intestine.

Peptides and epithelial growth regulation.

There is now considerable evidence implicating several peptides in the control of gastrointestinal epithelial cell proliferation and cell renewal. While some of these may act directly, many may be involved in regulating the powerful trophic effects of the intake and digestion of food on the gut epithelium. Several peptides have been associated with the regulation of intestinal cell proliferation. There is little doubt that gastrin is trophic to the stomach, but, its role in the rest of the gastrointestinal tract is debatable. Enteroglucagon has often been associated with increased intestinal epithelial proliferation, but at the moment all the evidence for this is circumstantial. The effects of peptide YY and bombesin warrant further study. The availability of recombinant epidermal growth factor (EGF) has recently enabled us to demonstrate a powerful trophic response to infused EGF throughout the gastrointestinal tract. The increasing availability of peptides will eventually allow the rigorous in vivo evaluation of the trophic role of these potentially very important peptides.

Changes in gastrin levels, food intake, and duodenal mucosal growth during lactation.

Gastrointestinal epithelial cell proliferation is stimulated during lactation in the rat. Serum gastrin levels and food intake are also increased during lactation. We investigated the role of gastrin and food intake as possible mediators of duodenal mucosal growth during the first 15 days of lactation. As the lactation period progressed, significant increases in the following crypt properties were noted: 1) crypt length; 2) cells/crypt; 3) labeling index; and 4) dimensions of the proliferative zone. Maternal serum gastrin levels rose abruptly by the first day of birth and remained elevated throughout lactation. The increases in crypt cell proliferation significantly correlated with food intake but not with serum gastrin levels during lactation. Mucosal mass and villus-crypt dimensions were also significantly increased above virgin levels in lactating antrectomized rats. These results suggest that the increase in duodenal growth during lactation most probably is not mediated by postpartum hypergastrinemia and that the increase in cell proliferation may be a direct response to an enhancement in food intake.

Ileal epithelial cell migration in acute renal failure. Autoradiographic studies in the mouse.

Previous investigations have shown an inhibition of gastrointestinal epithelial cell proliferation in acutely uremic mice. This paper gives the results of an autoradiographic investigation with3H-thymidine of the effect of acute renal failure on ileal epithelial cell migration. Acute renal failure was produced by urinary outflow obstruction and control mice subjected to sham operation. The mean number of cell positions between the cryptvillus junction and the leading labeled cell 30 hours after operation was decreased in the uremic group (P<0.01). No significant difference was found in the number of cells per villus column. Estimates showed a decrease in mean migration rate from 0.69 to 0.55 positions per hour and an increase in the life span of villus cells from 54.2 to 73.8 hours. Decreased crypt and villus cell renewal may contribute to the development of uremic gastrointestinal lesions.