Effects of growth factors and trefoil peptides on migration and replication in primary oxyntic cultures

Overexpression of trefoil factor 3 (TFF3) contributes to the malignant progression in cervical cancer cells

Background

There remains a great need for effective therapies for cervical cancers, the majority of which are aggressive leaving patients with poor prognosis.

Methods and results

Here, we identify a novel candidate therapeutic target, trefoil factor 3 (TFF3) which overexpressed in cervical cancer cells and was associated with reduced postoperative survival. Functional studies demonstrated that TFF3 overexpression promoted the proliferation and invasion of cervical cancer cells, and inhibited the apoptosis by inducing the mRNA changes in SiHa and Hela cell lines. Conversely, TFF3 silencing disrupted the proliferation and invasion of cervical cancer cells, and induced the apoptosis via Click-iT EdU test, flow cytometry analysis and two-dimensional Matrigel Transwell analysis. Western blot analysis showed that overexpression of TFF3 repressed E-cadherin (CDH1) expression to promote the invasion of cervical cancer cells. Furthermore, down-regulated CDH1 via overexpression of TFF3 was significantly up-regulated by virtue of inhibitor of p-STAT3.

Conclusions

These results suggested that TFF3 stimulated the invasion of cervical cancer cells probably by activating the STAT3/CDH1 signaling pathway. Furthermore, overexpression of TFF3 decreased the sensitivity of cervical cancer cells to etoposide by increasing P-glycoprotein (P-gp) functional activity. Overall, our work provides a preclinical proof that TFF3 not only contributes to the malignant progression of cervical cancers and but also is a potential therapeutic target.

Electronic supplementary material

The online version of this article (doi:10.1186/s12935-016-0379-1) contains supplementary material, which is available to authorized users.

Altered miRNA expression patterns in Tff2 knock-out mice correlate with cellular pathways of neoplastic development and caloric metabolism

The trefoil peptide family, consisting in mammals of three members namely TFF1, 2 and 3, plays a cytoprotective role in epithelial cells of various tissues, mainly in the digestive tract. Tff1, Tff2 or Tff3 knock-out mouse models developed various kinds of gastrointestinal impairment. microRNAs are known to be novel gene regulators. We aimed to investigate the physiological role of such miRNAs in Tff2 knock-out mice. Whole miRNome profiling and in silico analysis were performed for Tff2-KO and WT mice. Our latest data explored the role of miRNAs in the regulatory cascades and molecular processes of Tff2^−/− mice. As much as 6% of the Tff2-KO mice miRNome was significantly dys-regulated. Further in silico analysis suggests that the respective dys-regulated part of the miRNome is involved in human pathological processes, including pancreatic, colorectal and basal cell cancer. Additionally, the dys-regulated miRNome targets pathways involved in carbohydrate metabolism and adipocytokine signaling. The latter links deficient caloric maintenance in Tff2 and previous observation in Tff3-KO mice with miRNAs. In summary, our proof-of-concept study indicates that miRNAs may play an important role in the regulatory processes of the trefoil peptide family, especially in the regulation of cancer-related cascades.

Nitric oxide induces HIF-1α stabilization and expression of intestinal trefoil factor in the damaged rat jejunum and modulates ulcer healing

BACKGROUND

The induction of intestinal trefoil factor (ITF) has been reported to depend on hypoxia-inducible factor-1 (HIF-1). Nitric oxide modulates HIF-1 activity. The present study aims to analyze the role of nitric oxide in jejunum damage induced by indomethacin and its ability to modulate epithelial function through the expression of ITF.

METHODS

Rats received indomethacin (7.5 mg/kg, s.c., twice), and a time course analysis of damage was performed (24-96 h after the first administration). In these animals, the role of nitric oxide was analyzed by using 1400W, a selective iNOS activity inhibitor (5 mg/kg, i.p./day), on: (1) intestinal damage, (2) ulcer healing, (3) the presence of nitrated proteins in the jejunum and (4) the protein expression of inducible nitric oxide synthase (iNOS), HIF-1α and ITF.

RESULTS

Indomethacin induced damage in the jejunum that was apparent at 24 h and peaked at 48-72 h. An increase in iNOS, HIF-1α, ITF and nitrated proteins was observed in the injured jejunum. Immunoprecipitation of HIF-1α allowed determination of the nitration/nitrosylation of this protein by using nitrotyrosine and nitrocysteine antibodies. Blockade of iNOS activity did not significantly modify damage or iNOS expression, but did significantly impede ITF induction, HIF-1α stabilization and HIF-1α detection with antibodies against nitrated proteins. In parallel to these results, pre-treatment with 1400W delayed the healing of the ulcer provoked by indomethacin.

CONCLUSIONS

These results suggest that iNOS-derived NO is involved in HIF-1α stabilization, probably through S-nitrosylation, and ITF expression in goblet cells of the damaged jejunum of indomethacin-treated rats and mediates ulcer healing.

iNOS-derived nitric oxide mediates the increase in TFF2 expression associated with gastric damage: role of HIF-1

Trefoil (TFF) peptides are involved in gastrointestinal mucosal restitution. An hypoxia inducible factor 1 (HIF-1)-dependent induction of TFF genes has been reported in gastric epithelial cells. Nitric oxide (NO) is associated with mucosal damage and modulates HIF-1 activity. The aim of the present study was to analyze the role of iNOS-derived NO in HIF-1alpha stabilization and TFF gene expression in damaged gastric mucosa. Aspirin caused gastric injury that peaked 6 h after dosing and returned to normality at 24 h. iNOS mRNA expression occurs in the corpus in parallel with damage. Blockade of iNOS activity did not modify gastric lesions induced by aspirin but delayed mucosal healing. Aspirin induced HIF-1alpha stabilization and TFF2 mRNA up-regulation in the mucosa, but these effects were diminished when iNOS activity was inhibited. Results obtained using a coculture setup showed that iNOS-derived NO from activated macrophages induced HIF-1alpha stabilization, TFF gene expression, and accelerated wound healing in cultured epithelial cells. Finally, transient silencing of endogenous HIF-1alpha in epithelial cells significantly undermined activated macrophage-induced TFF gene expression. Evidence suggests that the iNOS-derived NO associated with NSAID-induced gastric injury is implicated in mucosal restitution via the HIF-1-mediated induction of TFF genes.

Induction of trefoil factor (TFF)1, TFF2 and TFF3 by hypoxia is mediated by hypoxia inducible factor-1: implications for gastric mucosal healing

BACKGROUND AND PURPOSE

Mucosal microcirculation is compromised during gastric damage induced by non-steroidal anti-inflammatory drugs, such as aspirin. Consequently, oxygen supply to epithelial cells is decreased. The trefoil factor (TFF) peptides are involved in mechanisms of defence and repair in the gastrointestinal tract but their regulation at sites of gastric injury is unknown.

EXPERIMENTAL APPROACH

Hypoxia and expression of TFF genes and peptides were measured in the damaged stomach of aspirin-treated rats. In a human gastric cell line (AGS cells), the effects of hypoxia and of hypoxia inducible factor (HIF)-1 (through transient transfection of HIF-1alpha siRNA or over-expression of HIF-1alpha) on TFF gene expression were evaluated.

KEY RESULTS

Hypoxyprobe immunostaining, up-regulation of TFF2 (1.9-fold) and TFF3 (1.8-fold) and a non-significant increase of TFF1 (1.5-fold) mRNA were observed in the damaged stomach of aspirin-treated rats, compared with control animals. Hypoxia (3% O(2), 16 h) induced mRNA for TFF1 (5.8-fold), TTF2 (9.1-fold) and TFF3 (9.3-fold) in AGS cells, an effect mediated by HIF-1, as transient transfection of HIF-1alpha siRNA reduced the effects of hypoxia. Over-expression of HIF-1alpha by transfection in non-hypoxic epithelial cells produced a similar pattern of TFF induction to that observed with hypoxia and transactivated a TFF1 reporter construct.

CONCLUSIONS AND IMPLICATIONS

Hypoxia inducible factor-1 mediated the induction of TFF gene expression by hypoxia in gastric epithelial cells. Low oxygen levels and up-regulation of TFF gene expression in the damaged stomach of aspirin-treated rats suggest that hypoxia induced expression of TFF genes at sites of gastric injury.

Novel roles of local insulin-like growth factor-1 activation in gastric ulcer healing: promotes actin polymerization, cell proliferation, re-epithelialization, and induces cyclooxygenase-2 in a phosphatidylinositol 3-kinase-dependent manner

The precise role of insulin-like growth factor (IGF)-1 in gastric ulcer healing is unknown. In experimental rat gastric ulcers, we examined expression of IGF-1 mRNA and protein by reverse transcriptase-polymerase chain reaction or enzyme-linked immunosorbent assay and immunostaining, respectively. In cultured rat gastric epithelial RGM1 cells, we examined effects of exogenous IGF-1 on cell migration, re-epithelialization, and proliferation-essential components of ulcer healing. We also examined whether IGF-1 induces cyclooxygenase (COX)-2 expression and determined the role of phosphatidylinositol 3-kinase and mitogen-activated protein kinase signaling pathways in mediating IGF-1 actions. Gastric ulceration triggered an approximately threefold increase in IGF-1 expression in epithelial cells of the ulcer margins (P < 0.001 versus control), especially in cells re-epithelizing granulation tissue and in mucosa in proximity to the ulcer margin. Treatment of RGM1 cells with IGF-1 caused a dramatic increase in actin polymerization, an eightfold increase in cell migration (P < 0.001), a 195% increase in cell proliferation (P < 0.05), and a sixfold increase in COX-2 expression (P < 0.01). Inhibitor of phosphatidylinositol 3-kinase abolished IGF-1-induced RGM1 cell migration and proliferation, actin polymerization, and COX-2 expression. The up-regulation of IGF-1 in gastric ulcer margin accelerates gastric ulcer healing by promoting cell re-epithelization, proliferation, and COX-2 expression via the phosphatidylinositol 3-kinase pathway.

Altered metaplastic response of waved-2 EGF receptor mutant mice to acute oxyntic atrophy

Metaplastic cell lineages are putative precursors for the development of gastric adenocarcinoma. The loss of parietal cells (oxyntic atrophy) is the initiating step in the evolution of gastric fundic mucosal lineage changes including metaplasia and hyperplasia. However, the intrinsic mucosal factors that promote and modulate the emergence of metaplastic phenotypes remain obscure. Over the past several years, we have studied pharmacologically induced, reversible oxyntic atrophy in rodents treated with DMP-777, a drug that acts as a parietal cell secretory membrane protonophore. DMP-777 elicits a rapid loss of parietal cells followed by the emergence of foveolar hyperplasia and spasmolytic polypeptide (SP)-expressing metaplasia (SPEM). The objective of the present study was to provide further insights into the intrinsic mucosal factors regulating the emergence of SPEM in the setting of oxyntic atrophy. We therefore studied the effects of DMP-777 administration on both SP/trefoil factor (TFF)2-deficient mice, which lack SP/TFF2, a marker of SPEM, and waved-2 mice, which harbor a point mutation in the EGF receptor that attenuates its tyrosine kinase activity. As in wild-type mice, treatment with DMP-777 for 7 days did elicit SPEM in SP/TFF2-deficient mice. These results suggest that SP/TFF2 does not impact on the development of metaplasia after the induction of parietal cell loss. In contrast, waved-2 homozygous mice displayed accelerated SPEM development by 3 days of treatment with DMP-777. These findings indicate that attenuation of EGF receptor signaling in waved-2 mice does elicit a more rapid emergence of SPEM. The results support a role for EGF receptor ligands in the regulation of gastric metaplasia.

Restitution of single-cell defects in the mouse colon epithelium differs from that of cultured cells

Integrity of colon epithelium is of crucial importance and, as small defects occur constantly, rapid repair (restitution) is essential. To investigate the mechanism of restitution, single-cell lesions were induced in mouse colonic surface epithelia by iontophoretic injection of Ca2+. Closure of the resulting defects was monitored using confocal laser scanning microscopy (CLSM), and functional sealing by electrophysiological techniques. Restitution was evaluated as the time constant tau of the exponential decrease in conductance of an induced leak and amounted to 0.28 min under control conditions. After 4 min, the leak was completely sealed. Repair was thus considerably faster than in previously investigated HT-29/B6 cells (tau=5.73 min). As in cultured cells, cytochalasin D delayed restitution in native colon epithelia (tau=0.69 min), indicating the involvement of actin in the healing process; however, no accumulation of actin surrounding the lesion was detected. Long-term incubation of epithelia with IFN-gamma alone or in combination with TNF-alpha increased tau to 0.49 and 0.59 min, respectively. In contrast to cultured cells, TNF-alpha alone did not affect restitution. A brief (<10 min) exposure to the sterile filtered supernatant of hemolytic E. coli O4 cultures did not affect the morphology of the epithelium, but delayed restitution. In CLSM studies, defects were still clearly visible 4 min after the onset of lesion induction. The supernatant of a nonhemolytic E. coli O4 mutant did not exhibit this effect. In conclusion, single-cell defects in native colon cause functional leaks that seal faster than in cell cultures. Proinflammatory cytokines and pathogenic bacteria delay restitution. This suggests a key role of very small lesions at the onset of pathogenic processes in the intestine.

Establishment of human gastric epithelial (HGE) cell lines exhibiting barrier function, progenitor, and prezymogenic characteristics

The unavailability of human cell lines representative of the gastric glandular epithelium while able to form a functional barrier restricts the application of a cell culture approach to the field of gastric epithelial physiology. In the current study, we have characterized new non-transfected clones isolated from gastric carcinoma cell lines known to express functional markers of the human gastric mucosa (J Cell Biochem 2001;81:241). Twenty-one clones exhibiting epithelial-type junctions (renamed HGE cell lines) were isolated from NCI-N87 (ATCC CRL 5822), whereas only squamous cell lines could be generated from other native strains. Of these 21 clones, HGE-17 and HGE-20 formed dense coherent monolayers and displayed true epithelial phenotype. E-cadherin and ZO-1 proteins were consistently localized at the periphery of all cells which also generated transepithelial electrical resistance. Moreover, growth factors known to be trophic for the gastric mucosa were able to stimulate mitogenesis at subconfluence. HGE-17 exhibited a poorly differentiated precursor-like status and responded strongly to EGF/TGFalpha treatment in restitution assays. HGE-20 cells, on the other hand, exhibited a higher degree of differentiation at the ultrastructural level as well as higher gastric lipase and pepsinogen levels. These latter zymogens were compartmentalized into granules which also contained mucin-6 (MUC6, prezymogenic-like status). Exogenous hormones, i.e., 1 mug/ml hydrocortisone and 5 microM retinoic acid, significantly increased enzyme levels in HGE-20. In conclusion, HGE-17 and HGE-20 represent the first human gastric cell lines with true epithelial characteristics, opening a venue to important applications for the study of re-epithelization, permeability, and regulation of digestive functions in the context of gastric physiology and pathology.

Preventive effect of hydrotalcite on gastric mucosal injury in rats induced by taurocholate

AIM: To study the preventive effect of hydrotalcite on gastric mucosal injury in rat induced by taurocholate, and to investigate the relationship between the protective mechanism of hydrotalcite and the expression of trefoil factor family 2 (TFF2) mRNA and c-fos protein.

METHODS: Forty five male Wistar rats were randomly divided into hydrotalcite group, ranitidine group and control group. Gastric mucosal injury was induced by introgastric acidified taurocholate. OD value of TFF2 mRNA expression in gastric mucous cells was determined by hybridization and computer image analysis system. OD value of c-fos protein expression in gastric mucous cells was measured by immunohistochemistry and computer image analysis system.

RESULTS: The gross mucosal injury index in hydrotalcite group was significantly lower than that in ranitidine group and control group (8.60 ± 2.20 vs 16.32 ± 4.27, 29.53 ± 5.39; P < 0.05, P < 0.01). The expression level of TFF2 mRNA in hydrotalcite group was markedly higher than that in ranitidine group and control group (0.56 ± 0.09 vs 0.30 ± 0.05, 0.28 ± 0.03, P < 0.05). The OD value of c-fos protein in hydrotalcite group was higher than that in ranitidine group and control group (0.52 ± 0.07 vs 0.31 ± 0.04, 0.32 ± 0.05, P < 0.05).

CONCLUSION: Hydrotalcite can protect gastric mucosal injury in rats induced by taurocholate, which may be related to the increased expression of TFF2 and c-fos protein.

Clinical, cellular, and molecular aspects of cancer invasion

Invasion causes cancer malignancy. We review recent data about cellular and molecular mechanisms of invasion, focusing on cross-talk between the invaders and the host. Cancer disturbs these cellular activities that maintain multicellular organisms, namely, growth, differentiation, apoptosis, and tissue integrity. Multiple alterations in the genome of cancer cells underlie tumor development. These genetic alterations occur in varying orders; many of them concomitantly influence invasion as well as the other cancer-related cellular activities. Examples discussed are genes encoding elements of the cadherin/catenin complex, the nonreceptor tyrosine kinase Src, the receptor tyrosine kinases c-Met and FGFR, the small GTPase Ras, and the dual phosphatase PTEN. In microorganisms, invasion genes belong to the class of virulence genes. There are numerous clinical and experimental observations showing that invasion results from the cross-talk between cancer cells and host cells, comprising myofibroblasts, endothelial cells, and leukocytes, all of which are themselves invasive. In bone metastases, host osteoclasts serve as targets for therapy. The molecular analysis of invasion-associated cellular activities, namely, homotypic and heterotypic cell-cell adhesion, cell-matrix interactions and ectopic survival, migration, and proteolysis, reveal branching signal transduction pathways with extensive networks between individual pathways. Cellular responses to invasion-stimulatory molecules such as scatter factor, chemokines, leptin, trefoil factors, and bile acids or inhibitory factors such as platelet activating factor and thrombin depend on activation of trimeric G proteins, phosphoinositide 3-kinase, and the Rac and Rho family of small GTPases. The role of proteolysis in invasion is not limited to breakdown of extracellular matrix but also causes cleavage of proinvasive fragments from cell surface glycoproteins.

Apical EGF receptors regulate epithelial barrier to gastric acid: endogenous TGF-alpha is an essential facilitator

In previous studies, we found that apical and basolateral EGF receptors (EGFR) on primary canine gastric monolayers decreased paracellular permeability, evident by increased transepithelial electrical resistance (TER) and decreased flux of [(3)H]mannitol (MF). After studying monolayers in Ussing chambers, we now report that treatment with apical, but not basolateral, EGF enhanced tolerance to apical H(+), evident by a slower decay in TER and an attenuated rise in MF. Enhanced tolerance to apical acid was evident within 10 min of treatment with apical EGF. Immunoneutralization of endogenous transforming growth factor (TGF)-alpha accelerated the drop in TER and the rise in MF in response to apical acidification; apical EGF reversed these effects. Study of monolayers cultured in Transwell inserts showed that immunoblockade of basolateral, but not apical, EGFR also impaired the resistance to apical acidification and enhanced MF. We conclude that apical EGFR regulates the barrier to apical acidification via effects on paracellular resistance. Although exogenous basolateral EGF has a less apparent effect on the barrier to acid, endogenous ligand active at basolateral EGFR plays an important role in maintaining the barrier to apical acid. Our data implicate a role for an apical EGFR ligand, which may be EGF or another member of the EGF family.

Secretin regulates paracellular permeability in canine gastric monolayers by a Src kinase-dependent pathway

Previous studies found that epidermal growth factor (EGF) decreased paracellular permeability in gastric mucosa, but the other physiological regulators and the molecular mechanisms mediating these responses remain undefined. We investigated the role of secretin and Src in regulating paracellular permeability because secretin regulates gastric chief cell function and Src mediates events involving the cytoskeletal-membrane interface, respectively. Confluent monolayers were formed from canine gastric epithelial cells in short-term culture on Transwell filter inserts. Resistance was monitored in the presence of secretin with or without specific kinase inhibitors. Tyrosine phosphorylation of Src at Tyr(416) was measured with a site-specific phosphotyrosine antibody. Basolateral, but not apical, secretin at concentrations from 1 to 100 nM dose dependently increased resistance; this response was rapid and sustained over hours. PP2 (10 microM), a selective Src tyrosine kinase inhibitor, but not the inactive isomer PP3, abolished the increase in resistance by secretin but only modestly attenuated apical EGF effects. AG-1478 (100 nM), a specific EGF receptor tyrosine kinase inhibitor, attenuated the resistance increase to EGF but not secretin. Secretin, but not EGF, induced tyrosine phosphorylation of Src at Tyr(416) in a dose-dependent fashion, with the maximal response observed at 1 min. PP2, but not PP3, dramatically inhibited this tyrosine phosphorylation. Secretin increases paracellular resistance in gastric mucosa through a Src-mediated pathway, while the effect of EGF is Src independent. Src appears to mediate the physiological effects of this G(s)-coupled receptor in primary epithelial cells.

Regulation of parietal cell migration by gastrin in the mouse

Recent studies suggest that gastrin regulates parietal cell maturation. We asked whether it also regulates parietal cell life span and migration along the gland. Dividing cells were labeled with 5'-bromo-2'-deoxyuridine (BrdU), and parietal cells were identified by staining with Dolichos biflorus lectin. Cells positive for D. biflorus lectin and BrdU were reliably identified 10-30 days after BrdU injection in mice in which the gastrin gene had been deleted by homologous recombination (Gas-KO) and wild-type (C57BL/6) mice. The time course of labeling was similar in the two groups. The distribution of BrdU-labeled parietal cells in wild-type mice was consistent with migration to the base of the gland, but in Gas-KO mice, a higher proportion of BrdU-labeled cells was found more superficially 20 and 30 days after BrdU injection. Conversely, in transgenic mice overexpressing gastrin, BrdU-labeled parietal cells accounted for a higher proportion of the labeled pool in the base of the gland 10 days after BrdU injection. Gastrin, therefore, stimulates movement of parietal cells along the gland axis but does not influence their life span.

In situ correlation of cytokine secretion and apoptosis in Helicobacter pylori-associated gastritis

Tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) are important for the pathogenesis of Helicobacter pylori-associated gastritis and peptic ulcer disease. Gastric biopsies from H. pylori-positive and -negative patients were used to examine the in situ correlation of TNF-alpha and IFN-gamma with epithelial cell apoptosis, bacterial load, and histological parameters of gastritis. From the same patients, we isolated H. pylori-specific T cell lines and clones and examined their ex vivo release of proinflammatory cytokines. We found a highly significant correlation of TNF-alpha and IFN-gamma production with activity and grade of gastritis (P < 0.01), H. pylori density (P = 0.01), epithelial cell apoptosis (P < 0.001), and Fas/Fas-ligand expression (P < 0.001). T cell lines and clones were all TCR-alphabeta(+) and showed T helper 1 functional phenotype. With the use of serial histological sections, this study showed for the first time the in situ correlation of TNF-alpha and IFN-gamma with epithelial cell apoptosis, bacterial load, and histological severity of disease and emphasizes the role of these cytokines in the pathophysiology of H. pylori-associated disease.

Inducible nitric oxide synthase mediates early epithelial repair of porcine ileum

Reports conflict regarding the effect of nitric oxide (NO) on intestinal epithelium. In chronic injury, NO appears detrimental by combining with reactive oxygen to form potent-free radicals. In contrast, inhibition of NO synthesis after acute injury exacerbates damage and inflammation. Recent studies have disclosed constitutive expression of inducible NO synthase (iNOS) by normal intestinal epithelia, yet little attention has been given to the role of iNOS in acute epithelial repair. We studied the local effects of iNOS on early epithelial repair of porcine ileal mucosa injured by deoxycholate within Ussing chambers. iNOS was constitutively expressed by the villous epithelium, and after deoxycholate injury, iNOS was expressed by injured and detaching enterocytes. Selective inhibition of iNOS abolished increases in NO synthesis and villous reepithelialization after injury. Exogenous L-arginine rescued baseline reepithelialization from NOS inhibitors but was only capable of stimulating additional repair in the presence of serum. These results demonstrate that iNOS-derived NO is a key mediator of early villous reepithelialization following acute mucosal injury.

Apical and basolateral EGF receptors regulate gastric mucosal paracellular permeability

Previous studies found that monolayers formed from canine oxyntic epithelial cells in primary culture displayed remarkable resistance to apical acidification and both mitogenic and migratory responses to epidermal growth factor (EGF) treatment. In our present studies, we found that EGF increased transepithelial resistance (TER) but not short-circuit current in these monolayers. Parallel effects of EGF on decreasing mannitol flux and increasing TER implicate direct regulation of paracellular permeability. EGF acting at either apical and basolateral receptors rapidly increased TER, but the apical response was sustained whereas the basolateral response was transient. (125)I-labeled EGF binding revealed specific apical binding, but receptor numbers were 25-fold lower than on the basolateral surface. Both apical and basolateral EGF activated tyrosine phosphorylation of EGF receptors (EGFR), beta-catenin, and cellular substrate as evident on confocal microscopy. Although apical EGF activated a lesser degree of receptor autophosphorylation than basolateral EGF, phosphorylation of beta-catenin was equally prominent with apical and basolateral receptor activation. Together, these findings indicate that functional apical and basolateral EGFR exist on primary canine gastric epithelial cells and that these receptors regulate paracellular permeability. The sustained effect of apical EGFR activation and prominent phosphorylation of beta-catenin suggest that apical EGFR may play a key role in this regulation.

Induction of scattering and cellular invasion by trefoil peptides in src- and RhoA-transformed kidney and colonic epithelial cells

Trefoil factors (TFFs) are protease-resistant peptides that promote epithelial cell migration and mucosal restitution during inflammatory conditions and wound healing in the gastrointestinal tract. To date, the molecular mechanism of TFFs action and their possible role in tumor progression are unclear. In the present study, we observed that premalignant human colonic PC/AA/C1 and canine kidney MDCK epithelial cells are not competent to invade collagen gels in response to exogenously added TFFs (pS2, spasmolytic polypeptide, and intestinal trefoil factor). In contrast, activated src and RhoA exert permissive induction of invasion by the TFFs that produce similar parallel dose-response curves in src-transformed MDCKts.src and PCmsrc cells (EC50=20-40 nM). Cell scattering is also induced by TFFs in MDCKts.src cells. Stable expression of the pS2 cDNA promotes constitutive invasiveness in MDCKts.src-pS2 cells and human colonic HCT8/S11-pS2 cells established from a sporadic tumor. Furthermore, we found that TFF-mediated cellular invasion is dependent of several signaling pathways implicated in cell transformation and survival, including phosphoinositide PI3'-kinase, phospholipase C, protein kinase C, and the rapamycin target TOR. Constitutive and intense expression of pS2 was revealed by Western blot analyses and immunohistochemistry in human colorectal tumors and their adjacent control mucosa during the neoplastic progression, from the adenoma to the liver metastases. Our studies indicated that TFFs can be involved in cell scattering and tumor invasion via autocrine loops and may serve as potential targets in the control of colon cancer progression.

Aging alters gastric mucosal responses to epidermal growth factor and transforming growth factor-alpha

Administration of pharmacological doses of epidermal growth factor (EGF) or transforming growth factor-alpha (TGF-alpha) in young rats stimulates gastric mucosal proliferation, but, in aged rats, the same treatment inhibits proliferation. This may be due to enhanced ligand-induced internalization of EGF receptor (EGFR). In support of this, we demonstrated that although a single injection of EGF (10 microg/kg) or TGF-alpha (5 microg/kg) in young (4-6 mo old) rats greatly increased membrane-associated EGFR tyrosine kinase activity, the same treatment slightly inhibited the enzyme activity in aged (24 mo old) rats. This treatment also produced a greater abundance of punctate cytoplasmic EGFR staining in gastric epithelium of aged rats, consistent with EGFR internalization. In vitro analyses demonstrated that exposure of isolated gastric mucosal cells from aged but not young rats to 100 pM TGF-alpha resulted in marked increases in intracellular EGFR tyrosine kinase activity and that induction of EGFR tyrosine kinase activity in mucosal membranes from aged rats occurred at doses 1,000-fold less than those required in young rats. Our data suggest that aging enhances sensitivity of the gastric mucosa to EGFR ligands. This may partly explain EGFR-mediated inhibition of gastric mucosal proliferation in aged rats.