TGF-beta signaling pathway: its role in gastrointestinal pathophysiology and modulation of ulcer healing

Gastrointestinal ulcer healing is a complex process, involving cell migration, proliferation, angiogenesis and extracellular matrix deposition, all ultimately leading to reconstruction of tissue architecture within the ulcer scar. These processes are controlled by growth factors, cytokines and hormones. Transforming growth factor-beta (TGF-beta), one of the multifunctional peptide growth factors, has been reported to positively regulate gastrointestinal ulcer healing. Although TGF-beta inhibits cell proliferation in a variety of cells, it induces cell migration, angiogenesis, and enhances extracellular matrix production necessary for gastrointestinal ulcer healing. TGF-beta exerts its action by binding to its transmembrane serine/threonine kinase receptors, which in turn triggers activation of various intracellular signaling pathways. Smads are intermediate effector proteins that play key roles in biological activities of TGF-beta by transmitting the signals from the cell surface directly into the nucleus and initiating transcription. New insight into the mechanisms underlying TGF-beta-Smad modulation of gastrointestinal ulcer healing will likely enhance our understanding of the mechanisms controlling the healing processes of gastrointestinal ulcers.

Reduced expression of epidermal growth factor receptor related protein in gastric cancer

OBJECTIVES

The recently cloned epidermal growth factor receptor related protein (ERRP) has been proposed to be a negative regulator of the epidermal growth factor receptor (EGFR). Because of the causal involvement of EGFR and its ligands in gastric cancer growth, we investigated expression of ERRP and cell proliferation in human gastric cancer.

METHODS

We examined ERRP expression and localisation in surgical specimens of gastric cancers from 47 patients versus non-malignant gastric mucosa and determined their relationship to cell proliferation and differentiation. We also examined expression of ERRP by western blotting in three different gastric cancer cell lines. To further determine the functional properties of ERRP, we examined the effect of ERRP on epidermal growth factor (EGF) induced EGFR phosphorylation essential for its activation in MKN-28 gastric cancer cells.

RESULTS

ERRP expression was dramatically reduced in gastric cancers (34% of all specimens positive) compared with non-malignant gastric mucosa (66% of specimens positive). Expression of ERRP in cancer cells inversely correlated with cell proliferation and grade of malignancy. Cell lines derived from metastatic gastric cancers had reduced ERRP expression compared with cell lines derived from a non-metastatic cancer. Exogenous ERRP protein markedly inhibited EGF induced EGFR phosphorylation in gastric cancer cells providing a novel molecular mechanism of its action.

CONCLUSIONS

Our data indicate that downregulation of ERRP could play an important role in gastric cancer differentiation and progression. ERRP is a negative regulator of tumour cell proliferation and may exert its inhibitory effect, in part, by attenuating EGFR activation.

Survivin: a novel target for indomethacin-induced gastric injury

BACKGROUND & AIMS

Nonsteroidal anti-inflammatory drugs (NSAIDs) cause gastrointestinal erosions and ulcers. Apoptosis is one of the mechanisms. The role of survivin, an antiapoptosis protein, in NSAID-induced gastric injury is unknown. We examined the role of survivin in NSAID-induced gastric mucosal and gastric cell injury.

METHODS

We examined: (1) the effects of indomethacin (nonselective NSAID), celecoxib and NS-398 (cyclooxygenase [COX]-2-selective NSAIDs), SC-560 (a COX-1-selective NSAID), and SC-560 plus celecoxib on survivin expression and extent of injury in rat gastric mucosa; (2) the effects of indomethacin, NS-398, SC-560, and SC-560 plus NS-398 on survivin expression and injury in gastric epithelial (RGM-1) cells; and (3) the effects of survivin suppression with small interfering RNA (siRNA) on RGM-1 cell integrity at baseline and following indomethacin injury.

RESULTS

Indomethacin treatment dose-dependently reduced survivin protein levels and caused severe injury of gastric mucosa and RGM-1 cells. Suppression of survivin expression with siRNA in RGM-1 cells caused cell damage and increased susceptibility to injury by indomethacin. Celecoxib treatment caused exfoliation of the mucosal surface epithelium, but neither caused deep erosions or altered survivin expression. Neither NS-398 nor SC-560 treatment altered survivin levels or produced injury in vivo or in vitro. COX-1 and COX-2 inhibitor combination caused injury in vivo and in vitro but did not decrease survivin expression.

CONCLUSIONS

(1) Indomethacin, but not selective COX-1 or COX-2 inhibitors alone or in combination, reduces survivin expression in gastric mucosal cells and (2) significant reduction of survivin precedes greater severity of gastric injury.

PTEN regulatory functions in tumor suppression and cell biology

PTEN is a dual-specificity phosphatase with both protein phosphatase and lipid phosphatase activity. PTEN is the first phosphatase identified as a tumor suppressor. Not since the discovery of p53 has a tumor suppressor generated such interest. Initial studies performed on cancer cell lines suggested that PTEN may be responsible for almost all types of cancer, both solid tumors and hematological malignancies. Biallelic deletion of PTEN has been associated with advanced stage tumors or metastatic disease. PTEN has been shown to play a pivotal role in apoptosis, cell cycle arrest, and possibly cell migration. Emerging data suggest that this may be an oversimplification of PTEN's role, and that PTEN may be haploinsufficient for tumor progression and may play important roles in other cellular functions such as angiogenesis and MAP kinase signaling.

Serum response factor is a critical requirement for VEGF signaling in endothelial cells and VEGF-induced angiogenesis

Angiogenesis, new capillary blood vessel formation, is essential for embryonic development, wound healing, and cancer growth. Vascular endothelial growth factor (VEGF) induces angiogenesis by activating endothelial cell migration and proliferation. Serum response factor (SRF) is a transcription factor important for embryonic development and activation of immediate early gene expression. The roles of SRF in endothelial cell biology and angiogenesis have not been explored. Here we demonstrate that SRF is a downstream mediator of VEGF signaling in endothelial cells and a critical requirement for VEGF-induced angiogenesis. Knockdown of SRF protein levels in human and rat endothelial cells abolished VEGF-induced in vitro angiogenesis, impaired endothelial cell migration and proliferation, and inhibited VEGF-induced actin polymerization and immediate early gene expression. Injection of SRF antisense expression plasmid into gastric ulcers in rats significantly inhibited in vivo angiogenesis in granulation tissue. Mechanistically, this study also revealed that VEGF promotes SRF expression and nuclear translocation and increases SRF binding activity to DNA in endothelial cells through both Rho-actin and MEK-ERK dependent signaling pathways. These findings have potential therapeutic implications, e.g., local anti-SRF treatment may inhibit angiogenesis crucial for tumor growth.

NSAIDs activate PTEN and other phosphatases in human colon cancer cells: novel mechanism for chemopreventive action of NSAIDs

Studies on chemoprevention of colorectal cancer have generated increasing interest. The mechanisms involved in NSAIDs chemopreventive action are not fully elucidated. In this study, we examined in human colon cancer cells the effect of indomethacin and NS-398 (a pre-clinical selective COX-2 inhibitor) on expression of 96 genes of the EGF/PDGF signaling pathways essential for cell proliferation, migration, and survival. We found that indomethacin and NS-398 treatment significantly upregulated expression of the tumor suppressor gene, PTEN, the MAP kinase phosphatase-3, MKP-3, and the protein tyrosine phosphatase, SHP2. Additionally, NS-398 treatment increased expression of apoptotic genes such as BAD, STAT1, and CASP3. These results suggest that as a consequence of increased expression of phosphatases such as PTEN and the resulting dephosphorylation of kinases, NSAIDs can negatively regulate the EGF/PDGF pathways in colon cancer cells-a novel mechanism for NSAIDs' chemopreventive actions.

Serum response factor promotes re-epithelialization and muscular structure restoration during gastric ulcer healing

BACKGROUND & AIMS

Serum response factor (SRF) regulates transcription of immediate early genes and muscle genes. In this study, we examined the role of SRF in gastric ulcer healing and the mechanisms involved.

METHODS

Gastric ulcers were induced in rats by serosal application of acetic acid. Gastric specimens were obtained sequentially after ulcer induction for analyses of SRF messenger RNA (mRNA), protein expression, and for immunohistochemistry. We examined the role of SRF in ulcer healing by local injection of an SRF expression plasmid into ulcers (gene therapy). To elucidate the cellular mechanisms of the action of SRF, we examined the effect of SRF overexpression on actin dynamics, cell migration, and proliferation in rat gastric epithelial cell (RGM1) and smooth muscle cell (A7R5). To determine the clinical relevance, we examined SRF expression in human gastric ulcer specimens.

RESULTS

Gastric ulceration activated SRF expression in epithelial cells lining regenerating glands and in myofibroblasts and smooth muscle cells of granulation tissue. SRF up-regulation in human gastric ulcers was similar to that found in rat gastric ulcers. Gene therapy with SRF significantly accelerated experimental gastric ulcer healing and promoted re-epithelialization and muscle restoration. Overexpression of SRF in RGM1 and A7R5 cells accelerates migration and proliferation of these cells by promoting actin polymerization and activation of immediately early genes.

CONCLUSIONS

Activation of SRF is an important component of ulcer healing. SRF promotes migration and proliferation of gastric epithelial and smooth muscle cells, which are essential for re-epithelialization and restoration of muscular structures.

Dual actions of nitric oxide on angiogenesis: possible roles of PKC, ERK, and AP-1

Regulation of angiogenesis by nitric oxide (NO) is controversial since NO has been shown to have both pro- and anti-angiogenic effects. In this study, we examined the effect of the NO donor, S-nitro-N-acetyl-penicillamine (SNAP), on in vitro angiogenesis, and the mechanisms involved: PKC activity, ERK and c-Jun phosphorylation, and AP-1 DNA binding activity, in microvascular endothelial cells. SNAP, at 0.5-4 mM, significantly and dose-dependently inhibited angiogenesis, PKC activity, and ERK and c-Jun phosphorylation up to 80%, 83%, and 63% and 73%, respectively. SNAP at concentrations > 2mM also abolished AP-1 binding activity. Lower concentrations of SNAP (0.1-0.3 mM) significantly increased angiogenesis, PKC activity, and ERK and c-Jun phosphorylation up to 46%, 60%, and 61% and 180%, respectively. These findings indicate that the dual pro- and anti-angiogenic actions of NO are dose-dependent and suggest that they are mediated by PKC and ERK acting on AP-1.

Deoxycholic acid activates beta-catenin signaling pathway and increases colon cell cancer growth and invasiveness

Colorectal cancer is often lethal when invasion and/or metastasis occur. Tumor progression to the metastatic phenotype is mainly dependent on tumor cell invasiveness. Secondary bile acids, particularly deoxycholic acid (DCA), are implicated in promoting colon cancer growth and progression. Whether DCA modulates beta-catenin and promotes colon cancer cell growth and invasiveness remains unknown. Because beta-catenin and its target genes urokinase-type plasminogen activator receptor (uPAR) and cyclin D1 are overexpressed in colon cancers, and are linked to cancer growth, invasion, and metastasis, we investigated whether DCA activates beta-catenin signaling and promotes colon cancer cell growth and invasiveness. Our results show that low concentrations of DCA (5 and 50 microM) significantly increase tyrosine phosphorylation of beta-catenin, induce urokinase-type plasminogen activator, uPAR, and cyclin D1 expression and enhance colon cancer cell proliferation and invasiveness. These events are associated with a substantial loss of E-cadherin binding to beta-catenin. Inhibition of beta-catenin with small interfering RNA significantly reduced DCA-induced uPAR and cyclin D1 expression. Blocking uPAR with a neutralizing antibody significantly suppressed DCA-induced colon cancer cell proliferation and invasiveness. These findings provide evidence for a novel mechanism underlying the oncogenic effects of secondary bile acids.

Cysteamine alters redox state, HIF-1alpha transcriptional interactions and reduces duodenal mucosal oxygenation: novel insight into the mechanisms of duodenal ulceration

Our recent studies demonstrated a critical role of enhanced transcriptional activity of early growth response factor-1 (Egr-1) in early stages of cysteamine-induced duodenal ulcer in rats. Since cysteamine is also a reducing agent, the aims of this study were to determine the effect of cysteamine on proximal duodenal mucosa: (a) redox status, (b) mucosal oxygenation, (c) expression of hypoxia-inducible factor 1 (HIF-1alpha) and its binding to DNA, and (d) HIF-1alpha interaction with Egr-1 and other redox-sensitive transcription factors. Here we demonstrate for the first time that cysteamine treatment reduced the duodenal oxygenation by 19% (vs. baseline) and markedly increased the redox status in duodenal mucosa (p<0.05). Cysteamine increased HIF-1alpha expression, its binding to DNA, and enhanced the HIF-1alpha interactions with Egr-1 and other transcription factors (e.g., AP-1, AP-2, L-III BP, NF-E1, NF-E2, STAT4, and MRE), their binding to DNA. Thus, these data demonstrate the involvement of the redox-dependent regulatory mechanisms in the early stages of duodenal ulceration.

Overexpression of metastatic tumor antigen 1 in hepatocellular carcinoma: Relationship to vascular invasion and estrogen receptor-alpha

The morbidity and mortality experienced by cancer patients is mainly due to the invasion and metastasis of the primary tumor. Recently, a potential metastasis-associated gene and its product, the metastatic tumor antigen 1 (MTA1), were identified; this gene has been found to be overexpressed in a variety of cancers. MTA1 is also known as a potent co-repressor of estrogen receptor element transcription in breast cancer cells. The expression of MTA1 in hepatocellular carcinoma (HCC) and its potential relationship to metastasis and to estrogen receptor alpha (ER-alpha) expression has not been examined, forming the basis for this study. Paraffin sections of 45 HCC specimens, 4 different HCC cell lines, and normal hepatocyte cell line (h NHeps) were immunostained with MTA1 and ER-alpha antibodies. In addition, we examined, by Western blotting, the MTA1 and ER-alpha expression levels in 4 human HCC lines (HepG2 [wild p53], HLE, HLF, and HuH-7 [mutant p53]). MTA1 was overexpressed in HCC cells versus nonmalignant hepatocytes in 31 of 45 HCC specimens (69%). Its expression was predominantly localized to the nucleus or cytoplasm of HCC cells. Nineteen of 20 HCC (95%) specimens with vascular invasion displayed strong MTA1 expression. Overexpression of MTA1 also significantly correlated with large tumor size. The cytoplasmic and nuclear immunoreactivity for ER-alpha was present in HCC specimens in 46% and 12%, respectively. Expression of MTA1 inversely correlated with the nuclear localization of ER-alpha. There was no marked difference in MTA1 and ER-alpha expression levels between HCC cell line expressing wild-type p53 and cell line with mutated p53 HCC. In conclusion, these findings indicate that overexpression of MTA1 is associated with HCC growth and vascular invasion. Nuclear translocation of ER-alpha inversely correlated with MTA1 expression, suggesting negative regulatory mechanisms.

Rebamipide activates genes encoding angiogenic growth factors and Cox2 and stimulates angiogenesis: a key to its ulcer healing action?

Clinical and experimental data indicate that rebamipide accelerates ulcer healing, improves scar quality, and prevents ulcer recurrence. However, the mechanisms responsible for these rebamipides' actions are not fully elucidated. We studied, using gene expression microarray analysis, which of the ulcer healing genes are activated by rebamipide treatment. Normal rat gastric epithelial cells (RGM1) were treated with either vehicle or rebamipide. Gene expression was determined using Affymetrix rat genome U34A gene chip arrays and data were analyzed using the GeneSpring program. Activation of some of the genes and protein translation were also examined by RT/PCR and Western blotting. Rebamipide significantly upregulated the proangiogenic genes encoding vascular endothelial growth factor (VEGF), by 7.5-fold, heparin binding epidermal growth-like factor (HB-EGF), by approximately 5-fold, fibroblast growth factor receptor-2 (FGFR2), by 4.4-fold, and cyclooxygenase-2 (Cox2), by 9.3-fold, as well as growth promoting genes, e.g., insulin growth factor-1 (IGF-1), by 5-fold. RT/PCR and Western blotting demonstrated that Cox2 mRNA and protein were upregulated; the latter, approximately 6-fold. Treatment of rat gastric mucosal endothelial cells with rebamipide stimulated in vitro angiogenesis by approximately 240% (vs. controls, P < 0.001). Conclusions are as follows. (1) Rebamipide activates in gastric epithelial RGM-1 cells a genetic program that promotes angiogenesis and signals cell growth and tissue regeneration. (2) In addition, rebamipide treatment directly stimulates angiogenesis in gastric microvascular endothelial cells. Thus rebamipide has two separate and distinct mechanisms of proangiogenic action: one through activation in gastric epithelial cells of proangiogenic growth factor genes and the second a direct angiogenic action on microvascular endothelial cells.

Reduced expression of epidermal growth factor receptor-related protein in hepatocellular carcinoma: implications for cancer growth

BACKGROUND/AIMS

The mitogenic signaling pathway of epidermal growth factor receptor (EGFR) is activated in a variety of cancers, including hepatocellular carcinoma (HCC). The recently cloned EGFR-related protein (ERRP) has been proposed to be a negative regulator of EGFR. The expression of ERRP in non-malignant liver cells and in HCC, and its relation to cell proliferation, have not been examined.

METHODS

Paraffin sections of formalin-fixed HCC specimens of 51 HCCs and 10 normal liver specimens were immunostained with anti-ERRP and anti-p53 antibodies. To determine the relationship between ERRP expression and cell proliferation, we performed double staining for ERRP and proliferating cell nuclear antigen (PCNA) in the same HCC specimens.

RESULTS

In normal liver, ERRP was expressed in 100% of specimens, while in non-malignant liver tissue from HCC, ERRP expression was present in 50% of the specimens (p < 0.001). In contrast, ERRP expression was present only in 14% of the HCC specimens. The expression of ERRP in cancer cells was inversely correlated with proliferative activity and tumor size (p < 0.001, p < 0.05, respectively). No significant correlation was found between p53 expression and the expression of ERRP.

CONCLUSIONS

Human HCC, which has been shown to be associated with increased activation of EGFR, exhibits a substantial reduction in ERRP expression. The inverse relationship between ERRP expression, proliferative activity of tumor cells and tumor size suggests that in some HCC, ERRP is a negative regulator of HCC growth.

Abnormal PTEN expression in portal hypertensive gastric mucosa: a key to impaired PI 3-kinase/Akt activation and delayed injury healing?

Phosphatase and tensin homologue deleted on chromosome ten (PTEN) is a dual-specificity phosphatase that has activity toward both phosphorylated peptides and phospholipids. PTEN inhibits activation of Akt, the downstream effector of PI 3-kinase, which is integral to cell proliferation, migration, survival, and angiogenesis essential for tissue injury healing. PTEN expression and activation during injury healing remain unexplored. Portal hypertensive (PHT) gastric mucosa has impaired injury healing, but the underlying mechanisms remain unknown. We investigated whether impaired healing of injured PHT gastric mucosa is due to abnormal PTEN expression/activation that leads to decreased Akt activation. We also investigated the possible involvement of Egr-1, which regulates PTEN in some cells (e.g., fetal kidney epithelial cells), and TNF-alpha, which can induce Egr-1 expression. In PHT gastric mucosa 6 h after injury, PTEN protein levels were increased by 2.7-fold; unphosphorylated PTEN (reflecting activated PTEN) was increased by 2.4-fold; Akt phosphorylation (reflecting Akt activation) was reduced by 2-fold; and Egr-1 expression was increased by 3.3-fold vs. normal gastric mucosa. TNF-alpha neutralization reversed all of the above abnormalities in PHT gastric mucosa, reduced mucosal injury, and enhanced healing. We conclude that, in injured PHT gastric mucosa, overexpressed/activated PTEN leads to the reduced activation of the PI 3-kinase/Akt pathway that results in impaired injury healing.

Helicobacter pylori infection inhibits healing of the wounded duodenal epithelium in vitro

Helicobacter pylori (Hp) infection causes duodenal ulcers, delays the healing of such ulcers, and is associated with ulcer recurrence. The pathogenic mechanisms involved in Hp-induced duodenal mucosal injury and delay in ulcer healing remain unclear. In this study we sought to investigate the possible pathogenic actions of Hp infection and vacuolating cytotoxin (Vac A) on duodenal epithelial wound healing, using an in vitro wound model consisting of excisionally scraped or eroded IEC-6 duodenal monolayers. Two isogenic strains of Hp were used: wild-type strain 60190, producing Vac A; and an isogenic mutant strain, 60190-v1, that lacks the gene to produce the cytotoxin. The addition of Vac A-positive or Vac A-negative Hp (50:1 ratio of bacterial to epithelial cells) to the eroded or "wounded" IEC-6 monolayers resulted in significant inhibition of wound reepithelialization. The Vac A-positive Hp produced significantly greater inhibition than did the Vac A-negative Hp (70% and 35% inhibition, respectively; P <.001). Additionally, the bacterial supernatant containing Vac A (but not the supernatant lacking the cytotoxin) caused significant inhibition of IEC-6 wound reepithelialization in the absence of Hp infection, indicating that Vac A has an independent inhibitory action on wound reepithelialization. The Vac A inhibition of IEC-6 reepithelialization correlated with down-regulation of actin stress fibers in the migrating cells. Epidermal growth factor (EGF) stimulated IEC-6 wound reepithelialization with a corresponding increase in the formation of actin stress fiber. Vac A-positive bacterial supernatant (but not Vac A-negative supernatant) prevented the EGF-stimulated increase in IEC-6 actin stress fiber formation and wound reepithelialization. These findings demonstrate that Hp infection inhibits the process of duodenal epithelial wound healing. Hp inhibition of duodenal wound healing may therefore be an important pathogenic factor contributing to duodenal mucosal injury and delay in ulcer healing in vivo.

COX-2 is essential for EGF induction of cell proliferation in gastric RGM1 cells

Growth factors upregulate cyclooxygenase-2 (COX-2) expression and extracellular signal-regulated kinase (ERK) activity, yet little is known regarding the interaction between COX-2 and ERK in terms of mitogenic signal transduction pathways in gastric epithelial cells. Therefore, we examined the role of COX-2 in EGF-induced proliferation of gastric epithelial RGM1 cells. EGF treatment significantly induced ERK activity (peaked at 30 min) and significantly increased COX-2 protein (peaked at 6 hr), production of prostaglandin E2 (PGE2), and cell proliferation. MEK inhibitor (PD98059) decreased ERK activity and cell proliferation induced by EGF. The selective COX-2 inhibitor (NS-398) significantly reduced EGF-induced cell proliferation. Exogenous PGE2 partly reversed the NS-398-induced inhibitory action on cell proliferation, clearly indicating the importance of PGE2 in mitogenic pathway. The induction of COX-2 protein by EGF was completely blocked by preincubation with MEK inhibitor. These results suggest that the ERK-COX-2 pathway is critical for EGF-induced proliferation of gastric epithelial cells.

Nuclear translocation of survivin in hepatocellular carcinoma: a key to cancer cell growth?

Survivin is a recently described anti-apoptosis protein and regulator of cell division. Its expression and localization in hepatocellular carcinoma (HCC) and in normal liver tissue has not been fully elucidated. We examined the expression of survivin, Fas, proliferating cell nuclear antigen (PCNA), and apoptosis in 47 specimens of hepatocellular carcinoma (HCC) and surrounding nonmalignant hepatic tissues. To further determine the relationship between survivin expression and cell proliferation and apoptosis, we performed double immunostaining for survivin and PCNA TUNEL staining in the same HCC specimens. Positive immunostaining for survivin was present in 35 of 47 (74%) HCCs. Twenty-two of 35 survivin-positive HCCs (63%) showed punctate nuclear staining in HCC cells, and the remaining 13 showed predominant cytoplasmic staining. In contrast, nonmalignant hepatocytes showed only cytoplasmic staining. HCC cells had significantly higher PCNA-labeling and apoptotic indices compared with the case of nonmalignant hepatic tissue (P<0.001). Furthermore, nucleus-positive HCC specimens for survivin showed the highest PCNA labeling index. The nuclear localization of survivin in HCC cells correlated with tumor cell de-differentiation with the exception of the HepG2 cell line. Survivin expression was inversely associated with apoptosis and was strongly associated with Fas expression (P=0.01). All 4 HCC cell lines examined showed survivin expression and punctate nuclear localization. Our results indicate that survivin is localized to the cytoplasm in quiescent nonmalignant liver cells to suppress apoptosis and translocates into the nucleus in HCC cells. In conclusion, translocation of survivin from the cytoplasm to the nucleus may constitute an important regulatory mechanism for cell proliferation and differentiation in HCC.

Inhibition of angiogenesis by NSAIDs: molecular mechanisms and clinical implications

Angiogenesis, the formation of new capillary blood vessels, is a fundamental process essential for reproduction and embryonic development. It is crucial to the healing of tissue injury because it provides essential oxygen and nutrients to the healing site. Angiogenesis is also required for cancer growth and progression since tumor growth requires an increased nutrient and oxygen supply. Nonsteroidal anti-inflammatory drugs (NSAIDs) are the most widely used drugs worldwide for treating pain, arthritis, cardiovascular diseases, and more recently for colon cancer prevention. However, NSAIDs produce gastrointestinal ulcers and delay ulcer healing. Recently NSAIDs have been demonstrated to inhibit angiogenesis, but the underlying mechanisms are only beginning to be elucidated. The inhibition of angiogenesis by NSAIDs is a causal factor in the delay of ulcer healing, and it is becoming clear that this is also likely to be one of the mechanisms by which NSAIDs can reduce or prevent cancer growth. Based on the experimental data and the literature, the mechanisms by which NSAIDs inhibit angiogenesis appear to be multifactorial and likely include local changes in angiogenic growth factor expression, alteration in key regulators and mediators of vascular endothelial growth factor (VEGF), increased endothelial cell apoptosis, inhibition of endothelial cell migration, recruitment of inflammatory cells and platelets, and/or thromboxane A2 mediated effects. Some of these mechanisms include: inhibition of mitogen-activated protein (Erk2) kinase activity; suppression of cell cycle proteins; inhibition of early growth response (Egr-1) gene activation; interference with hypoxia inducible factor 1 and VEGF gene activation; increased production of the angiogenesis inhibitor, endostatin; inhibition of endothelial cell proliferation, migration, and spreading; and induction of endothelial apoptosis.

Prostaglandins promote colon cancer cell invasion; signaling by cross-talk between two distinct growth factor receptors

Colorectal cancer is the second most frequent cancer in the Western world, often lethal when invasion and/or metastasis occur. In addition to hepatocyte growth factor (HGF), colon cancer invasion may be driven by prostaglandins, especially the E2 series (PGE2), generated by the cyclooxygenase-2 (Cox-2) enzyme. While concentration of PGE2 as well as expression of Cox-2, HGF receptor (c-Met-R), epidermal growth factor receptor (EGFR), and beta-catenin are all dramatically increased in colon cancers and implicated in their growth and invasion, the precise role of PGE2 in the latter process remains unclear. Here we provide evidence that PGE2 transactivates c-Met-R (contingent upon functional EGFR), increases tyrosine phosphorylation and nuclear accumulation of beta-catenin, and induces urokinase-type plasminogen activator receptor (uPAR) mRNA expression. This is accompanied by increased beta-catenin association with c-Met-R and enhanced colon cancer cell invasiveness. Inactivation of EGFR and c-Met-R significantly reduced PGE2-induced cancer cell invasiveness. Clinical relevance of these findings is confirmed by our immunohistochemical studies demonstrating that cancer cells in the invasive front overexpress Cox-2, c-Met-R, and beta-catenin. Our findings explain a functional relationship between prostaglandins, EGFR, and c-Met-R in colon cancer growth and invasion.

Overexpression of VEGF and angiopoietin 2: a key to high vascularity of hepatocellular carcinoma?

Hepatocellular carcinoma (HCC) is becoming one of the most common malignant tumors worldwide and is characterized by a high vascularity. Angiogenesis, formation of new microvessels, is critical for the growth and progression of various human solid tumors. Vascular endothelial growth factor (VEGF) and angiopoietins (Ang1 and Ang2) are endothelial cell-specific vasculogenic and angiogenic growth factors, but their expression and roles in HCC have not been extensively explored. The aim of this study was to determine the expression and cellular localization of VEGF, Ang1, and Ang2 in specimens of resected human HCC using in situ hybridization and immunohistochemical staining and to examine their relationship to microvessel density (MVD) and tumor size. We also investigated whether mutation of p53 protein might affect the expression of the above angiogenic growth factors. VEGF and Ang2 were strongly expressed and localized predominantly to cancer cells, whereas Ang1 was detected in supportive cells of large blood vessels, stromal cells, endothelial cells, and tumor cells. Expression of the VEGF protein and the Ang2 (but not Ang1) mRNA were strongly correlated with MVD (P <.05, P =.001) and tumor size (P <.05). There was also a strong correlation between VEGF protein and Ang2 mRNA expression (P <.001). However, no significant correlation was found between overexpression of p53 and the expression of VEGF, angiopoietins, or MVD. These findings suggest that overproduction of the angiogenic growth factors VEGF and Ang2 by HCC cells may increase vascularity and tumor growth in a paracrine manner. Our findings also suggest that interaction between VEGF and Ang2 may play a critical role in tumor angiogenesis in HCC.

Survivin expression in the stomach: implications for mucosal integrity and protection

Survivin, an apoptosis inhibitor, is highly expressed in a majority of human cancers and is required during embryonic development. Our present studies show that survivin is also expressed in normal gastric mucosa of adult humans and rats. In both human and rat gastric mucosa, survivin is expressed predominantly in the nuclei of mucosal surface epithelial cells. In rats, survivin is also detected in the nuclei of some neck cells, whereas in the humans, survivin is expressed in both nuclei and cytoplasm of chief and parietal cells. Furthermore, survivin is expressed at higher levels in the nuclei of cultured gastric mucosal epithelial cells than in gastric microvascular endothelial cells, which supports the expression pattern in intact tissues. Based on these expression studies, and the known role of survivin as an anti-apoptosis protein, survivin may play a role in maintaining gastric mucosal integrity and regulating cell renewal in the gastric mucosa.

Survivin - an anti-apoptosis protein: its biological roles and implications for cancer and beyond

Survivin is a protein that inhibits apoptosis and regulates cell division. Survivin contains a baculovirus inhibitor of apoptosis repeat (BIR) protein domain that classifies it as a member of the inhibitor of apoptosis protein (IAP) family. Survivin inhibits apoptosis, via its BIR domain, by either directly or indirectly interfering with the function of caspases. Survivin is also a chromosomal passenger protein that is required for cell division. Survivin is expressed in embryonic tissues as well as in the majority of human cancers, but is not expressed in most normal adult tissues. The cancer-specific expression of survivin, coupled with its importance in inhibiting cell death and in regulating cell division, makes it a useful diagnostic marker of cancer and a potential target for cancer treatment. Recently, there is emerging evidence that survivin is involved in tissue injury and its healing. Understanding the mechanism of survivin function can potentially allow for the development of therapeutic strategies for cancer and other diseases.

Interaction of hepatocyte growth factor and non-steroidal anti-inflammatory drugs during gastric epithelial wound healing

BACKGROUND/AIMS

Expression of the hepatocyte growth factor (HGF) and cyclooxygenase-2 (COX-2) is upregulated at the margins of healing gastric ulcers. We investigated in vitro the interference of HGF, the selective COX-2 inhibitor NS-398 and the nonselective COX inhibitor indomethacin with gastric epithelial wound healing and actin microfilament (actin-MF) formation.

METHODS

Standardized gastric epithelial wounds, created in confluent RGM1 rat cell monolayers were treated with: HGF (10 ng/ml), NS-398 (1-100 microM) or indomethacin (0.01- 0.5 mM). The areas of re-epithelialization and cell proliferation were measured 24 h after wounding. Actin-MFs were labeled with fluorescein-conjugated phalloidin and their distribution was examined using a Nikon epifluorescence microscope.

RESULTS

HGF caused a significant increase in gastric monolayer wound re-epithelialization and this was not affected by mitomycin C. Both indomethacin and NS-398 inhibited HGF-stimulated re-epithelialization, but the basal wound re-epithelialization rate and cell proliferation was only significantly inhibited by indomethacin. HGF triggered actin stress fiber formation which was inhibited by both indomethacin and NS-398, but only indomethacin interfered with actin-MF formation at the baseline condition.

CONCLUSIONS

HGF significantly increased gastric wound re-epithelialization by activating cell migration which may be mediated by the COX-2 pathway.

Esophageal ulceration triggers expression of hypoxia-inducible factor-1 alpha and activates vascular endothelial growth factor gene: implications for angiogenesis and ulcer healing

Our previous studies demonstrated that enhanced epithelial cell proliferation is important for healing of experimental esophageal ulcers. However, the roles of angiogenesis, its major mediator, vascular endothelial growth factor (VEGF), and the mechanism(s) regulating VEGF expression during esophageal ulcer healing remain unknown. Esophageal ulcers were induced in rats by focal application of acetic acid. We studied expressions of hypoxia-inducible transcription factor-1 alpha (HIF-1 alpha), an activator of the VEGF gene, and VEGF by reverse transcriptase-polymerase chain reaction, Western blotting, and immunostaining. To determine the efficacy of VEGF gene therapy in esophageal ulcer healing, we studied whether a single local injection of plasmid cDNA encoding recombinant human VEGF(165) affects ulcer healing and angiogenesis. Esophageal ulceration induced HIF-1 alpha protein expression and VEGF gene activation reflected by increased VEGF mRNA (240%) and VEGF protein (310%) levels. HIF-1 alpha protein was expressed in microvessels bordering necrosis where it co-localized with VEGF. Injection of cDNA encoding VEGF(165) significantly enhanced angiogenesis and accelerated esophageal ulcer healing. These results: 1) suggest that HIF-1 alpha may mediate esophageal ulceration-triggered VEGF gene activation, 2) indicate an essential role of VEGF and angiogenesis in esophageal ulcer healing, and 3) demonstrate the feasibility of gene therapy for the treatment of esophageal ulcers.