The role of epidermal growth factor (EGF) and its receptor in mucosal protection, adaptation to injury, and ulcer healing: involvement of EGF-R signal transduction pathways

Regulation of mucin expression: mechanistic aspects and implications for cancer and inflammatory diseases

Mucins are large multifunctional glycoproteins whose primary functions are to protect and lubricate the surfaces of epithelial tissues lining ducts and lumens within the human body. Several lines of evidence also support the involvement of mucins in more complex biological processes such as epithelial cell renewal and differentiation, cell signaling, and cell adhesion. Recent studies have uncovered the role of select mucins in the pathogenesis of cancer, underscoring the importance of a detailed knowledge about mucin biology. Under normal physiological conditions, the production of mucins is optimally maintained by a host of elaborate and coordinated regulatory mechanisms, thereby affording a well-defined pattern of tissue-, time-, and developmental state-specific distribution. However, mucin homeostasis may be disrupted by the action of environmental and/or intrinsic factors that affect cellular integrity. This results in an altered cell behavior that often culminates into a variety of pathological conditions. Deregulated mucin production has indeed been associated with numerous types of cancers and inflammatory disorders. It is, therefore, crucial to comprehend the underlying basis of molecular mechanisms controlling mucin production in order to design and implement adequate therapeutic strategies for combating these diseases. Herein, we discuss some physiologically relevant regulatory aspects of mucin production, with a particular emphasis on aberrations that pertain to pathological situations. Our views of the achievements, the conceptual and technical limitations, as well as the future challenges associated with studies of mucin regulation are exposed.

Cellular and molecular mechanisms of gastrointestinal ulcer healing

This paper reviews cellular and molecular mechanisms of gastrointestinal ulcer healing. Ulcer healing, a genetically programmed repair process, includes inflammation, cell proliferation, re-epithelialization, formation of granulation tissue, angiogenesis, interactions between various cells and the matrix and tissue remodeling, all resulting in scar formation. All these events are controlled by the cytokines and growth factors (EGF, PDGF, KGF, HGF, TGFbeta, VEGF, angiopoietins) and transcription factors activated by tissue injury in spatially and temporally coordinated manner. These growth factors trigger mitogenic, motogenic and survival pathways utilizing Ras, MAPK, PI-3K/Akt, PLC-gamma and Rho/Rac/actin signaling. Hypoxia activates pro-angiogenic genes (e.g., VEGF, angiopoietins) via HIF, while serum response factor (SRF) is critical for VEGF-induced angiogenesis, re-epithelialization and muscle restoration. EGF, its receptor, HGF and Cox2 are important for epithelial cell proliferation, migration re-epithelializaton and reconstruction of gastric glands. VEGF, angiopoietins, nitric oxide, endothelin and metalloproteinases are important for angiogenesis, vascular remodeling and mucosal regeneration within ulcer scar. Circulating progenitor cells are also important for ulcer healing. Local gene therapy with VEGF + Ang1 and/or SRF cDNAs dramatically accelerates esophageal and gastric ulcer healing and improves quality of mucosal restoration within ulcer scar. Future directions to accelerate and improve healing include the use of stem cells and tissue engineering.

Mechanisms of nitric oxide-mediated intestinal barrier failure in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the leading intestinal emergency in premature infants. The underlying etiology of NEC remains elusive, but hypoxic conditions and early enteral feeding are consistently implicated as the main risk factors in the pathogenesis of NEC. We postulate that nitric oxide (NO) plays a key role as a molecular signaling "hub" in the generation of gut barrier failure in NEC. Clinical studies suggest that inflammatory cytokines and excessive NO production may contribute to the pathogenesis of NEC. One of the major challenges in defining the critical signaling pathways that lead to the development of NEC is the lack of specific biochemical markers that consistently delineate the early stages of NEC. Intestinal pathology and molecular markers derived from late-stage NEC represent end-stage findings and thus provide little insight into the early events that led to intestinal inflammation. Such markers may not represent viable therapeutic targets for the treatment or prevention of NEC. Therefore, novel strategies are needed to identify the patients at risk for NEC and define the clinically relevant molecules that characterize the early stages of NEC. This review will examine the mechanisms of NO-mediated gut barrier failure and propose novel genetic-based approaches for elucidating the critical molecular pathways in NEC.

The mechanism of cleavage of EGFR ligands induced by inflammatory cytokines in gastric cancer cells

BACKGROUND & AIMS

The epidermal growth factor (EGF) receptor (EGFR) can be transactivated by many factors including G-protein-coupled receptor agonists and cytokines. Although this EGFR transactivation reportedly requires a disintegrin and metalloproteinase (ADAM) that sheds the ectodomain of EGFR ligands, the detailed mechanisms are still unknown. This study evaluated the mechanism of interleukin (IL)-8- and IL-1beta-dependent shedding of the EGFR ligand in KATO III cells.

METHODS

We established transfectants stably expressing alkaline phosphatase-tagged heparin-binding EGF-like growth factor (HB-EGF), transforming growth factor alpha, or amphiregulin precursors, and depleted ADAM proteins, using short interfering RNA against ADAM10, 12, or 17. We assessed shedding of EGFR ligands by measuring AP activities in the conditioned media after IL-1beta or IL-8 stimulation. EGFR activation was examined by immunoprecipitation and Western blotting using antiphosphotyrosine antibody. KB-R7785 and anti-IL-8 neutralizing antibody were used to inhibit activities of ADAMs and IL-8 action, respectively.

RESULTS

IL-8 dose dependently released the EGFR ligands and transiently phosphorylated EGFR, with a peak at 15 minutes. KB-R7785 completely blocked IL-8-induced shedding and EGFR transactivation. Depletion of ADAM10 also dramatically reduced IL-8-induced shedding and EGFR transactivation, but depletion of ADAM12 and 17 did not. IL-1beta dose dependently enhanced shedding of HB-EGF, which was not blocked by KB-R7785 in the early phase. In the late phase, however, the EGFR transactivation was blocked by KB-R7785 and abrogated by anti-IL-8 neutralizing antibody.

CONCLUSIONS

IL-8 induces shedding of EGFR ligands because of an ADAM10-dependent pathway in gastric cancer cells, whereas IL-1beta acts principally by an ADAM-independent pathway. IL-1beta-dependent prolonged EGFR transactivation involves multiple pathways, including an IL-8-dependent pathway.

Effects of enterally administering granulocyte colony-stimulating factor to suckling mice

Gastrointestinal (GI) tract development is influenced by multiple growth factors, some of which are delivered directly to the GI lumen, as they are swallowed constituents of amniotic fluid, colostrum, and milk. Granulocyte colony-stimulating factor (G-CSF), traditionally known as a granulocytopoietic growth factor, is an example of one such factor. However, it is not clear whether the large amounts of G-CSF that are normally swallowed by the fetus and neonate have systemic effects on circulating neutrophils or local effects in the developing intestine. To assess this, we administered either active or heat-denatured (control) recombinant human G-CSF to 5- to 7-d-old C57BL/6 x 129SvJ mice. Pups received either a low dose (3 ng) that was calculated to approximate the amount of G-CSF swallowed in utero from amniotic fluid or an isovolemic high dose 100 times larger (300 ng). Oral dosing was performed daily for either 3 or 7 d, after which pups were killed and measurements were made on the blood and the GI tract. Absolute blood neutrophil counts and immature to total neutrophil ratios did not differ from controls in any of the test groups. However, intestinal villus area, perimeter, length, crypt depth, and proliferating cell nuclear antigen index increased significantly among those that were treated with active G-CSF. Thus, in suckling mice, enterally administered G-CSF had no effect on the concentration of circulating neutrophils but had trophic effects on the intestine. We speculate that the G-CSF present in amniotic fluid, colostrum, and milk acts as a topical intestinal growth factor and has little or no granulocytopoietic action.

Naringenin Inhibits Glucose Uptake in MCF-7 Breast Cancer Cells: A Mechanism for Impaired Cellular Proliferation

Certain flavonoids inhibit glucose uptake in cultured cells. In this report, we show that the grapefruit flava-none naringenin inhibited insulin-stimulated glucose uptake in proliferating and growth-arrested MCF-7 breast cancer cells. Our findings indicate that naringenin inhibits the activity of phosphoinositide 3-kinase (PI3K), a key regulator of insulin-induced GLUT4 translocation, as shown by impaired phosphorylation of the downstream signaling molecule Akt. Naringenin also inhibited the phosphorylation of p44/p42 mitogen-activated protein kinase (MAPK). Inhibition of the MAPK pathway with PD98059, a MAPK kinase inhibitor, reduced insulin-stimulated glucose uptake by approximately 60%. The MAPK pathway therefore appears to contribute significantly to insulin-stimulated glucose uptake in breast cancer cells. Importantly, decreasing the availability of glucose by lowering the glucose concentration of the culture medium inhibited proliferation, as did treatment with naringenin. Collectively, our findings suggest that naringenin inhibits the proliferation of MCF-7 cells via impaired glucose uptake. Because a physiologically attainable dose of 10 micro M naringenin reduced insulin-stimulated glucose uptake by nearly 25% and also reduced cell proliferation, naringenin may possess therapeutic potential as an anti-proliferative agent.

Epidermal growth factor and necrotizing enterocolitis

As the number of extremely low-birth-weight infants increases,necrotizing enterocolitis remains a critical eminent problem. Supplementation of enteral feeds with biologically active substances normally present in breast milk, such as epidermal growth factor, seems to be a logical and safe way to reduce the incidence of intestinal inflammation and necrotizing enterocolitis. Continuing basic research and clinical studies are essential before epidermal growth factor can be introduced as an efficient therapeutic approach in the treatment of neonatal necrotizing enterocolitis.

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.

Cross-talk between the receptor tyrosine kinases Ron and epidermal growth factor receptor

Heterogeneous receptor-receptor interactions may play a role in intracellular signaling. Accordingly, the interaction of two dissimilar tyrosine kinase receptors, Ron and epidermal growth factor receptor (EGFR) was investigated. The functional interaction of Ron and EGFR in cell scatter and oncogenic transformation was investigated in vivo. Transfection of a dominant negative form of EGFR into human embryonic kidney cells stably expressing Ron (293-Ron) dramatically reduced the scatter response induced by the Ron ligand hepatocyte growth factor-like protein/macrophage stimulating protein (HGFL). The scatter response of the 293-Ron cells was also attenuated by treatment of the cells with the specific EGFR inhibitor AG 1478. Co-transfection of Ron and dominant-negative EGFR, or co-transfection of EGFR and a dominant-negative form of Ron reduced focus formation in NIH/3T3 cells. Western analysis of NIH/3T3 cells overexpressing murine Ron and expressing endogenous levels of EGFR was used to demonstrate that Ron and EGFR co-immunoprecipitate. Stimulation of the cells in vitro with the Ron ligand HGFL or with the EGFR ligand epidermal growth factor (EGF) appeared to induce phosphorylation of both receptors. Co-immunoprecipitation and phosphorylation of phosphatidyl inositol 3-kinase (PI3-K) was also observed. This novel finding of a functional and biochemical interaction between Ron and EGFR suggests that heterologous tyrosine kinase receptor interactions may play a role in cellular processes such as scatter and transformation.

Peroxynitrite inhibits enterocyte proliferation and modulates Src kinase activity in vitro

Overproduction of nitric oxide (NO) or its toxic metabolite, peroxynitrite (ONOO-), after endotoxemia promotes gut barrier failure, in part, by inducing enterocyte apoptosis. We hypothesized that ONOO- may also inhibit enterocyte proliferation by disrupting the Src tyrosine kinase signaling pathway, thereby blunting repair of the damaged mucosa. We examined the effect of ONOO- on enterocyte proliferation and Src kinase activity. Sprague-Dawley rats were challenged with LPS or saline, whereas intestinal epithelial cell line cells were treated with ONOO- or decomposed ONOO- in vitro. Enterocyte proliferation in vivo and in vitro was measured by 5-bromo-2'-deoxyuridine (BrdU) or [3H]thymidine incorporation. Src kinase activity in cell lysates was determined at various times. LPS challenge in vivo and ONOO- treatment in vitro inhibited enterocyte proliferation. ONOO- treatment blunted the activity of Src and its downstream target, focal adhesion kinase, in a time-dependent manner. ONOO- blocked mitogen (FBS, EGF)-induced enterocyte proliferation and Src phosphorylation while increasing Src nitration. Thus ONOO- may promote gut barrier failure not only by inducing enterocyte apoptosis but also by disrupting signaling pathways involved in enterocyte proliferation.

Clinical implications of the EGF receptor/ligand system for tumor progression and survival in gastrointestinal carcinomas: evidence for new therapeutic options

The epidermal growth factor (EGF) receptor and its various ligands (EGF, TGF-alpha, amphiregulin, heparin-binding (HB)-EGF, heregulin, betacellulin) seem to be involved in the growth regulation of intestinal mucosa and might be related to the development and progression of gastrointestinal tumors. However, few quantitative data investigating the impact of tumor-EGF receptor levels in gastrointestinal carcinomas on tumor stage and prognosis are available. Therefore, EGF receptors were quantitatively determined in colorectal carcinomas in comparison to adjacent normal mucosa by 125I[EGF]-binding studies. EGFR capacity was increased in advanced invasive colorectal carcinomas (T1/2 vs. T3/4 tumors, p<0.001) and advanced UICC stages (UICC I vs. UICC II/III, p<0.001). These findings were confirmed with quantitative 125[I]EGF autoradiography performed on frozen tissue slides and analyzed by laser densitometry (p=0.020). EGF receptor analysis with immunohistochemistry with EGFR antibodies directed against the extracellular domain of the receptor was not correlated with tumor invasion or prognosis. mRNA-expression of EGFR ligands was investigated using semiquantitative RT-PCR amplification using specific primers. RT-PCR transcripts of EGFR ligands (EGF, TGF-alpha, HB-EGF, and amphiregulin) were detected in both carcinomas and normal mucosa, indicating that autocrine growth stimulation of colorectal carcinomas is mediated by coexpression of EGF receptor ligands and upregulation of EGF receptors. Survival of colorectal cancer patients with increased tumor EGF receptor levels was significantly reduced in comparison to patients with low/unchanged tumor EGF receptor levels (mean survival+/-SD, 36.2+/-4.0 vs. 46.8+/-4.3 months; p=0.017). Further studies investigating EGF receptor levels in gastric cancer patients have shown that increased tumor EGF receptor levels were associated with poor prognosis in gastric cancer patients with tumors localized distal from the cardia. Several specific EGF receptor tyrosine kinase inhibitors have recently entered clinical phase I-III studies, with promising antitumor effects in several tumors, including gastrointestinal cancer. Therefore, patients with invasive gastric or colorectal carcinomas might benefit from therapies specifically blocking EGFR-mediated signal transduction.

Controlled release of epidermal growth factor (EGF) from EGF-loaded polymeric nanoparticles composed of polystyrene as core and poly(methacrylic acid) as corona in vitro

Polymeric nanoparticles composed of polystyrene (PS) as core and poly(methacrylic acid) (PMA) as corona were prepared by the dispersion copolymerization. The potential of the nanoparticles as carriers for recombinant human epidermal growth factor (EGF) was investigated. The nanoparticles showed monodispersity and good water-dispersibility. The loading content of EGF to the nanoparticles was very high due to electrostatic interaction between EGF and nanoparticles. EGF was released as a pseudo-zero order pattern after initial burst effect. The nanoparticles were sufficient for A431 cells proliferation.

Occurrence of peptic ulcer disease in connective tissue disease patients associated with xerostomia

BACKGROUND

Saliva plays a role in mucosal protection and ulcer healing.

AIM

: To study whether decreased salivary production leads to peptic ulcer disease in connective tissue disease patients associated with xerostomia.

PATIENTS AND METHODS

Two hundred and two connective tissue disease patients (90 with xerostomia and 112 without xerostomia) were enrolled. Their demographic data and use of medications were recorded. Peptic ulcer disease was confirmed by endoscopy. The stimulated salivary output and secretory epidermal growth factor level were measured.

RESULTS

Compared with non-xerostomic counterparts, xerostomic patients manifested a higher occurrence of peptic ulcer disease (31% vs. 12%, P = 0.001), lower stimulated salivary output (9.3 +/- 4.1 vs. 22.9 +/- 5.9 mL/15 min, P < 0.001) and lower stimulated salivary epidermal growth factor output (1.40 +/- 0.77 vs. 3.00 +/- 0.96 ng/min, P < 0.001). Multivariate analysis disclosed that an older age (> or = 60 years) (odds ratio, 4.71; P < 0.001), xerostomia with stimulated salivary output of < or =1 mL/min (odds ratio, 7.54; P = 0.014) and the use of non-steroidal anti-inflammatory drugs (odds ratio, 5.76; P = 0.031) were the risk factors leading to peptic ulcer disease. In addition, xerostomic connective tissue disease patients receiving non-steroidal anti-inflammatory drugs manifested an extremely high risk of development of peptic ulcer disease (odds ratio, 19.78; P < 0.001).

CONCLUSIONS

Ageing, the use of non-steroidal anti-inflammatory drugs and poor salivary function are potential risk factors for the development of peptic ulcer disease in patients with connective tissue disease. If these xerostomic subjects consume non-steroidal anti-inflammatory drugs, they will encounter an extremely high peptic ulcer disease risk.

Effect of Helicobacter pylori infection on epidermal growth factor receptor (EGFR) expression and cell proliferation of gastric epithelial mucosa: correlation to macroscopic and microscopic diagnosis

Our aim was to compare the expression of EGFR and proliferative cell nuclear antigen (PCNA) in different histological and endoscopic diagnostic groups, in cases of Helicobacter pylori infection, in vivo. Paraffin embedded human gastric biopsy samples (86) were analysed by EGFR and PCNA immunohistochemistry and classified both on the basis of histology and endoscopic findings. In normal epithelia (NE), a positive correlation was found between PCNA and EGFR and in H. pylori-negative gastritis with and without intestinal metaplasia (P < 0.01). On the other hand, a negative correlation was detected between the two immunohistochemical findings in H. pylori-associated gastritis with intestinal metaplasia (HPGIM) and in the atrophic gastritis (AG) group. In HPGIM the percentage of EGFR-positive cells was significantly lower (32.4 +/- 30.4) when compared to either the NE (50.3 +/- 23.7) or H. pylori-negative gastritis with intestinal metaplasia (HNGIM) (48.3 +/- 23.7). In AG, EGFR was significantly lower when compared to the NE (P < 0.05). Based on the endoscopic findings, a significant decrease of EGFR expression was found in gastric ulcer cases as compared to NE, gastritis or erosion cases (P < 0.01). PCNA showed no significant alterations between the NE and gastritis, AG groups. The presence of H. pylori has an inverse effect on PCNA and EGFR expression in HPGIM.

Distribution of epidermal growth factor receptor (EGFr) in normal and acute peptic-injured equine gastric squamous epithelium

Growth factors are important in healing and restoration of injured gastrointestinal tissues and, therefore, we characterised temporally the distribution and density of epidermal growth factor receptor (EGFr) in normal and peptic-injured gastric squamous epithelium of horses. Lesions were induced in the equine gastric squamous epithelium using a feed deprivation protocol that results in prolonged increased gastric acidity. Fifteen mature horses, 9 geldings and 6 mares, age 3 to 20 years, were used and divided into 3 groups: Group 1 (n = 5) were subjected to euthanasia for problems unrelated to the gastrointestinal tract and had normal-appearing gastric squamous mucosal epithelium; Groups 2 (n = 5) and 3 (n = 5) had lesions induced in the gastric squamous epithelium by alternating 24 h periods of feed deprivation and ad libitum access to hay, for a total of 48 h and 96 h, respectively. Following lethal injection of a barbiturate, stomachs were removed and fixed by filling with 4- 6 l 10% buffered formalin. Sections were made from normal stomachs and lesions in the gastric squamous epithelium adjacent to the margo plicatus along the right side of the stomach/greater curvature and the lesser curvature. A modified avidin-biotin immunoperoxidase technique was used to stain the formalin-fixed tissue specimens for EGFr. A computerised image analysis system was used to measure area occupied by EGFr (EGFr area) and mean EGFr density in 4 zones within the epithelium extending from the basal cell layers toward the lumen. Measurements were made of epithelium in an erosion bed, at the margin of an ulcer or erosion, and 10-15 mm distant from the lesion margin. Additionally, EGFr area and density were measured in epithelial cells adjacent to capillaries in the epithelium. Intermittent feed deprivation resulted in erosion and ulceration of the gastric squamous epithelium of each horse. Mean EGFr area and density were greatest (P<0.05) in the basal layer of epithelia from all horses, and EGFr staining diminished progressively toward the lumen. Tissues from Group 3 had significantly greater EGFr area in the lesion margin than epithelia from Group 2. EGFr density was less in the epithelia of erosion beds from Groups 2 and 3 compared to normal epithelium, and EGFr area in Group 2 erosion bed epithelia was significantly less than in normal epithelium and epithelia of Group 3. EGFr area in cells adjacent to epithelial capillaries of Group 3 was significantly greater than that of Group 1. Mitotic cell activity was significantly greater in epithelia associated with ulcers and erosions in Groups 2 and 3 compared to normal tissues from Group 1 horses. Staining for EGFr in the glandular mucosa adjacent to squamous epithelium at the margo plicatus was inconsistent and typically faint when present. EGFr distribution in equine gastric squamous epithelium was greatest in regions of greatest cell proliferation, and these areas were in the basal layers of epithelium and immediately adjacent to capillaries. There was evidence that EGFr is induced in peptic-injured equine gastric squamous epithelium. A receptor ligand, EGF or transforming growth factoralpha, may be a factor in healing of gastric squamous mucosal ulcers in horses. Further research should be directed at identifying this ligand and determining its origin in equine gastric mucosa.

Peptide growth factors in the intestine

A continuously increasing number of regulatory peptides has been demonstrated to be expressed in the intestine and to modulate several functional properties of various intestinal cell populations, including the intestinal epithelium and lamina propria cell populations. These regulatory peptides include members of the epidermal growth factor (EGF) family, the transforming growth factor beta (TGF-beta) family, the insulin-like growth factor (IGF) family, the fibroblast growth factor (FGF) family, the trefoil factor (TFF) family, the colony-stimulating factor (CSF) family, and a few other seemingly unrelated regulatory peptides, such as hepatocyte growth factor (HGF), platelet-derived growth factor (PDGF), and various interleukins, interferons and tumour necrosis factor-related proteins. In addition to the well-known effects on cell proliferation, these regulatory peptide factors regulate several other functional properties of epithelial and other cell populations, such as differentiation, migration, and extracellular matrix deposition and degradation. This review is designed not to discuss all the identified factors in detail but to highlight some of the basic principles of growth factor action in the intestine. It focuses mainly on classical growth factors rather than interleukins and interferons.

EGF family ligand-dependent phenotypic modulation of smooth muscle cells through EGF receptor

The phenotypic modulation of smooth muscle cells (SMCs) is closely associated with the development and progression of various SMC diseases. We investigated the molecular mechanism of phenotypic modulation triggered by EGF family ligands using a primary culture system of differentiated SMCs. Among four EGF-receptor (EGFR) family members, the EGFR was solely activated by EGF, heparin-binding EGF (HB-EGF), transforming growth factor alpha (TGF alpha), epiregulin (ER), and betacellulin (BTC), resulting in induction of phenotypic modulation of SMCs. This effect was mediated through the coordinated activation of the extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (p38MAPK) pathways. These results suggest that EGF family ligand- and EGFR-triggered signaling pathways are critically involved in the phenotypic modulation of SMCs.

Regeneration of gastric mucosa during ulcer healing is triggered by growth factors and signal transduction pathways

An ulcer is a deep necrotic lesion penetrating through the entire thickness of the gastrointestinal mucosa and muscularis mucosae. Ulcer healing is a complex and tightly regulated process of filling the mucosal defect with proliferating and migrating epithelial and connective tissue cells. This process includes the re-establishment of the continuous surface epithelial layer, glandular epithelial structures, microvessels and connective tissue within the scar. Epithelial cells in the mucosa of the ulcer margin proliferate and migrate onto the granulation tissue to re-epithelialize the ulcer. Growth factors, such as epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), trefoil peptides (TP), platelet derived growth factor (PDGF) and other cytokines produced locally by regenerating cells, control re-epithelialization and the reconstruction of glandular structures. These growth factors, most notably EGF, trigger epithelial cell proliferation via signal transduction pathways involving EGF-R- MAP (Erk1/Erk2) kinases. Granulation tissue, which develops at the ulcer base, consists of fibroblasts, macrophages and proliferating endothelial cells, which form microvessels under the control of angiogenic growth factors. These growth factors [bFGF, vascular endothelial growth factor (VEGF) and angiopoietins] promote angiogenesis--capillary vessel formation--thereby allowing for the reconstruction of microvasculature in the mucosal scar, which is essential for delivery of oxygen and nutrients to the healing site. The primary trigger to activate expression of angiogenic growth factors and their receptors appears to be hypoxia. During ulcer healing expression of growth factor genes is tightly regulated in a temporally and spatially ordered manner.

Interleukin-1beta augments in vitro alveolar epithelial repair

Biologically active interleukin (IL)-1beta is present in the pulmonary edema fluid obtained from patients with acute lung injury and has been implicated as an important early mediator of nonpulmonary epithelial wound repair. Therefore, we tested the hypothesis that IL-1beta would enhance wound repair in cultured monolayers from rat alveolar epithelial type II cells. IL-1beta (20 ng/ml) increased the rate of in vitro alveolar epithelial repair by 118 +/- 11% compared with that in serum-free medium control cells (P < 0.01). IL-1beta induced cell spreading and migration at the edge of the wound but not proliferation. Neutralizing antibodies to epidermal growth factor (EGF) and transforming growth factor-alpha or inhibition of the EGF receptor by tyrphostin AG-1478 or genistein inhibited IL-1beta-induced alveolar epithelial repair, indicating that IL-1beta enhances in vitro alveolar epithelial repair by an EGF- or transforming growth factor-alpha-dependent mechanism. Moreover, the mitogen-activated protein kinase pathway is involved in IL-1beta-induced alveolar epithelial repair because inhibition of extracellular signal-regulated kinase activation by PD-98059 inhibited IL-1beta-induced alveolar epithelial repair. In conclusion, IL-1beta augments in vitro alveolar epithelial repair, indicating a possible novel role for IL-1beta in the early repair process of the alveolar epithelium in acute lung injury.

Gastric retention and stability of lipidized Bowman-Birk protease inhibitor in mice

Bowman-Birk protease inhibitor (BBI) was modified with a reversible lipidizing agent. The palmitoylated product, Pal-BBI, and BBI were iodinated and orally administered to mice using a gavage needle. A prolonged retention of Pal-BBI was found in the stomach. Furthermore, a significant amount of Pal-BBI was detected as intact polypeptide in the stomach of mice fed with Pal-BBI, while only degradation products were detected with BBI. There was also a significant increase of radioactivity in the blood and liver in mice 1.5 h post-administration of Pal-BBI. These results indicate that lipidized polypeptide can have a longer retention and lower digestion in the stomach. They also suggest that the Pal-BBI may have a higher gastrointestinal absorption than the original polypeptide.

Tumor necrosis factor-alpha and interleukin-1beta inhibit apolipoprotein B secretion in CaCo-2 cells via the epidermal growth factor receptor signaling pathway

In inflammatory conditions of the gut, cytokines are released into the mucosa and submucosa propagating and sustaining the inflammatory response. In CaCo-2 cells, we have shown that various inflammatory cytokines interfere with the secretion of lipids, an effect that is likely caused by the release of a ligand to the epidermal growth factor (EGF) receptor. In the present study, the role of the EGF receptor signaling pathway and the effects of the cytokines tumor necrosis factor-alpha (TNF-alpha) and and interleukin 1beta (IL-1beta) on triacylglycerol-rich lipoprotein secretion were investigated. CaCo-2 cells were incubated with oleic acid to enhance triacylglycerol-rich lipoprotein secretion. TNF-alpha and IL-1beta significantly decreased the basolateral secretion of apolipoprotein B (apoB) mass, with IL-1beta being more potent. Tyrphostin, an inhibitor of the EGF receptor intrinsic tryosine kinase, prevented or markedly attenuated the decrease in apoB secretion by TNF-alpha or IL-1beta. Both cytokines increased the phosphorylation of the EGF receptor by 30 min. Moreover, phosphotyrosine immunoblots of the EGF receptor demonstrated an increase in tyrosine residues phosphorylated by 0.5 and 6.5 h. At both these time points, TNF-alpha and IL-1beta also decreased the binding of EGF to its cell surface receptor. At 6.5 h, activation of the EGF receptor was sustained. In contrast, the early activation of the receptor was only transient as receptor phosphorylation and binding of EGF to its receptor returned to basal levels by 2 h. Preventing ligand binding to the EGF receptor by a receptor-blocking antibody attenuated receptor activation observed after 6.5 h. This did not occur at 0.5 h, suggesting that early activation of the EGF receptor was non-ligand-mediated. Similarly, apoB secretion was inhibited by an early non-ligand-mediated process; whereas at the later time, inhibition of apoB secretion was ligand-mediated. Thus, the inflammatory cytokines TNF-alpha and IL-1beta interfere with the secretion of triacylglycerol-rich lipoproteins by both early and delayed signaling events mediated by the EGF receptor signaling pathway.

Antacid talcid activates in gastric mucosa genes encoding for EGF and its receptor. The molecular basis for its ulcer healing action

In previous studies [Gut 35 (1994) 896-904], we demonstrated that antacid talcid (TAL) accelerates gastric ulcer healing and provides better quality of mucosal restoration within the scar than the omeprazole (OME). However, the mechanisms of TAL-induced ulcer healing are not clear. Since growth factors promote cell proliferation, re-epithelization, angiogenesis and ulcer healing, we studied whether TAL and/or OME affect expression of epidermal growth factor (EGF) and its receptors (EGF-R) in both normal and ulcerated gastric mucosae. Rats with or without acetic acid-induced gastric ulcers (n = 64) received i.g. twice daily 1 mL of either: A) placebo (PLA); B) TAL 100 mg; or C) OME 50 mg x kg(-1) for 14 d. Studies of gastric specimens: 1) ulcer size; 2) quantitative histology; 3) expression of EGF mRNAs was determined by RT/PCR; 4) gastric sections were immunostained with antibodies against EGF and its receptors. In non-ulcerated gastric mucosa of placebo or omeprazole treated group, EGF expression was minimal, while EGF-R was localized to few cells in the mucosal proliferative zone. Gastric ulceration triggered overexpression of EGF and its receptor in epithelial cells of the ulcer margin and scar. In ulcerated gastric mucosa TAL treatment significantly enhanced (versus PLA and omeprazole) expression of EGF and EGF-R. OME treatment reduced expression of EGF in ulcerated mucosa by 55 +/- 2% (P < 0.01). It is concluded that: 1) treatment with TAL activates genes for EGF and its receptor in normal and ulcerated gastric mucosae; 2) since EGF promotes growth of epithelial cells and their proliferation and migration, the above actions of TAL provide the mechanism for its ulcer healing action and improved (versus OME) quality of mucosal restoration.

Gastroduodenal mucosal defense

Research performed in the laboratory and the clinic over the past several years has added to our understanding of the mechanisms that are operative in protecting the epithelial lining of the stomach and duodenum from injury and ulceration, most frequently caused by necrotic agents in the lumen. The defensive mechanism of the gastroduodenal mucosa comprises a series of physical, chemical, biologic, and immunologic barriers or mechanisms that act in concert to either prevent or limit cellular injury or transformation. The field of gastroduodenal defense can be subdivided into the following four areas: extracellular mucus barrier properties; membrane and ion transport properties; cellular factors promoting growth and restitution; and vascular, neural, and inflammatory factors ensuring optimal tissue perfusion and immune responsiveness, respectively. In addition, a great deal can be learned about gastroduodenal defense by studying the effects of ulcerogenic factors and conditions on the defensive mechanisms described here and specifically how they may be compromised by nonsteroidal anti-inflammatory drugs and Helicobacter pylori infection. This review presents interesting and noteworthy findings impacting on these properties contributing to gastroduodenal defense since the prior review article on this subject appearing in this journal.