Mice harboring a defective epidermal growth factor receptor (waved-2) have an increased susceptibility to acute dextran sulfate-induced colitis

A Saccharomyces boulardii-derived antioxidant protein, thioredoxin, ameliorates intestinal inflammation through transactivating epidermal growth factor receptor

Saccharomyces boulardii (Sb) is a probiotic yeast for the treatment of gastrointestinal disorders, including inflammatory bowel disease (IBD). Little is known about the modulatory capacity of the Sb in IBD. Here, we found that oral gavage of Sb supernatant (SbS) alleviated gut inflammation, protected the intestinal barrier, and reversed DSS-induced down-regulated activation of epidermal growth factor receptor (EGFR) in colitis. Mass spectrum analysis showed that thioredoxin (Trx) is one of the critical secreted soluble proteins participating in EGFR activation detected in SbS. Trx exerted an array of significant effects on anti-inflammatory activity, including alleviating inflammation, protecting gut barrier, suppressing apoptosis, as well as reducing oxidative stress. Mechanistically, Trx promoted EGFR ligand gene expression and transactivated EGFR in a concentration-dependent manner. EGFR kinase inhibitor could block Trx-mediated preventive effects of intestinal epithelial injury. Our data suggested that Sb-derived soluble protein Trx could serve as a potential prophylactic, as a novel postbiotic against colitis, which provides a new strategy for the precision prevention and treatment of IBD.

ADAM-Mediated Signalling Pathways in Gastrointestinal Cancer Formation

Tumour growth is not solely driven by tumour cell-intrinsic mechanisms, but also depends on paracrine signals provided by the tumour micro-environment. These signals comprise cytokines and growth factors that are synthesized as trans-membrane proteins and need to be liberated by limited proteolysis also termed ectodomain shedding. Members of the family of A disintegrin and metalloproteases (ADAM) are major mediators of ectodomain shedding and therefore initiators of paracrine signal transduction. In this review, we summarize the current knowledge on how ADAM proteases on tumour cells but also on cells of the tumour micro-environment contribute to the formation of gastrointestinal tumours, and discuss how these processes can be exploited pharmacologically.

Caveolar communication with xenobiotic-stalled ribosomes compromises gut barrier integrity

In response to internal and external insults, the intestinal lining undergoes various types of epithelial adaptation or pathologic distress via stress-responsive eIF2α kinase signaling and subsequent cellular reprogramming. As a vital platform for growth factor-linked adaptive signaling, caveolae were evaluated for epithelial modulation of the insulted gut. Patients under ulcerative insult displayed enhanced expression of caveolin-1, the main structural component of caveolae, which was positively associated with expression of protein kinase R (PKR), the ribosomal stress-responsive eIF2α kinase. PKR-linked biological responses were simulated in experimental gut models of ribosome-inactivating stress using mice and Caenorhabditis elegans. Caveolar activation counteracted the expression of wound-protective epidermal growth factor receptor (EGFR) and its target genes, such as chemokines that were pivotal for epithelial integrity in the ribosome-inactivated gut. Mechanistic findings regarding ribosomal inactivation-associated disorders in the gut barrier provide crucial molecular evidence for detrimental caveolar actions against EGFR-mediated epithelial protection in patients with IBD.

Functional Characterization of Colon Cancer-Associated Mutations in ADAM17: Modifications in the Pro-Domain Interfere with Trafficking and Maturation

Colorectal cancer is one of the most commonly diagnosed malignancies in the Western world and is associated with elevated expression and activity of epidermal growth factor receptors (EGF-R). The metalloproteinase ADAM17 is involved in EGF-R activation by processing EGF-R ligands from membrane-bound pro-ligands. Underlining the link between colon cancer and ADAM17, genetic intestinal cancer models in ADAM17-deficient mice show a reduced tumor burden. In this study, we characterize point mutations within the ADAM17 gene found in the tissue of colon cancer patients. In order to shed light on the role of ADAM17 in cancer development, as well as into the mechanisms that regulate maturation and cellular trafficking of ADAM17, we here perform overexpression studies of four ADAM17 variants located in the pro-, membrane-proximal- and cytoplasmic-domain of the ADAM17 protein in ADAM10/17-deficient HEK cells. Interestingly, we found a cancer-associated point mutation within the pro-domain of ADAM17 (R177C) to be most impaired in its proteolytic activity and trafficking to the cell membrane. By comparing this variant to an ADAM17 construct lacking the entire pro-domain, we discovered similar functional limitations and propose a crucial role of the pro-domain for ADAM17 maturation, cellular trafficking and thus proteolytic activity.

Topical administration of EGF suppresses immune response and protects skin barrier in DNCB-induced atopic dermatitis in NC/Nga mice

Atopic dermatitis (AD) is a common inflammatory skin disease characterized by a complex, heterogeneous pathogenesis including skin barrier dysfunction, immunology, and pruritus. Although epidermal growth factor (EGF) is essential for epithelial homeostasis and wound healing, the effect of EGF on AD remains to be explored. To develop a new therapy for AD, the anti-AD potential of EGF was investigated by inducing AD-like skin lesions in NC/Nga mice using 2,4-dinitrochlorobenzene (DNCB). EGF was administrated to NC/Nga mice to evaluate its therapeutic effect on DNCB-induced AD. EGF treatment improved dermatitis score, ear thickness, epidermal hyperplasia, serum total immunoglobulin E level, and transepidermal water loss in NC/Nga mice with DNCB-induced AD. In addition, levels of skin barrier-related proteins such as filaggrin, involucrin, loricrin, occludin, and zonula occludens-1 (ZO-1) were increased by EGF treatment. These beneficial effects of EGF on AD may be mediated by EGF regulation of Th1/Th2-mediated cytokines, mast cell hyperplasia, and protease activated receptor-2 (PAR-2) and thymic stromal lymphopoietin (TSLP), which are triggers of AD. Taken together, our findings suggest that EGF may potentially protect against AD lesional skin via regulation of skin barrier function and immune response.

ADAM17 is required for EGF-R-induced intestinal tumors via IL-6 trans-signaling

Schmidt et al. show that loss of the membrane-bound metalloprotease ADAM17 led to impaired intestinal cancer development in the murine APC^min/+ model, which also depended on IL-6 trans-signaling via the soluble IL-6R and could be blocked by the specific IL-6 trans-signaling inhibitor sgp130Fc.

Colorectal cancer is treated with antibodies blocking epidermal growth factor receptor (EGF-R), but therapeutic success is limited. EGF-R is stimulated by soluble ligands, which are derived from transmembrane precursors by ADAM17-mediated proteolytic cleavage. In mouse intestinal cancer models in the absence of ADAM17, tumorigenesis was almost completely inhibited, and the few remaining tumors were of low-grade dysplasia. RNA sequencing analysis demonstrated down-regulation of STAT3 and Wnt pathway components. Because EGF-R on myeloid cells, but not on intestinal epithelial cells, is required for intestinal cancer and because IL-6 is induced via EGF-R stimulation, we analyzed the role of IL-6 signaling. Tumor formation was equally impaired in IL-6^−/− mice and sgp130Fc transgenic mice, in which only trans-signaling via soluble IL-6R is abrogated. ADAM17 is needed for EGF-R–mediated induction of IL-6 synthesis, which via IL-6 trans-signaling induces β-catenin–dependent tumorigenesis. Our data reveal the possibility of a novel strategy for treatment of colorectal cancer that could circumvent intrinsic and acquired resistance to EGF-R blockade.

Loss of PACS-2 delays regeneration in DSS-induced colitis but does not affect the ApcMin model of colorectal cancer

PACS-2 is a multifunctional sorting protein that mediates cell homeostasis. We recently identified PACS-2 in a functional genome-wide siRNA screen for novel regulators of the metalloproteinase ADAM17, the main sheddase for ligands of the ErbB receptor family. Of note, we showed that Pacs2^-/- mice have significantly reduced EGFR activity and proliferative index in the intestinal epithelium. As EGFR signaling is highly mitogenic for intestinal epithelial stem cells, and plays essential roles in intestinal epithelial regeneration and tumor development, we have now examined the role of PACS-2 in these processes. Specifically, we analyzed the role of Pacs2-deficiency in a DSS-induced colitis model as well as in the genetic Apc^Min colon cancer model. We now report that loss of PACS-2 delays tissue regeneration after colonic injury with little effect on key inflammatory parameters. We did however not observe any apparent effects on tumor formation driven by excessive proliferative signaling downstream from APC-deficiency. Our findings reveal that the role of PACS-2 in regulating ADAM17-mediated shedding is not an obligate requirement for the epithelium to respond to the strong inflammatory or tumorigenic inducers in the models assessed here.

MET Signaling Mediates Intestinal Crypt-Villus Development, Regeneration, and Adenoma Formation and Is Promoted by Stem Cell CD44 Isoforms

BACKGROUND & AIMS

Resistance of metastatic human colorectal cancer cells to drugs that block epidermal growth factor (EGF) receptor signaling could be caused by aberrant activity of other receptor tyrosine kinases, activating overlapping signaling pathways. One of these receptor tyrosine kinases could be MET, the receptor for hepatocyte growth factor (HGF). We investigated how MET signaling, and its interaction with CD44 (a putative MET coreceptor regulated by Wnt signaling and highly expressed by intestinal stem cells [ISCs] and adenomas) affects intestinal homeostasis, regeneration, and adenoma formation in mini-gut organoids and mice.

METHODS

We established organoid cultures from ISCs stimulated with HGF or EGF and assessed intestinal differentiation by immunohistochemistry. Mice with total epithelial disruption of MET (Ah^Cre/Met^fl/fl/LacZ) or ISC-specific disruption of MET (Lgr5^Creert2/Met^fl/fl/LacZ) and control mice (Ah^Cre/Met^+/+/LacZ, Lgr5^Creert2/Met^+/+/LacZ) were exposed to 10 Gy total body irradiation; intestinal tissues were collected, and homeostasis and regeneration were assessed by immunohistochemistry. We investigated adenoma organoid expansion stimulated by HGF or EGF using adenomas derived from Lgr5^Creert2/Met^fl/fl/Apc^fl/fl and Lgr5^Creert2/Met^+/+/Apc^fl/fl mice. The same mice were evaluated for adenoma prevalence and size. We also quantified adenomas in Ah^Cre/Met^fl/fl/Apc^fl/+ mice compared with Ah^Cre/Met^+/+/Apc^fl/+ control mice. We studied expansion of organoids generated from crypts and adenomas, stimulated by HGF or EGF, that were derived from mice expressing different CD44 splice variants (Cd44^+/+, Cd44^-/-, Cd44^s/s, or Cd44^v4-10/v4-10 mice).

RESULTS

Crypts incubated with EGF or HGF expanded into self-organizing mini-guts with similar levels of efficacy and contained all differentiated cell lineages. MET-deficient mice did not have defects in intestinal homeostasis. Total body irradiation reduced numbers of proliferating crypts in Ah^Cre/Met^fl/fl/LacZ mice. Lgr5^Creert2/Met^fl/fl/LacZ mice had impaired regeneration of MET-deficient ISCs. Adenoma organoids stimulated with EGF or HGF expanded to almost twice the size of nonstimulated organoids. MET-deficient adenoma organoids did not respond to HGF stimulation, but did respond to EGF. ISC-specific disruption of Met (Lgr5^Creert2/Met^fl/fl/Apc^fl/fl mice) caused a twofold increase in apoptosis in microadenomas, resulting in an approximately 50% reduction of microadenoma numbers and significantly reduced average adenoma size. Total epithelial disruption of Met (Ah^Cre/Met^fl/fl/Apc^fl/+ mice) resulted in an approximate 50% reduction in (micro)adenoma numbers. Intestinal crypts from Cd44^-/- mice did not expand to the same extent as crypts from Cd44^+/+ mice on stimulation with HGF, but had the same response to EGF. The negative effect on HGF-mediated growth was overcome by expression of CD44v4-10, but not by CD44s. Similarly, HGF-mediated expansion of adenoma organoids required CD44v4-10.

CONCLUSIONS

In studies of intestinal organoid cultures and mice with inducible deletion of MET, we found HGF receptor signaling to regulate intestinal homeostasis and regeneration, as well as adenoma formation. These activities of MET are promoted by the stem cell CD44 isoform CD44v4-10. Our findings provide rationale for targeting signaling via MET and CD44 during anti-EGF receptor therapy of patients with colorectal cancer or in patients resistant to EGF receptor inhibitors.

EGFR in Tumor-Associated Myeloid Cells Promotes Development of Colorectal Cancer in Mice and Associates With Outcomes of Patients

BACKGROUND & AIMS

Inhibitors of the epidermal growth factor receptor (EGFR) are the first-line therapy for patients with metastatic colorectal tumors without RAS mutations. However, EGFR inhibitors are ineffective in these patients, and tumor level of EGFR does not associate with response to therapy. We screened human colorectal tumors for EGFR-positive myeloid cells and investigated their association with patient outcome. We also performed studies in mice to evaluate how EGFR expression in tumor cells and myeloid cells contributes to development of colitis-associated cancer and ApcMin-dependent intestinal tumorigenesis.

METHODS

We performed immunohistochemical and immunofluorescent analyses of 116 colorectal tumor biopsies to determine levels of EGFR in tumor and stroma; we also collected information on tumor stage and patient features and outcomes. We used the Mann-Whitney U and Kruskal-Wallis tests to correlate tumor levels of EGFR with tumor stage, and the Kaplan-Meier method to estimate patients' median survival time. We performed experiments in mice lacking EGFR in intestinal epithelial cells (Villin-Cre; Egfrf/f and Villin-CreERT2; Egfrf/f mice) or myeloid cells (LysM-Cre; Egfrf/f mice) on a mixed background. These mice were bred with ApcMin/+ mice; colitis-associated cancer and colitis were induced by administration of dextran sodium sulfate (DSS), with or without azoxymethane (AOM), respectively. Villin-CreERT2 was activated in developed tumors by administration of tamoxifen to mice. Littermates that expressed full-length EGFR were used as controls. Intestinal tissues were collected; severity of colitis, numbers and size of tumors, and intestinal barrier integrity were assessed by histologic, immunohistochemical, quantitative reverse transcription polymerase chain reaction, and flow cytometry analyses.

RESULTS

We detected EGFR in myeloid cells in the stroma of human colorectal tumors; myeloid cell expression of EGFR associated with tumor metastasis and shorter patient survival time. Mice with deletion of EGFR from myeloid cells formed significantly fewer and smaller tumors than the respective EGFR-expressing controls in an ApcMin/+ background as well as after administration of AOM and DSS. Deletion of EGFR from intestinal epithelial cells did not affect tumor growth. Furthermore, tamoxifen-induced deletion of EGFR from epithelial cells of established intestinal tumors in mice given AOM and DSS did not reduce tumor size. EGFR signaling in myeloid cells promoted activation of STAT3 and expression of survivin in intestinal tumor cells. Mice with deletion of EGFR from myeloid cells developed more severe colitis after DSS administration, characterized by increased intestinal inflammation and intestinal barrier disruption, than control mice or mice with deletion of EGFR from intestinal epithelial cells. EGFR-deficient myeloid cells in the colon of DSS-treated LysM-Cre; Egfrf/f mice had reduced expression of interleukin 6 (IL6), and epithelial STAT3 activation was reduced compared with controls. Administration of recombinant IL6 to LysM-Cre; Egfrf/f mice given DSS protected them from weight loss and restored epithelial proliferation and STAT3 activation, compared with administration of DSS alone to these mice.

CONCLUSIONS

Increased expression of EGFR in myeloid cells from the colorectal tumor stroma associates with tumor progression and reduced survival time of patients with metastatic colorectal cancer. Deletion of EGFR from myeloid cells, but not intestinal epithelial cells, protects mice from colitis-induced intestinal cancer and ApcMin-dependent intestinal tumorigenesis. Myeloid cell expression of EGFR increases activation of STAT3 and expression of survivin in intestinal epithelial cells and expression of IL6 in colon tissues. These findings indicate that expression of EGFR by myeloid cells of the colorectal tumor stroma, rather than the cancer cells themselves, contributes to tumor development.

The activation of EGFR promotes myocardial tumor necrosis factor-α production and cardiac failure in endotoxemia

To study the effect of EGFR activation on the generation of TNF-α and the occurrence of cardiac dysfuncetion during sepsis, PD168393 and erlotinib (both are EGFR inhibitors) were applied to decreased the production of TNF-α and phosphrylation of ERK1/2 and p38 induced by LPS in cardiomyocytes. These results were further proved by specifically knocked down the expression of EGFR in vitro. Both TAPI-1, a TNF-α converting enzyme (TACE) inhibitor, and TGF-α neutralizing antibody could inhibit the activation of EGFR and the generation of TNF-α mRNA after LPS treatment. The increase of TGF-α in response to LPS could also be suppressed by TAPI-1. On the other hand, exogenous TGF-α increased the expression of TNF-α mRNA and partially reversed the inhibitory effect of TAPI-1 on expression of TNF-α mRNA in response to LPS indicating that the transactivation of EGFR by LPS in cardiomyocytes needs the help of TACE and TGF-α. In endotoxemic mice, inhibition the activation of EGFR not only decreased TNF-α production in the myocardium but also improved left ventricular pump function and ameliorated cardiac dysfunction and ultimately improved survival rate. All these results provided a new insight of how EGFR regulation the production of TNF-α in cardiomyocytes and a potential new target for the treatment of cardiac dysfunction in sepsis.

When Insult Is Added to Injury: Cross Talk between ILCs and Intestinal Epithelium in IBD

Inflammatory bowel disease (IBD) is characterized by an impairment of the integrity of the mucosal epithelial barrier, which causes exacerbated inflammation of the intestine. The intestinal barrier is formed by different specialized epithelial cells, which separate the intestinal lumen from the lamina propria. In addition to its crucial role in protecting the body from invading pathogens, the intestinal epithelium contributes to intestinal homeostasis by its biochemical properties and communication to underlying immune cells. Innate lymphoid cells (ILCs) are a recently described population of lymphocytes that have been implicated in both mucosal homeostasis and inflammation. Recent findings indicate a critical feedback loop in which damaged epithelium activates these innate immune cells to restore epithelial barrier function. This review will focus on the signalling pathways between damaged epithelium and ILCs involved in repair of the epithelial barrier and tissue homeostasis and the relationship of these processes with the control of IBD.

Pathway-based Genome-wide Association Studies Reveal the Association Between Growth Factor Activity and Inflammatory Bowel Disease

BACKGROUND

The inflammatory bowel diseases known as Crohn's disease (CD) and ulcerative colitis (UC) are related autoimmune conditions with a complex etiology composed of genetic and environmental factors. Genetic studies have revealed 200 susceptibility loci for inflammatory bowel diseases, but these only account for a small fraction of the genetic heritability of the disease. We employed pathway-based approaches to identify genes that cooperatively make contributions to the genetic etiology of CD.

METHODS

We exploited the largest CD dataset (20,000 cases + 28,000 controls) and UC dataset (17,000 cases + 33,500 controls) to date. We conducted a meta-analysis of 5 CD cohorts of European ancestry using 3 pathway-based approaches and further performed replication studies in an independent cohort genotyped on the Immunochip and in another pediatric cohort of European ancestry. Similar meta-analysis was performed for UC cohorts.

RESULTS

In addition to the multiple immune-related pathways that have been implicated in the genetic etiology of inflammatory bowel diseases before, we found significant associations involving genes in growth factor signaling for CD. This result was replicated in 2 independent cohorts of European ancestry. This association with growth factor activity is not unique to CD. We found a similar significant association with UC cohorts.

CONCLUSIONS

Our findings suggest that genes involved in pathways of growth factor signaling may make joint contributions to the etiology of CD and UC, providing novel insight into the genetic mechanisms of these diseases.

Loss of ADAM17-Mediated Tumor Necrosis Factor Alpha Signaling in Intestinal Cells Attenuates Mucosal Atrophy in a Mouse Model of Parenteral Nutrition

Total parenteral nutrition (TPN) is commonly used clinically to sustain patients; however, TPN is associated with profound mucosal atrophy, which may adversely affect clinical outcomes. Using a mouse TPN model, removing enteral nutrition leads to decreased crypt proliferation, increased intestinal epithelial cell (IEC) apoptosis and increased mucosal tumor necrosis factor alpha (TNF-α) expression that ultimately produces mucosal atrophy. Upregulation of TNF-α signaling plays a central role in mediating TPN-induced mucosal atrophy without intact epidermal growth factor receptor (EGFR) signaling. Currently, the mechanism and the tissue-specific contributions of TNF-α signaling to TPN-induced mucosal atrophy remain unclear. ADAM17 is an ectodomain sheddase that can modulate the signaling activity of several cytokine/growth factor receptor families, including the TNF-α/TNF receptor and ErbB ligand/EGFR pathways. Using TPN-treated IEC-specific ADAM17-deficient mice, the present study demonstrates that a loss of soluble TNF-α signaling from IECs attenuates TPN-induced mucosal atrophy. Importantly, this response remains dependent on the maintenance of functional EGFR signaling in IECs. TNF-α blockade in wild-type mice receiving TPN confirmed that soluble TNF-α signaling is responsible for downregulation of EGFR signaling in IECs. These results demonstrate that ADAM17-mediated TNF-α signaling from IECs has a significant role in the development of the proinflammatory state and mucosal atrophy observed in TPN-treated mice.

EGFR signaling blunts allergen-induced IL-6 production and Th17 responses in the skin and attenuates development and relapse of atopic dermatitis

Despite the important role for epidermal growth factor (EGF) in epithelial homeostasis and wound healing, it has not been investigated in atopic dermatitis (AD). We used AD animal models to explore the role of EGF in AD. In an acute AD model, skin transepidermal water loss was significantly attenuated in EGF-treated mice. Blockade of EGFR signaling genetically or pharmacologically confirms a protective role for EGFR signaling in AD. In a chronic/relapsing AD model, EGF treatment of mice with established AD resulted in an attenuation of AD exacerbation (skin epithelial thickness, cutaneous inflammation, and total and allergen specific IgE) following cutaneous allergen rechallenge. EGF treatment did not alter expression of skin barrier junction proteins or antimicrobial peptides in the AD model. However, EGF treatment attenuated allergen-induced expression of IL-17A, CXCL1, and CXCL2 and neutrophil accumulation in AD skin following cutaneous allergen exposure. IL-17A production was decreased in the in vitro restimulated skin-draining lymph node cells from the EGF-treated mice. Similarly, IL-17A was increased in waved-2 mice skin following allergen exposure. Whereas IL-6 and IL-1β expression was attenuated in the skin of EGF-treated mice, EGF treatment also suppressed allergen-induced IL-6 production by keratinocytes. Given the central role of IL-6 in priming Th17 differentiation in the skin, this effect of EGF on keratinocytes may contribute to the protective roles for EGFR in AD pathogenesis. In conclusion, our study provides evidence for a previously unrecognized protective role for EGF in AD and a new role for EGF in modulating IL-17 responses in the skin.

ErbB receptors and their growth factor ligands in pediatric intestinal inflammation

The ErbB tyrosine kinases (epidermal growth factor receptor (EGFR), ErbB2/HER2, ErbB3, and ErbB4) are cell surface growth factor receptors widely expressed in many developing mammalian tissues, including in the intestinal tract. Signaling elicited by these receptors promotes epithelial cell growth and survival, and ErbB ligands have been proposed as therapeutic agents for intestinal diseases of pediatric populations, including inflammatory bowel disease (IBD), necrotizing enterocolitis (NEC), and inflammation associated with total parenteral nutrition (TPN). Furthermore, emerging evidence points to reduced ErbB ligand expression and thus reduced ErbB activity in IBD, NEC, and TPN models. This review will discuss the current understanding of the role of ErbB receptors in the pathogenesis and potential treatment of pediatric intestinal inflammation, with focus on the altered signaling in disease and the molecular mechanisms by which exogenous ligands are protective.

The role of growth factors in intestinal regeneration and repair in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a devastating intestinal disease resulting in major neonatal morbidity and mortality. The pathology is poorly understood, and the means of preventing and treating NEC are limited. Several endogenous growth factors have been identified as having important roles in intestinal growth as well as aiding intestinal repair from injury or inflammation. In this review, we will discuss several growth factors as mediators of intestinal regeneration and repair as well as potential therapeutic agents for NEC.

Tumor fibroblast-derived epiregulin promotes growth of colitis-associated neoplasms through ERK

Molecular mechanisms specific to colitis-associated cancers have been poorly characterized. Using comparative whole-genome expression profiling, we observed differential expression of epiregulin (EREG) in mouse models of colitis-associated, but not sporadic, colorectal cancer. Similarly, EREG expression was significantly upregulated in cohorts of patients with colitis-associated cancer. Furthermore, tumor-associated fibroblasts were identified as a major source of EREG in colitis-associated neoplasms. Functional studies showed that Ereg-deficient mice, although more prone to colitis, were strongly protected from colitis-associated tumors. Serial endoscopic studies revealed that EREG promoted tumor growth rather than initiation. Additionally, we demonstrated that fibroblast-derived EREG requires ERK activation to induce proliferation of intestinal epithelial cells (IEC) and tumor development in vivo. To demonstrate the functional relevance of EREG-producing tumor-associated fibroblasts, we developed a novel system for adoptive transfer of these cells via mini-endoscopic local injection. It was found that transfer of EREG-producing, but not Ereg-deficient, fibroblasts from tumors significantly augmented growth of colitis-associated neoplasms in vivo. In conclusion, our data indicate that EREG and tumor-associated fibroblasts play a crucial role in controlling tumor growth in colitis-associated neoplasms.

Epidermal growth factor receptor expression and signaling are essential in glutamine's cytoprotective mechanism in heat-stressed intestinal epithelial-6 cells

Epidermal growth factor receptor (EGFR) expression and signaling can induce cellular protection after intestinal inflammation. L-Glutamine (GLN) is known to prevent apoptosis after intestinal injury by activating MAPK and phosphatidylinositol 3-kinase (PI3-K)/Akt pathways. However, the role of EGFR expression and signaling in GLN-mediated cellular protection in intestinal epithelial-6 (IEC-6) cells after heat stress (HS) is unknown. To address the role of EGFR in GLN-mediated protection, IEC-6 cells were treated with GLN in the presence or absence of EGFR small interfering RNA, the EGFR tyrosine kinase inhibitor AG1478, the ERK1/2 inhibitor PD98059, the p38MAPK inhibitor SB203580, or the PI3-K/Akt inhibitor LY294002 under basal and HS conditions. GLN-mediated cell survival was measured using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay. Phosphorylated and/or total levels of EGFR, cleaved caspase-3, poly(ADP-ribose) polymerase-1, ERK1/2, p38MAPK, and Akt were assessed by Western blotting. We showed that HS induced a decrease in total, cytoplasmic, and nuclear EGFR levels in IEC-6 cells, which was prevented by GLN supplementation, leading to attenuated apoptosis via EGFR small interfering RNA. Furthermore, the protective effect of GLN was lessened by AG1478, PD98059, and LY294002 but was not affected by SB203580. AG1478 attenuated GLN-mediated increases in ERK1/2 and decreases in p38MAPK phosphorylation. However, AG1478 had no effect on GLN-mediated augmentations in Akt phosphorylation. In summary, EGFR expression was important in the protective mechanism of GLN, as well as GLN-mediated activation of EGFR tyrosine kinase activity. GLN-mediated EGFR signaling activated ERK1/2 and decreased p38MAPK signaling. However, GLN-mediated Akt phosphorylation after HS seems to be independent of EGFR signaling.

Neuregulin-4 is a survival factor for colon epithelial cells both in culture and in vivo

Expression of the ErbB4 tyrosine kinase is elevated in colonic epithelial cells during inflammatory bowel disease, whereas ErbB4 overexpression in cultured colonocytes blocks TNF-induced apoptosis in a ligand-dependent manner. Together, these observations suggest that ErbB4 induction may be a protective response. However, the effects of ErbB4 signaling in the colonic epithelium in vivo are not known. Furthermore, previous work on ErbB4 used ligands shared with other receptors, raising the question of whether the observed responses are explicitly due to ErbB4. In this study, we used the ErbB4-specific ligand neuregulin-4 (NRG4) to activate ErbB4 and define its role in colonocyte biology. NRG4 treatment, either in cultured cells or in mice, blocked colonic epithelial apoptosis induced by TNF and IFN-γ. It was also protective in a murine experimental colitis model. NRG4 stimulated phosphorylation of ErbB4 but not other ErbB receptors, indicating that this is a specific response. Furthermore, in contrast to related ligands, NRG4 enhanced cell survival but not proliferation or migration, and stimulated phosphorylation of the anti-apoptotic mediator Akt but not ERK MAPK. Pharmacological inhibition of PI3K/Akt signaling reversed the anti-apoptotic effects of NRG4, confirming the role of this cascade in NRG4-induced cell survival. With regard to the potential clinical importance of this pathway, NRG4 expression was decreased in human inflammatory bowel disease samples and mouse models of colitis, suggesting that activation of ErbB4 is altered in disease. Thus, exogenous NRG4 may be beneficial for disorders in which epithelial apoptosis is part of the pathology.

Enterocyte expression of epidermal growth factor receptor is not required for intestinal adaptation in response to massive small bowel resection

PURPOSE

Intestinal adaptation after massive small bowel resection (SBR) permits improved absorption of enteral nutrition despite significant loss of bowel length. Epidermal growth factor (EGF) and its receptor (EGFR) have previously been established to play major roles in the pathogenesis of adaptation. This study tested the hypothesis that EGFR signaling within the epithelial cell compartment (enterocytes) is required for intestinal adaptation.

METHODS

We developed a tamoxifen-inducible Villin-Cre/LoxP recombinant system for enterocyte-directed EGFR deletion using EGFR-floxed mice. Epidermal growth factor receptor-null mice and wild-type littermates underwent either 50% proximal SBR or sham operation. Ileal tissue was harvested on postoperative day 7. To assess for adaptation, villus height and crypt depth as well as rates of crypt cell proliferation and apoptosis were measured.

RESULTS

Adaptation after SBR occurred normally, as demonstrated by significant increases in villus height, crypt depth, and crypt proliferative and apoptotic index in both the wild-type and EGFR-null mice.

CONCLUSION

Enterocyte EGFR expression is not required for the adaptation response to massive SBR. This novel finding suggests that enterocyte proliferation during adaptation is regulated by EGFR signaling in cells other than enterocytes, perhaps within the mesenchymal cell compartment of the bowel wall via factor(s) that are presently unknown.

Epidermal growth factor receptor inhibits colitis-associated cancer in mice

Inflammatory bowel disease (IBD) is a chronic illness caused by complex interactions between genetic and environmental factors that propagate inflammation and damage to the gastrointestinal epithelium. This state of chronic inflammation increases the risk for development of colitis-associated cancer in IBD patients. Thus, the development of targeted therapeutics that can disrupt the cycle of inflammation and epithelial injury is highly attractive. However, such biological therapies, including those targeting epidermal growth factor receptor pathways, pose a risk of increasing cancer rates. Using two mouse models of colitis-associated cancer, we found that epidermal growth factor receptor inactivation accelerated the incidence and progression of colorectal tumors. By modulating inflammation and epithelial regeneration, epidermal growth factor receptor optimized the response to chronic inflammation and limited subsequent tumorigenesis. These findings provide important insights into the pathogenesis of colitis-associated cancer and suggest that epidermal growth factor-based therapies for IBD may reduce long-term cancer risk.

ErbB2 and ErbB3 regulate recovery from dextran sulfate sodium-induced colitis by promoting mouse colon epithelial cell survival

ErbB2 and ErbB3 receptor tyrosine kinases are key regulators of proliferation, migration, differentiation and cell survival; however, their roles in gastrointestinal biology remain poorly defined. We hypothesized that ErbB2 and ErbB3 promote colon epithelial cell survival in the context of the wound-healing response following colitis. In this study, mice bearing intestinal epithelial-specific deletion of ErbB2 or ErbB3 were treated with dextran sulfate sodium (DSS). Colon sections were examined for injury, cytokine expression, epithelial cell proliferation and apoptosis. Deletion of epithelial ErbB2 did not affect the extent of intestinal injury in response to DSS, whereas deletion of ErbB3 slightly increased injury. However, the roles of both receptors were more apparent during recovery from DSS colitis, in which ErbB2 or ErbB3 epithelial deletion resulted in greater inflammation and crypt damage during the early reparative period. Moreover, loss of ErbB3 prevented normal epithelial regeneration in the long term, with damage persisting for at least 6 weeks following a single round of DSS. Delayed recovery in mice with epithelial deletion of ErbB2 or ErbB3 was associated with increased colonic expression of tumor necrosis factor alpha and increased epithelial apoptosis. Furthermore, epithelial ErbB3 deletion increased apoptosis at baseline and during DSS injury. Additionally, epithelial cell hyperproliferation during recovery was exacerbated by deletion of either ErbB2 or ErbB3. These results suggest that ErbB2 and ErbB3 have important cytoprotective and reparative roles in the colonic epithelium following injury, by promoting colon epithelial cell survival.

Interferon-γ alters downstream signaling originating from epidermal growth factor receptor in intestinal epithelial cells: functional consequences for ion transport

The epidermal growth factor receptor (EGFr) regulates many cellular functions, such as proliferation, apoptosis, and ion transport. Our aim was to investigate whether long term treatment with interferon-γ (IFN-γ) modulates EGF activation of downstream signaling pathways in intestinal epithelial cells and if this contributes to dysregulation of epithelial ion transport in inflammation. Polarized monolayers of T(84) and HT29/cl.19A colonocytes were preincubated with IFN-γ prior to stimulation with EGF. Basolateral potassium transport was studied in Ussing chambers. We also studied inflamed colonic mucosae from C57BL/6 mice treated with dextran sulfate sodium or mdr1a knock-out mice and controls. IFN-γ increased intestinal epithelial EGFr expression without increasing its phosphorylation. Conversely, IFN-γ caused a significant decrease in EGF-stimulated phosphorylation of specific EGFr tyrosine residues and activation of ERK but not Akt-1. In IFNγ-pretreated cells, the inhibitory effect of EGF on carbachol-stimulated K(+) channel activity was lost. In inflamed colonic tissues, EGFr expression was significantly increased, whereas ERK phosphorylation was reduced. Thus, although it up-regulates EGFr expression, IFN-γ causes defective EGFr activation in colonic epithelial cells via reduced phosphorylation of specific EGFr tyrosine residues. This probably accounts for altered downstream signaling consequences. These observations were corroborated in the setting of colitis. IFN-γ also abrogates the ability of EGF to inhibit carbachol-stimulated basolateral K(+) currents. Our data suggest that, in the setting of inflammation, the biological effect of EGF, including the inhibitory effect of EGF on Ca(2+)-dependent ion transport, is altered, perhaps contributing to diarrheal and other symptoms in vivo.

Colon-specific delivery of a probiotic-derived soluble protein ameliorates intestinal inflammation in mice through an EGFR-dependent mechanism

Probiotic bacteria can potentially have beneficial effects on the clinical course of several intestinal disorders, but our understanding of probiotic action is limited. We have identified a probiotic bacteria-derived soluble protein, p40, from Lactobacillus rhamnosus GG (LGG), which prevents cytokine-induced apoptosis in intestinal epithelial cells. In the current study, we analyzed the mechanisms by which p40 regulates cellular responses in intestinal epithelial cells and p40's effects on experimental colitis using mouse models. We show that the recombinant p40 protein activated EGFR, leading to Akt activation. Activation of EGFR by p40 was required for inhibition of cytokine-induced apoptosis in intestinal epithelial cells in vitro and ex vivo. Furthermore, we developed a pectin/zein hydrogel bead system to specifically deliver p40 to the mouse colon, which activated EGFR in colon epithelial cells. Administration of p40-containing beads reduced intestinal epithelial apoptosis and disruption of barrier function in the colon epithelium in an EGFR-dependent manner, thereby preventing and treating DSS-induced intestinal injury and acute colitis. Furthermore, p40 activation of EGFR was required for ameliorating colon epithelial cell apoptosis and chronic inflammation in oxazolone-induced colitis. These data define what we believe to be a previously unrecognized mechanism of probiotic-derived soluble proteins in protecting the intestine from injury and inflammation.

MyD88 signaling in nonhematopoietic cells protects mice against induced colitis by regulating specific EGF receptor ligands

Toll-like receptors (TLRs) trigger intestinal inflammation when the epithelial barrier is breached by physical trauma or pathogenic microbes. Although it has been shown that TLR-mediated signals are ultimately protective in models of acute intestinal inflammation [such as dextran sulfate sodium (DSS)-induced colitis], it is less clear which cells mediate protection. Here we demonstrate that TLR signaling in the nonhematopoietic compartment confers protection in acute DSS-induced colitis. Epithelial cells of MyD88/Trif-deficient mice express diminished levels of the epidermal growth factor receptor (EGFR) ligands amphiregulin (AREG) and epiregulin (EREG), and systemic lipopolysaccharide administration induces their expression in the colon. N-ethyl-N-nitrosourea (ENU)-induced mutations in Adam17 (which is required for AREG and EREG processing) and in Egfr both produce a strong DSS colitis phenotype, and the Adam17 mutation exerts its deleterious effect in the nonhematopoietic compartment. The effect of abrogation of TLR signaling is mitigated by systemic administration of AREG. A TLR→MyD88→AREG/EREG→EGFR signaling pathway is represented in nonhematopoietic cells of the intestinal tract, responds to microbial stimuli once barriers are breached, and mediates protection against DSS-induced colitis.

Toll-like receptor 4 differentially regulates epidermal growth factor-related growth factors in response to intestinal mucosal injury

Epiregulin (EPI) and amphiregulin (AR) are epidermal growth factor receptor (EGFR) ligands implicated in mucosal repair and tumorigenesis. We have shown that Toll-like receptor 4 (TLR4) induces intestinal epithelial cell (IEC) proliferation by activating EGFR through AR expression. We examined whether TLR4 differentially regulates expression of EGFR ligands in response to mucosal injury. The human IEC line SW480 was examined expression of EGFR ligands, EGFR phosphorylation, and proliferation in response to lipopolysaccharide (LPS). Small-interfering RNA (siRNA) was used to block TLR4. Neutralizing antibodies to EGFR ligands were used to examine inhibition of LPS-dependent EGFR activation. Acute colitis and recovery were examined in the mice given 2.5% dextran sodium sulfate (DSS). Colonic secretion of EPI and AR was analyzed by enzyme-linked immunosorbent assay. LPS selectively induces EPI and AR but not other EGFR ligands. LPS induced early EPI mRNA expression between 30 min and 24 h. The neutralizing antibodies to EPI and AR prevented activation of EGFR by LPS. LPS induces IEC proliferation (200%, P=0.01) in 24 h but blocking EPI and AR significantly decreased proliferation. In vivo, mucosal EPI and AR expression are significantly decreased in TLR4(-/-) mice (P=0.02) compared to wild-type mice during acute colitis. EPI and AR exhibit different kinetics in response to mucosal damage: EPI expression is upregulated acutely at day 7 of DSS, but falls during recovery at day 14. By contrast, a sustained upregulation of AR expression is seen during mucosal injury and repair. We show that TLR4 regulates EPI and AR expression and that both these EGFR ligands are necessary for optimal proliferation of IEC. The diverse kinetics of EPI and AR expression suggest that they function in distinct roles with respect to acute injury vs repair. Our results highlight the role of bacterial sensing for IEC homeostasis and may lead to targeted therapy for mucosal healing and prevention of tumorigenesis.

Carbachol induces TGF-alpha expression and colonic epithelial cell proliferation in sensory-desensitised rats

OBJECTIVE/BACKGROUND

Signals for the expression of the peptide growth factors epidermal growth factor and transforming growth factor-alpha (TGFalpha) in the gastrointestinal mucosa are largely unknown. We have shown earlier that extrinsic afferents in the gastrointestinal tract induce TGFalpha expression in colonic mucosa via the deliberation of neurotransmitters substance P and calcitonin gene-related peptide. The aim of our present study was to determine the effects of carbachol on mucosal TGFalpha expression and epithelial cell proliferation in vivo.

DESIGN/METHODS

Rats were divided in three groups. Group 1 was treated with vehicle only, group 2 received one single subcutaneous injection of 250 microg/kg of carbachol and animals in group 3 were sensory-desensitised prior to the injection of 250 microg/kg carbachol. TGFalpha expression and epithelial cell proliferation was evaluated by polymerase chain reaction, Western blot analysis and bromodeoxyuridine staining.

RESULTS

Carbachol induced a significant increase in mucosal epithelial cell proliferation and TGFalpha expression. Sensory desensitisation did neither abolish the increased TGFalpha expression nor the increase in epithelial cell proliferation.

CONCLUSION

Parasympathetic pathways are involved in the control of TGFalpha expression in gastrointestinal mucosa as well as in epithelial cell proliferation.

Placental and embryonic growth restriction in mice with reduced function epidermal growth factor receptor alleles

Embryos lacking an epidermal growth factor receptor (EGFR) exhibit strain-specific defects in placental development that can result in mid-gestational embryonic lethality. To determine the level of EGFR signaling required for normal placental development, we characterized congenic strains homozygous for the hypomorphic Egfr(wa2) allele or heterozygous for the antimorphic Egfr(Wa5) allele. Egfr(wa2) homozygous embryos and placentas exhibit strain-dependent growth restriction at 15.5 days post-coitus while Egfr(Wa5) heterozygous placentas are only slightly reduced in size with no effect on embryonic growth. Egfr(wa2) homozygous placentas have a reduced spongiotrophoblast layer in some strains, while spongiotrophoblasts and glycogen cells are almost completely absent in others. Our results demonstrate that more EGFR signaling occurs in Egfr(Wa5) heterozygotes than in Egfr(wa2) homozygotes and suggest that Egfr(wa2) homozygous embryos model EGFR-mediated intrauterine growth restriction in humans. We also consistently observed differences between strains in wild-type placenta and embryo size as well as in the cellular composition and expression of trophoblast cell subtype markers and propose that differential expression in the placenta of Glut3, a glucose transporter essential for normal embryonic growth, may contribute to strain-dependent differences in intrauterine growth restriction caused by reduced EGFR activity.

The ErbB4 growth factor receptor is required for colon epithelial cell survival in the presence of TNF

BACKGROUND & AIMS

The ErbB4 receptor tyrosine kinase regulates cell growth, survival, and differentiation in several tissues, but its role in the gastrointestinal tract has not been reported. We tested the hypothesis that ErbB4 promotes intestinal cell survival and restitution following injury or inflammation.

METHODS

ErbB4 expression in human inflammatory bowel disease was determined by immunohistochemistry. Mice were subjected to dextran sulfate sodium (DSS, 3%) colitis or injected with tumor necrosis factor (TNF), and ErbB4 expression was quantified by immunohistochemistry and Western blot. Cultured young adult mouse colon (YAMC) cells were exposed to TNF, and ErbB4 messenger RNA, protein, and phosphorylation levels were measured. Cells transfected with ErbB4 small interfering RNA (siRNA), or over expressing ErbB4, were subjected to wound healing and apoptosis assays.

RESULTS

ErbB4 levels increased in Crohn's colitis and the colon epithelium of mice with DSS colitis or injected with TNF. In YAMC cells, TNF induced ErbB4 messenger RNA, protein, and phosphorylation; nuclear factor kappaB activation also stimulated ErbB4 accumulation. ErbB4 siRNA sensitized cells to TNF-stimulated apoptosis, while over expression blocked apoptosis induced by TNF plus cycloheximide. Additionally, ErbB4 siRNA decreased YAMC cell wound healing. ErbB4 knockdown attenuated, while over expression elevated, phosphorylation of Akt in response to TNF. Inhibition of the phosphatidylinositol 3-kinase/Akt signaling cascade reversed the ability of ErbB4 over expression to protect from cytokine-induced apoptosis.

CONCLUSIONS

ErbB4 expression and signaling are key elements for TNF responses in vivo and in cell culture, protecting intestinal epithelial cells from apoptosis in the inflammatory environment, possibly through Akt activation.

ERBBs in the gastrointestinal tract: recent progress and new perspectives

The gastrointestinal epithelium does much more than provide a physical barrier between the intestinal lumen and our internal milieu. It is actively engaged in absorption and secretion of salt and water via ion transporters, exchangers and selective ion channels. It is also a continuously self-renewing epithelium that undergoes ordered growth and differentiation along its vertical axis. From this dual perspective, we will consider the actions of the ERBB family of ligands and receptors in the maintenance of gastrointestinal homeostasis and discuss instances when the actions of this family go awry such as in cancer and Ménétrier's disease.

Role of epidermal growth factor and other growth factors in the prevention of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) presents as the most common gastrointestinal emergency during the neonatal period and results in ulceration and necrosis of the distal small intestine and proximal colon. The etiology of NEC remains unknown. Based on the complexity of gut development, multiple growth factors and cytokines may be needed to synergistically support the developing gut. Epidermal growth factor (EGF) has been shown to play an important role in intestinal cell restitution, proliferation, and maturation. EGF is found in abundant quantities in many fluids, including the gastrointestinal tract, amniotic fluid, breast milk, and saliva. Preliminary clinical trials using EGF in neonates diagnosed with NEC have been shown to promote repair of intestinal epithelium. Additionally, other growth factors are also emerging as potential treatment modalities, including erythropoietin, granulocyte colony stimulating factor, and heparin-binding EGF. The role of EGF and other growth factors in the pathogenesis and prevention of NEC will be reviewed.

Systemic treatment of patients who have colorectal cancer and inflammatory bowel disease

Colorectal cancer is the most common malignant complication in patients who have IBD. The disease is difficult to diagnose because there is an overlap in symptoms in patients who have colon cancer and those who have IBD. Much has been learned about the incidence of colorectal cancer in patients who have IBD and its correlation with disease activity, duration, and anatomic location; however, almost no data are available regarding specific therapeutic considerations during adjuvant or palliative chemotherapy for these patients with respect to their underlying disease. Patients who have IBD who develop colorectal cancer are at higher risk for developing severe diarrhea during chemotherapy that may be due to the toxic effects of cytotoxic drugs or a flare of the IBD. Continuous infusional 5-FU alone, in combination with leucovorin, or in combination with oxaliplatin (FOLFOX) seems to be tolerated best. Bolus infusions of 5-FU (Roswell Park or Mayo regimens) and combination therapy of irinotecan with 5-FU should be avoided because of severe diarrhea and the possibility of sepsis. When diarrhea develops or worsens, empiric aminosalicylates may be given. Although it is theoretically possible that anti-EGFR therapies could affect IBD activity adversely, clinical experience with cetuximab in patients who have colorectal cancer has not shown any significant gastrointestinal side effects. Therefore, it seems reasonable to use it in patients who have colorectal cancer and IBD. The administration of bevacizumab has been associated with rare episodes of intestinal perforation; it should be used with great care in patients who have IBD. More studies and an integrative, multidisciplinary approach from oncologists and gastroenterologists are needed to provide optimal care for patients who have IBD during chemotherapy for colorectal cancer

Cox-2 is regulated by Toll-like receptor-4 (TLR4) signaling: Role in proliferation and apoptosis in the intestine

BACKGROUND & AIMS

We recently showed that mice deficient in Toll-like receptor 4 (TLR4) or its adapter molecule MyD88 have increased signs of colitis compared with wild-type (WT) mice after dextran sodium sulfate (DSS)-induced injury. We wished to test the hypothesis that cyclooxygenase 2 (Cox-2)-derived prostaglandin E2 (PGE2) is important in TLR4-related mucosal repair.

METHODS

Cox-2 expression was analyzed by real-time polymerase chain reaction, immunohistochemistry, Western blotting, and luciferase reporter constructs. Small interfering RNA was used to inhibit expression of MyD88. TLR4-/- or WT mice were given 2.5% DSS for 7 days. Proliferation and apoptosis were assessed using bromodeoxyuridine staining and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assays, respectively. PGE2 was given orally to DSS-treated mice.

RESULTS

Intestinal epithelial cell lines up-regulated Cox-2 expression in a TLR4- and MyD88-dependent fashion. Lipopolysaccharide-mediated stimulation of PGE2 production was blocked by a selective Cox-2 inhibitor or small interfering RNA against MyD88. After DSS injury, Cox-2 expression increased only in WT mice. TLR4-/- mice have significantly reduced proliferation and increased apoptosis after DSS injury compared with WT mice. PGE2 supplementation of TLR4-/- mice resulted in improvement in clinical signs of colitis and restoration of proliferation and apoptosis to WT values. The mechanism for improved epithelial repair may be through PGE2-dependent activation of the epidermal growth factor receptor.

CONCLUSIONS

We describe an important link between TLR4 signaling and Cox-2 expression in the gut. TLR4 and MyD88 signaling are required for optimal proliferation and protection against apoptosis in the injured intestine. Although TLR4 signaling is beneficial in the short term, chronic signaling through TLR4 may lower the threshold for colitis-associated cancer.

Role of epidermal growth factor in the pathogenesis of neonatal necrotizing enterocolitis

Neonatal necrotizing enterocolitis (NEC) is an increasingly frequent condition encountered in premature infants for which the etiology is not well understood. Epidermal growth factor (EGF) is abundant in many fluids bathing the fetal and neonatal gastrointestinal tract, including amniotic fluid, saliva, and breast milk. EGF is acknowledged to be important for normal intestinal development as well as repair following injury to the gastrointestinal mucosa. There appears to be mounting evidence to support a possible link between deficient EGF production and the development of NEC. The relevant evidence for the role of EGF in intestinal development and mucosal repair, as well as its potential involvement in the genesis of NEC will be reviewed.

Wa5 is a novel ENU-induced antimorphic allele of the epidermal growth factor receptor

Mice heterozygous for the N-ethyl-N-nitrosourea-induced Waved-5 (Wa5) mutation, isolated in a screen for dominant, visible mutations, exhibit a wavy coat similar to mice homozygous for the recessive Tgfa wa1 or Egfr wa2 alleles. In this study, we show that Wa5 is a new allele of Egfr (Egfr Wa5) containing a missense mutation within the coding region for the highly conserved DFG motif of the tyrosine kinase domain. In vivo analysis of placental development, modification of Apc Min tumorigenesis, and levels of EGF-dependent EGFR phosphorylation demonstrates that Egfr Wa5 functions as an antimorphic allele, recapitulating many abnormalities associated with reduced EGFR activity. Furthermore, Egfr wa5 enhances Egfr Wa2 compound or Tgfa tm1Dcl double mutants exposing additional EGFR-dependent phenotypes. In vitro characterization shows that the antimorphic property of Egfr Wa5 is caused by a kinase-dead receptor acting as a dominant negative.

Epiregulin is not essential for development of intestinal tumors but is required for protection from intestinal damage

Epiregulin, an epidermal growth factor family member, acts as a local signal mediator and shows dual biological activity, stimulating the proliferation of fibroblasts, hepatocytes, smooth muscle cells, and keratinocytes while inhibiting the growth of several tumor-derived epithelial cell lines. The epiregulin gene (Ereg) is located on mouse chromosome 5 adjacent to three other epidermal growth factor family members, epigen, amphiregulin, and betacellulin. Gene targeting was used to insert a lacZ reporter into the mouse Ereg locus and to ablate its function. Although epiregulin is broadly expressed and regulated both spatially and temporally, Ereg null mice show no overt developmental defects, reproductive abnormalities, or altered liver regeneration. Additionally, in contrast to previous hypotheses, Ereg deficiency does not alter intestinal cancer susceptibility, as assayed in the ApcMin model, despite showing robust expression in developing tumors. However, Ereg null mice are highly susceptible to cancer-predisposing intestinal damage caused by oral administration of dextran sulfate sodium.

Modeling the cancer patient with genetically engineered mice: prediction of toxicity from molecule-targeted therapies

Current trends foretell the use of cancer treatments customized to each patient. Genetic and molecular profiling of tumors and an increasing number of molecule-targeted therapies contribute to making this a reality. However, as targets of anticancer therapies become specific proteins or pathways, unanticipated side effects may emerge. In addition, the chronic use of these treatments may contribute to the development of degenerative toxicity not predicted by short-term clinical trials. Here we review and propose how genetically engineered mouse models can serve as valuable tools to predict targeted therapy toxicity, as well as to identify allelic variants that predispose individuals to side effects.

Glucagon-like peptide-2 and common therapeutics in a murine model of ulcerative colitis

The intestinal hormone glucagon-like peptide-2 (GLP-2) enhances bowel growth and reduces the severity of colonic injury in dextran sulfate sodium (DSS)-induced colitis in mice. In humans, ulcerative colitis is normally treated with aminosalicylates (ASAs) and corticosteroids (CSs) to reduce inflammation. However, whether the intestinotropic effects of GLP-2 are altered when combined with ASAs and/or CSs has not previously been explored. Thus, each agent [vehicle, ASA (sulfasalazine), CS (methylprednisolone), and ASA + CS] was administered alone or with GLP-2 to normal mice or mice with 3.5% DSS in the drinking water, for 10 consecutive days. GLP-2 treatment of DSS-mice increased survival and small intestinal weight (p < 0.05), and decreased body weight loss and colonic damage (p < 0.05). Furthermore, GLP-2 increased the number of proliferating cells in the colonic crypts of DSS-mice (p < 0.05). Administration of ASA, CS, or ASA + CS alone did not affect growth of the intestine in DSS-mice. However, administration of GLP-2 in combination with ASA was permissive for the beneficial effects of GLP-2 on survival and colonic damage, whereas CS treatment prevented these effects of GLP-2. Concomitant administration of GLP-2 with ASA + CS resulted in intermediate effects. No differences between colonic myeloperoxidase activity or IkappaB levels (an inhibitor of the nuclear factor-kappaB pro-inflammatory pathway) were found for any of these therapeutic agents. When taken together, the ability of GLP-2 to protect colonic mucosal architecture in DSS-colitis, and its effectiveness when given in combination with ASA, but not with CS, suggests a novel approach for the treatment of patients with colitis.

Effects of dosmalfate, a new cytoprotective agent, on acute and chronic trinitrobenzene sulphonic acid-induced colitis in rats

Activated neutrophils and proinflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha) are clearly involved in the pathogenesis of bowel disease. Increased expression of epidermal growth factor-receptor (EGF receptor) has been reported for the colon mucosa surrounding areas of ulceration, suggesting a pivotal role in mucosal defence and repair. In this study, we examined the effects of dosmalfate, a new flavonoid derivative compound (diosmin heptakis) with antioxidant and cytoprotective properties, on acute and chronic experimental trinitrobenzene sulphonic acid (TNBS)-induced colitis in rats. The inflammation response was assessed by neutrophil infiltration as evaluated by histology and myeloperoxidase activity. Mucosal TNF-alpha production and histological analysis of the lesions was also carried out. In addition, we studied the expression of the EGF receptor inmunohistochemically during the healing of TNBS-induced chronic colitis. A 2-day treatment with 400 or 800 mg/kg of dosmalfate ameliorated the colon damage score and the incidence of adhesions. It also significantly (P<0.05) decreased myeloperoxidase activity and colonic mucosal production of TNF-alpha. Chronic treatment (14 days) with 800 mg/kg/day of dosmalfate also had significant protective effects on TNBS-induced colitis which were reflected by significant attenuation (P<0.05) of the damage score while the inflammatory indicators were not improved. The chronic beneficial effect of dosmalfate was apparently related to the enhancement of EGF receptor expression. These findings confirm the protective effects of dosmalfate in acute and chronic experimental colitis.

Role of epidermal growth factor and its receptor in chemotherapy-induced intestinal injury

Several growth factors are trophic for the gastrointestinal tract and able to reduce the degree of intestinal damage caused by cytotoxic agents. However, studies of epidermal growth factor (EGF) for chemotherapy-induced intestinal injury are conflicting. The development of a transgenic mouse that specifically overexpresses EGF in the small intestine provided a unique opportunity to assess the contribution of EGF in mucositis. After a course of fluorouracil, transgenic mice fared no better than control mice. Weight recovery was inferior, and mucosal architecture was not preserved. Apoptosis was not decreased and proliferation was not increased in the crypts. To corroborate the findings in transgenic mice, ICR mice were treated with exogenous EGF after receiving fluorouracil. Despite ileal upregulation of native and activated EGF receptor, the mice were not protected from intestinal damage. No benefits were observed with different EGF doses or schedules or routes of EGF administration. Finally, mucositis was induced in mutant mice with specific defects of the EGF signaling axis. Compared with control mice, clinical and histological parameters of intestinal injury after fluorouracil were no different in waved-2 mice, which have functionally diminished EGF receptors, or waved-1 mice, which lack transforming growth factor-alpha, another major ligand for the EGF receptor. These findings do not support a critical role for EGF or its receptor in chemotherapy-induced intestinal injury.

Importance of epidermal growth factor receptor signaling in establishment of adenomas and maintenance of carcinomas during intestinal tumorigenesis

We used the hypomorphic Egfr(wa2) allele to genetically examine the impact of impaired epidermal growth factor receptor (Egfr) signaling on the Apc(Min) mouse model of familial adenomatous polyposis. Transfer of the Apc(Min) allele onto a homozygous Egfr(wa2) background results in a 90% reduction in intestinal polyp number relative to Apc(Min) mice carrying a wild-type Egfr allele. This Egfr effect is potentially synergistic with the actions of the modifier-of-min (Mom1) locus. Surprisingly, the size, expansion, and pathological progression of the polyps appear Egfr-independent. Histological examination of the ilea of younger animals revealed no differences in the number of microadenomas, the presumptive precursor lesions to gross intestinal polyps. Pharmacological inhibition with EKI-785, an Egfr tyrosine kinase inhibitor, produced similar results in the Apc(Min) model. These data suggest that normal Egfr activity is required for establishment of intestinal tumors in the Apc(Min) model between initiation and subsequent expansion of initiated tumors. The role of Egfr signaling during later stages of tumorigenesis was examined by using nude mice xenografts of two human colorectal cancer cell lines. Treatment with EKI-785 produced a dose-dependent reduction in tumor growth, suggesting that Egfr inhibitors may be useful for advanced colorectal cancer treatment.