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Biomedical subjects

M P Peppelenbosch

Publications and source records attributed to M P Peppelenbosch.

At least 19 recordsLinked to original sources
PubMed2006

Effect of aspirin on the Wnt/beta-catenin pathway is mediated via protein phosphatase 2A.

Nonsteroidal anti-inflammatory drugs show chemopreventive efficacy in colon cancer, but the mechanism behind this remains unclear. Elucidating this mechanism is seen as vital to the development of new chemopreventive agents. We studied the effects of aspirin on the oncogenic Wnt/beta-catenin pathway activity in colorectal cancer cell lines and observed that aspirin dose-dependently decreased the activity of this pathway, as judged by TCF-driven luciferase activity, reduced Wnt target gene expression and increased phosphorylation of beta-catenin by immunoblotting. Furthermore, the ubiquitination and cytoplasmic levels of beta-catenin were assessed by immunoblotting, and also the localization of beta-catenin was shown by green fluorescent protein-tagged beta-catenin and time-lapse fluorescent imaging. Importantly, aspirin treatment caused increased phosphorylation of protein phosphatase 2A (PP2A), an event associated with inhibition of PP2A enzymatic activity, which was confirmed by a reduction in enzymatic PP2A activity. Moreover, this inhibition of PP2A enzymatic activity was essential for the effects of aspirin on the Wnt/beta-catenin pathway as shown by transient transfection with PP2A constructs. The findings in this article provide a molecular explanation for the efficacy of aspirin in chemoprevention of colorectal cancer and shows biochemical evidence that PP2A is an important regulator of Wnt/beta-catenin pathway activity in these cells.

Anaphase-Promoting Complex-Cyclosome↗
PubMed2006

Altered bone morphogenetic protein signalling in the Helicobacter pylori-infected stomach.

Morphogens regulate epithelial cell fate decisions in the adult gastrointestinal tract. The authors hypothesized that influx of inflammatory cells into the lamina propria may disturb the normal expression gradients of morphogens (morphogenetic landscape) in gastrointestinal epithelia. Changes in the activity of the bone morphogenetic protein (BMP) pathway in normal and Helicobacter pylori-infected gastric mucosa were therefore examined. It is shown that BMP receptors, the activated (phosphorylated) form of the intracellular BMP signal transduction protein SMAD1, and BMP target ID2 all localize to gastric epithelial cells that are at the end of the axis of epithelial renewal in normal mucosa. Colonization of human gastric mucosa with H. pylori was associated with an increase in BMP2 expression due to influx of inflammatory cells that produce BMP2. Furthermore, whereas no BMP4 was detected in the normal antrum, focal infiltrates of BMP4-expressing cells were found in the H. pylori-infected stomach. This influx of BMP-expressing cells was associated with an increase in epithelial BMP signalling. Interestingly, a shift in activity of the BMP pathway was observed towards the precursor cell compartment (isthmus) of the gastric units. Thus, H. pylori infection results in an influx of inflammatory cells that disturb the normal activity gradient of a morphogenetic pathway with an established role in epithelial cell fate regulation. The data suggest that morphological changes in epithelial histology may result from alterations in the morphogenetic landscape secondary to changes in the cellular composition of the lamina propria.

Bone Morphogenetic Protein 2↗
PubMed2004

COX-2 inhibition as a tool to treat and prevent colorectal cancer.

The cyclooxygenase-2 (COX-2) enzyme has a fundamental role in the carcinogenesis of colorectal cancer. The anticarcinogenic mechanisms of NSAIDs are not completely understood and appear to be only partially dependent on inhibition tumoral COX-2. Moreover, the mechanisms of NSAIDs depend on the concentration. In experimental setting, at low levels NSAIDs downregulate the COX-2 gene in colorectal cancer cells, whereas at clinical relevant concentrations the production of prostaglandin E2 by enzymatic activity of COX-2 is diminished resulting in inhibition of the tumor angiogenesis. At higher levels NSAIDs and especially some selective COX-2 inhibitors are capable of COX-2 independent effects, such as apoptosis induction of tumor cells. In animal models, NSAIDs administration results in inhibition of angiogenesis and proliferation, induction apoptosis and prevention of metastasis. In clinical setting, NSAIDs and selective COX-2 inhibitors have the capacity to prevent the development of colorectal adenomas. We have summarized data regarding the role of COX-2 in CRC and discuss the multiple targets of NSAIDs in their anticarcinogenic action. However, the translation of these anticarcinogenic effects of NSAIDs to its clinical application as adjuvant therapy in CRC is hampered by a lack of randomized clinical trials with long-term follow-up.

Animals↗
PubMed2003

Regulation of the p21Ras-MAP kinase pathway by factor VIIa.

BACKGROUND: In recent years it has become clear that factor (F)VIIa is not a passive mediator involved in the linear transduction of the coagulation cascade, but actively engages target cells to induce signal transduction and that this signal transduction fulfills critical functions in angiogenesis, arteriosclerosis and inflammatory processes. OBJECTIVES: The details of coagulation factor-dependent signal transduction are among the least understood in biology and thus we set out to establish the molecular events responsible for MAP kinase activation induced by the interaction of FVIIa with its cellular binding partner tissue factor (TF). METHODS: Two different TF-expressing cell types, BHKTF and HaCaT cells, were assayed for p21Ras activation using a pull-down assay that is specific for activated Ras. This activation was visualized by means of Western blotting. In addition, the upstream pathways leading to FVIIa-induced Ras activation were characterized using phosphospecific antibodies and specific inhibitors. RESULTS: We observed that in both BHKTF and HaCaT cells FVIIa-induced MAP kinase activation correlates with p21Ras activation, and that this p21Ras activation is essential for FVIIa-induced MAP kinase activation. In BHKTF cells, early p21Ras activation was mediated by the activation of protein kinase C (PKC), whereas late p21Ras activation employed alternative mechanisms. In HaCaT cells, stimulation of the Src kinase family mediated FVIIa-dependent p21Ras activation. Finally, in both cell types, Raf activity was mandatory for MAP kinase activation. CONCLUSIONS: p21Ras activation is instrumental in FVIIa signal transduction and the FVIIa-dependent activation of p21Ras involves either PKC or Src-dependent mechanisms, depending on the cell type investigated.

Animals↗
PubMed2003

Mitogen activated protein (MAP) kinase signal transduction pathways and novel anti-inflammatory targets.

Over the last decade important advances have been made in our understanding of the molecular events underlying cellular responses to extracellular signals. Increased understanding of signal transduction mechanisms and gene regulation involved in immune responses has created opportunities for the discovery of novel therapeutic compounds useful in treating inflammatory disorders. One of the best studied signalling routes is the mitogen activated protein (MAP) kinase signal transduction pathway which plays a crucial role in many aspects of immune mediated inflammatory responses. Here, our current understanding of the MAP kinase pathway is reviewed, as well as recent advances in the design of novel agents that are able to modulate the activity of these signalling cascades.

Eukaryotic Cells↗
PubMed2002

Immunomodulatory effect of oxygen and pressure.

The immunomodulatory effect of hyperbaric oxygen, involving altered cytokine release by macrophages, is well described. Importantly, however, it is not known what the relative contribution is of the hyperbaric environment of the cells vs. increased oxygen tension on these hyperbaric oxygen-dependent effects. We compared, therefore, cytokine release by murine macrophages under hyperbaric oxygen, hyperpressure of normal air and normobaric conditions. We observed that hyperbaric oxygen enhanced cytokine release of both unstimulated as well as lipopolysaccharide (LPS)-challenged macrophages. Hyperpressure of normal air, however, enhanced LPS-induced cytokine production but did not elicit cytokine release in unstimulated macrophages. To further investigate the molecular details underlying the effects of hyperbaric oxygen, we investigated the effect of the p42/p44 mitogen-activated protein (MAP) kinase inhibitor PD98059 and the p38 MAP kinase inhibitor SB203580. Neither inhibitor, however, had a significant effect on the modulatory effects of hyperbaric oxygen on cytokine release. We concluded that the immunomodulatory effect of hyperbaric oxygen contains a component for which hyperpressure is sufficient and a component that apart from hyperpressure also requires hyperoxygenation.

Animals↗
PubMed2002

Infliximab treatment induces apoptosis of lamina propria T lymphocytes in Crohn's disease.

BACKGROUND AND AIMS: Treatment with infliximab induces remission in about 70% of patients with steroid refractory Crohn's disease. Because Crohn's disease is considered to be mediated by uncontrolled activation of mucosal T lymphocytes, we hypothesised that infliximab could induce apoptosis of T lymphocytes. METHODS: Induction of apoptosis in vivo was studied in 10 patients with therapy refractory Crohn's disease. In vitro, resting or stimulated Jurkat T cells were incubated with infliximab. RESULTS: Infusion of infliximab (5 mg/kg) in steroid refractory patients with Crohn's disease induced a clinical response in 9/10 patients but did not influence expression of activation markers, homing receptors, memory cells, Fas expression, or Bax/Bcl-2 expression on peripheral blood T lymphocytes. In contrast, a significant increase in CD3 and TUNEL positive cells within colonic biopsies was detected 24 hours after infusion of infliximab, suggesting that infliximab stimulates apoptosis of activated T lymphocytes but not of resting T cells. To test this hypothesis, the effects of infliximab on Jurkat T cells were investigated. We observed that infliximab induced apoptosis and an increase in the Bax/Bcl-2 ratio of CD3/CD28 stimulated Jurkat T cells but not of unstimulated Jurkat cells. CONCLUSIONS: Our data indicate that infliximab treatment causes a rapid and specific increase in apoptosis of T lymphocytes in the gut mucosa. These findings may explain the rapid and sustained therapeutic effects of infliximab in Crohn's disease.

Adult↗
PubMed2002

Dichotomal role of inhibition of p38 MAPK with SB 203580 in experimental colitis.

BACKGROUND: Crohn's disease is characterised by a chronic relapsing inflammation of the bowel in which proinflammatory cytokines play an important perpetuating role. Mitogen activated protein kinase p38 (p38 MAPK) has been established as a major regulator of the inflammatory response, especially with regard to production of proinflammatory cytokines, but its role in inflammatory bowel disease is unexplored. In this paper we describe the effects of a specific p38 MAPK inhibitor, SB 203580, in trinitrobenzene sulphonic acid (TNBS) induced colitis in mice. RESULTS: SB 203580 had a dichotomal effect in TNBS mice. Weight loss of TNBS mice treated with SB 203580 was significantly worse and colon weight on sacrifice was significantly increased in MAPK inhibitor treated TNBS mice (229.2 mg and 289.1 mg, respectively). However, the total number of cells in the caudal lymph node decreased to 188.8 x 10(4) cells in SB 203580 treated TNBS mice compared with 334 x 10(4) cells in vehicle treated mice. CD3/CD28 double stimulated caudal lymph node cells of SB 203580 treated mice showed decreased interferon gamma production but increased tumour necrosis factor alpha production. The concentration of interleukin 12p70 in colon homogenates was significantly decreased in SB 203580 treated mice whereas concentrations of interleukin 12p40, tumour necrosis factor alpha, and interleukin 10 were similar in vehicle and SB 203580 treated TNBS mice. CONCLUSION: Our results reveal a dichotomy in p38 MAPK action during experimental colitis.

Animals↗
PubMed2002

Sonic hedgehog expression correlates with fundic gland differentiation in the adult gastrointestinal tract.

BACKGROUND: Sonic hedgehog (Shh) is an important endodermal morphogenetic signal during the development of the vertebrate gut. It controls gastrointestinal patterning in general, and gastric gland formation in particular. We have previously shown that Shh regulates gastric gland proliferation in the adult but detailed analysis of its expression along the adult gastrointestinal tract has never been undertaken. We therefore studied Shh expression along the normal human and rodent adult gastrointestinal tract as well as in intestinal metaplasia of the stomach, gastric and intestinal metaplasia of the oesophagus, and gastric heterotopia in Meckel's diverticulum. METHODS: The studies were performed with in situ hybridisation and by immunohistochemistry using an antibody that recognises the Shh precursor form. RESULTS: We found that in the normal gastrointestinal tract, high levels of Shh were expressed in the fundic glands of the stomach. Shh expression was also found in fundic gland metaplasia and heterotopia. However, Shh expression was lost in intestinal metaplasia of the stomach. CONCLUSION: We found a strong correlation between Shh expression and fundic gland differentiation. Our current study therefore provides evidence that in addition to its role in gastric epithelial development, Shh plays a unique role in gastric epithelial differentiation in adults.

Adult↗
PubMed2001

Mice lacking the multidrug resistance protein 1 are resistant to Streptococcus pneumoniae-induced pneumonia.

Leukotrienes (LTs) are considered important for antibacterial defense in the lung. Multidrug resistance protein 1 (mrp1) is a transmembrane protein responsible for the cellular extrusion of LTC(4). To determine the role of mrp1 in host defense against pneumonia, mrp1(-/-) and wild-type mice were intranasally inoculated with Streptococcus pneumoniae. mrp1(-/-) mice displayed a diminished outgrowth of pneumococci in lungs and a strongly reduced mortality. These findings were related to an effect of mrp1 on LT metabolism, because survival was similar in mrp1(-/-) and wild-type mice treated with the 5-lipoxygenase-activating protein inhibitor MK-886. Although LTC(4) levels remained low in the bronchoalveolar lavage fluid of mrp1(-/-) mice, LTB(4) concentrations were higher than in wild-type mice. These elevated LTB(4) concentrations were important for the relative protection of mrp1(-/-) mice, because the LTB(4) antagonist LTB(4)-dimethyl amide abolished their survival advantage. In vitro experiments suggested that the intracellullar accumulation of LTC(4) in mrp1(-/-) mice results in product inhibition of LTC(4)-synthase, diminishing substrate competition between LTA(4)-hydrolase (which yields LTB(4)) and LTC(4)-synthase for the available LTA(4). We conclude that mrp1(-/-) mice are resistant against pneumococcal pneumonia by a mechanism that involves increased release of LTB(4). These results identify mrp1 as a novel target for adjunctive therapy in pneumonia.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

NF-kappaB, p38 MAPK and JNK are highly expressed and active in the stroma of human colonic adenomatous polyps.

The factors that govern the progression from colonic adenomatous polyp to colon cancer are poorly understood. The observation that NSAIDs act as chemopreventative agents and reduce the size of colonic polyps suggests the involvement of inflammatory signalling, but inflammatory signalling in colonic polyps has not been studied. We investigated the expression of the active forms of NF-kappaB, JNK and p38 MAPK using immunohistochemistry with activation specific antibodies in human colonic adenomas. We show that active NF-kappaB is seen in stromal macrophages that also express COX-2 and TNF-alpha, active JNK is seen in stromal and intraepithelial T-lymphocytes and periendothelial cells of new blood vessels, and active p38 MAPK is most highly expressed in macrophages and other stromal cells. These results demonstrate the presence of active inflammatory signal transduction in colonic polyps and that these are predominantly in the stroma. In the case of NF-kappaB this coincides with the cellular localisation of COX-2. These results support evidence that NSAIDs may act through effects on stromal cells rather than epithelial cells.

Adenomatous Polyps↗
PubMed2001

p38 mitogen-activated protein kinase inhibition increases cytokine release by macrophages in vitro and during infection in vivo.

p38 mitogen-activated protein kinase (MAPK) has been suggested as a mediator of cytokine release and is currently being targeted for anti-inflammatory therapy. However, experimental data are contradictory and lack sufficient affirmation in vivo. We tested the effect of p38 MAPK inhibition in several cell types and in different murine models of infectious disease. We observed that most cell types react to p38 MAPK inhibition with diminished cytokine release, but that this treatment induced increased cytokine release in macrophages. Furthermore, we observed increased cytokine production in mouse models of pneumococcal pneumonia and tuberculosis accompanied by severely reduced bacterial clearance. This apparent inefficacy of p38 MAPK inhibition in reducing cytokine release in infectious disease, as well as its immune-compromising action, suggest that targeting p38 MAPK may not be a suitable anti-cytokine strategy in patients with such disease or at risk for infection.

Animals↗
PubMed2001

Cell biology of tissue factor, an unusual member of the cytokine receptor family.

Tissue factor (TF) is a 47-kDa transmembrane protein, involved in the onset of coagulation. However, it also influences pathophysiological processes such as inflammation and tumor angiogenesis. Although the molecular mechanisms responsible for these phenomena remain unclear, it is thought that they are brought about by the action of intracellular signaling, resulting in gene transcription and subsequent protein synthesis. In this review we focus on FVIIa/TF-induced intracellular signaling and its possible role in physiology.

Angiogenesis Inducing Agents↗
PubMed2001

Leptin is a growth factor for colonic epithelial cells.

BACKGROUND AND AIMS: Obesity increases the risk of colon cancer, whereas physical activity reduces the risk. Plasma levels of leptin increase in proportion to the level of obesity and are reduced by physical activity. Leptin acts as a growth factor for several cell types and thus may provide a biological explanation for the observed epidemiological risk factors. The aim of this study was to investigate whether leptin is a growth factor for colonic epithelial cells. METHODS: The presence of the leptin receptor in human colon cancer cell lines was assessed using reverse-transcription polymerase chain reaction and immunoblotting, and its presence in human colonic tissue was assessed by immunohistochemistry. The effects of leptin in vitro on HT29 cells were assessed by assessing p42/44 mitogen-activated protein kinase phosphorylation, thymidine incorporation, and cell numbers and in vivo in C57BL/6 mice by colonic bromodeoxyuridine incorporation. RESULTS: The leptin receptor is expressed in human colon cancer cell lines and human colonic tissue. Stimulation with leptin leads to phosphorylation of p42/44 mitogen-activated protein kinase and increases proliferation in vitro and in vivo. CONCLUSIONS: Leptin is a growth factor in colonic epithelial cells and one that may provide a biological explanation for the observed associations between obesity, physical activity, and colon cancer.

Adenocarcinoma↗