Publications (46) View all
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Article: Serotonin and the 5-HT7 receptor: the link between Hepatocytes, IGF-1 and Small intestinal neuroendocrine tumors.
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ABSTRACT: Platelet-derived serotonin (5-HT) is involved in liver regeneration. The liver is also the metastatic site for malignant enterochromaffin (EC) cell "carcinoid" (neuroendocrine) neoplasms, the principal cellular source of 5-HT. We hypothesized that 5-HT produced by metastatic EC cells played a role in the hepatic tumor-microenvironment principally via 5-HT7 receptor-mediated activation of hepatocyte IGF-1 synthesis and secretion. Using isolated rat hepatocytes, we evaluated 5-HT7 receptor expression (PCR, sequencing, western blot). ELISA, cell transfection and western blots delineated 5-HT-mediated signaling pathways (pCREB, AKT, ERK). IGF-1 synthesis/secretion was evaluated using QPCR and ELISA. IGF-1 was tested on SI NEN proliferation while IGF-1 production and 5-HT7 expression were examined in an in vivo SCID metastasis model. Our results demonstrated evidence for a functional 5-HT7 receptor. 5-HT i activated cAMP/PKA activity, pCREB (130-205%, p<0.05) and pERK/pAKT (1.2-1.75, p<0.05). Signaling was reversed by the 5-HT7 receptor antagonist SB269970. IGF-1 significantly stimulated proliferation of two SI NEN cell lines (EC50 :7-70pg/ml) and could be reversed by the small molecule inhibitor, BMS-754807. IGF-1 and 5-HT were elevated (40-300x) in peri-tumoral hepatic tissue in nude mice while 5-HT7 was increased 4-fold compared to sham-operated animals. We conclude that hepatocytes express a cAMP-coupled 5-HT7 receptor which, at elevated 5-HT concentrations that occur in liver metastases, signals via CREB/AKT and is linked to IGF-1 synthesis and secretion. Since IGF-1 regulates NEN proliferation, identification of a role for 5-HT7 in the hepatic metastatic tumor microenvironment suggests the potential for novel therapeutic strategies for amine-producing midgut tumors.Cancer Science 04/2013; · 3.33 Impact Factor -
Article: The influence of glutamate receptors on proliferation and metabolic cell activity of neuroendocrine tumors.
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ABSTRACT: Neuroendocrine tumors are relatively insensitive to radiation therapy, as well as chemotherapy. Thus, new approaches for alternative therapies are needed. We found that glutamate receptor antagonists are capable of suppressing tumor growth and cell activity of different peripheral malignancies. In the present article we review scientific literature in this field of science. Subtype-specific, non-competitive, metabotropic glutamate receptor-1 antagonists differently suppressed the growth and metabolic cell activity of one human medullary thyroid carcinoma cell line, as well as of four different human midgut neuroendocrine tumor cell lines. Furthermore, PCR analyses revealed that this subtype of glutamate receptor is expressed in these cell lines. These first results indicate that specific metabotropic glutamate receptor antagonists suppress the proliferation and cell activity of neuroendocrine tumor cells, which makes them possible targets in cancer therapy.Anticancer research 04/2013; 33(4):1267-72. · 1.73 Impact Factor -
Article: Christia vespertilionis plant extracts as novel antiproliferative agent against human neuroendocrine tumor cells.
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ABSTRACT: Neuroendocrine tumors respond poorly to radiation and conventional chemotherapy, hence surgical removal of the neoplastic tissue is still the most effective way of treatment. In an attempt to find new therapeutic plant extracts of Christia vespertilionis (CV) their antitumor potential in human medullary thyroid carcinoma (MTC) and human small intestinal neuroendocrine tumor (SI-NET) cell lines were tested. Proliferation and viability were analyzed using cell counting and WST-1 assay. Apoptosis was determined by microscopy, luminescence assays for caspases 3/7, and expression studies of apoptosis-related genes. CV extracts showed antiprolife-rative and proapoptotic effects in all MTC and SI-NET cell lines, whereby high growth inhibition was observed by treatment with the ethylacetate-extracts (CV-45) in tumor cell lines but not in normal human fibroblasts. Furthermore CV-45 treatment resulted in alterations of gene expression of PDCD5, MTDH and TNFRSF10b in MTC as well as in SI-NET cells. The results indicate that Christia vespertilionis could serve as an anticancer therapeutic for treatment of neuroendocrine tumors.Oncology Reports 03/2013; · 1.84 Impact Factor -
Article: The Stimulatory Adenosine Receptor ADORA2B Regulates Serotonin (5-HT) Synthesis and Release in Oxygen-Depleted EC Cells in Inflammatory Bowel Disease.
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ABSTRACT: We recently demonstrated that hypoxia, a key feature of IBD, increases enterochromaffin (EC) cell 5-HT secretion, which is also physiologically regulated by the ADORA2B mechanoreceptor. Since hypoxia is associated with increased extracellular adenosine, we wanted to examine whether this nucleotide amplifies HIF-1α-mediated 5-HT secretion. The effects of hypoxia were studied on IBD mucosa, isolated IBD-EC cells, isolated normal EC cells and the EC cell tumor derived cell line KRJ-1. Hypoxia (0.5% O2) was compared to NECA (adenosine agonist), MRS1754 (ADORA2B receptor antagonist) and SCH442146 (ADORA2A antagonist) on HIF signaling and 5-HT secretion. Antisense approaches were used to mechanistically evaluate EC cells in vitro. PCR and western blot were used to analyze transcript and protein levels of HIF-1α signaling and neuroendocrine cell function. An animal model of colitis was evaluated to confirm hypoxia:adenosine signaling in vivo. HIF-1α is upregulated in IBD mucosa and IBD-EC cells, the majority (∼90%) of which express an activated phenotype in situ. Hypoxia stimulated 5-HT release maximally at 30 mins, an effect amplified by NECA and selectively inhibited by MRS1754, through phosphorylation of TPH-1 and activation of VMAT-1. Transient transfection with Renilla luciferase under hypoxia transcriptional response element (HRE) control identified that ADORA2B activated HIF-1α signaling under hypoxic conditions. Additional signaling pathways associated with hypoxia:adenosine included MAP kinase and CREB. Antisense approaches mechanistically confirmed that ADORA2B signaling was linked to these pathways and 5-HT release under hypoxic conditions. Hypoxia:adenosine activation which could be reversed by 5'-ASA treatment was confirmed in a TNBS-model. Hypoxia induced 5-HT synthesis and secretion is amplified by ADORA2B signaling via MAPK/CREB and TPH-1 activation. Targeting ADORA2s may decrease EC cell 5-HT production and secretion in IBD.PLoS ONE 01/2013; 8(4):e62607. · 4.09 Impact Factor -
Article: Differential signal pathway activation and 5-HT function: the role of gut enterochromaffin cells as oxygen sensors.
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ABSTRACT: Introduction: The chemomechanosensory function of the gut enterochromaffin (EC) cell enables it to respond to dietary agents and mechanical stretch. We hypothesized the EC cell also sensed alterations in luminal or mucosal oxygen level, was physiologically sensitive to fluctuations in O(2). Given that low oxygen levels induce 5-HT production and secretion through a hypoxia inducible factor 1α (HIF-1α) dependent pathway, we also hypothesized that increasing O(2) would reduce 5-HT production and secretion. Material and Methods: Isolated normal EC cells as well as the well-characterized EC cell model KRJ-I were used to examine HIF signaling (luciferase-assays), HRE-mediated transcription (PCR), signaling pathways (western blot) and 5-HT release (ELISA) during exposure to different oxygen levels. Results: Normal EC cells and KRJ-I cells express HIF-1α, and transient transfection with Renilla luciferase under HRE control identified a hypoxia-mediated pathway in these cells. PCR confirmed activation of HIF-downstream targets, GLUT1, IGF2 and VEGF under reduced O(2) levels (0.5%). Reducing O(2) also elevated 5-HT secretion (2-3.2 fold) as well as protein levels of HIF-1α (1.7-3 fold). Increasing O(2) to 100% inhibited HRE-mediated signaling, transcription, reduced 5-HT secretion and significantly lowered HIF-1α levels (~75% of control). NFκB signaling was also elevated during hypoxia (1.2-1.6 fold) but no significant changes were noted in PKA/cAMP. Conclusion: Gut EC cells are oxygen-responsive and alterations in O(2) levels differentially activate HIF-1α and TPH1 as well as NFkB signaling. This results in alterations in 5-HT production and secretion and identifies that the chemomechanosensory role of EC cells extends to oxygen-sensing.AJP Gastrointestinal and Liver Physiology 08/2012; · 3.43 Impact Factor
