title: Raf-1 activation suppresses neuroendocrine marker and hormone levels in human gastrointestinal carcinoid cells.
abstract: Gastrointestinal carcinoid cells secrete multiple neuroendocrine markers and hormones including 5-HT and chromogranin A. The intracellular signaling pathways that regulate production of bioactive molecules are not completely understood. Our aim was to determine whether activation of the raf-1/MEK/MAPK signal transduction pathway in carcinoid cells could modulate production of neuroendocrine markers and hormones. Human pancreatic carcinoid cells (BON) were stably transduced with an estrogen-inducible raf-1 construct creating BON-raf cells. Activation of raf-1 in BON-raf cells led to a marked induction of phosphorylated MEK and ERK1/2 within 48 h. Importantly, raf-1 activation resulted in morphological changes accompanied by a marked decrease in neuroendocrine secretory granules by electronmicroscopy. Moreover, induction of raf-1 in BON-raf cells led to significant reductions in 5-HT, chromogranin A, and synaptophysin levels. Furthermore, treatment of BON-raf cells with MEK inhibitors PD-98059 and U-0126 blocked raf-1-mediated morphological changes and hormone suppression but not ERK1/2 phosphorylation. These results show that raf-1 induction suppresses neuroendocrine marker and hormone production in human gastrointestinal carcinoid cells via a pathway dependent on MEK activation.
authors.affiliation: Dept. of Surgery, Univ. of Wisconsin Medical School, University of Wisconsin Comprehensive Cancer Center, Madison 53792, USA.
authors.forename: Rebecca S
authors.initials: RS
authors.lastname: Sippel
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Carpenter
authors.forename: Muthusamy
authors.initials: M
authors.lastname: Kunnimalaiyaan
authors.forename: Sara
authors.initials: S
authors.lastname: Lagerholm
authors.forename: Herbert
authors.initials: H
authors.lastname: Chen
mesh_terms: D014408:Biomarkers, Tumor / Q000032:analysis*; D002276:Carcinoid Tumor / Q000737:chemistry / Q000201:enzymology* / Q000648:ultrastructure; D002455:Cell Division; D053379:Chromogranin A; D002864:Chromogranins / Q000032:analysis; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D048728:MAP Kinase Kinase Kinase 1; D008854:Microscopy, Electron; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009490:Neurosecretory Systems; D010190:Pancreatic Neoplasms / Q000737:chemistry / Q000201:enzymology* / Q000648:ultrastructure; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000235:genetics / Q000378:metabolism*; D022142:Secretory Vesicles / Q000648:ultrastructure; D012701:Serotonin / Q000032:analysis; D015398:Signal Transduction; D016708:Synaptophysin / Q000032:analysis; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D014408:Biomarkers, Tumor; D053379:Chromogranin A; D002864:Chromogranins; D004791:Enzyme Inhibitors; D016708:Synaptophysin; D012701:Serotonin; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; C482576:MAP3K1 protein, human