title: Regulation of neuroendocrine differentiation in gastrointestinal carcinoid tumor cells by notch signaling.
abstract: BACKGROUND
  Gastrointestinal (GI) carcinoid tumors elaborate serotonin and other vasoactive substances, causing the carcinoid syndrome. Based on developmental biology data, we hypothesized that basic helix-loop-helix transcription factors, including achaete-scute complex homolog-like 1 (Ascl1)/hASH1, and the Notch signaling pathway might regulate the neuroendocrine phenotype in GI carcinoids.
  
  
  OBJECTIVE
  The aim of this study was to evaluate expression of developmental transcription factors and Notch signaling components in GI carcinoids and model their interaction in a relevant GI carcinoid cell line.
  
  
  METHODS
  Fourteen GI carcinoid tumor specimens, five paired adjacent normal tissues, fetal tissues, and tumor cell lines were analyzed by RT-PCR and immunoblot. BON carcinoid cells were further analyzed after Notch overexpression for neuroendocrine marker expression, serotonin production, and growth.
  
  
  METHODS
  The study was conducted in an academic referral center.
  
  
  METHODS
  Deidentified archival pathology specimens were examined.
  
  
  RESULTS
  Among a panel of six developmental transcription factors tested, only Ascl1 mRNA was overexpressed compared with surrounding normal tissue (seven of 10 GI carcinoid tumors and in BON cells, none of five normal tissues). Ascl1 protein was also expressed in four of four carcinoid tumors and BON cells). Notch pathway ligands, receptors, and downstream effectors were widely expressed in tumor and normal specimens. Overexpression of activated Notch1 in BON cells led to induction of the Notch effector hairy and enhancer of split 1 (Hes1), loss of Ascl1, reductions in neuron-specific enolase, synaptophysin, and chromogranin A, and most significantly, an 89% decrease in serotonin concentration and equivalent reductions in serotonin-reactive cells and repression of tryptophan hydroxylase 1 mRNA.
  
  
  CONCLUSIONS
  The Notch signaling pathway is a significant regulator of neuroendocrine differentiation and serotonin production in GI carcinoid tumors.
authors.affiliation: Department of Surgery, University of California, San Francisco, California 94115, USA. NakakuraE@surgery.ucsf.edu
authors.forename: Eric K
authors.initials: EK
authors.lastname: Nakakura
authors.forename: Virote R
authors.initials: VR
authors.lastname: Sriuranpong
authors.forename: Muthusamy
authors.initials: M
authors.lastname: Kunnimalaiyaan
authors.forename: Edward C
authors.initials: EC
authors.lastname: Hsiao
authors.forename: Kornel E
authors.initials: KE
authors.lastname: Schuebel
authors.forename: Michael W
authors.initials: MW
authors.lastname: Borges
authors.forename: Ning
authors.initials: N
authors.lastname: Jin
authors.forename: Brendan J
authors.initials: BJ
authors.lastname: Collins
authors.forename: Barry D
authors.initials: BD
authors.lastname: Nelkin
authors.forename: Herbert
authors.initials: H
authors.lastname: Chen
authors.forename: Douglas W
authors.initials: DW
authors.lastname: Ball
mesh_terms: D051792:Basic Helix-Loop-Helix Proteins; D002276:Carcinoid Tumor / Q000473:pathology*; D002454:Cell Differentiation; D049109:Cell Proliferation; D004268:DNA-Binding Proteins / Q000032:analysis / Q000235:genetics; D005770:Gastrointestinal Neoplasms / Q000473:pathology*; D006801:Humans; D008565:Membrane Proteins / Q000502:physiology*; D009490:Neurosecretory Systems / Q000166:cytology*; D012333:RNA, Messenger / Q000032:analysis; D051880:Receptors, Notch; D012701:Serotonin / Q000096:biosynthesis; D015398:Signal Transduction / Q000502:physiology*; D014157:Transcription Factors / Q000032:analysis / Q000235:genetics
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D008565:Membrane Proteins; D012333:RNA, Messenger; D051880:Receptors, Notch; D012701:Serotonin; D014157:Transcription Factors; C065500:ASCL1 protein, human