Regulation of neuroendocrine differentiation in gastrointestinal carcinoid tumor cells by notch signaling.
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.
Nakakura
Eric K
EK
Department of Surgery, University of California, San Francisco, California 94115, USA. NakakuraE@surgery.ucsf.edu
Sriuranpong
Virote R
VR
Kunnimalaiyaan
Muthusamy
M
Hsiao
Edward C
EC
Schuebel
Kornel E
KE
Borges
Michael W
MW
Jin
Ning
N
Collins
Brendan J
BJ
Nelkin
Barry D
BD
Chen
Herbert
H
Ball
Douglas W
DW
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
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