Heterogeneity in Signaling Pathways of Gastrointestinal Neuroendocrine Cell Tumors: A Critical Look at Notch Signaling Pathway.
He Wang, Yili Chen, Vikram Deshpande. Massachusetts General Hospital/Harvard Medical School, Boston; Delaware University, Newark, DE
Background: The molecular pathogenesis of gastrointestinal neuroendocrine tumors (GI-NET) is largely unknown, as are their signaling pathways. We hypothesize that GI-NETs are heterogeneous with regards to these signaling pathways and the differences could have a significant impact on the outcome of clinical trials. Herein, we explore differences in the signaling pathways of GI-NETs emphasizing heterogeneity in the Notch signaling pathway.
Design: We selected 120 well-differentiated NETs including tumors originating in pancreas (n=74), ileum (n=31), and rectum (n=15). Immunohistochemistry was performed on tissue microarrays using the following antibodies: Notch-1, Hes-1, Hey 1, pIGF1R, and bFGFR. Tumor mRNA were extracted from formalin-fixed paraffin-embedded tissue blocks after macro-dissection. Gene profiling study was performed by using human genome U133A 2.0 array and data were analyzed using Array Studio (Omics Soft, NC). The gene profiling results were selectively confirmed by using quantitative reverse transcription polymerase chain reaction (qRT-PCR).
Results: Initial immunohistochemical analysis showed Notch-1 was uniformly expressed in rectal NETs (100%), a subset of pancreatic NETs (34%), and negative in ileal NETs. Similarly, a downstream target of Notch-1, Hes1 was preferentially expressed in rectal NETs (64%), a subset of pancreatic NETs (10%), and uniformly negative in ileal NETS. Messenger RNAs for Notch-1, Hes 1 and Hey 1 were 2.32, 2.44 and 2.39 folds higher in rectal NETs as compared to ileal NETs. Global gene expression profiling showed more than 100 genes were differentially expressed in small intestinal vs. rectal NETs, with changes as high as 50 fold. These genes were concentrated in several signal transduction pathways including cancer endocrine pathway and cell growth/proliferation pathway. The differential expression of selected genes including ISL LIM homeobox 1, cathepsin B, FGF receptor 3, glucagan, and tryptophan hydroxylase 1 were confirmed by qPCR and immunohistochemistry.
Conclusions: Our results confirm the heterogeneity in signaling pathways of GI-NETs. We demonstrate an active Notch-1 signaling in rectal NETs, conversely, ileal NETs lack such activity. Notch-1 inhibitors are unlikely to provide benefit in ileal NETs, conversely, their efficacy in rectal NETs needs further study. Further analysis of signaling pathways is critical for designing clinical trials in GI-NETs.
Tuesday, March 1, 2011 1:00 PM
Poster Session IV # 64, Tuesday Afternoon