BRAF Gene Mutations Are Rare Events in Gastroenteropancreatic Neuroendocrine Tumors

Abstract

The BRAF gene, one of the human isoforms of RAF, is activated by ras, leading to cooperative effects in cells responsive to growth factor signals. We studied the frequency of BRAF and k-ras-2 mutations in primary neuroendocrine gastroenteropancreatic (GEP) tumors. Mutation analysis of the BRAF and k-ras-2 genes was performed in 40 primary neuroendocrine tumors of the GEP system. The expression of extracellular signaling-related kinase (ERK) 1/2, an important downstream point of convergence in the ras-RAF-mitogen-activated protein-ERK pathway was analyzed immunohistochemically. We detected one 1796 T-->A BRAF mutation that led to a substitution of valine by glutamic acid at position 599 (V599E) in 40 primary neuroendocrine GEP tumors (3%). We failed to detect specific mutation of the k-ras-2 gene. We identified constitutively activated ERK in almost all neuroendocrine tumor tissues tested irrespective of BRAF mutation or localization or functional activity. These results suggest that BRAF mutations do not have a role in tumorigenesis of neuroendocrine tumors. Nevertheless, activation of the RAF/mitogen-activated protein kinase pathway might have a causative role in the development of neuroendocrine tumors, independent of BRAF or k-ras-2 mutation.

Small bowel carcinoid (enterochromaffin cell) neoplasia exhibits transforming growth factor–β1‐mediated regulatory abnormalities including up‐regulation of C‐Myc and MTA1

“…It is notable that a recent report suggests that an activated ERK pathway is a feature of many GI carcinoids. 29 In summary, the results of the current study demonstrate that alterations in expression and function of SMADs in the KRJ-I cell line result in a decreased expression of p21 WAF1/CIP1 and up-regulation of c-Myc and altered regulation of carcinoid malignancy-associated factors. These data support the hypothesis that an escape from TGFb1-mediated growth inhibition occurs in small intestinal carcinoids.…”

“…MTA1 was examined because it is a metastasis factor overexpressed in malignant primary GI carcinoids and their metastases 27 and has been linked to a worse prognosis in patients with EC cellderived appendiceal carcinoids. 28 E-cadherin is of interest because reduced expression correlates with malignant carcinoid behavior, 21 whereas the ERK pathway is relevant because it is active in the majority of GI carcinoids, 29 and may be cross-activated either by TGFb1 30 or by growth factors directly released by TGFb1. 11 It has not been possible to address these mechanistic questions previously because to our knowledge no homogenous human EC cell preparations or cell lines existed until we developed the methodology to isolate and culture normal human small intestinal EC cells.…”

Blood and tissue neuroendocrine tumor gene cluster analysis correlate, define hallmarks and predict disease status

“…Growth factor expression and signaling is a well-known regulator of NET proliferation (Kidd et al 2005) and signaling pathways (e.g. the RAS/RAF/MAPK signaling pathway) is typically activated (Perren et al 2004, Tannapfel et al 2005 while expression of the BRAF activator Rap1 as well as B-Raf itself can be detected by immunohistochemistry (75%) (Karhoff et al 2007). Other examples include secretion, e.g.…”

Expression and therapeutic relevance of heat-shock protein 90 in pancreatic endocrine tumors

“…AKT, as part of the PI3K/AKT pathway, is activated in w70% of PET (Guo et al 2003), and its activation has been associated with a resistance to apoptosis and increased cell proliferation in part by increasing the activity of CDK4 (Hay 2005, Fatrai et al 2006). ERK1/2, which is part of the Ras-Raf-MEK-Erk pathway, was reported to be activated in PET to a much greater extent than in non-neoplastic b cells (Tannapfel et al 2005). We show that upon HSP90 inhibition in PET cells, these key proteins are degraded or inactivated.…”

“…In the human PET cell line BON and the murine PET cell line b-TC-3, the HSP90 inhibitors 17-AAG and 17-DMAG lead to a degradation and/or inactivation of these proteins. The latter proteins are part of or associated with important cell signaling pathways, in particular the PI3K/AKT pathway that contributes to cell growth and survival (Hennessy et al 2005) and the Ras-Raf-MEK-Erk pathway that controls cell proliferation (Mebratu & Tesfaigzi 2009), and are shown to also affect PET (Guo et al 2003, Sippel et al 2003, Tannapfel et al 2005, Missiaglia et al 2010. Both pathways can be activated by IGF1R, which is thought to be part of an autocrine feedback loopstimulating proliferation of PET cells (von Wichert et al 2000), and MET, which seems to support metastasization in PET (Hansel et al 2004).…”