847l Biliary Phospholipids Sustain Intestinal Mucosa Regeneration and Tumorigenesis

Abstract

Carcinoid tumors are slow growing and highly vascular neuroendocrine neoplasms that have been increasing in incidence. Carcinoid tumors express vascular endothelial growth factor receptor 2 (VEGFR-2); however, its role is not completely understood. The aims of this study were: 1) to assess the expression and regulation of VEGFR-2 in carcinoid tumors and cells, and 2) to evaluate the effect of VEGFR-2 on carcinoid growth and metastasis. METHODS. 1) The expression of VEGFR-2 in carcinoid tumor sections and in the carcinoid cell line BON, which was established and characterized in our laboratory, was assessed by immunohistochemistry and Western blot, respectively. Signaling through Akt was adjusted chemically and through RNAi to delineate its effect on VEGFR-2 expression. 2) A BON cell line with stably decreased VEGFR-2 expression, designated as BON shVEGFR-2, was generated by transfecting cells with shRNA to VEGFR-2. Boyden chamber and scratch assays were performed on BON shVEGFR-2 cells to assess the effect of VEGFR-2 on invasion and migration. RESULTS. 1) Immunhistochemical analysis confirmed positive expression of VEGFR-2 in the endothelial and epithelial components of carcinoid tumor sections. Consistent with this finding, BON cells also expressed membrane bound (mb) VEGFR-2, as well as the truncated soluble form of VEGFR-2 (sVEGFR-2). Regulation of VEGFR-2 expression is inversely related to PI3K/Akt signaling, as inhibition of PI3K/Akt signaling with wortmannin upregulated VEGFR-2 expression. shRNA against PTEN increased phospho-Akt, resulting in decreased expression of VEGFR-2 in BON cells. BON shPTEN cells injected into the pancreas of nude mice formed increased liver metastases, compared to BON shControl cells, and the liver metastatic cells retained decreased VEGFR-2 expression. 2) BON shVEGFR-2 cells have decreased expression of mbVEGFR-2, sVEGFR-2, and E-cadherin compared to BON shControl cells. The migratory and invasive potential of BON shVEGFR-2 cells was increased approximately 4and 1.8-fold, respectively, at 48 h compared with BON shControl cells. CONCLUSIONS. The expression of VEGFR-2 in the epithelial component of carcinoid tumors and in the BON cell line, suggests an alternate role for VEGFR-2, in addition to its well-defined role in angiogenesis. The finding that decreased VEGFR-2 expression results in increased invasion and migration suggests that VEGFR-2 may inhibit carcinoid metastasis by the presence of sVEGFR-2 which binds and prevents VEGF ligand from acting on mbVEGFR-2. Thus, while VEGFR-2 inhibition prevents angiogenesis, it may also increase the metastatic potential of surviving carcinoid cells.