Abstract 5212: Akt signaling enhances carcinoid cell secretion, migration, and invasion

Carcinoid tumors are slow growing neuroendocrine tumors characterized by the secretion of peptides and biogenic amines such as serotonin (5-HT) and TGF-β. Although relatively indolent, carcinoid tumors of the GI tract can metastasize to the liver and release secretory products into the systemic circulation resulting in the carcinoid syndrome. PI3K/Akt signaling is increased in carcinoid tumors and is hypothesized to promote carcinoid progression. The purpose of our current study was to delineate the role of Akt signaling in carcinoid cell secretion, migration, and invasion using the BON cell line, derived from a human pancreatic carcinoid tumor. Methods. i.) BON cells were transfected with either non-targeting control shRNA (BON shControl) or shRNA to PTEN (BON shPTEN), the natural inhibitor of Akt activation. Conditioned media was collected from BON shControl and shPTEN cells and assessed for 5-HT and TGF-β by ELISA. Western blots were performed to assess changes in the expression of 5-HT and TGF-β. ii.) Scratch and Boyden chamber assays were performed to compare the migration and invasion, respectively, of BON shControl and shPTEN cells. The protein levels of the epithelial-to-mesenchymal transition (EMT) markers E-cadherin, a cell adhesion protein, and snail were assessed in both cell groups with western blot. Cells were injected into the pancreas of athymic nude mice and liver metastases were assessed via immunofluorescence. Results. i.) Knockdown of PTEN increased the secretion of 5-HT and TGF-β from BON cells. Compared to control, lysates from BON shPTEN cells displayed increased expression of tryptophan hydroxylase, the rate limiting enzyme of 5-HT biosynthesis, and TGF-β. ii.) Compared to BON shControl cells, BON shPTEN cells exhibited a 3.2- and a 1.6-fold increase in migration at 24 h and 48 h, respectively. At 24 h BON shPTEN cells displayed an 8-fold increase in invasion, while at 48 h a 2.6-fold increase in invasion was noted compared to BON shControl cells. Knockdown of PTEN in BON cells significantly decreased E-cadherin expression, whereas snail expression was increased. BON shPTEN and BON shControl cells formed liver metastases in 60% and 10% of mice, respectively. Conclusions. The Akt pathway enhances carcinoid cell secretion and metastatic potential by increasing expression and synthesis of secretory products and by altering expression of EMT markers, respectively. In addition to promoting metastasis, Akt signaling may also contribute to carcinoid syndrome. These results suggest that targeting Akt signaling may provide a dual strategy to decrease peptide secretion and inhibit carcinoid cell invasion. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5212.