Abstract 3791: Secreted plectin-rich exosomes from pancreatic cancer cells promote tumor aggressiveness.

Abstract

Abstract Background & Aims: We recently demonstrated that the aberrant extracellular localization of the cytoskeletal linker protein plectin is a robust biomarker for the progression of pancreatic ductal adenocarcinoma (PDAC), one of the most aggressive malignancies. Exosomes are nanometer-sized particles containing cytoplasm and plasma membrane that are secreted by both normal and cancerous cells. Recently the importance of exosomes in cross-talk in the tumor microenvironment has been demonstrated. Fusion of exosomes to the cellular membrane in either a paracrine or autocrine manner can result in aberrant protein localization. Here, we assess the mechanism for plectin mislocalization and its functional role in PDAC. Methods: A plectin-binding assay was developed to assess the presence of cell-surface localized plectin. To examine their potential contribution to aberrant extracellular localization of plectin, we determined whether plectin was present in PDAC-secreted exosomes collected by ultracentrifugation and evaluated by immunoblotting. Based on these observations, we then determined whether exosomes with or without plectin altered gross phenotypic tumor characteristics in vitro in tumor stromal and endothelial cells. Finally, we tested the ability to alter outgrowth kinetics by directly injecting exosomes with or without plectin in tumors in vivo. Results: Plectin was localized on the cell surface as well as present in exosomes derived from PDAC cell lines but not from non-transformed human pancreatic ductal epithelial (HPDE) cells. Plectin presence in the exosomes hinged on the expression of integrin β4, a protein known to interact with cytosolic plectin. shRNA and overexpression studies collectively demonstrated a positive role of plectin and its localization in the exosomes in proliferation, migration, and invasion of PDAC cells and migratory capacity of microenvironment cells. Finally, plectin-rich exosomes enhanced in vivo tumor growth. Conclusions: Plectin is expressed in PDAC and is aberrantly localized to the cell surface via exosomes in an integrin β4-dependent manner. Additionally, plectin-rich exosomes induce pronounced increase in tumor growth in vitro and in vivo further they increased invasion and migration in vitro. Plectin-positive exosomes had profound effects on stromal and endothelial cells. Because cell surface plectin has been shown to be a biomarker for transition of pre-invasive to invasive PDAC, the elucidation of the mechanisms of its deregulation may provide important insights for successful detection and management of PDAC. Citation Format: Soo J. Shin. Secreted plectin-rich exosomes from pancreatic cancer cells promote tumor aggressiveness. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3791. doi:10.1158/1538-7445.AM2013-3791