Abstract 1985: Reassessment of exosome composition

The heterogeneity of small extracellular vesicles and the presence of non-vesicular extracellular matter is a major obstacle to the study of exosomes. Here we employ two complementary methods, high-resolution density gradient fractionation and direct immunoaffinity capture, to demonstrate separation of small extracellular vesicles from non-vesicular material, and exosomes from other types of small extracellular vesicles. Cells secrete Argonaute 1-4 independently of exosomes. Extracellular RNA and RNA-binding proteins are differentially expressed between exosome and non-vesicle compartments. Exosomes do not possess a cytoskeleton and exclude glycolytic enzymes. Annexin A1 is a novel and specific membrane-associated protein marker of microvesicles shed directly from the cell plasma membrane, distinct from exosomes in vitro and in vivo. Small extracellular vesicles are not vehicles of active DNA release. Instead we propose a new model for active secretion of extracellular DNA through an autophagy- and multivesicular endosome-dependent but exosome-independent mechanism. A reassessment of exosome composition is necessary. Citation Format: Dennis K. Jeppesen, Jeffrey L. Franklin, James N. Higginbotham, Qin Zhang, Robert J. Coffey. Reassessment of exosome composition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1985.