Extracellular Vesicles derived from Cancer demonstrate Autophagosome Properties

Abstract

Cancer extracellular vesicles (EVs) are considered candidates for early detection of cancer and infectious diseases. EVs made by tumor cells and non-tumor cells come in a variety of sizes with different antigenic compositions. Although some information is known about classical EVs, the smallest EVs, very little is known regarding the function and composition of large EVs. We set out to study the differences in the composition of shed large (2K), medium (10K), and small  (100K) EVs and how they play a role in the process of autophagy. Secondly, we addressed whether a specific size class of EVs preferentially induce angiogenesis. We cultured GFP-4T1 cells which are a syngeneic metastatic mouse carcinoma line. Shed EVs of differing sizes were harvested from cell media by centrifugation at varying speeds. Using transmission electron microscopy, western blot, and immunoblot methods we analyzed EVs and the markers present in each of the EV sizes. We looked at the time course of EV classes released when cells were treated with an autophagy flux inhibitor, chloroquine. We found that large 2K and 10K EVs have differential expression of VEGF, p62, IL-33, PD-L1, compared to the smaller classical exosomes. This study highlights the variety of functions that large EVs play in immune evasion, angiogenesis, and cancer progression, while additionally emphasizing the potential new role of shed autophagosomes as new markers for understanding cancer pathogenesis.