Cancer Cell-Monocyte Communication Mediated by Small Extracellular Vesicles

Communication between cells is mediated through the release of extracellular vesicles (EVs), which may be composed of a number of molecules including proteins and nucleic acids. In cancer, these vesicles mediate the communication between cancer cells and normal cells and play an important role in cancer progression. They differ in size and their biological contents, but in this thesis, we focused on small extracellular vesicles (sEVs) isolated from cell culture media by ultracentrifugation and iodixanol density gradient. sEVs range in size from 50-200 nm and are enriched with tetraspanins including (CD9, CD63, and CD81) as well as other endosomal markers such as TSG101, and Alix. Other proteins are also enriched in sEVs, including integrins. Our laboratory has demonstrated the enrichment of αvβ6 integrin in these vesicles and its role in mediating cellular signaling pathways in prostate cancer. This integrin is over-expressed in prostate cancer and this overexpression increases cell motility and tumor growth. Immune cells are known to infiltrate tumors; among others, tumor-associated macrophages (TAM) play a role in inhibiting the recruitment of T cells to the tumor and therefore promote tumor progression. TAMs are categorized into two major subtypes. Classically activated macrophages (M1) and alternatively activated macrophages (M2). M1 has an anti-tumorigenic effect while M2 has a pro-tumorigenic effect on tumor. TAMs are originated from recruited monocytes. Targeting these TAMs is crucial to understand the pathobiology of the disease. Our laboratory has implicated sEVs enriched with αvβ6 integrin in the communication between cancer cells and monocytes. These cancerous sEVs induced monocyte polarization by increasing the expression of M2 markers such as CD163 and CD204. Our laboratory has shown that down-regulation of αvβ6 integrin up-regulates the STAT1-MX1/2 signaling pathway in cancer cells and in sEVs released by cancer cells. In order to investigate whether prostate cancer cell-derived vesicular STAT1 has a causal effect, I down-regulated αvβ6 and STAT1 in PC3 derived sEVs, using siRNA as well as CRISPR-Cas9 strategies, and measured the levels of CD163. The results show that sEVs lacking both αvβ6 and STAT1 inhibit CD163 levels in a STAT1-independent manner. I also evaluated the levels of cytokines released by PBMC upon incubation with sEVs lacking both αvβ6 and STAT1. My findings demonstrate that upon incubation with sEVs lacking both αvβ6 and STAT1, PBMC selectively up-regulate the levels of IL-10 and IL-6, predominantly anti-tumorigenic interleukins, but not of a pro-angiogenic cytokine such as VEGF. These findings demonstrate that vesicular αvβ6 integrin affect monocyte phenotype thus affecting the tumor microenvironment