Abstract 4056: Immune regulation by miR-1227 LO
Authors: Andrew R. Chin, Dolores Di Vizio, Valentina R. Minciacchi, Mariana Sobreiro, Cristiana Spinelli
Journal: Cancer Research (2018)

Abstract Immunotherapy offers great promise for the treatment of prostate cancer; however prostate cancer often acquires mechanisms to dampen the tumoricidal immune response. Understanding how prostate cancer dampens the immune system will facilitate the generation of more effective immunotherapies. Here we investigate how large oncosomes (LO)-mediated transfer of miR-1227 to immune cells modulates the immune response. Extracellular vesicle (EV)-encapsulated miRNAs are being increasingly recognized for playing a key role in cancer progression and immune modulation. miR-1227 is a poorly characterized miRNA that is enriched in EV secreted by prostate cancer cells in comparison to non-malignant prostate epithelial cells. miR-1227 expression is increased in migratory glioblastoma cells in comparison to non-migratory glioblastoma cells, and in radiation resistant esophageal cells and colorectal cancer stromal cells indicating that miR-1227 is upregulated in different cancer types. However, the role of miR-1227 in cancer is poorly understood. We demonstrate here that EV obtained from prostate cancer cells overexpressing miR-1227, induce the migration of prostate cancer cells and fibroblasts. A comparative analysis between different EV subtypes indicates that miR-1227 is enriched in LO, a class of EV that are secreted by highly invasive amoeboid-migrating cells. We also show that LO carry more RNA than the more widely studied exosomes indicating that LO may be a more robust source of EV-encapsulated miRNA. RNA sequencing from miR-1227 stably expressing prostate cancer cells and 5 different in silico miRNA target prediction methods were used to identify putative miR-1227 targets. IPA pathway analysis from these predicted targets highlighted several functions related to the immune system, including T cell homeostasis, T cell development, and development of Th17 cells. A more in-depth analysis of the 51 genes involved in T cell homeostasis showed enrichment of genes associated with Th17 and Th1 T cell differentiation. Alterations in Th17 and Th1 differentiation modulates T cell cytokine secretion, which are important mediators of cancer growth and progression. Transient transfection of miR-1227 in immune cells altered the cytokine expression profile, resulting in the upregulation of several cytokines that promote cancer growth including CCL5 and IL6. We tested whether LO can be taken up by activated T cells to directly modulate cytokine secretion. To determine whether miR-1227 can be functionally transferred to recipient cells via LO we isolated LO from prostate cancer cells stably expressing miR-1227 using ultracentrifugation followed by density gradient purification. The isolated LO were used to treat immune cells to show that LO-encapsulated miR-1227 alters cytokine profiles. These results indicate that LO-encapsulated miR-1227 may be involved in cancer immune modulation through targeting specific genes involved in T-cell differentiation. Citation Format: Andrew R. Chin, Dolores Di Vizio, Valentina R. Minciacchi, Mariana Sobreiro, Cristiana Spinelli. Immune regulation by miR-1227 LO [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4056.