Abstract 430: MiRNA profiling of prostate cancer cell-derived large oncosomes identifies a signature of invasion and metastasis

Abstract

Abstract Introduction: We recently demonstrated that amoeboid prostate cancer (PCa) cells shed large (1-10µm diameter), bioactive membrane particles, representing a new class of tumor microvesicles termed large oncosomes (LO). LO can transfer oncogenic signals horizontally within the tumor microenvironment, as demonstrated by activation of phospho-tyrosines and Akt in recipient cells. Methods: We used differential ultracentrifugation and immuno-flow cytometry with size beads to isolate oncosomes in the 1-10µm diameter range. The method was applied to culture medium as well as to the plasma of mice with prostate cancer. In order to identify oncosome miRNAs relevant to metastasis, we performed a GeneChip® miRNA 2.0 Array screen of oncosomes shed by tumorigenic RWPE-2 PCa cells. Non-tumorigenic RWPE-1 cells were also analyzed. Results: LO contained protease and significantly stimulated migration of tumor and endothelial cells. LO also contained Caveolin-1, the GTPase ARF6 and other proteins that we used as markers to identify them in the circulation of mice with PCa, and in murine and human tissues with metastatic disease. Oncosomes also contained RNA. The miRNA profile of the oncosomes was compared to the miRNA profile of the cells of origin. While the miRNA profile of RWPE-2 almost completely matched the profile of RWPE-1 cells, the profiles differed significantly between LO isolated from the two cell lines. In particular, RWPE-2-derived LO contained miR-1228*, miR-150*, miR-373*, miR-135a*, miR-34b and miR-491-3p, which have been implicated in cancer cell proliferation and migration. In particular, the miRNAs miR-135a* and miR-373* target and inhibit the focal adhesion kinase (FAK), which plays a role in promoting a mesenchymal to amoeboid transition. miR-135a* and miR-373* have also been demonstrated to stimulate cell invasion, and are up-regulated in metastatic prostate and breast cancer. Target prediction analysis identified members of pathways involved in metabolic deregulation, and in oncogenic intercellular signaling and cell-cell interaction specifically in the LO purified from the tumorigenic cell line. Conclusions: Collectively, our results indicate that tumor cells can use oncosome formation to actively export pro-oncogenic miRNAs and that oncosomes therefore serve as a potential source of biomarkers of tumor progression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 430. doi:1538-7445.AM2012-430