Abstract 5060: Exosome transfer from ovarian cancer cells to mesothelial cells promotes cell invasion by upregulating MMP-9 secretion and increasing clearance of mesothelial cells
Authors: Koji Nakamura, Kenjiro Sawada, Yasuto Kinose, Akihiko Yoshimura, Erika Nakatsuka, Seiji Mabuchi, Tadashi Kimura
Journal: Cancer Research (2015)

Abstract Ovarian cancer cells metastasize to organs in the abdominal cavity, such as the omentum, which are covered by a single layer of mesothelial cells. Thus, the cell-cell connection between ovarian cancer cells and mesothelial cells is the crucial step of metastasis. Exosomes are 30-100 nm membrane vesicles of endocytic origin, mediating diverse biological functions through transfer of proteins, mRNAs and microRNAs. However, whether exosome-mediated transfer plays any role in ovarian cancer cell invasion remains poorly understood. Thus, the aim of this study is to identify the functional role of ovarian cancer-derived exosomes during the process of ovarian cancer metastasis. Methods: Exosomes were isolated from two ovarian cancer cell lines (HeyA8 and TYK-NU) and immortalized normal ovarian epithelial cell line (IOSE) using differential centrifugation. Human peritoneal mesothelial cells (HPMCs) were isolated from normal omentum of patients undergoing gynecologic surgery. The isolation of exosomes was confirmed by electron microscope and the transfer of exosomes into HPMCs was confirmed by fluorescent-labeling exosomes. The effects of exosome transfer from ovarian cancer cells to mesothelial cells were analyzed in vitro 3D culture model, morphological assessment, Western Blotting and gelatin zymography. We found that CD44 was enriched in cancer derived exosome. Thus, gain or loss of function of CD44 was analyzed. CD44 expression of ovarian cancer omental metastasis and surrounding organs in clinical samples was assessed by immunohistochemistry. Results: Fluorescent-labeled exosomes were evidently transferred into HPMCs. Exosome-treated HPMCs changed in cellular morphology to spindle phenotype. Ovarian cancer invasion was significantly promoted in the presence of exosome-treated HPMCs. In exosome-treated HPMCs, MMP-9 secretion was up-regulated and E-cadherin expression was down-regulated. The clearance of mesothelial barrier was increased in exosome-treated HPMC monolayer. By Western Blotting, we confirmed CD44 was enriched in exosomes and exosome-treated HPMCs display high-level of CD44. When CD44 expression was knocked down by siRNA in ovarian cancer cells, these effects to HPMCs were significantly attenuated. In contrast, the enforced expression of CD44 into HPMCs promoted cancer invasion by secreting MMP-9 and increasing mesothelial clearance. In human omentum with microscopic metastasis of ovarian cancer, positive CD44 expression was confirmed in a mesothelial cell layer when cancer cells are attaching onto it, while CD44 expression was generally negative in normal mesothelial cells. Conclusion: Herein, we revealed that ovarian cancer-derived exosomes transfer CD44 to HPMCs, which can facilitate ovarian cancer invasion by up-regulating of MMP-9 secretion and increasing clearance of HPMCs. Citation Format: Koji Nakamura, Kenjiro Sawada, Yasuto Kinose, Akihiko Yoshimura, Erika Nakatsuka, Seiji Mabuchi, Tadashi Kimura. Exosome transfer from ovarian cancer cells to mesothelial cells promotes cell invasion by upregulating MMP-9 secretion and increasing clearance of mesothelial cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5060. doi:10.1158/1538-7445.AM2015-5060