Abstract 3202: Radiation increases invasive activity of breast cancer cells via altering lysosome exocytosis

Radiotherapy is a standard treatment for many localized solid cancers. However, previous studies have shown that radiation may increase the invasive activity of cancer cells and potentially distant metastasis. Recently, lysosome exocytosis has been linked to cancer cell invasiveness and progression. In this study, we evaluate the role of lysosome exocytosis on invasive activity of breast cancer cells upon radiation.We used both human and murine breast cancer cell lines (MDA-MB-231 and 4T1). The cells were treated with a single radiation dose of 4 Gy. Cell invasive activity was measured by matrigel chemoinvasion assay. Lysosome exocytosis was quantified by fluorescein isothiocyanate conjugated dextran (FITC-dextran) intake assay, cell-surface lysosomal associated membrane protein 1 (LAMP1) expression and cellular lysosome distribution assay. To validate the lysosome function, lysosome inhibitors, bafilomycin A1 and chloroquine were used. Short hairpin RNA (shRNA) was used to knockdown ARL8B, which is a small GTPase protein that regulates lysosome distribution and exocytosis. The invasive activity and lysosome exocytosis of tested breast cancer cell lines were increased after radiation treatment. Treatment with lysosome inhibitor bafilomycin A1 or chloroquine decreased the invasive activity of cancer cells, with or without radiation treatment. The protein level of ARL8B increased in the lysosome fraction upon radiation. Down-regulation of ARL8B with shRNA led to a decrease in lysosome exocytosis with a concomitant inhibition radiation induced invasive activity of the breast cancer cells without affecting the basal invasiveness. In addition, overexpression of ARL8B increased the invasive activity of breast cancer cells, which was similar to the result obtained after radiation.In summary, radiation enhances lysosome exocytosis in breast cancer cells that can lead to their increased invasive activity. Our findings provide a novel mechanism to understand cancer invasion after radiotherapy and suggest novel approaches to counteract this undesirable effect of radiotherapy in the future. Citation Format: Ping-Hsiu Wu, Yasuhito Onodera, Amato J. Giaccia, Quynh-Thu Le, Hiroki Shirato, Jin-Min Nam. Radiation increases invasive activity of breast cancer cells via altering lysosome exocytosis [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 3202.