Abstract MIP-052: THE ROLES OF CD24 IN OVARIAN CANCER DEVELOPMENT

Abstract

Abstract OBJECTIVES: CD24 is recently reported as ovarian cancer stem cell markers, and the expression of CD24 is increased from borderline tumors to invasive ovarian carcinomas. However, the underlying pathways controlled by CD24 in ovarian pathogenesis were poorly understood. We investigated the potential roles of CD24 in normal fallopian tube epithelial (FTE) cells and ovarian cancer development. METHODS: Lentiviral particles harboring CD24 shRNAs targeting CD24 expression were used to establish FTE cell lines and ovarian cancer cell lines with CD24 knockdown. The resulting cell lines were compared with the correspondent cells with non target shRNA control in colony formation assay, BrdU incorporation, cell growth and drug resistance. Western blot was used for analyzing downstream pathways affected by the knockdown of CD24. Expression of CD24 and its downstream effectors identified from western blot, including Pax 2 and Gli1 were studied in normal FTE, non–serous and serous tumor tissues by immunohistochemistry (IHC) to confirm whether the in vitro study is clinically relevant. RESULTS: Western blot analysis showed that CD24 expression was absent in normal ovarian surface epithelial (OSE) cells but was relatively high in normal FTE cells. In addition, serous cancer cell lines have a lower CD24 expression when compared to non–serous cancer cell lines. Knockdown of CD24 in FTE cells caused slower growth, lower ability in colony formation, reduced percentage of cells in S phase and decrease in expression of p–stat3 in JAK pathway and the JAK downstream targets Nanog and OCT3/4; and Pax2, which is normally expressed in FTE but lost in FTE secretory cell outgrowth (SCOUT). The loss of Pax2 in SCOUT is associated with serous carcinoma. IHC showed cytoplasmic co–localized expression of CD24 and Pax2 in the normal FTE tissue, suggesting the possibility of interaction between these two proteins in vivo. In contrast, knockdown of CD24 in ovarian cancer cells caused faster growth, higher ability in colony formation, increased percentage of cells in S phase, more resistant to carboplatin and higher expression of Shh and Gli1 in Sonic hedgehog (SHH) pathway. The above effects were more obvious in the non–serous cancer cell line. Activation of SHH pathway requires translocation of Gli1 into the nucleus. Concurrent with the in vitro results, IHC showed that the expression of Gli1 was found inside the nucleus in the non–serous tumor tissues but in the cytoplasm in serous–tissue, suggesting that the effect brought by SHH pathway is more prominent in the non–serous cancer cells. CONCLUSION: Our study is the first study revealing the linkage between CD24 and PAX2, and suggesting normal FTE cells depends on CD24/JAK pathway for growth and the loss of CD24 expression and hence, the loss of PAX2 may be associated with serous type tumor development, basing on other studies that SCOUTs were significantly associated with serous carcinoma. Moreover, the study also suggests CD24 pathway affects Type I and Type II (HGSOC) tumors differently. The CD24/SHH pathways may be responsible in controlling cell growth and drug resistance in ovarian cancer cells, hence, warrant further studies. Citation Format: Pui–Wah Choi, Brooke E. Howitt, Christopher P. Crum, Ross S. Berkowitz, and Shu–Wing Ng. THE ROLES OF CD24 IN OVARIAN CANCER DEVELOPMENT [abstract]. In: Proceedings of the 11th Biennial Ovarian Cancer Research Symposium; Sep 12-13, 2016; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(11 Suppl):Abstract nr MIP-052.