Abstract B21: Exostosin 1 regulates cancer cell stemness in breast cancer cells

Cancer stem cells (CSCs), a group of cancer cells, are associated with resistance to radiation and chemotherapy and are implicated in recurrent of cancer. Exostosin 1 (EXT1) gene is widely reported as tumor suppressor and its indispensable role in elongation of heparan sulfate (HS) can speculate probable role as tumor promotor. In recent years, a number of tumors are reported to over express EXT1. Here, we investigated the role of EXT1 in the maintenance of cancer cell stemness. MCF7/ADR cells developed by exposing MCF7, breast cancer cells, to doxorubicin for several months in culture, showed high resistance to doxorubicin compared to MCF7, parental cell line. Doxorubicin resistant MCF7/ADR cells have enhanced P-glycoprotein (P-gp) expression. In FACs analysis, MCF7/ADR cells were accounted for high number of CSC population; they possessed large number of ALDH + and CD44 + /CD24 - population compared to MCF7. CSC marker, CD44, was found overexpressed in MCF7/ADR compared to MCF7. Besides that, in mammosphere culture, MCF7/ADR cells formed large number of mammospheres in contrast to MCF7. In microarray data analysis, several genes were found upregulated in MCF7/ADR cells and EXT1 was selected as a candidate gene. Overexpressed EXT1 in MCF7/ADR cells was confirmed by real time PCR. The critical role of EXT1 in maintaining cancer cell stemness was confirmed by siRNA mediated knockdown of EXT1. Knockdown of EXT1 repressed CSC markers, reduced population of ALDH + and CD44 + /CD24 - , and suppressed expression of CD44. As a molecular mechanism, we detected suppressed expression of heparan sulfate, syndecan1(SDC1) with siEXT1. With these results, we can suggest that EXT1 level might be a determining factor for doxorubicin sensitive breast cancer cells and enhanced expression of EXT1 can take part in development of CSC phenotype on exposure to anthracycline based therapy through upregulation of SDC1. Citation Format: Sarala Manandhar, Chang-gu Kim, Su Young Oh, Sun-Hee Lee, Jiyoon Seok, Yuk-Dong Jung, Hye-Eun Lee, Young-Sun Choi, You Mie Lee*. Exostosin 1 regulates cancer cell stemness in breast cancer cells. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr B21.