Abstract 4938: APC in breast cancer: the ABCs of gene expression

Breast cancer is the most common malignancy and cancer-related cause of death in non-smoking women in the United States. Due to the heterogeneity of this disease, the oncogenic and signaling pathways contributing to these tumors are distinct. The Adenomatous Polyposis Coli (APC) tumor suppressor is mutated or hypermethylated in up to 70% of sporadic breast cancers; however, the mechanism by which APC mutation impacts tumorigenesis remains unexplored. Up-regulation of the zinc finger transcription factor EGR-1 has been associated with cell invasion and enhanced drug resistance, which is an important property of cancer stem cells (CSCs). ALDH1 and STAT3 have been useful in the identification of CSCs, which are associated with poor clinical outcomes including increased tumor survival and invasion. We utilized two human breast cancer cell lines, MDA-MB-157 and DU4475, and cells isolated from the Mouse Mammary Tumor Virus-Polyoma middle T (MMTV-PyMT);Apc Min/+ mouse model. APC was knocked down in the MDA-MB-157 cells through shRNA lentiviral transduction, or transfected into DU4475 cells. First we looked at the expression of the transcription factor EGR-1 through Real-Time PCR in the MDA-MB-157 and DU4475 cell lines. Next, ALDH1 and STAT3 were measured in the MMTV-PyMT;Apc Min/+ mouse model and in MDA-MB-157 cells through western blots. In addition, an ALDEFLUOR assay was used to measure ALDH1 activity in the mouse model. To translate our findings to an in vivo model, we injected MMTV-PyMT;Apc Min/+ cells into the mammary fat pads of FVB-N syngeneic mice. EGR-1 expression was increased in both MDA-MB-157 APC-knockdown and DU4475 APC-mutant cells compared to cells expressing APC. In addition, STAT3 expression was found to be increased in MDA-MB-157 APC-knockdown and MMTV-PyMT;Apc Min/+ cells compared to MDA-MB-157 APC-wildtype and MMTV-PyMT;Apc +/+ cells. ALDH1 activity and tumor development were enhanced in Apc Min/+ cells compared to control cells. Combined, these data suggest that APC knockdown increases tumorigenic properties of cancer cells through EGR-1 overexpression and modulation of known cancer stem cell markers, ALDH1 and STAT3. Future studies will include measuring the expression of EGR-1 in the MMTV-PyMT;Apc Min/+ cells as well as ALDH1 in the human cell lines. Furthermore, because of the overexpression of these genes and markers, strategies designed to target positive populations might lead to more effective therapies of APC-mutant breast cancers. Citation Format: Katia Fernandez Soto, Monica K. VanKlompenberg, Jennifer Cole, Jenifer R. Prosperi. APC in breast cancer: the ABCs of gene expression. [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 4938. doi:10.1158/1538-7445.AM2015-4938