Abstract 1971: ESE-1 controls transformation properties in HER2+ breast cancer cells, and predicts poor prognostic status and survival in breast cancer patients

Abstract

Abstract The ETS transcription factor ESE-1 belongs to the top 5% of all overexpressed genes in ductal and lobular breast carcinomas. We have previously established that cytoplasmic expression of ESE-1 initiates transformation in benign MCF10A and MCF12A mammary epithelial cells, while nuclear ESE-1 maintains the transformed phenotype in luminal MCF7 and ZR-75-1 breast cancer cells. ESE-1 is also a transcriptional regulator of HER2 gene expression, and is highly expressed in HER2+ BT474 and SKBR3 cells. In this study we have delineated how ESE-1 controls transformation properties in HER2+ breast cancer cells, and have validated the clinical significance of ESE-1 overexpression in breast cancer patients. Here we show that ESE-1 not only maintains transformation properties in HER2-dependent, Herceptin (anti-HER2) sensitive HER2+ breast cancer cell lines BT474 and SKBR3, but also in HER2-independent, Herceptin-resistant clones of BT474 and SKBR3 cells, named BT474/HR20 and SKBR3/pool2 respectively. Using crystal violet growth assays, BrdU labeling, 2D clonogenic assays, and 3D colony formation in soft agar we show that knocking down ESE-1 inhibits proliferation, clonogenicity, and anchorage independent growth in SKBR3, BT474, BT474/HR20, and SKBR3/pool2 cell lines in-vitro. Mechanistically, ESE-1 knocked down Herceptin sensitive cells evinced a delay in cell cycle progression through G1, along with down-regulation of cyclin D1. Long-term stable inhibition of ESE-1 in these cells resulted in down-regulation of pAKT, which was not always correlated with inhibition of HER2 and pHER2. In the HER2-independent BT474/HR20 and SKBR3/pool2 cells, stable ESE-1 knockdown inhibited pAKT independent of HER2 down-regulation. Evaluation of the clinical significance of ESE-1 expression was done by IHC analysis on 319 patient tumor samples. While ≥ 20% nuclear ESE-1 expression associated with aggressive LN metastasis, ≥30% of cytoplasmic ESE-1 associated with poor prognosis in LN+ breast cancer patients. High cytoplasmic ESE-1 significantly associated with 27% of ER-negative, 35% of PR-negative, and 25% of HER2+ metastatic tumors. Log-rank analysis of disease free survival (DFS) in LN+ patients revealed that patients with ≥ 30% cytoplasmic ESE-1 had half the length of median DFS compared to LN+ patients with ≤ 30% cytoplasmic ESE-1 (p = 0.027). Analysis in all patients irrespective of their prognostic status depicted that patients expressing ≥ 20% nuclear ESE-1 or ≥ 30% cytoplasmic ESE-1 associated with poor median DFS compared to patients with < 20% nuclear ESE-1 or < 30% cytoplasmic ESE-1. Overall we established that ESE-1 is critical in both HER2-dependent, and HER2-independent tumorigenesis and provided novel mechanistic insights into ESE-1's mode of transformation. Finally, the data warrants a global role for ESE-1 as a prognostic marker in all breast cancer patients. Citation Format: Adwitiya Kar, Susan Edgerton, Ann Thor, Arthur Gutierrez-Hartmann. ESE-1 controls transformation properties in HER2+ breast cancer cells, and predicts poor prognostic status and survival in breast cancer patients. [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 1971. doi:10.1158/1538-7445.AM2015-1971