Abstract 1985: PBX1 regulated lipid metabolism gene expression and epithelial-mesenchymal transition independent of estrogen receptor

Introduction: Pre-B-cell leukemia homeobox-1 (PBX1) is a member of the three amino acid loop extension (TALE) family of homeodomain proteins that bind to DNA and regulate gene transcription by forming heterodimeric transcription complexes with Meis and Prep1. PBX1 is involved in cell fate determination during organogenesis and contributes to oncogenic activity in breast cancer. As a pioneer factor, PBX1 was found to drive ER signaling in ER+ breast cancer by remodeling the chromatin and increasing DNA accessibility. But the role of PBX1 in benign breast and ER- cancer cells is not clear. In our previous studies, we identified and validated that the expression of a set of lipid metabolism genes was higher in the contralateral breast of ER- tumor. Bioinformatic analysis on lipid metabolism gene promoter regions and revealed that PBX1 may act as a potential transcription factor to co-regulate those genes. In this study, we further investigate the function of PBX1 in ER- cells. Methods: Among the ER- cell lines, we infected cell lines expressing low endogenous PBX1 (MCF10A and MDA-MB-231) with PBX1 gene in lentiviral vector. We also infected cell lines expressing high endogenous PBX1 (MDA-MB-453 and SK-BR-3) with PBX1-shRNA to knockdown PBX1. The expression of lipid metabolism genes was detected by qRT-PCR. Markers for epithelial-to-mesenchymal transition (EMT) including E-cadherin, vimentin, β-catenin and α-SMA were detected using Western blot. The effects of overexpression or knock-down of PBX1 on proliferation, migration, and invasion were measured using IncuCyte live cell imaging system. The expression of PBX1 protein was measured in benign contralateral breast and in the matching tumor using mmnunohistochemistry. Results: Over-expression of PBX1 in ER- cell lines (MCF10A and MDA-MB-231) up-regulated lipid metabolism genes and promoted cell migration and invasion by inducing EMT (increased vimentin and decreased E-cadherin and β-catenin). In contrast, knocking-down PBX1 using shRNA in ER- cell lines (MDA-MB-453 and SK-BR-3) suppressed lipid metabolism gene expression. PBX1 was more highly expressed in benign tissues associated with ER- tumors compared to ER+ tumors. In tumor tissue, on the contrary, ER+ tumors shower higher PBX1 expression levels than ER- tumors. Conclusion: PBX1 is a master regulator of lipid metabolism genes. PBX1 promoted cell migration and invasion by inducing EMT. PBX1 may play different roles and interact with different co-factors in ER+ tumors and in benign tissues associated with ER- tumors. Citation Format: Ali Shidfar, Liannian Liu, Vamsi Parini, MiRan Choi, David Ivancic, Megan E. Sullivan, Demirkan B. Gursel, Seema A. Khan, Jun Wang. PBX1 regulated lipid metabolism gene expression and epithelial-mesenchymal transition independent of estrogen receptor. [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 1985. doi:10.1158/1538-7445.AM2015-1985