Abstract 1812: The Role of the BP1 homeobox gene in triple negative breast cancer .
Authors: Gill Mandeep , Kirolikar Saurab , Ghimbovschi Svetlana , Cavalli Luciane R. , Berg Patricia E. 
Published: August 2014

Background: Triple negative breast cancers (TNBC) lack the expression of ER, PR and HER2 receptors, thus targeted treatments against these receptors are not effective. We are studying BETA PROTEIN 1, a member of homeobox gene family, which we cloned and showed is activated in 80% of invasive breast cancers; its expression correlates with breast cancer progression and invasion. The BP1 gene is located on 17q21, a region that is reported to be altered in 30% of breast tumors. Since BP1 mRNA and protein are highly expressed in ER and PR negative and clinically aggressive tumors, we hypothesize that BP1 may play a relevant role in TNBC. Our main objective was to evaluate the gene copy number and mRNA/protein expression status of BP1 in TNBC, in both clinical cases and established TNBC cell lines. Methods: We have characterized seven cell lines (5 TNBC and 2 normal breast cell lines) for the expression of BP1 using qPCR and Western blot analysis. To delineate pathways in TNBC cells that are dysregulated by BP1 expression, we studied both the seven parental cell lines and a stably overexpressed BP1 TNBC cell line, Hs578T-OE. Microarray analysis was performed in all these cell lines and the data obtained was verified using qPCR and ELISA. Formalin-Fixed, Paraffin-Embedded tissues of TNBC were analyzed by array-CGH and confirmed by Taqman copy number (using a BP1-TAM specific probe) and FISH (using our constructed BP1-BAC probe) assays. Results: All of the parental TNBC cells had at least 2.8-fold more pBP1 than the normal breast cell lines suggesting that TNBC tumors have higher levels of pBP1 than non-TNBC tumors. Gene expression microarrays in the TNBC cell lines revealed up/down regulation of several genes in comparison to the normal breast cell lines, including the EGFR. Interestingly, the IL-6 and IL-8 genes were significantly upregulated in TNBC cells overexpressing BP1. ELISA assays confirmed a correlation between elevated levels of IL-6 and IL-8 production and BP1 in the conditioned media from Hs578T cells overexpressing BP1 compared with the empty vector. Studies are underway to establish the mechanism by which these pathways are regulated by BP1. BP1 increase copy number was observed in 37% (25/67) of the cases by array-CGH. Confirmation of these changes by FISH and TaqMan copy number assays revealed increased copy number in 20% (13/66) and 23% (9/38) of the cases, respectively. Protein expression analysis by IHC is currently been conducted in these cases to determine if BP1 increase DNA copy number can be one of the mechanisms that leads to pBP1overexpression. Conclusions: Both BP1 copy number and protein expression are dysregulated in TNBC. Microarray analysis in TNBC cell lines have revealed important cancer related genes and oncogenic pathways that may be upregulate by BP1, suggesting that BP1 could be a valuable molecular marker and therapeutic target in this aggressive form of breast cancer.

Citation Format: Mandeep Gill, Saurab Kirolikar, Svetlana Ghimbovschi, Luciane R. Cavalli, Patricia E. Berg. The Role of the BP1 homeobox gene in triple negative breast cancer . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1812. doi:10.1158/1538-7445.AM2013-1812