Abstract 3150: Exploring the role of Rap1Gap in the progression from DCIS to invasive breast carcinoma

Abstract

Abstract Understanding the underlying mechanisms that drive malignant progression of breast cancer is important. The purpose of this study is to define the role of Rap1Gap in the progression of ductal carcinoma in-situ (DCIS) to invasive cancer. We employed an in-vitro three-dimensional (3D) overlay model that provides a physiologically relevant microenvironment to study mechanisms of mammary gland development and malignant progression. We previously employed next generation sequencing (NGS) and identified 63 consistently upregulated genes in three DCIS lines (SUM102, SUM225, MCF10.DCIS) compared to non-transformed mammary epithelial cells. To gain insight into common transcriptional elements of co-regulated genes that may be critical to the DCIS phenotype, we have mined our NGS data using Frameworker (Genomatix). The 63 upregulated genes are associated with 244 candidate promoters out of a total of 82,703 promoters in the entire human genome. Our analysis shows that the common framework RXRF-ZF02-ZF02-PLAG-HDBP is only present in the promoters of three genes: RAP1GAP, SPRY4 and PDGFB. All of these genes are upregulated in our DCIS signature, which means that this framework is hugely enriched (336-fold) over what would be expected by chance. Rap1Gap has tumor suppressor properties; its functions, via regulation of Rap1 activity, include regulation of cell adhesion, suppression of cell proliferation and metastasis. In other epithelial cancers, loss of Rap1Gap has been linked to epithelial to mesenchymal transition (EMT) and invasion. To begin study of Rap1Gap in breast cancer progression, we performed immunohistochemistry. We show strong Rap1Gap staining in DCIS with little to no expression in myoepithelial and stromal components. Immunoblotting results show that Rap1Gap levels in MCF10.CA1d cells (a model of invasive carcinoma) are reduced compared to those in MCF10.DCIS cells. Rap1Gap expression is low in additional basal breast cancer cell lines, but high in luminal ER+ /PR+ cell lines. We propose that over-expression of Rap1Gap may serve as a tumor suppressive mechanism in DCIS; subsequent reduction of Rap1Gap may be a switch for EMT and progression to an invasive phenotype. Citation Format: Seema Shah, Kingsley Osuala, Shihong Mao, Quanwen Li, Bonnie Sloane, Stephen Krawetz, Raymond R. Mattingly. Exploring the role of Rap1Gap in the progression from DCIS to invasive breast carcinoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3150. doi:10.1158/1538-7445.AM2014-3150