Abstract 3297: PTEN loss enhances amphiregulin-specific signaling and gene expression in triple-negative breast cancer
Authors: Kappler Christiana , Wilson Robert , Varughese Bridget , Ethier Stephen P. 
Published: May 2015

The epidermal growth factor receptor (EGFR) is frequently overexpressed in triple-negative breast cancer, and approximately half of all basal breast cancers show autocrine activation of EGFR by amphiregulin (AREG). When AREG is the activating ligand, the dynamics of EGFR signaling are different than those of EGF-bound EGFR. AREG-ligated EGFR accumulates at the cell surface, resulting in altered receptor trafficking and downstream signaling. To further explore the role of amphiregulin in cell signaling, we performed reverse-phase protein array (RPPA) analysis on SUM149 cells, a highly tumorigenic and metastatic cell line that expresses high levels of AREG and EGFR, and MCF10A cells, a non-transformed mammary epithelial cell line cultured in the presence of either EGF or AREG. This analysis identified a number of signaling components mediated specifically by amphiregulin, including decreased caspase expression, increased Gab2 expression, elevated fibronectin levels and marked changes in integrin expression. In addition, AREG-mediated EGFR signaling resulted in increased expression and activation of c-src. Thus, a major effect of AREG signaling in both cell lines was enhanced activation of the canonical focal adhesion signaling pathway. In addition to increased expression of EGFR and AREG, SUM149 cells are known to have a genomic alteration at the PTEN locus resulting in complete abrogation of PTEN message and protein expression. RPPA analysis of signaling in SUM-149 cells confirmed this PTEN loss and, not surprisingly, revealed elevated AKT activity. In addition, several proteins in the WNT signaling pathway were altered in SUM-149 cells, including reduced expression of GSK3β, increased phosphorylation of GSK3β, and increased expression of Dvl. These results suggest enhanced Wnt-beta catenin activity in SUM-149 cells that is likely the result of enhanced AKT activity resulting from PTEN loss. Although we previously had difficulty measuring Wnt signaling in SUM-149 cells in monolayer culture, mammosphere assays performed with SUM149 cells expressing a Wnt reporter construct confirmed that Wnt signaling was highly active in mammospheres in 3D culture. We also analyzed the genes that are regulated in expression by EGFR in MCF-10A cells in the presence of EGF or AREG, and in SUM-149 cells. These results identified AREG-specific gene expression profiles in the isogenic system. In addition, SUM-149 cell-specific genes regulated by EGFR were also identified, some of which are likely to be the result of PTEN loss and enhanced AKT signaling in these cells. Finally, we found that AREG knockdown in SUM-149 cells significantly reduced the tumorigenicity of SUM149 cells in NOD-SCID mice. Analysis of signaling and gene expression in these AREG knock-down cells are consistent with the importance of AREG expression levels and of the modulation of the focal adhesion canonical pathway in tumor potential of the cells in vivo.

Citation Format: Christiana Kappler, Robert Wilson, Bridget Varughese, Stephen P. Ethier. PTEN loss enhances amphiregulin-specific signaling and gene expression in triple-negative breast cancer. [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 3297. doi:10.1158/1538-7445.AM2014-3297