Abstract P4-06-16: TWEAK/Fn14 Signaling Axis as a Driver of Breast Cancer Cell Invasion and Metastasis

The molecular events associated with the multi-step process of cell invasion and metastasis are poorly understood. Tumor necrosis factor receptor family member fibroblast growth factor-inducible 14 (Fn14) and its ligand TWEAK (tumor necrosis factor-like weak inducer of apoptosis) have recently emerged as a pro-invasive signaling mechanism and indicator of poor prognosis in breast cancer. Our laboratory has recently reported enhanced Fn14 expression in a significant proportion of breast tumor samples, but not in normal breast epithelium. Analysis of publicly available breast cancer data indicates that high Fn14 expression positively correlates with HER2/neu positivity, estrogen receptor negativity, high tumor grade, positive lymph nodes, and metastasis. Modulation of Fn14 expression in breast cancer cell lines either by exogenous overexpression or siRNA-mediated blockade is sufficient to regulate breast cancer cell invasive behavior in vitro. However, the mechanisms leading to Fn14 overexpression, and how activation of the TWEAK/Fn14 signaling axis contributes to breast tumor malignant progression remain unclear. We hypothesized that genomic alterations and inappropriate autocrine or paracrine growth factor signaling may play a role in aberrant Fn14 regulation. Using array genomic hybridization and fluorescence in situ hybridization, we found increased Fn14 gene copy number relative to centromere 16 in two out of four Fn14-expressing, invasive breast cancer cell lines and in 28% of primary breast tumors. We also investigated the role of exogenous growth factors known to play important roles in the breast tumor microenvironment in stimulating Fn14 expression in vitro. TWEAK, EGF, IGF1, HRG and HGF/SF were sufficient to stimulate Fn14 expression de novo in a variety of biologic contexts. Many of these growth factors converge on the MAPK signaling axis. We have confirmed a functional role for the MAPK pathway in facilitating Fn14-mediated invasion. Consistent with this observation, Fn14 expression in primary breast tumors is high in the context of K-RAS mutation. We are currently evaluating the presence of important key regulatory regions within the Fn14 promoter that may be contributing Fn14 over expression in breast cancer cells. To define mechanisms by which Fn14 contributes to a malignant cell phenotype we have identified an Fn14-specific invasion signature using gene expression microarray profiling. Analysis of this data points to key malignant mechanisms likely to be impacted by Fn14 activation within different biologic contexts that warrants further investigation. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P4-06-16.