NEDD9 Overexpression Causes Hyperproliferation of Luminal Cells and Cooperates with HER2 Oncogene in Tumor Initiation: A Novel Prognostic Marker in Breast Cancer

SIMPLE SUMMARY: Neural precursor cell expressed, developmentally downregulated protein 9 (NEDD9) is an adaptor protein that promotes integrin/RTK signaling. The overexpression of NEDD9 in HER2+ breast cancer correlates with reduced relapse-free survival. We generated a conditional transgenic mouse model of NEDD9 overexpression. When crossed with MMTV-Cre+ mice, NEDD9 upregulation led to mammary intraepithelial neoplasia (MIN) at an early age, and this phenotype was further exacerbated by Erbb2/(neu) oncogene. NEDD9 overexpression induces expansion of the mammary epithelial tree, with increased tertiary and terminal end buds (TEBs). The expression of NEDD9 increased the number of luminal epithelial cells, as shown by Keratin 8/Keratin 5 and Ki67 staining. Consistent with these studies, NEDD9 promoted the 2D proliferation and 3D mammary acini formation by normal human MCF10A cells. These findings support the role of NEDD9 in the early stages of HER2+ cancer, selectively impacting the proliferation of luminal epithelial cells, hence setting permissive conditions for tumorigenesis. ABSTRACT: HER2 overexpression occurs in 10–20% of breast cancer patients. HER2+ tumors are characterized by an increase in Ki67, early relapse, and increased metastasis. Little is known about the factors influencing early stages of HER2- tumorigenesis and diagnostic markers. Previously, it was shown that the deletion of NEDD9 in mouse models of HER2 cancer interferes with tumor growth, but the role of NEDD9 upregulation is currently unexplored. We report that NEDD9 is overexpressed in a significant subset of HER2+ breast cancers and correlates with a limited response to anti-HER2 therapy. To investigate the mechanisms through which NEDD9 influences HER2-dependent tumorigenesis, we generated MMTV-Cre-NEDD9 transgenic mice. The analysis of mammary glands shows extensive ductal epithelium hyperplasia, increased branching, and terminal end bud expansion. The addition of oncogene Erbb2 (neu) leads to the earlier development of early hyperplastic benign lesions (~16 weeks), with a significantly shorter latency than the control mice. Similarly, NEDD9 upregulation in MCF10A-derived acini leads to hyperplasia-like DCIS. This phenotype is associated with activation of ERK1/2 and AURKA kinases, leading to an increased proliferation of luminal cells. These findings indicate that NEDD9 is setting permissive conditions for HER2-induced tumorigenesis, thus identifying this protein as a potential diagnostic marker for early detection.