The role of NEDD9 in HER2-driven breast cancer.

Tumor initiation is often driven by unrestricted proliferation. One such driver of proliferation is Human epidermal growth factor receptor 2 (HER2). HER2 is a receptor tyrosine kinase that is part of the epidermal growth factor receptor family (EFGR) that is commonly overexpressed in breast cancer. HER2 positive (+) breast cancers often respond to anti- HER2 therapy, yet many patients eventually develop resistance. Multiple mechanisms contribute to resistance, including activation of HSP90, PI3K/Akt or Src that rely on adaptor molecules (GRB2, p130cas, NEDD9). Neural precursor cell expressed, developmentally downregulated protein 9 (NEDD9) is an adaptor protein that promotes integrin signaling. We found that higher expression of NEDD9 in HER2+ human breast cancer correlates with disease progression, reduced relapse free survival and resistance to anti-HER2 therapy. The central hypothesis is NEDD9 can play a role in mammary gland development, differentiation and proliferation of cells, and response to targeted therapy in HER2 driven breast cancer. To evaluate role of NEDD9 protein in physiologically relevant settings we generated a conditional transgenic mouse model, placing extra copy of human NEDD9 cDNA under the control of cre recombinase. When crossed with mice expressing mammary gland-specific cre recombinase, NEDD9 overexpression promoted early occurrence of benign lesions such as mammary intraepithelial neoplasia (MIN) and ductal carcinoma in situ (DCIS). This phenotype was accelerated by co-expression of HER2 oncogene. The NEDD9 overexpressing mice showed altered development of the mammary gland, with more tertiary and terminal end buds (TEBs), that is indicative of NEDD9’s role in controlling proliferation. The increase in cell proliferation, was further supported by Ki67 staining. The lineage tracing analysis shows that NEDD9 specifically increased the number of luminal progenitor cells, as shown by dual Keratin 5/8 staining. Consistent with these studies, NEDD9 promoted the 2D and 3D cell proliferation of human MCF10A cells. Mechanistically, NEDD9 upregulation resulted in MAPK and AURKA activation inducing cell proliferation. The depletion of NEDD9 in HER2+ cancer cell lines increased their sensitivity to anti-HER2 therapy. These findings support the role of NEDD9 in early stages of HER2-driven tumorigenesis, selectively impacting proliferation of luminal progenitor cells and lay foundation for potential use of NEDD9 expression in early diagnostics of HER2+ BCs and treatment