N-Myc and STAT Interactor (NMI) is an evolutionarily conserved protein that is widely expressed in fetal and adult tissues. Early studies implicated its role in regulating the activities of transcription factors (such as MYC, STATs, BRCA1, TIP60 etc.) critical to tumor progression and metastasis. However, the functional relevance of these regulatory activities of NMI remains unknown. Recent findings from our lab have revealed that NMI protein expression is decreased by 70% in primary tumor specimens from patients with metastatic breast cancer. Most recently, we have found that lack of NMI expression in breast cancer cells confers resistance to chemotherapy by blocking autophagy-induced cell death. Thus the status of NMI expression in breast cancer patients may be an important clinical consideration. Additionally, our functional studies have demonstrated that loss of NMI expression allows manifestation of TGFβ and Wnt driven EMT that results in increased invasion and metastatic dissemination. Overall, we have noticed a profound impact of NMI on multiple developmental signaling pathways that are essential for mammary development as well as tumor progression.

To further elucidate the biological role of NMI, we have created a genetically engineered mammary specific Nmi knock out model. We observed that in normal murine mammary tissue Nmi is expressed in the mammary epithelium during all stages of mammary development. However, it's expression is strikingly induced at the onset of pregnancy, implicating an important role of NMI in mammary ductal development and/or lactation. Remarkably, the Nmi knock out mice exhibit distinctly increased number of alveolar structures (30% more than in control mice) during lactation. Moreover, these Nmi-/- mammary glands also show 20% more proliferating mammary epithelial cells (MECs) compared to respective littermate controls. In addition, 3D-alveologenesis of Nmi knock out MECs is highly responsive to induction by growth factors such as TGFα and FGFs when compared to MECs from littermate controls. Hyper-proliferative phenotype has been implicated as one of the key factors for breast cancer initiation as well as progression. Overall, our work describes a direct evidence for the role of NMI as a key regulator of mammary epithelial cell proliferation.

Citation Format: Hawley C. Pruitt, Brandon J. Metge, Sarah K. Bailey, Lalita A. Shevde, Rajeev S. Samant. N-Myc and STAT Interactor knock out in the mammary epithelium prompts hyper-proliferation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 657.