Overexpression of Activated Murine Notch1 and Notch3 in Transgenic Mice Blocks Mammary Gland Development and Induces Mammary Tumors

Abstract

The mouse mammary tumor virus (MMTV) provirus was found to target the Notch1 gene, producing insertional mutations in mammary tumors of MMTV/neu transgenic (Tg) mice. In these mammary tumors, the Notch1 gene is truncated upstream of the transmembrane domain, and the resulting Notch1 intracellular domain (Notch1(intra)), deleted of most extracellular sequences, is overexpressed. Although Notch1(intra) transforms mammary epithelial cells in vitro, its role in mammary gland tumor formation in vivo was not studied. Therefore, we generated MMTV/Notch1(intra) Tg mice that overexpress murine Notch1(intra) in the mammary glands. We observed that MMTV/Notch1(intra) Tg females were unable to feed their pups because of impaired ductal and lobulo-alveolar mammary gland development. This was associated with decreased proliferation of ductal and alveolar epithelial cells during rapid expansion at puberty and in early pregnancy, as well as decreased production of beta-casein. Notch1(intra) repressed expression of the beta-casein gene promoter, as assessed in vitro with a beta-casein/luciferase reporter construct. The MMTV/Notch1(intra) Tg females developed mammary gland tumors, confirming the oncogenic potential of Notch1(intra) in vivo. Furthermore, MMTV/Notch3(intra) Tg mice exhibited a very similar phenotype. Thus, these Tg mice represent novel models for studying the role of Notch1 or Notch3 in the development and transformation of the mammary gland.

The lymphovascular embolus of inflammatory breast cancer exhibits a Notch 3 addiction

“…The effects of Notch 3 knockdown were identical to the effects of g-secretase inhibition in vitro, namely decreased expression of Notch 3 targets and profound apoptosis. It had been shown previously that Notch signaling can regulate apoptosis (Jhappan et al, 1992;Hu et al, 2006;Klinakis et al, 2006). Results of our in vitro studies were cleaner than our in vivo results that relied on the diffusion of a drug, in this case, GSI-I.…”

“…Sorting of the ALDEFLUOR þ (ALDH þ ) population of the MARY-X spheroids revealed an even higher amount of Notch 3 signaling. , 2005), and has also been seen in animal models (Gallahan and Callahan, 1997;Dievart et al, 1999;Callahan and Egan, 2004;Hu et al, 2006). Overexpression of active forms of murine Notch 1-4 The gene expression profile of CD44 þ immunosorted cells was obtained from a published study (Shipitsin et al, 2007).…”

EZH2 expands breast stem cells through activation of NOTCH1 signaling

“…Despite interest in the association between EZH2 functions, breast TICs, and TN breast cancer (13), the molecular mechanisms underlying the tumorigenic function of EZH2 in this cancer subtype and the relationship to NOTCH1 signaling have not yet been considered. Furthermore, whereas a role for NOTCH1 in breast tumorigenesis has been established in vivo (30), the factors regulating increased NOTCH1 expression and signaling in breast cancer cells are largely unknown (31,32). We show that EZH2 is a regulator of NOTCH1 expression and pathway activation in TN breast cancer and that NOTCH signaling activation is required for EZH2-dependent stem cell expansion.…”

Notch1-induced mammary tumor development is cyclin D1-dependent and correlates with expansion of pre-malignant multipotent duct-limited progenitors

“…IC (Hu et al, 2006), and human N1 IC (Kiaris et al, 2004) also cause mammary tumors in transgenic (Tg) mice. Moreover, overexpression of Notch1 and Notch3 was documented in human breast tumors, and was associated with poor prognosis (Reedijk et al, 2005;Stylianou et al, 2006).…”

“…IC and developing mammary tumors at high incidence (Hu et al, 2006) to gain insights into the mechanisms of Notch1-induced mammary tumors and to investigate the impact of N1 IC overexpression on mammary stem/progenitor cells in vivo.…”