RANK Overexpression in Transgenic Mice with Mouse Mammary Tumor Virus Promoter-Controlled RANK Increases Proliferation and Impairs Alveolar Differentiation in the Mammary Epithelia and Disrupts Lumen Formation in Cultured Epithelial Acini

Abstract

RANK and RANKL, the key regulators of osteoclast differentiation and activation, also play an important role in the control of proliferation and differentiation of mammary epithelial cells during pregnancy. Here, we show that RANK protein expression is strictly regulated in a spatial and temporal manner during mammary gland development. RANK overexpression under the control of the mouse mammary tumor virus (MMTV) promoter in a transgenic mouse model results in increased mammary epithelial cell proliferation during pregnancy, impaired differentiation of lobulo-alveolar structures, decreased expression of the milk proteins β-casein and whey acidic protein, and deficient lactation. We also show that treatment of three-dimensional in vitro cultures of primary mammary cells from MMTV-RANK mice with RANKL results in increased proliferation and decreased apoptosis in the luminal area, resulting in bigger acini with filled lumens. Taken together, these results suggest that signaling through RANK not only promotes proliferation but also inhibits the terminal differentiation of mammary epithelial cells. Moreover, the increased proliferation and survival observed in a three-dimensional culture system suggests a role for aberrant RANK signaling during breast tumorigenesis.

SUPPLEMENTAL MATERIAL

We thank Ken Schooley for technical support with the confocal microscopy and the Cellomics software; Jim Petrorius for in situ hybridization analysis; Michael Wiley, William Lawrence, Moira Glaccum, the Animal Facility and the Pathology Department, including Kathy Rohrbach, Larry Wood, Angie Warren, Deanna Hill, Julie Hahn, Michelle Pace and Brenda Heron, and Phenopath Laboratories for their technical assistance; Helen Hathaway (University of New Mexico School of Medicine) for her support and advice; and Michelle Chaisson for helpful discussions and critical comments on the manuscript.