Receptor Activator of NF-κB Ligand Regulates the Proliferation of Mammary Epithelial Cells via Id2

Abstract

Receptor activator of NF-κB ligand (RANKL) is a key regulator for mammary gland development during pregnancy. RANKL-deficient mice display impaired development of lobulo-alveolar mammary structures. Similar mammary gland defects have been reported in mice lacking Id2. Here we report that RANKL induces the proliferation of mammary epithelial cells via Id2. RANKL triggers marked nuclear translocation of Id2 in mammary epithelial cells. In vivo studies further demonstrated the defective nuclear translocation of Id2, but the normal expression of cyclin D1, in the mammary epithelial cells of rankl ^−/− mice. In vitro studies with nuclear localization sequence-tagged Id2 revealed that the nuclear localization of Id2 itself is critical for the downregulation of p21 promoter activity. Moreover, RANKL stimulation failed to induce cell growth and to downregulate p21 expression in Id2 ^−/− mammary epithelial cells. Our results indicate that the inhibitor of helix-loop-helix protein, Id2, is critical to control the proliferation of mammary epithelial cells in response to RANKL stimulation.

We thank J. Lee and M. Kong for technical support and animal husbandry; Y. Lee for confocal imaging; and R. Song, M. Yoon, and K. J. Yoon for helpful comments.

J.M.P. was supported by a Marie Curie Excellence Grant from the European Union. This study was supported by grants from the 21C Frontier Functional Human Genome Project from the Ministry of Science and Technology of Korea (FG04-22-05), the Basic Research Program of the Korea Science and Engineering Foundation (R02-2003-000-10057-0), the Korea Research Foundation (KRF-2000-015-DS0041), and the Vascular System Research Center from KOSEF.