Targeting RANKL to a specific subset of murine mammary epithelial cells induces ordered branching morphogenesis and alveologenesis in the absence of progesterone receptor expression

Abstract

Despite support for receptor of activated NF-κB ligand (RANKL) as a mediator of mammary progesterone action, the extent to which this cytokine can functionally contribute to established progesterone-induced mammary morphogenetic responses in the absence of other presumptive effectors is still unclear. To address this uncertainty, we developed an innovative bigenic system for the doxycycline-inducible expression of RANKL in the mammary epithelium of the progesterone receptor knockout (PRKO) mouse. In response to acute doxycycline exposure, RANKL is specifically expressed in the estrogen receptor α (ER) positive/progesterone receptor negative (ER(+)/PR(-)) cell type in the PRKO mammary epithelium, a cell type that is equivalent to the ER(+)/PR(+) cell type in the wild-type (WT) mammary epithelium. Notably, the ER(+)/PR(+) mammary cell normally expresses RANKL in the WT mammary epithelium during pregnancy. In this PRKO bigenic system, acute doxycycline-induced expression of RANKL results in ordered mammary ductal side branching and alveologenesis, morphological changes that normally occur in the parous WT mouse. This mammary epithelial expansion is accompanied by significant RANKL-induced luminal epithelial proliferation, which is driven, in part, by indirect induction of cyclin D1. Collectively, our findings support the conclusion that RANKL represents a critical mediator of mammary PR action and that restricted expression of this effector to the ER(+)/PR(+) mammary cell-type is necessary for a spatially ordered morphogenetic response to progesterone.

Bringing androgens up a NOTCH in breast cancer

“…Prolactin signalling is essential for lobuloalveolar differentiation at pregnancy (Grimm et al 2002 and central to the function of HS-MECs during early pregnancy to promote the expression of paracrine growth factors associated with alveolar cell differentiation (Dontu et al 2004, Mukherjee et al 2010, Tarulli et al 2013, and significant cross-talk between prolactin and progesterone pathways has been reported (Lee & Ormandy 2012, Obr et al 2013. Importantly, expression of PIP has been associated with breast tumours with apocrine features, a subtype with an important emergent role for AR regulation of tumour growth (Mazoujian et al 1983, 1989, Farmer et al 2005, Doane et al 2006.…”

Progesterone/RANKL Is a Major Regulatory Axis in the Human Breast

“…Genetic evidence was provided that RANKL is important as a paracrine mediator of progesterone-induced proliferation in the adult mouse mammary gland (8,9). Systemic inhibition of RANKL signaling by intravenous injection of recombinant osteoprotegerin (rOPG), its decoy receptor, blocked progesterone-induced proliferation in the mammary epithelium (8), suggesting that RANKL may be used as a drug target in the breast epithelium.…”

Progesterone signalling in breast cancer: a neglected hormone coming into the limelight

“…ECM, extracellular matrix. double-transgenic approach, resulted in side branching and alveologenesis 74 . Similarly, ectopic RANKL expression in Pgr −/− mammary epithelium by means of a retroviral approach, rescued the Pgr −/− phenotype, indicating that RANKL is a crucial mediator of PR signalling function.…”