Membrane expression of the estrogen receptor ERα is required for intercellular communications in the mammary epithelium

Abstract

17β-Estradiol induces the postnatal development of mammary gland and influences breast carcinogenesis by binding to the estrogen receptor ERα. ERα acts as a transcription factor but also elicits rapid signaling through a fraction of ERα expressed at the membrane. Here, we have used the C451A-ERα mouse model mutated for the palmitoylation site to understand how ERα membrane signaling affects mammary gland development. Although the overall structure of physiological mammary gland development is slightly affected, both epithelial fragments and basal cells isolated from C451A-ERα mammary glands failed to grow when engrafted into cleared wild-type fat pads, even in pregnant hosts. Similarly, basal cells purified from hormone-stimulated ovariectomized C451A-ERα mice did not produce normal outgrowths. Ex vivo, C451A-ERα basal cells displayed reduced matrix degradation capacities, suggesting altered migration properties. More importantly, C451A-ERα basal cells recovered in vivo repopulating ability when co-transplanted with wild-type luminal cells and specifically with ERα-positive luminal cells. Transcriptional profiling identified crucial paracrine luminal-to-basal signals. Altogether, our findings uncover an important role for membrane ERα expression in promoting intercellular communications that are essential for mammary gland development.

Estrogen receptor-α signaling in post-natal mammary development and breast cancers

“…The target cells of the non-genomic membrane actions of ERα signaling within the mammary epithelium remain to be precisely identified. However, data from transgenic mouse models revealed that this non-classical mode of action, active for example in endothelial cells, participates in the control of mammary development by regulating intercellular communication [212]. Similarly, classical and nonclassical progesterone signaling pathways through nuclear and membrane receptors have been identified in mammary epithelial and cancer cells [153].…”

“…Greb-1 is well-known as an early response gene in the ERα-regulated pathway and was shown to be a chromatin-bound ER coactivator essential for ER-mediated transcription that stabilizes interactions between ER and additional cofactors [89,213]. Importantly, loss of membrane signaling in luminal cells also altered Jak2 and Stat5a gene expression, a pathway found at the crossroad of hormonal and growth factor signaling which uncovers an important role of membrane ERα as a key regulator of growth factor response [212].…”

“…Keratins (K5, K14, K8, K18); α-smooth muscle actin (α-SMA); oxytocin receptor (OXTR). B: ERα expression in ductal and alveolar struc-tures, as revealed by IHC on PFA-fixed paraffin sections, using mouse monoclonal anti-ERα (Santa Cruz, sc-542, MC-20, described in [212]). Left: sections through a duct and a TEB (insert) from a pubertal mouse.…”

“…To analyze the potential implication of MISS in tissue development, two groups have generated similar knock-in mouse models mutated for the palmitoylation site (theoretically the same point mutation), i.e., the ERα-C451A [114] and the NOER mice [115]. In contrast to mice deleted for nuclear effects of ERα, NOER and ERα-C451A mice have a developed mammary gland that completely filled the fat pad but showed diminished ductal side branching and decreased number of blunted duct termini [115,212].…”

“…The specific mechanisms that control the ability of basal and luminal cells to respond to membrane ERα signaling have been investigated in details using the ERα-C451A mouse model and grafting assays [212]. The data demonstrated that mutation of the palmitoylation site of ERα was necessary in promoting intercellular communications essential for mammary gland development.…”