Mammary gland development and EDC-driven cancer susceptibility in mesenchymal ERα-knockout mice

Development of the mammary gland requires both proper hormone signaling and cross talk between the stroma and epithelium. While estrogen receptor (ERα) expression in the epithelium is essential for normal gland development, the role of this receptor in the stroma is less clear. Moreover, several lines of evidence suggest that mouse phenotypes of in utero exposure to endocrine disruption act through mesenchymal ERα in the developing fetus. We utilized a Twist2-cre mouse line to knock out mesenchymal ERα. Herein, we assessed mammary gland development in the context of mesenchymal ERα deletion. We also tested the effect of in utero bisphenol A (BPA) exposure to alter the tumor susceptibility in the mouse mammary tumor virus-neu (MMTV-neu) breast cancer mouse model. Mesenchymal ERα deletion resulted in altered reproductive tract development and atypical cytology associated with estrous cycling. The mammary gland demonstrated mature epithelial extension unlike complete ERα-knockout mice, but ductal extension was delayed and reduced compared to ERα-competent mice. Using the MMTV-Neu cancer susceptibility model, ERα-intact mice exposed to BPA had reduced tumor-free survival and overall survival compared to BPA-exposed mice having mesenchymal ERα deletion. This difference is specific for BPA exposure as vehicle-treated animals had no difference in tumor development between mice expressing and not expressing mesenchymal ERα. These data demonstrate that mesenchymal ERα expression is not required for ductal extension, nor does it influence cancer risk in this mouse model but does influence the cancer incidence associated with in utero BPA exposure.

Abstract 2687: The estrogenic activities of endocrine disruptors alter the extracellular matrix and tissue stiffness in the mammary gland

In utero exposure to estrogenic endocrine disrupting compounds (EDCs) increases a woman’s lifetime risk of breast cancer. Similarly, mice exposed in utero to the estrogenic EDC bisphenol A (BPA) have increased susceptibility to mammary gland tumors. It is unclear which BPA-induced alterations predispose the mammary gland to cancer transformation. There is a critical need to understand the mechanisms that drive increased cancer risk in order to assess the impact of BPA and BPA alternatives that retain estrogenic activity. We have utilized in utero BPA exposure as a model system for in utero estrogenic endocrine disruption to study the long-term consequences to the mouse mammary stroma. We found that BPA exposed fibroblasts showed significant transcriptional deregulation, with the extracellular matrix being the most altered cellular component and multiple collagen genes being more highly expressed. The fibroblasts from the BPA exposed mice decreased fluid permeability of the extracellular matrix, indicative of an increased density in the extracellular matrix. Also, in utero BPA exposure increased mammary gland stiffness. Changes to breast density, stiffness, and collagen deposition are all associated with breast cancer risk. Further, we test BPA alternative compounds with varying affinities for the estrogen receptor in our in utero model to assess the phenotypes in the mouse mammary stroma which are associated with breast cancer risk. Additionally, we use a mesenchymal estrogen receptor alpha (ERα) knockout mouse model to dissect the in utero cellular target of EDCs.

Citation Format: Clarissa Wormsbaecher, Andrea R. Hindman, Alex Avendano, Marcos Cortes-Medina, Jonathan W. Song, Craig J. Burd. The estrogenic activities of endocrine disruptors alter the extracellular matrix and tissue stiffness in the mammary gland [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2687.

In utero estrogenic endocrine disruption alters the stroma to increase extracellular matrix density and mammary gland stiffness

BACKGROUND

In utero endocrine disruption is linked to increased risk of breast cancer later in life. Despite numerous studies establishing this linkage, the long-term molecular changes that predispose mammary cells to carcinogenic transformation are unknown. Herein, we investigated how endocrine disrupting compounds (EDCs) drive changes within the stroma that can contribute to breast cancer susceptibility.

METHODS

We utilized bisphenol A (BPA) as a model of estrogenic endocrine disruption to analyze the long-term consequences in the stroma. Deregulated genes were identified by RNA-seq transcriptional profiling of adult primary fibroblasts, isolated from female mice exposed to in utero BPA. Collagen staining, collagen imaging techniques, and permeability assays were used to characterize changes to the extracellular matrix. Finally, gland stiffness tests were performed on exposed and control mammary glands.

RESULTS

We identified significant transcriptional deregulation of adult fibroblasts exposed to in utero BPA. Deregulated genes were associated with cancer pathways and specifically extracellular matrix composition. Multiple collagen genes were more highly expressed in the BPA-exposed fibroblasts resulting in increased collagen deposition in the adult mammary gland. This transcriptional reprogramming of BPA-exposed fibroblasts generates a less permeable extracellular matrix and a stiffer mammary gland. These phenotypes were only observed in adult 12-week-old, but not 4-week-old, mice. Additionally, diethylstilbestrol, known to increase breast cancer risk in humans, also increases gland stiffness similar to BPA, while bisphenol S does not.

CONCLUSIONS

As breast stiffness, extracellular matrix density, and collagen deposition have been directly linked to breast cancer risk, these data mechanistically connect EDC exposures to molecular alterations associated with increased disease susceptibility. These alterations develop over time and thus contribute to cancer risk in adulthood.

Plant Endocytosis Requires the ER Membrane-Anchored Proteins VAP27-1 and VAP27-3

Through yet-undefined mechanisms, the plant endoplasmic reticulum (ER) has a critical role in endocytosis. The plant ER establishes a close association with endosomes and contacts the plasma membrane (PM) at ER-PM contact sites (EPCSs) demarcated by the ER membrane-associated VAMP-associated-proteins (VAP). Here, we investigated two plant VAPs, VAP27-1 and VAP27-3, and found an interaction with clathrin and a requirement for the homeostasis of clathrin dynamics at endocytic membranes and endocytosis. We also demonstrated direct interaction of VAP27-proteins with phosphatidylinositol-phosphate lipids (PIPs) that populate endocytic membranes. These results support that, through interaction with PIPs, VAP27-proteins bridge the ER with endocytic membranes and maintain endocytic traffic, likely through their interaction with clathrin.

TGNap1 is required for microtubule-dependent homeostasis of a subpopulation of the plant trans-Golgi network

Defining convergent and divergent mechanisms underlying the biogenesis and function of endomembrane organelles is fundamentally important in cell biology. In all eukaryotes, the Trans-Golgi Network (TGN) is the hub where the exocytic and endocytic pathways converge. To gain knowledge in the mechanisms underlying TGN biogenesis and function, we characterized TGNap1, a protein encoded by a plant gene of unknown function conserved with metazoans. We demonstrate that TGNap1 is a TGN protein required for the homeostasis of biosynthetic and endocytic traffic pathways. We also show that TGNap1 binds Rab6, YIP4 and microtubules. Finally, we establish that TGNap1 contributes to microtubule-dependent biogenesis, tracking and function of a TGN subset, likely through interaction with Rab6 and YIP4. Our results identify an important trafficking determinant at the plant TGN and reveal an unexpected reliance of post-Golgi traffic homeostasis and organelle biogenesis on microtubules in plants.

TGNap1 is required for microtubule-dependent homeostasis of a subpopulation of the plant trans-Golgi network

Defining convergent and divergent mechanisms underlying the biogenesis and function of endomembrane organelles is fundamentally important in cell biology. In all eukaryotes, the Trans-Golgi Network (TGN) is the hub where the exocytic and endocytic pathways converge. To gain knowledge in the mechanisms underlying TGN biogenesis and function, we characterized TGNap1, a protein encoded by a plant gene of unknown function conserved with metazoans. We demonstrate that TGNap1 is a TGN protein required for the homeostasis of biosynthetic and endocytic traffic pathways. We also show that TGNap1 binds Rab6, YIP4 and microtubules. Finally, we establish that TGNap1 contributes to microtubule-dependent biogenesis, tracking and function of a TGN subset, likely through interaction with Rab6 and YIP4. Our results identify an important trafficking determinant at the plant TGN and reveal an unexpected reliance of post-Golgi traffic homeostasis and organelle biogenesis on microtubules in plants.