Expansion Of Luminal Cells Research Articles

A transcriptional response to replication stress selectively expands a subset of Brca2-mutant mammary epithelial cells

Germline BRCA2 mutation carriers frequently develop luminal-like breast cancers, but it remains unclear how BRCA2 mutations affect mammary epithelial subpopulations. Here, we report that monoallelic Brca2mut/WT mammary organoids subjected to replication stress activate a transcriptional response that selectively expands Brca2mut/WT luminal cells lacking hormone receptor expression (HR-). While CyTOF analyses reveal comparable epithelial compositions among wildtype and Brca2mut/WT mammary glands, Brca2mut/WT HR- luminal cells exhibit greater organoid formation and preferentially survive and expand under replication stress. ScRNA-seq analysis corroborates the expansion of HR- luminal cells which express elevated transcript levels of Tetraspanin-8 (Tspan8) and Thrsp, plus pathways implicated in replication stress survival including Type I interferon responses. Notably, CRISPR/Cas9-mediated deletion of Tspan8 or Thrsp prevents Brca2mut/WT HR- luminal cell expansion. Our findings indicate that Brca2mut/WT cells activate a transcriptional response after replication stress that preferentially favours outgrowth of HR- luminal cells through the expression of interferon-responsive and mammary alveolar genes.

Lgr6 labels a rare population of mammary gland progenitor cells that are able to originate luminal mammary tumours.

The mammary gland is composed of a complex cellular hierarchy with unusual postnatal plasticity. The identities of stem/progenitor cell populations, as well as tumour-initiating cells that give rise to breast cancer, are incompletely understood. Here we show that Lgr6 marks rare populations of cells in both basal and luminal mammary gland compartments in mice. Lineage tracing analysis showed that Lgr6+ cells are unipotent progenitors, which expand clonally during puberty but diminish in adulthood. In pregnancy or following stimulation with ovarian hormones, adult Lgr6+ cells regained proliferative potency and their progeny formed alveoli over repeated pregnancies. Oncogenic mutations in Lgr6+ cells resulted in expansion of luminal cells, culminating in mammary gland tumours. Conversely, depletion of Lgr6+ cells in the MMTV-PyMT model of mammary tumorigenesis significantly impaired tumour growth. Thus, Lgr6 marks mammary gland progenitor cells that can initiate tumours, and cells of luminal breast tumours required for efficient tumour maintenance.

P130Cas alters the differentiation potential of mammary luminal progenitors by deregulating c-Kit activity

It has recently been proposed that defective differentiation of mammary luminal progenitors predisposes to basal-like breast cancer. However, the molecular and cellular mechanisms involved are still unclear. Here, we describe that the adaptor protein p130Cas is a crucial regulator of mouse mammary epithelial cell (MMEC) differentiation. Using a transgenic mouse model, we show that forced p130Cas overexpression in the luminal progenitor cell compartment results in the expansion of luminal cells, which aberrantly display basal cell features and reduced differentiation in response to lactogenic stimuli. Interestingly, MMECs overexpressing p130Cas exhibit hyperactivation of the tyrosine kinase receptor c-Kit. In addition, we demonstrate that the constitutive c-Kit activation alone mimics p130Cas overexpression, whereas c-Kit downregulation is sufficient to re-establish proper differentiation of p130Cas overexpressing cells. Overall, our data indicate that high levels of p130Cas, via abnormal c-Kit activation, promote mammary luminal cell plasticity, thus providing the conditions for the development of basal-like breast cancer. Consistently, p130Cas is overexpressed in human triple-negative breast cancer, further suggesting that p130Cas upregulation may be a priming event for the onset of basal-like breast cancer.

Abstract P2-04-08: Targeted Expression of the Human Chaperone BAG3 to the Murine Mammary Gland Dysregulates Mammary Gland Development and Differentiation By Unrestricted Expansion of Luminal Cells

Abstract BAG3 is a pro-survival pro-invasion chaperone. We hypothesized that human BAG3 overexpression in murine breast would contribute to mammary tumorigenesis. We generated transgenic mice ectopically expressing hBAG3 in the mammary gland under the control of the Mouse Mammary Tumor Viral promoter (MMTV-hBAG3). hBAG3 was expressed in luminal cells throughout the ductal tree in multiple transgenic lines. Targeted expression of hBAG3 dysregulated mammary gland development by both increasing proliferation and differentiation. hBAG3 mammary glands had increased epithelial elongation at 5 weeks of age, premature glandular differentiation at 10 weeks, and features of ductal hyperplasia at week 13 with increased Ki67 and p-Histone H3 in the luminal compartment. At week 13 hBAG3 induced acinar differentiation. BAG3 pro-survival gain of function was recapitulated post-partum with delayed involution. Mammary glands of MMTV-hBAG3 had alveolar persistence three days after forced involution where non-transgenic controls demonstrated typical involution-driven apoptosis and remodeling. We crossed heterozygous MMTV-hBAG3 to WAP-Int3 mice with absent alveolar development in pregnancy. hBAG3 caused alveolar budding in the WAP-Int3 background. We hypothesized hBAG3 gain of function in the mammary gland would promote tumorigenesis. On aging, mammary glands of heterozygous MMTV-hBAG3 displayed densely crowded acinar structures with atypia, consistent with hyperplastic alveolar nodule (HAN). We subjected MMTV-hBAG3 mice to either multiparity or chemical carcinogenesis. After two pregnancies, most MMTV-hBAG3 animals had hyperplastic mammary ductal lesions (MMTV-hBAG3 6/7, 86%; FVB/N 1/7, 14%). Eighteen weeks post 7,12-dimethylbenz(a)antracene (DMBA) treatment, virgin females from five different transgenic lines had more hyperplastic lesions (MMTV-hBAG3 mean 6.3 lesions/gland, N=13, FVB/N mean 3.6 lesions/gland, N=9; p = 0.04), some with atypical hyperplasia. Transgenic MMTV-hBAG3 females developed ER and PR (+) malignant tumors (5/19), 26% while non-transgenic controls had none (0/12). WAP-Int3 mice developed tumors as early as two pregnancies. Heterozygous WAP-Int3xMMTV-BAG3 had the same tumor frequency but preliminary data suggest increased aggressiveness and metastasis. Collectively, our results indicate that MMTV-hBAG3 promotes proliferation, dysregulates mammary gland development and promotes hyperplasia and tumorigenesis and may provide a novel mouse model to represent the human ER+ luminal breast cancer subtype. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P2-04-08.