Irradiation of Juvenile, but not Adult, Mammary Gland Increases Stem Cell Self-Renewal and Estrogen Receptor Negative Tumors

Abstract

Children exposed to ionizing radiation have a substantially greater breast cancer risk than adults; the mechanism for this strong age dependence is not known. Here we show that pubertal murine mammary glands exposed to sparsely or densely ionizing radiation exhibit enrichment of mammary stem cell and Notch pathways, increased mammary repopulating activity indicative of more stem cells, and propensity to develop estrogen receptor (ER) negative tumors thought to arise from stem cells. We developed a mammary lineage agent-based model (ABM) to evaluate cell inactivation, self-renewal, or dedifferentiation via epithelial-mesenchymal transition (EMT) as mechanisms by which radiation could increase stem cells. ABM rejected cell inactivation and predicted increased self-renewal would only affect juveniles while dedifferentiation could act in both juveniles and adults. To further test self-renewal versus dedifferentiation, we used the MCF10A human mammary epithelial cell line, which recapitulates ductal morphogenesis in humanized fat pads, undergoes EMT in response to radiation and transforming growth factor b (TGFb) and contains rare stem-like cells that are Let-7c negative or express both basal and luminal cytokeratins. ABM simulation of population dynamics of double cytokeratin cells supported increased self-renewal in irradiated MCF10A treated with TGFb. Radiation-induced Notch concomitant with TGFb was necessary for increased self-renewal of Let-7c negative MCF10A cells but not for EMT, indicating that these are independent processes. Consistent with these data, irradiating adult mice did not increase mammary repopulating activity or ERnegative tumors. These studies suggest that irradiation during puberty transiently increases stem cell self-renewal, which increases susceptibility to developing ER-negative breast cancer.

Densely Ionizing Radiation Acts via the Microenvironment to Promote Aggressive Trp53-Null Mammary Carcinomas

“…Genes decreased in MaSC signature were also decreased in K18-IHPsi (P ¼ 7 Â 10 À5 ), consistent with their ER-negative status, and likely reflecting the MaSC as cell of origin (36). This signature was not evident in K14/18-IHPsi, suggesting that host irradiation has tumorspecific engagement ( Supplementary Fig.…”

“…Our prior studies show that irradiating hosts with either sparsely or densely ionizing radiation shifted the dominant tumor type from ER-positive to ER-negative (30,36). Most (62%, n ¼ 15/24) tumors arising in sham-irradiated mice were ER-positive, compared with 33% (n ¼ 4/12) in g-irradiated hosts and 43% (n ¼ 15/35) in Si-irradiated (combined dose groups) hosts.…”

Distinct Luminal-Type Mammary Carcinomas Arise from Orthotopic Trp53-Null Mammary Transplantation of Juvenile versus Adult Mice

“…The tumor growth rate of tumors arising from transplantation to adults was comparable to that observed in previous experiments(23). Moreover the difference of tumor growth rate was replicated in cohort of mice transplanted as adults versus juveniles in an independent study(28). Mitotic figures that included the spectrum of condensed chromosome states (Figure 2B) were quantified in high-powered fields of view (n=10) per hematoxylin and eosin (H&E)-stained tumor.…”

Impact of Environmental Contaminants on Breast Cancer / Wpływ Zanieczyszczenia Środowiska Na Raka Piersi

“…It was shown that pubertal murine mammary glands exposed to sparsely or densely ionizing radiation transiently increased stem cell self-renewal that increased susceptibility to developing ER-negative breast cancer [247]. An exposure of six to eight week old female mouse to a clinically relevant radiation dose (2 Gy of whole body γ-radiation) caused longterm activation of mammary gland genes involved in proliferative and metabolic pathways, which are known to have roles in carcinogenesis [248], and a study which evaluated mammary carcinogenesis initiated by combined exposure to various doses of γ-radiation and chemical carcinogens (1-methyl-1-nitrosourea or 1-methyl-6-phenyl-1H-imidazo [4,5-b]pyridin-2-amine), using a rat model and molecular biological approaches, provided evidence of a multilevel interaction: a synergistic interaction between radiation and a chemical carcinogen at the initiation level and an additive interaction in the incidence of resulting carcinomas [249].…”