Abstract 3326: Low dose radiation alters stromal epithelial interactions to enrich for estrogen receptor(ER)α-negative stem cells and subsequent ER-negative tumors
Authors: Nguyen David H. , Bochaca Irineu I. , Mao Jian-Hua , Barcellos-Hoff Mary Helen 
Published: June 2012

Abstract
What determines the prevalence of ERα in breast cancer is not well-understood. ER-negative breast cancer is most frequent in young women and certain racial groups, particularly African-American women. We have used a model in which p53 null mammary epithelium is orthotopically transplanted to an irradiated mouse to study radiation effects on host interactions during the development of breast cancer. We observed that host irradiation increased the rate of tumor development, which were significantly more likely to be ERα-negative and PR-negative tumors. These data implicate radiation-induced heterotypic signaling in determining critical clinical features of breast cancer. We then asked how different the expression profiles of ER-negative tumors were in sham and irradiated hosts as a means to infer whether they develop via similar paths. SAM-tandem-bootstrap identified 115 genes that cluster ER-negative tumors from irradiated versus sham-irradiated hosts, but not ER-positive tumors. Mouse Trp53 null tumors are similar to claudin-low breast cancer and both are enriched in the mammary stem cell (MaSC) signature reported by Visvader and colleagues. Since the mammary stem cell is ER-negative, as are tumors that are enriched in the MaSC signature, we asked how the MaSC profile related to the ER-115 profile that clusters tumors from irradiated hosts. Genes up-regulated in the ER-115 signature showed a highly significant (p=0.01) enrichment for genes up-regulated in the MaSC profile using ConceptGen. We also found that MaSC genes were significantly enriched in irradiated mammary glands. Together these data suggested the hypothesis that low dose radiation might affect the mammary lineage hierarchy by altering self-renewal in mammary stem cells. To test this idea, mice were irradiated with 10 or 100 cGy at 3 weeks of age and mammary cells isolated from fully mature 12 week old mice were analyzed by FACS using Cd24med/Cd49hi mammary repopulation markers. The proportion of lin-/ Cd24med/Cd49hi cells in irradiated mice was significantly increased (p&lt;0.05) compared to sham-irradiated mice. Functional analysis of repopulating potential is the gold standard to assess the number of stem cells in rodent mammary gland. Thus we isolated mammary cells from 8 week old mice that were sham-irradiated or irradiated with 10 cGy at 3 weeks. Mammary repopulating activity was increased ∼1.7 fold (p&lt;0.05) in irradiated mice compared to sham-irradiated mice, again without evidence of dose dependence. Together our data suggest that low dose host irradiation increases mammary repopulating activity, which increases the propensity for neoplastic transformation and the prevalence of ER-negative tumors.
Supported by DOE Low Dose Radiation Program, NIEHS Breast Cancer and the Environment Research Center, and DOD Breast Cancer Research Fellowship to DHN.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3326. doi:10.1158/1538-7445.AM2011-3326