Differential Contextual Responses of Normal Human Breast Epithelium to Ionizing Radiation in a Mouse Xenograft Model

Abstract

Radiotherapy is a key treatment option for breast cancer, yet the molecular responses of normal human breast epithelial cells to ionizing radiation are unclear. A murine subcutaneous xenograft model was developed in which nonneoplastic human breast tissue was maintained with the preservation of normal tissue architecture, allowing us to study for the first time the radiation response of normal human breast tissue in situ. Ionizing radiation induced dose-dependent p53 stabilization and p53 phosphorylation, together with the induction of p21(CDKN1A) and apoptosis of normal breast epithelium. Although p53 was stabilized in both luminal and basal cells, induction of Ser392-phosphorylated p53 and p21 was higher in basal cells and varied along the length of the ductal system. Basal breast epithelial cells expressed DNp63, which was unchanged on irradiation. Although stromal responses themselves were minimal, the response of normal breast epithelium to ionizing radiation differed according to the stromal setting. We also demonstrated a dose-dependent induction of g-H2AX foci in epithelial cells that was similarly dependent on the stromal environment and differed between basal and luminal epithelial cells. The intrinsic differences between human mammary cell types in response to in vivo irradiation are consistent with clinical observation that therapeutic ionizing radiation is associated with the development of basal-type breast carcinomas. Furthermore, there may be clinically important stromal-epithelial interactions that influence DNA damage responses in the normal breast. These findings demonstrate highly complex responses of normal human breast epithelium following ionizing radiation exposure and emphasize the importance of studying whole-tissue effects rather than single-cell systems. Cancer Res; 70(23); 9808-15. Ó2010 AACR.

Maintenance of genomic integrity after DNA double strand breaks in the human prostate and seminal vesicle epithelium: The best and the worst

“…Moreover, the results suggest that p53 response of epithelial cells in their tissue context differs from what is seen in proliferating cell cultures. Interestingly, similar results of attenuated p53 response after IR have been described in primary human breast epithelial cells and ex vivo cultured breast tissues (Coates et al., 2010; Huper and Marks, 2007; Meyer et al., 1999). In fibroblasts the response pattern is reversed: p53 is stabilized and transcriptionally active in cell culture, but compared to the epithelium, the stromal responses in ex vivo ‐cultures are minimal (Coates et al., 2010; Jäämaa et al., 2010, 2012; Zhang et al., 2011).…”

A Tissue Graft Model of DNA Damage Response in the Normal and Malignant Human Prostate

“…23–25 Coates et al engrafted breast tissue in the sub-cutaneous site of mice, enabling studies of the radiation responses of normal human breast tissue in situ. 26 However, most studies of DDR have been done in proliferating in vitro cell lines and the results of these experimental models may not always reflect situations in vivo. For example, Barreto-Andrade et al reported that radiosensitization by a PARP inhibitor in vitro failed to predict comparable results in tumors in vivo.…”

Mechanisms of Injury to Normal Tissue after Radiotherapy

“…The γ-H2AX signal protein can be visualized within seconds of initiation of a DSB and persists until repair is complete—for typical cells, approximately 24 to 48 hours. Other proteins (the effectors) are also present within minutes of detection of a DSB, including P53 binding protein 53BP1, and either guide the cell toward repair or ultimately force apoptosis by stimulating release of mitochondrial cytochrome c and subsequent activation of caspase-3 [16]. DSBs are the most difficult lesion for a cell to accurately repair and can lead to mutations such as deletions and insertions.…”