Office of Biological and Environmental Research

DOE Lowdose Radiation Program Workshop IV

Abstract

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Title: TGF-ß Protects Human Mammary Epithelial Cells from Radiation-Induced Centrosome Amplification

Authors: Mary Helen Barcellos-Hoff, Bahram Parvin, Anna C. Erickson and Rishi Gupta

Institutions: Department of Cell and Molecular Biology, Life Sciences Division, Ernest Orlando Lawrence, Berkeley National Laboratory, Berkeley, California 94720

In recent studies we have shown that ionizing radiation (IR), a known carcinogen of human and murine mammary gland, compromises human mammary epithelial cell (HMEC) polarity and multicellular organization in a manner characteristic of neoplastic progression through a heritable, non-mutational mechanism (1). Thus, when all cells are irradiated with a significant dose (2 Gy), the daughters of irradiated cells lose their ability to interact with each other and the microenvironment.
We have postulated that abnormal cells may accumulate under these circumstances and would then contribute to the development of neoplasia in vivo (2). To test this we determined the frequency of centrosome defects, which frequently accompany tumor progression, in HMEC as a function of radiation dose (0.1-5 Gy). Non-malignant S1 HMT-3522 HMEC were seeded as monolayers and subjected to IR 4 hours post plating. Daughters of the surviving cells were analyzed for centrosome
abnormalities six days later by immunofluorescent staining for (-tubulin. IR increased the frequency of S1 cells with 3 or more centrosomes as a function of radiation dose up to 2 Gy.

The irradiated HMEC phenotype is augmented by TGF-ß which is rapidly activated in response to IR in mouse mammary gland (3) and plays a critical role in epithelial cell fate decisions (4). TGF-ß can either suppress or promote tumor progression via a variety of mechanisms (5). We asked whether TGF-ßaffected radiation-induced centrosome instability. Culture with additional TGF-ß (400 pg/ml) following radiation exposure decreased the frequency of surviving HMEC with abnormal centrosomes numbers. Consistent with our studies in irradiated mice, irradiated HMEC
also activate more TGF-ß than control cells. Addition of TGF-ß neutralizing antibodies to irradiated cells resulted in increased frequency of cells with centrosome amplification. Thus, TGF-ß plays a dual role in response to IR by protecting against genomic instability that would be generated by radiation-induced centrosome amplification, while promoting phenotypic neoplastic progression.