Radiation and Genomic Instability in Finite Lifespan Human Mammary Epithelium

描述（由申请人提供）：电离辐射是1928年H.J.穆勒发现的第一个环境诱变原，辐射是已知的人类致癌物。来自日本原子弹幸存者的流行病学证据表明，女性乳房对放射性致癌极为敏感。接受乳腺癌治疗的妇女与接受胸部放射治疗的霍奇金病妇女一样，有患新疗法相关乳腺癌的风险。最近的数据表明，年轻女性（< 40岁）患放射性乳腺癌的风险更高。我们对辐射如何作为致癌物的了解是有限的。其他人的研究表明，在未经治疗的乳腺活检标本中，从良性增生到恶性肿瘤的早期阶段发生向基因组不稳定的过渡，这表明不稳定基因组的发展是该疾病病因学的关键步骤。我们将验证电离辐射（x射线）暴露会引起有限寿命人类乳腺上皮细胞（HMEC）克隆后代染色体不稳定的中心假设。这是基于我们的初步发现，一个有限寿命HMEC菌株的辐照导致单次辐照细胞在单次剂量2 Gy或更高剂量下存活的后代中核型不稳定。使用的HMEC菌株（选择后184）来自一个年轻的供体，已经通过了第一个衰老屏障，p16表达缺失，但它们保持有限的寿命。这种类型的细胞在组织学上正常的乳腺组织的局灶斑中发现，但大多数有限寿命的HMEC（预停滞细胞）没有通过第一个衰老屏障。提出了两个目标。目的1使用来自40岁以下供体的细胞，验证电离辐射暴露导致选择后有限寿命HMEC核型不稳定的假设。Aim 2验证了一个假设，即与Aim 1中评估的来自同一供体的选择后有限寿命HMEC相比，停滞前HMEC中辐射诱导的核型不稳定性的建立减少了。机制研究将确定在建立辐射诱导的核型不稳定性时p16INK4a或pRb沉默的要求。这些研究将确定辐射诱导的核型不稳定是罕见的还是辐照后的常见现象，以及是否需要通过第一个衰老屏障的过渡来建立表型。

DESCRIPTION (provided by applicant): Ionizing radiation was the first environmental mutagen identified by H.J. Muller in 1928, and radiation is a known human carcinogen. Epidemiological evidence from the Japanese atomic bomb survivors indicates that the female breast is exquisitely sensitive to radiogenic cancer. Women treated for breast cancer are at risk for a new treatment associated breast cancer as are women treated with radiation to the chest for Hodgkin's disease. Recent data indicate that younger women (<age 40) are at a higher risk for radiogenic breast cancer. Our understanding of how radiation acts as a carcinogen is limited. Work by others demonstrated that a transition to genomic instability occurs at the transition from benign hyperplasia to the earliest stages of malignancy in untreated breast biopsy specimens, suggesting that development of an unstable genome is a key step in the etiology of the disease. We will test the central hypothesis that exposure to ionizing radiation (x-rays) will elicit chromosomal instability in the clonal descendants of finite lifespan human mammary epithelial cells (HMEC). This is based on our preliminary finding that irradiation of one strain of finite lifespan HMEC led to karyotypic instability amongst the progeny of single irradiated cells surviving exposure to single doses of 2 Gy or more. The strain of HMEC used (post-selection 184) is from a young donor, and has passed the first senescence barrier with a loss of p16 expression but they retain finite lifespan. Cells of this type are found in focal patches in histologically normal breast tissue, but the majority of finite lifespan HMEC (pre-stasis cells) have not passed the first senescence barrier. Two aims are proposed. Aim 1 tests the hypothesis that ionizing radiation exposure elicits karyotypic instability in post-selection finite lifespan HMEC using cells derived from donors below the age of 40. Aim 2 tests the hypothesis that the establishment of radiation-induced karyotypic instability is reduced in pre-stasis HMEC compared with post-selection finite lifespan HMEC from the same donors evaluated in Aim 1. Mechanistic studies will determine the requirements for silencing of p16INK4a or pRb in the establishment of radiation-induced karyotypic instability. These studies will determine whether radiation-induced karyotypic instability is a rare or a common occurrence after irradiation and whether a transition past the first senescence barrier is required for establishment of the phenotype. PUBLIC HEALTH RELEVANCE: Ionizing radiation is a human carcinogen, and results from the Japanese atomic bomb survivors and medically exposed populations have demonstrated that the young female breast is very sensitive to radiation-induced cancer. Others have shown that genomic instability first appears in human breast biopsy materials at the earliest malignant stage - ductal carcinoma in situ - suggesting that instability is an important early feature in the development of breast cancer. The experiments proposed address whether radiation exposure elicits persistent genomic instability in the progeny of apparently normal finite lifespan human mammary epithelial cells from donors below age 40, whether this is a common phenotype amongst individuals, and whether transition past the first senescence barrier is required for finite lifespan human mammary epithelial cells to exhibit radiation induced genomic instability.