Regulation of Genomic Instability in Early Breast Cancer

描述(由申请人提供)：我们最近对人类乳腺细胞的研究使我们能够在罕见的人类乳腺上皮细胞亚群(HMEC)中识别出以前未检测到的表型。正如之前报道的那样，从健康女性的活检组织中生长出来的大多数上皮细胞在培养后对大约15到20个群体倍增的增殖障碍做出反应。在短暂的停滞(在培养中称为“选择”)之后，一个罕见的细胞亚群(大约10-4到10-5)会超过最初的屏障并在培养中繁殖数月。这些“后选择”的HMEC以失去特定的细胞周期控制和大量的染色体异常积累为典型。随着这些细胞在培养中生长，它们接近第二个生长平台，在这个平台上，几乎100%的细胞都有染色体异常。这些观察结果挑战了细胞如何以及何时在癌症中获得基因组变化的传统观点，因为它们提供了一种细胞内在机制，该机制在肿瘤过程的早期产生多个同时的基因变化。这些细胞是在不强制暴露于已知的物理、病毒或化学诱变剂的情况下产生的。最后，这些细胞具有在癌细胞中经常发现的明确特征，并可能解释其来源。“后选择”的HMEC不表达p16，p16是一种重要的细胞周期蛋白依赖的激酶抑制物，它们缺乏适当的检查点控制，也不能维持基因组的完整性。如果这些细胞在体内出现，它们可能是人类乳腺癌发生的最早步骤。这些观察也发现了新的机会。它们可能为评估个体对肿瘤转化的易感性以及预防和治疗的潜在靶点提供潜在的标记物。多个标记物在体外清楚地识别不同的细胞状态，并允许在体内识别具有这些特性的细胞。值得注意的是，我们在“选择后”HMEC中检测到的变化模仿了乳腺癌癌前病变中的许多变化。我们推测，在体外“后选择”的HMEC的上述特性与体内乳腺上皮细胞的转化过程密切相关。这项应用的目标是(1)确定p16失活如何促进“选择后”HMEC表型，(2)确定“选择后”HMEC的起源，3)确定体内检测到的类似细胞是否存在(A)乳腺癌高危个体频率增加，以及(B)显示干细胞的特征，以及(4)检查HMEC中选择性细胞周期检查点控制。这些研究可能为乳腺癌的预防或治疗提供新的靶点。

DESCRIPTION (provided by applicant): Our recent studies on human mammary cells have allowed us to identify a previously undetected phenotype in a rare subpopulation of human mammary epithelial cells (HMEC). As previously reported, the majority of epithelial cells that grow from biopsy tissue from healthy women respond to a proliferation barrier around 15 to 20 population doublings after placement in culture. After a transient arrest (called "selection" in culture), a rare subpopulation of cells (approximately 10-4 to 10-5) grows beyond the initial barrier and propagate for months in culture. These "post-selection" HMEC are typified by loss of specific cell cycle controls and the accumulation of a tremendous number of chromosomal abnormalities. As this population of cells is grown in culture, they approach a second growth plateau in which virtually 100% of the cells have chromosomal abnormalities. These observations challenge traditional views of how and when cells acquire genomic changes in cancer by providing a cell intrinsic mechanism that, early in the neoplastic process, generates multiple simultaneous genetic changes. These cells are generated without obligatory exposure to known physical, viral or chemical mutagenic agents. Finally, these cells possess defined characteristics that are often found in cancer cells and may explain their origin. "Post-selection" HMEC do not express p16, an important cyclin dependent kinase inhibitor, they lack proper checkpoint control and they do not maintain genomic integrity. Should these cells arise in vivo, they could represent the earliest steps in human mammary carcinogenesis. These observations also identify novel opportunities. They may provide potential markers for assessing susceptibility to neoplastic transformation in individuals as well as potential targets for prevention and therapy. Multiple markers clearly identify the different cellular states in vitro and have allowed for the identification of cells with these properties in vivo. Remarkably, the changes we detect in "post-selection" HMEC mimic many of the changes seen in premalignant lesions in breast cancer. We hypothesize that the above-described properties of "post-selection" HMEC in vitro are critically relevant to the transformation processes of mammary epithelial cells in vivo. The goals of this application are to (1) determine how p16 inactivation contributes to the "post-selection" HMEC phenotype, (2) determine the origins of "post-selection" HMEC, 3) determine if similar cells detected in vivo are (a) present in increased frequencies in individuals at high risk for breast cancer, and (b) exhibit characteristics of stem cells, and (4) examine selective cell cycle checkpoint controls in HMEC. These studies may provide novel targets for prevention or treatment of breast cancer.