NON-GENETIC CELL HETEROGENEITY IN TUMOR EVOLUTION

肿瘤进化中的非遗传​​细胞异质性

• 批准号: 7129775
• 负责人: Sui Huang
• 金额: $ 16.06万
• 依托单位: BOSTON CHILDREN'S HOSPITAL
• 依托单位国家: 美国
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-07-18 至 2008-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7129775
• 关键词: drug resistance; epigenetics; evolution; genetics; neoplasm /cancer; phenotype; stem cells

DESCRIPTION (provided by applicant): If normal somatic cells can generate distinct, stable cell phenotypes, such as quiescent stem cells, proliferating progenitors and the large variety of differentiated cell types without altering the genome, then why is the acquisition of one malignant trait by progressing tumors, such as drug-resistance, stem cell-like self-renewal, invasion, etc., usually explained by genetic mutations? Tumor cell populations are highly heterogeneous which reflects to some extent normal tissue organization into compartments of stem cells and more differentiated cells. Thus, tumors may use the same non-genetic ("epi-genetic") regulatory mechanisms to generate a variety of stable phenotypes as do normal tissues. Gene regulatory networks ol metazoan in fact appear to be wired so as to produce either a gradual stochastic dispersion of a trait (expression level of a gene) across a cell population or the distinct, stable variants of gene expression patterns (attractor states) - as epitomized by the various discrete cell types. Therefore, it is here hypothesized that this epigenetic cell population heterogeneity may produce phenotypic variants persistent enough to be selected for and hence, contribute to the classical (mutation-based) evolution of cells in tumor progression. Specifically, the rapid, population-wide appearance and disappearance of multi-drug-resistance in entire cell cultures support the idea of epigenetic adaptation. Moreover, expression of MDR1 that confers drug resistance is not an isolated idiosyncratic trait but an intrinsic property of adult stem cells, suggesting that tumors may in fact epigenetically switch between entire stable cellular programs that can be subjected to selection. To begin to address this new paradigm of epigenetic dynamics in tumor evolution, the Specific Aim 1 of this proposal will be to quantitate the dynamics of population dispersion in the expression of the multi-drug resistance gene, MDR1, in HL60 cells and the stability of epigenetic variants. Specific Aim 2 is to create a "genetic random-number generator" based on random recombination that can be externally initialized and is readable in single cells. It will be used in Specific Aim 3 to determine whether acquisition of drug resistance in vitro is mediated by clonal expansion of a random mutant or by a stochastic transitions between epigenetic states independently in multiple cells. In addition, gene expression profiling in this last Aim will reveal whether acquisition of drug resistance is linked to adoption of a stem cell phenotype, as would be expected if this process mirrors normal epigenetic switching between "preprogrammed" cellular behaviors, since stem cells normally express MDR1. A better, quantitative knowledge of the neglected phenomenon of dynamic epigenetic heterogeneity not only will open a new perspective to metazoan cell regulation and cancer, but also could help optimize scheduling of chemotherapy so as to suppress selection of resistance and better target tumor stem cells.

说明（申请人提供）：如果正常体细胞可以产生不同的、稳定的细胞表型，如静止干细胞、增殖祖细胞和大量不同的分化细胞类型而不改变基因组，那么为什么通过进展肿瘤获得一种恶性性状，如耐药性、干细胞样自我更新、侵袭等，通常用基因突变来解释肿瘤细胞群是高度异质的，这在一定程度上反映了正常组织成干细胞和更分化细胞的区室。因此，肿瘤可以使用与正常组织相同的非遗传（“表观遗传”）调节机制来产生多种稳定的表型。事实上，后生动物的基因调控网络似乎是有线的，以便在整个细胞群体中产生一种性状（基因表达水平）的逐渐随机分散，或者是基因表达模式（吸引子状态）的独特稳定变体-如各种离散细胞类型所体现的那样。因此，这里假设这种表观遗传细胞群体异质性可能产生足够持久的表型变体以被选择，因此有助于肿瘤进展中细胞的经典（基于突变的）进化。具体来说，在整个细胞培养中，多药耐药性的快速、群体范围的出现和消失支持了表观遗传适应的观点。此外，赋予耐药性的MDR 1表达不是孤立的特异质特征，而是成体干细胞的内在特性，这表明肿瘤实际上可能在整个稳定的细胞程序之间进行表观遗传转换，这些程序可以进行选择。为了开始解决肿瘤演变中表观遗传动力学的新范例，本提案的具体目标1将是定量HL 60细胞中多药耐药基因MDR 1表达中的群体分散动力学和表观遗传变异体的稳定性。具体目标2是创建一个基于随机重组的“遗传随机数发生器”，可以在外部初始化，并在单细胞中可读。它将用于特定目标3，以确定体外耐药性的获得是由随机突变体的克隆扩增介导的，还是由多个细胞中独立的表观遗传状态之间的随机转换介导的。此外，基因表达谱在这最后一个目的将揭示是否收购耐药性与采用干细胞表型，如果这一过程反映了正常的表观遗传转换之间的“预编程”的细胞行为，因为干细胞通常表达MDR 1。对被忽视的动态表观遗传异质性现象的更好的定量认识不仅将为后生动物细胞调控和癌症开辟新的视角，而且还可以帮助优化化疗方案，以抑制耐药选择并更好地靶向肿瘤干细胞。