Transcriptional Regulation Of Ctcf And Boris Expression

Ctcf 和 Boris 表达的转录调控

• 批准号: 6674068
• 负责人: VICTOR LOBANENKOV
• 金额: --
• 依托单位: NATIONAL INSTITUTE OF ALLERGY AND INFECTIOUS DISEASES
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/6674068
• 关键词: Wilms' tumor; breast neoplasms; gene mutation; genetic promoter element; genomic imprinting; neoplasm /cancer genetics; prostate neoplasms; protooncogene; tissue /cell culture; transcription factor

The first comprehensive review on CTCF -published in "Trends in Genetics" in 2001 by V. Lobanenkov and collaborators -provided a summary of experimental results which show that CTCF is a uniquely versatile transcriptional regulator with diverse functions linked to epigenetics and disease. Our earlier results demonstrated that CTCF is the ubiquitously expressed gene upregulated during the S/G2-stage of the cell cycle. A 2002 review by Klenova et.al. (see refs) established CTCF as a true "multivalent multifunctional" protein which utilizes different sets of ZF to form distinct complexes with varying ~50 bp CTCF-target sites (CTS) that mediate distinct functions in regulation of gene expression. Others and we have shown that these functions include context-dependent promoter repression or activation, creation of modular hormone-responsive gene silencers, and formation of diverse vertebrate enhancer-blocking elements (chromatin insulators or boundaries). Functions of varying CTCF/DNA complexes may be regulated by post-translational protein modifications; by physical interactions with other multifunctional nuclear proteins that include, among others, RNA/DNA binding factor YB-1 and the repression-associated mSin3A/HDACs; and by attenuation of the interactions with DNA via specific methylation of CpG pairs involved in recognition of specific CTS by the protein. For example, the latter class of conserved targets which require particular sets of CTCF ZF for formation of the very high-affinity complexes with CTCF, were characterized [see Trends in Genetics 17:520-7 (2001) for review] within the Imprinting Control Region (ICR) between growth-regulating gene IGF2 and a candidate tumor suppressor gene, H19. We showed that specific CpG methylation eliminates interaction of CTCF with the ICR, allowing the protein to distinguish normally differentially methylated maternal versus paternal IGF2/H19 alleles IN VIVO; and that methylation-regulated formation of CTCF/ICR complexes controls activity and conformation of the chromatin insulator that regulates imprinted IGF2 and H19 expression. In addition to the IGF2/H19 ICR CTSs, critical regulatory regions at the promoters of vertebrate MYC oncogenes have been shown to contain CTS that mediate negative transcriptional control by CTCF modulated by the carboxyterminal phosphorylation. Moreover, a number of novel functional CTS were identified; in respect to cell proliferation control, some of these are neutral while some others are important - for example, the CTS in mouse/human WT1, PLK and p19ARF genes and mouse/human PIM1 oncogene among others. We have also found that disrupting the spectrum of functional CTCF/DNA complexes either (i) by selective ZF point-mutations observed in some tumors with frequent LOH at CTCF locus mapped on chromosome 16q22 (10) or (ii) by abnormal CpG-methylation of CTS that constitute insulator sites upstream of IGF2 observed in tumors with LOI, is associated with cancer development. Moreover, ability of CTCF to apparently freeze cells at any stage of cell cycle progression seems to be unprecedented and suggests that CTCF may control expression of genes that arrest cells at each stage in this progression. This model implies function of CTCF as a universal coordinator of an intertwined network of genes in which, if considered separately one from another, each network may perform only strictly specialized tasks in cell cycle control. Our unexpected discovery of the gene termed BORIS has turned every known CTCF-target site into target for BORIS because it shares with CTCF the same 11 Zn-finger DNA-binding domain. CTCF and BORIS are expressed in a mutually-exclusive pattern that correlates with re-setting of methylation marks during male germ cell differentiation thus suggesting that BORIS directs epigenetic reprogramming at CTCF target-sites. Human BORIS maps to the cancer-associated region 20q13. We showed that BORIS belongs to the -cancer-testis- gene family because it is aberrantly activated in substantial proportions of different cancers. BORIS and CTCF compete for site-specific binding to DNA. Thus, BORIS and CTCF may normally act successively to govern epigenetic states in male germ cells. The sibling rivalry occasioned by aberrant expression of BORIS in cancer may interfere with normal functions of CTCF including growth suppression, and contribute to epigenetic dysregulation. Our current efforts are directed to understanding of how CTCF and BORIS can be regulated in such a unique coordinated fashion titgtly coupled with DNA re-methylation, and how this regulation is disturbed in cancers with LOH at 16q22 (locus of CTCF) and amplifications at 20q13 (locus of BORIS). We have mapped first critical elements in the promoters of both genes, and apply bisulfite-sequencing methods to elucidate effects of mutually-dependent methyaltion on transcription of CTCF versus BORIS.

关于CTCF的第一个全面综述-由V. Lobanenkov和合作者于2001年发表在“遗传学趋势”上-提供了实验结果的总结，表明CTCF是一种独特的多功能转录调节因子，具有与表观遗传学和疾病相关的多种功能。我们早期的研究结果表明，CTCF是在细胞周期的S/G2期上调的普遍表达的基因。Klenova等人（参见参考文献）在2002年的综述中确定CTCF为真正的“多价多功能”蛋白，其利用不同组的ZF形成具有不同的~50 bp CTCF-靶位点（CTS）的不同复合物，所述CTCF-靶位点（CTS）介导基因表达调控中的不同功能。其他人和我们已经表明，这些功能包括上下文依赖的启动子抑制或激活，创建模块化的沉默应答基因沉默，并形成不同的脊椎动物增强子阻断元件（染色质绝缘体或边界）。不同的CTCF/DNA复合物的功能可以通过以下方式调节：翻译后蛋白质修饰;与其他多功能核蛋白的物理相互作用，包括RNA/DNA结合因子YB-1和抑制相关的mSin 3A/HDAC等;以及通过参与蛋白质识别特异性CTS的CpG对的特异性甲基化减弱与DNA的相互作用。例如，后一类保守的靶标需要特定的CTCF ZF组以与CTCF形成非常高亲和力的复合物，其特征在于[参见Trends in Genetics 17：520-7（2001）综述]在生长调节基因IGF 2和候选肿瘤抑制基因H19之间的印记控制区（ICR）内。我们发现，特异性CpG甲基化消除了CTCF与ICR的相互作用，使蛋白质能够在体内区分正常差异甲基化的母本与父本IGF 2/H19等位基因;甲基化调节的CTCF/ICR复合物的形成控制了调节印迹IGF 2和H19表达的染色质绝缘体的活性和构象。除了IGF 2/H19 ICR CTS之外，脊椎动物MYC癌基因启动子处的关键调控区已显示含有CTS，其通过由羧基末端磷酸化调节的CTCF介导负转录控制。此外，还鉴定了许多新的功能性CTS;就细胞增殖控制而言，其中一些是中性的，而另一些是重要的-例如，小鼠/人WT 1、PLK和p19 ARF基因以及小鼠/人PIM 1癌基因中的CTS等。我们还发现，（i）通过在染色体16 q22上定位的CTCF基因座处频繁出现洛杂合性缺失的一些肿瘤中观察到的选择性ZF点突变（10）或（ii）通过异常的CTS CpG甲基化（构成了在具有LOI的肿瘤中观察到的IGF 2上游的绝缘子位点），破坏功能性CTCF/DNA复合物的谱与癌症的发展相关。此外，CTCF在细胞周期进展的任何阶段明显冷冻细胞的能力似乎是前所未有的，并且表明CTCF可以控制在该进展的每个阶段阻滞细胞的基因的表达。这个模型暗示了CTCF作为一个交织的基因网络的通用协调者的功能，如果将每个网络单独考虑，每个网络可能只执行严格的细胞周期控制中的专门任务。我们意外地发现了称为BORIS的基因，将每个已知的CTCF靶位点变成了BORIS的靶点，因为它与CTCF共享相同的11个锌指DNA结合结构域。CTCF和BORIS以相互排斥的模式表达，该模式与雄性生殖细胞分化期间甲基化标记的重置相关，因此表明BORIS指导CTCF靶位点处的表观遗传重编程。人类BORIS映射到癌症相关区域20 q13。我们发现BORIS属于-cancer-testis- gene家族，因为它在不同癌症的相当大比例中被异常激活。BORIS和CTCF竞争与DNA的位点特异性结合。因此，BORIS和CTCF通常可以连续作用于男性生殖细胞中的表观遗传状态。在癌症中由BORIS异常表达引起的同胞竞争可能干扰CTCF的正常功能，包括生长抑制，并导致表观遗传失调。我们目前的努力是针对理解CTCF和BORIS如何以这样一种独特的协调方式与DNA再甲基化相结合进行调控，以及这种调控在16 q22（CTCF基因座）洛和20 q13（BORIS基因座）扩增的癌症中如何受到干扰。我们绘制了这两个基因的启动子中的第一个关键元件，并应用亚硫酸氢盐测序方法来阐明相互依赖的甲基化对CTCF与BORIS转录的影响。