Role Of CTCF In Tumor Development

由Victor V.Lobanenkov博士领导的免疫病理学实验室(LIP)NIAID分子病理科(MPS)成立于1999年9月。V.Lobanenkov博士1977年在物理与工程研究所获得核物理硕士学位，之后转到癌症生物学作为第二研究领域，并于1981年在莫斯科癌症研究中心获得实验肿瘤学博士学位。在伦敦皇家癌症医院工作后，他被任命为前苏联癌症发生研究所分子癌变小组组长，以及伦敦皇家癌症医院癌症研究所的访问学者。1990年，他应邀在华盛顿州西雅图的弗雷德·哈钦森癌症研究中心工作，在那里他担任外国常驻教师的职位，独立研究议程由NIH/NCI RO1拨款资助，直到1999年移居到NIH。在LIP MPS中开展的研究大多集中在CTCF基因的结构和功能上，该基因是由V.Lobanenkov和他的同事于1990年鉴定和克隆的，最初被鉴定为脊椎动物MYC癌基因的进化保守的负转录调节因子。CTCF含有11个锌指(ZF)DNA结合域，从果蝇到青蛙到鸟类到小鼠到人都是保守的。不同的CTCF靶点(CTS)由CTCFZF的不同组合识别，执行不同的调节功能。根据上下文的不同，不同的CTS在CTCF的转录调控中发挥着不同的作用，包括启动子的抑制、激活和甲状腺激素反应沉默的产生。这些研究结果发表了30多篇论文，并于1999年获得了美国和外国的专利。2001年，V.Lobanenkov和他来自德国和瑞典的主要合作者在《遗传学的趋势》上发表了关于CTCF的第一篇综述，总结了实验结果，这些结果共同表明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。它是一种进化上异常保守的锌指(ZF)磷蛋白，它通过组合利用11个锌指(ZF)到~50bp长的DNA靶点结合在一起，具有显著的序列差异。不同的CTCF-DNA复合体的形成导致不同的功能，包括基因激活、抑制、沉默或染色质隔离。通过ZF突变或某些CTCF靶标的异常选择性甲基化扰乱靶标的特异性光谱与癌症有关。因此，CTCF在连接表达结构域与表观遗传学和细胞生长调控过程的网络中扮演着中心角色。因此，近年来人们对CTCF基因的兴趣迅速增长也就不足为奇了。除了LIP NIAID，CTCF生物学的不同方面已经成为NIH国内外其他几个实验室的主要研究重点。在2000-01年间，MPS LIP继续致力于一个项目，旨在更好地了解CTCF在发育、细胞周期调节和基因印迹中的正常功能，以及癌症和其他与位置特异性DNA甲基化异常相关的人类疾病(例如先天性强直性肌营养不良)中的CTCF功能障碍。该程序利用了易患癌症的小鼠CTCF基因敲除模型，以及基于果蝇CTCF同源物的鉴定和克隆的果蝇遗传学。2001年，包括《癌症研究》和《自然遗传学》在内的几份新出版物问世，另有几份正在提交。癌症相关CTCF突变的鉴定和功能鉴定可以看作是大自然的实验，它揭示了参与CTCF功能调节的至关重要的CTCF靶基因和蛋白质伙伴。确定这样的基因和伙伴揭示了定义肿瘤表型的调控基因网络和途径(S)，并因此使分子病理科远远超出了对CTCFs本身的研究，因为突变的CTCFs途径中的新基因反过来将是潜在的癌基因或肿瘤抑制基因。到2001年9月，这些专利基因中的一些已经被NIAID NIH确定了特征，现在正在申请专利，并为诊断和治疗目的进行了评估。编码ctcf相互作用蛋白的其他几个基因正处于破译其作用的初始阶段(S)。

The Molecular Pathology Section (MPS) lead by Dr. Victor V. Lobanenkov within the Laboratory of Immunopathology (LIP) NIAID was established in September 1999. Dr. V. Lobanenkov received Master Degree in Nuclear Physics from the Institute of Physics and Engineering in 1977, switched to cancer biology as a second field of study, and received his Ph.D. degree in experimental oncology from the Cancer Research Center in Moscow in 1981. Following his work at the Royal Cancer Hospital in London, he was appointed as a Head of Molecular Carcinogenesis group at the Institute of Carcinogenesis: All-Union Cancer Center of the former USSR and a Visiting Scholar at the Institute of Cancer Research, Royal Cancer Hospital of London. In 1990, he was invited to work at the Fred Hutchinson Cancer Research Center in Seattle, WA where he held a position of the Foreign Faculty in Residence with an independent research agenda funded by NIH/NCI RO1 grants until moving to NIH in 1999. Most of the research projects carried out in LIP MPS are focused on structure and function of CTCF gene that was identified and cloned by V. Lobanenkov and co-workers in 1990, and was initially characterized as an evolutionarily conserved negative transcriptional regulator of vertebrate MYC oncogenes. CTCF contains 11 Zn finger (ZF) DNA-binding domain conserved from Drosophila to frogs to birds to mice to men. Different CTCF-target sites (CTSs), recognized by different combinations of CTCF ZFs, perform distinct regulatory functions. Depending on the context, different CTSs play distinct roles in transcriptional regulation by CTCF including promoter repression, activation, and creation of the thyroid hormone-responsive silencers. These studies resulted in more then 30 publications, and the USA and foreign Patents issued in 1999. The very first review on CTCF published in "Trends in Genetics" in 2001 by V. Lobanenkov and his major collaborators from Germany and Sweden, provides a summary of experimental results which together show that CTCF is a uniquely versatile transcriptional regulator with diverse functions linked to epigenetics and disease. It is an exceptionally evolutionarily conserved Zinc Finger (ZF) phosphoprotein that binds via combinatorial utilization of the eleven ZFs to ~ 50 bp long DNA target sites with remarkable sequence variation. Formation of different CTCF-DNA complexes, a subset of which is CpG-methylation-sensitive, results in distinct functions including gene activation, repression, silencing or chromatin insulation. Disrupting the spectrum of target specificities by ZF mutations or by abnormal selective methylation of certain CTCF-targets is associated with cancer. CTCF emerged, therefore, as a central player in networks linking expression domains with epigenetics and cell growth regulatory processes. It is thus not surprising that in recent years there has been a rapidly growing interest in the CTCF gene. Besides LIP NIAID, different aspects of CTCF biology have become a major focus of research in several other laboratories both within and outside NIH, and abroad. In 2000-01, MPS LIP continued to work on a program directed to better understanding of CTCF normal function in development, cell-cycle regulation, and gene imprinting; and of CTCF malfunction in cancer, and in other human diseases associated with abnormal site-specific DNA methylation (for instance, in congenital myotonic dystrophy). This program takes advantage of cancer-prone mouse CTCF knock-out models, and of Drosophila genetics based on identification and cloning of the CTCF homologue in flies. Several new publications, including those in "Cancer Research" and in "Nature Genetics", came out in 2001, while several more are being submitted. Identification and functional characterization of cancer-associated CTCF mutations can be viewed as experiments of Nature that reveal critically important CTCF target genes and protein partners that are involved in regulation of CTCF function. Identifying such genes and partners reveals regulatory gene networks and pathways which define tumor phenotype(s), and thus leads the Molecular Pathology Section well beyond studies of CTCF per se because novel genes in a pathway of mutant CTCF are to be, in turn, potential oncogenes or tumor suppressor genes. By September 2001, some of these proprietary genes have already been characterized and are now being patented by NIAID NIH, and evaluated for diagnostic and therapeutic purposes. Several other genes encoding CTCF-interacting proteins are at the initial stages of deciphering their role(s).