Functional analysis of the CYLD tumor suppressor

描述（申请人提供）：CYLD是通过定位克隆16q12染色体上家族性圆柱状病（FC）连锁区间发现的一种新型肿瘤抑制基因。FC是一种常染色体显性遗传综合征，以毁损皮肤附属物肿瘤为特征，如圆柱状瘤、毛上皮瘤和螺旋腺瘤。这些肿瘤通常位于头皮和面部，在儿童或成年早期出现，并在一生中逐渐增大大小和数量。此外，这些肿瘤可能发生恶性转化，具有局部侵袭行为，也可能发生远处转移。在FC家族中已经发现了CYLD的种系突变，并且在这些肿瘤中发现了CYLD位点的杂合性缺失，这表明CYLD具有肿瘤抑制作用。CYLD的蛋白产物是956个氨基酸，包含在去泛素化酶和微管结合蛋白中发现的序列基序。它在多种组织中表达，有趣的是，它在皮肤中的表达在表皮和皮肤附属物中都有观察到。导致原癌基因功能获得或肿瘤抑制基因功能丧失的突变导致肿瘤的发生。肿瘤抑制基因通过调控不同的细胞通路（其中之一是NF-KB信号通路）抑制增殖、促进细胞凋亡或增强分化，维持基因组完整性。最近的数据表明CYLD具有去泛素化靶蛋白的酶活性。它已被证明与NF-KB信号通路的几个成员相互作用，如TRAF-2、TRIP和IKKy/NEMO，并负向调节NF-KB激活。然而，CYLD抑制肿瘤的分子和细胞机制在很大程度上是未知的。NF-KB信号对于外胚层器官发生至关重要。NF-KB抑制导致包括毛囊和汗腺在内的表皮附属物发育的严重缺陷。此外，NF-KB信号的异常在表皮瘤变中起作用。然而，与NF-KB信号相关的肿瘤发展机制，特别是cyld依赖性肿瘤发生的作用，尚不清楚。我们的总体目标是明确CYLD在皮肤肿瘤发生中的功能。我们已经在FC患者中发现了CYLD基因的多种突变。然而，目前关于CYLD的突变数据有限。在目标1中，我们将评估FC的基因型和表型相关性，这将导致基于分子的皮肤附件肿瘤的理解。作为明确cyld介导的肿瘤抑制机制的关键一步，我们将在Aim 2中建立小鼠FC模型。最后，我们的初步研究表明，CYLD在稳定状态下存在于HeLa细胞的细胞核和细胞质中，并且leptomycin B处理增加了其核定位。这一观察结果表明CYLD以依赖于crml的方式组成性地穿梭于细胞质和核室之间。然而，它在细胞核中的作用尚未确定。在Aim 3中，我们首先计划确定一个负责CYLD核-胞质穿梭的功能性核输出信号，并评估NF-KB激活过程中CYLD的定位。其次，为了深入了解其核作用，我们将尝试确定其在核中的相互作用伙伴。我们期望在这些研究过程中对CYLD调控的肿瘤抑制途径有重要的见解，从而扩大我们对肿瘤发生的理解。

DESCRIPTION (provided by applicant): CYLD is a novel tumor suppressor gene that was discovered by positional cloning of the linkage interval for Familial Cylindromatosis(FC) on chromosome 16q12. FC is an autosomal dominantly inherited syndrome characterized by disfiguring skin appendage tumors, such as cylindromas, trichoepitheliomas and spiradenomas. Typically these tumors are located on the scalp and face,appear in childhood or early adulthood, and gradually increase in size and number throughout life. Moreover, malignant transformation of these tumors with locally invasive behavior as well as distant metastasis can occur. Germline mutations in CYLD have been demonstrated in families with FC, and loss of heterozygosity at the CYLD locus has been found in these neoplasms, suggesting that CYLD functions as a tumor suppressor. The protein product of CYLD is 956 amino acids and contains sequence motifs found in deubiquitinating enzymes and microtubule binding proteins. It is expressed in a variety of tissues, and of interest, its expression in the skin is observed in the epidermis as well as in the skin appendages. Mutations leading to gain of function of proto-oncogenes or loss of function of tumor suppressor genes result in tumor development. Tumor suppressor genes either inhibit proliferation, promote apoptosis, or enhance differentiation, and maintain genomic integrity via regulation of distinct cellular pathways, one of which is the NF-KB signaling pathway. Recent data suggests that CYLD has enzymatic activity to deubiquitinate target proteins. It has been shown to interact with several members of the NF-KB signaling pathway, such as TRAF-2, TRIP, and IKKy/NEMO, and negatively regulate NF-KB activation. However, the molecular and cellular mechanism(s) of CYLD tumor suppression is largely unknown. NF-KB signaling is essential for ectodermal organogenesis. NF-KB suppression results in severe defects in the development of epidermal appendages including hair follicles and sweat glands. In addition, abnormalities in NF-KB signaling play a role in epidermal neoplasia. However, the mechanisms of tumor development related to NF-KB signaling, and in particular the role of CYLD-dependent tumorigenesis, are not well understood. Our overall goal is to define the functions of CYLD in cutaneous tumorigenesis. We have identified a variety of mutations in the CYLD gene in patients with FC. However, the mutational data on CYLD is currently limited. In Aim 1, we will evaluate genotype and phenotype correlation in FC that will lead to a molecular-based understanding of the skin appendage tumors. As a crucial step in defining the mechanisms of CYLD-mediated tumor suppression, we will establish a mouse model for FC in Aim 2. And lastly, our Preliminary Studies demonstrate that CYLD is present in both the nucleus and the cytoplasm of HeLa cells at steady state and that leptomycin B treatment increases its nuclear localization. This observation suggests that CYLD constitutively shuttles between cytoplasmic and nuclear compartments in a CRMl-dependent manner. However, its role in the nucleus has not been defined. In Aim 3, we first plan to identify a functional nuclear export signal responsible for nucleo-cytoplasmic shuttling of CYLD and evaluate localization of CYLD during NF-KB activation. Second, to provide insights into its nuclear role, we will attempt to identify its interaction partners in the nucleus. We anticipate that significant insights into the pathway of CYLD regulated tumor suppression will arise in the course of these studies, thereby extending our understanding of tumorigenesis.