Keratin proteins and non-melanoma skin tumors

描述（由申请人提供）：基底细胞癌（BCC）是北美最常见的癌症。它占美国每年诊断出的所有癌症的三分之一以上，而且发病率还在上升。虽然它很少转移，但BCC可能是毁灭性的，因为肿瘤可以局部侵袭，导致溃疡和毁容。目前对BCC肿瘤生物学的生化决定因素所知相对较少。I型角蛋白17 （K17）在BCC病变中一致被诱导，无论是在人皮肤中还是在相关的转基因小鼠模型中，使其成为体内这类肿瘤的可靠标志物。从分子上讲，K17和BCC之间的关联是gli介导的K17基因启动子反激活的直接结果。Gli家族成员是sonic hedgehog （Shh）信号转导的转录因子和末端效应因子。遗传上，大多数bcc与编码Shh信号关键效应因子的位点突变有关，导致其持续激活，并在毛囊和表皮中产生超增殖状态，这有利于肿瘤转化所需的额外“遗传撞击”。最近的研究表明，K17在皮肤上皮中具有多种功能。像其他角蛋白和所有其他中间丝蛋白一样，K17提供结构支持。到目前为止，K17在皮肤上皮中独特的功能包括保护角质形成细胞免受tnfa介导的凋亡，这在毛囊循环的生长期表现出来，以及刺激mTOR依赖的蛋白质合成和角质形成细胞的细胞生长的能力，这需要维持组织的快速生长，就像组织损伤后发生的那样。这三种功能中的每一种都代表了肿瘤生物学的关键决定因素。本项目的总体目标是评估K17在成熟的BCC转基因小鼠模型中的功能贡献。我们将通过将先前表征的K17缺失小鼠（其中K17蛋白完全缺失）与在皮肤祖角质形成细胞中组成性表达Gli2的转基因小鼠配对来实现这一目标，这些转基因小鼠在年轻成年时可再生地发展为BCC皮肤肿瘤。携带K14空等位基因的小鼠将为这些研究提供合适的参考。我们有强有力的初步证据表明K17（而不是K14）的缺失导致BCC肿瘤生长的延迟。在Aim 1中，宏观、微观、分子和生化结果将用于评估缺乏K17或K14的肿瘤生物学。在目标2中，我们将利用原代角化细胞来确定体内肿瘤生长明显延迟的细胞和分子基础。一个特别的重点将放在细胞增殖，程序性细胞死亡和蛋白质合成的调节。总之，拟议的研究将阐明角蛋白作为非黑色素瘤皮肤肿瘤生长和侵袭性的决定因素的作用。

DESCRIPTION (provided by applicant): Basal cell carcinoma (BCC) is the most frequent cancer in North America. It represents more than one-third of all cancers diagnosed in the U.S. every year, and its incidence is on the rise. Whereas it rarely metastasizes, BCC can be devastating in that tumors can be locally aggressive, leading to ulceration and disfigurement. There is relatively little known about the biochemical determinants of BCC tumor biology. The type I keratin 17 (K17) is consistently induced in BCC lesions, whether in human skin or in relevant transgenic mouse models, making it a reliable marker of this type of tumor in vivo. Molecularly, the association between K17 and BCC is the direct result of Gli-mediated transactivation of the K17 gene promoter. Gli family members are transcription factors and terminal effectors of sonic hedgehog (Shh) signaling. Genetically, most BCCs are associated with mutations at loci encoding key effectors of Shh signaling, resulting in its sustained activation, and creating a hyperproliferative state in hair follicles and epidermis that is conducive to the additional "genetic hits" required for neoplastic transformation. Recent work has shown that K17 serves multiple functions in skin epithelia. Like other keratins and all other intermediate filament proteins, K17 provides structural support. Examples of functions that are so far unique to K17 in skin epithelia are the protection of keratinocytes against TNFa-mediated apoptosis, which is manifested during the anagen (growth) phase in cycling hair follicles, and an ability to stimulate mTOR- dependent protein synthesis and cell growth in keratinocytes called upon to sustain rapid tissue growth, as occurs following tissue injury. Each of these three functions represents a key determinant of tumor biology. The overall objective of this project is to assess the functional contribution of K17 in the context of a well-established transgenic mouse model of BCC. We will do so by mating previously characterized K17 null mice, in which the K17 protein is completely missing, with transgenic mice that constitutively express Gli2 in progenitor keratinocytes of the skin, and which reproducibly develop BCC skin tumors as young adults. Mice carrying a null allele in K14 will provide a suitable reference for those studies. We have strong preliminary evidence indicating that loss of K17 (nut not K14) results in a delay in BCC tumor growth. In Aim 1, macroscopic, microscopic, molecular and biochemical outcomes will be used to assess tumor biology in the absence of either K17 or K14. In Aim 2, we will exploit keratinocyte primary to define the cellular and molecular basis for the apparent delay in tumor growth in vivo. A particular emphasis will be placed on the regulation of cell proliferation, programmed cell death, and protein synthesis. Altogether, the proposed studies will shed light on the role of keratins as determinants of the growth and aggressiveness of non-melanoma skin tumors. Project Narrative: Basal cell carcinoma (BCC) is the most frequent cancer in North America. It represents more than one-third of all cancers diagnosed in the U.S. every year, and its incidence is on the rise. Whereas it rarely metastasizes, BCC can be devastating in that tumors can be locally aggressive, leading to ulceration and disfigurement. There is relatively little known about the biochemical determinants of BCC tumor biology. A cytoskeletal protein named keratin 17 (K17) serves as a very useful marker for BCC lesions. Its potential contribution to the growth and fate of BCC lesions has not yet been examined. K17 normally functions to provide mechanical support, and participates in the regulation of programmed cell death as well as protein synthesis, in various types of skin epithelial cells. All of these roles represent key determinants of tumor biology. In this study, we will examine how BCC tumors fare in the complete absence of K17 protein in the context of an established experimental mouse model. We hope that our findings lead to new ideas for the therapeutic management of aggressive and recurring forms of these tumors.