P63 mechanisms and mediators in HNSCC

描述（由申请人提供）：该项目的长期目标是通过了解p53家族成员p63和p73的功能和调控，为头颈部鳞状细胞癌（HNSCC）和相关癌症找到新的、更有效的、毒性更小的治疗方法。p53蛋白家族在HNSCC的发病机制中起关键作用。在超过50%的这些肿瘤中，p53基因本身是突变失活的靶标，无论治疗方式如何，p53突变肿瘤都是高度致命的。相反，相关的家族成员p63没有突变，但在大多数情况下显著过表达和/或受到基因组扩增的影响。我们和其他人已经证明p63在正常上皮发育过程中促进增殖、粘附信号传导和再生潜能的重要作用进一步支持了p63对HNSCC的贡献。在HNSCC细胞中，p63也作为相关家族成员p73介导的细胞凋亡的抑制因子。促凋亡p73本身在p53突变的HNSCC中过度表达，p63通过与p73的物理关联和直接结合p73调控的促凋亡基因中的调控元件来抑制这些肿瘤的凋亡。这些观察结果的生理学意义得到了支持，证明p63/p73是HNSCC化疗敏感性的直接介质，而Bcl-2上调是治疗耐药的介质。综上所述，这些发现为进一步研究p63/p73在HNSCC中的生化调控和功能贡献提供了强有力的理论基础。该提案描述了一种系统的方法来揭示p63/p73的调控及其在体内肿瘤维持中的作用。我们假设p63/p73调控子的一个子集在HNSCC中作为内源性凋亡抑制因子起作用。我们已经进行了基因组宽屏幕来识别这些调节因子，并辅以生化研究来识别直接与p63相关的转录调节因子。在目标1中，我们将基于我们对基本p63转录辅助因子的鉴定，进行靶向HNSCC染色质的原理验证研究。在目标2中，我们将验证额外的p53相关辅助因子，我们假设这些辅助因子介导与肿瘤进展相关的不同转录程序。在目标3中，我们将使用基因工程小鼠HNSCC模型直接测试这些转录程序的贡献。在Aim 4中，我们将专注于挖掘新的p63调节因子的原始筛选，对最有吸引力的候选物进行直接验证，将其表达与原发性肿瘤标本的临床结果相关联，并进行生化研究以确定其机制。除了提高我们对HNSCC基础生物学的认识外，这些研究将促进发现新的可行的治疗靶点，以改善这种疾病的治疗效果。

DESCRIPTION (provided by applicant): The long-term objective of this project is to identify new, more effective, and less toxic therapies for Head and Neck Squamous Cell Carcinoma (HNSCC) and related cancers, by understanding the function and regulation of the p53 family members p63 and p73. The p53 family of proteins plays a key role in the pathogenesis of HNSCC. The p53 gene itself is a target of mutational inactivation in more than 50% of these tumors, and p53-mutant tumors are highly lethal regardless of treatment modality. In contrast, the related family member p63 is not mutated but is dramatically overexpressed and/or subject to genomic amplification in the majority of cases. A contribution of p63 to HNSCC is further supported by the essential role we and others have demonstrated for p63 in promoting proliferation, adhesion signaling, and regenerative potential during normal epithelial development. In HNSCC cells p63 also functions as a repressor of apoptosis mediated by the related family member p73. Pro-apoptotic p73 itself is overexpressed particularly in p53-mutant HNSCC, and p63 suppresses apoptosis in these tumors through both physical association with p73 and direct binding to regulatory elements within p73-regulated pro- apoptotic genes. The physiologic significance of these observations is supported by the demonstration that p63/p73 are direct mediators of chemosensitivity in HNSCC which is abrogated by Bcl-2 up-regulation, a mediator of therapeutic resistance. Taken together, these findings provide a strong rationale for further studies to understand the biochemical regulation and functional contribution of p63/p73 in HNSCC. This proposal describes a systematic approach to uncovering the regulation of p63/p73 and their role in tumor maintenance in vivo. We hypothesize that a subset of p63/p73 regulators functions as endogenous apoptosis suppressors in HNSCC. We have conducted a genome wide-screen to identify such regulators, complemented by biochemical studies to identify direct p63-associated transcriptional regulators. In Aim 1 we will perform proof-of-principle studies for targeting chromatin in HNSCC based on our identification of essential p63 transcriptional co-factors. In Aim 2 we will validate additional p63-associated co-factors which we hypothesize to mediate distinct transcriptional programs relevant to tumor progression. In Aim 3 we will test the contribution of these transcriptional programs directly using a genetically engineered mouse HNSCC model. In Aim 4 we will focus on mining our original screen for new p63-regulators, performing direct validation of the most attractive candidates, correlating their expression with clinical outcome in primary tumor specimens, and performing biochemical studies to determine their mechanism. In addition to improving our knowledge of the basic biology of HNSCC, these studies will advance the goal of uncovering novel and viable therapeutic targets to improve treatment outcomes in this disease.