The molecular regulation of Gli2 in Hedgehog signaling

描述(申请人提供)：Hedgehog(HH)分泌信号蛋白家族在大脑和脊髓、肢体和许多其他结构的腹侧神经细胞类型的模式中发挥着基础作用。HH信号通路活性的丧失或降低会导致严重的发育缺陷，而HH信号通路的不适当激活也与几种常见的人类癌症类型有关，包括基底细胞癌和髓母细胞瘤。对该通路的深入了解对于预防或治疗由HH通路激活缺陷或不受调控引起的异常是至关重要的。在脊椎动物中，HH信号由Gli/Ci转录因子家族的三个成员介导：Gli1、Gli2和Gli3。基因分析强调了这三个基因各自的生物学作用。Glil是一个HH靶标，是一个很强的转录激活剂，但对小鼠的HH信号转导不是必需的。Gli2的积极作用是介导HH信号所必需的。Gli3在该途径中主要起负性作用。与此一致，Gli3蛋白的大部分是在没有HH信号的情况下被处理的。与Gli3相比，Gli2蛋白的活性是如何在分子水平上调节的知之甚少。这项应用的目的是了解Gli2被调控的分子机制。我们的初步研究表明，尽管Gli2和Gli3类似地被PKA、CKI和GSK3磷酸化，但与Gli3不同的是，Gli2经历的是降解而不是加工。Gli2的降解可能是由泛素和蛋白酶体系统通过B-TrCP介导的。这个应用程序侧重于三个目标。1)阐明Gli2降解的分子机制；2)确定Shh信号在调节Gli2稳定性中的作用以及Gli2磷酸化和降解的意义；3)了解Gli2和Gli3蛋白不同命运的分子基础。这项研究的完成将极大地促进我们对Gli2转录因子如何调控以及它如何介导Shh信号的分子机制的理解。这也可能使我们深入了解与Shh信号异常相关的人类出生缺陷和癌症的分子机制。此外，它还可能揭示一种新的机制，即Beta-TrCP调控Gli2的降解，并可能调控Gli3的加工。

DESCRIPTION (provided by applicant): The Hedgehog (Hh) family of secreted signaling proteins plays fundamental roles in the patterning of ventral neuronal cell types of the brain and spinal cord, limb, and many other structures. Loss of or decrease in the Hh signaling pathway activity results in severe developmental birth defects, whereas inappropriate activation of the Hh signaling pathway is also associated with several common types of human cancer including basal cell carcinoma and medulloblastoma. A thorough understanding of this pathway is crucial for prevention or remedy of the abnormalities resulting from defective or unregulated Hh pathway activation. In vertebrates, Hh signal is mediated by three members of the Gli/Ci family of transcription factors: Glil, Gli2, and Gli3. Genetic analysis has underlined the biological roles of each of the three genes. Glil is a Hh target and a strong transcriptional activator but not essential for the Hh signal transduction in the mouse. Gli2, acting positively, is absolutely required for mediating Hh signal. Gli3 mainly plays a negative role in the pathway. Consistent with this, the majority of Gli3 protein is processed in the absence of Hh signal. In contrast to Gli3, little is known about how the activity of Gli2 protein is regulated at the molecular level. The objective of this application is to understand the molecular mechanism by which Gli2 is regulated. Our preliminary studies have provided the evidence that although Gli2 and Gli3 are phosphorylated similarly by PKA, CKI and GSK3, unlike Gli3, Gli2 undergoes degradation instead processing. The degradation of Gli2 is likely mediated by the ubiquitin and proteasome system through B-TrCP. This application focuses on three aims. 1) Elucidate the molecular mechanism of Gli2 degradation; 2) Determine the role of Shh signaling in the regulation of Gli2 stability and the significance of Gli2 phosphorylation and degradation; and 3) Understand the molecular basis of the distinct fate of Gli2 and Gli3 proteins. The completion of the proposed study will significantly advance our understanding of the molecular mechanism of how Gli2 transcription factor is regulated and how it may mediate Shh signal. It may also give us insight into the understanding of molecular mechanism of human birth defects and cancer associated with abnormal Shh signaling. In addition, it may reveal a novel mechanism by which Beta-TrCP regulates Gli2 degradation and possibly Gli3 processing.