The molecular regulation of Gli2 in Hedgehog signaling

描述（由申请人提供）：Hedgehog （Hh）家族分泌的信号蛋白在脑、脊髓、肢体和许多其他结构的腹侧神经元细胞类型的模式中起着重要作用。Hh信号通路活性的丧失或降低会导致严重的发育性出生缺陷，而Hh信号通路的不适当激活也与几种常见的人类癌症相关，包括基底细胞癌和成神经管细胞瘤。彻底了解这一途径对于预防或补救由Hh途径激活缺陷或不受调节导致的异常至关重要。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：Glil、Gli2和Gli3。遗传分析强调了这三个基因各自的生物学作用。Glil是一个Hh靶点和一个强大的转录激活因子，但不是小鼠Hh信号转导所必需的。Gli2是介导Hh信号所必需的。Gli3在该通路中主要起负向作用。与此一致的是，大部分Gli3蛋白是在Hh信号缺失的情况下加工的。与Gli3相反，我们对Gli2蛋白的活性如何在分子水平上受到调控知之甚少。本应用程序的目的是了解Gli2被调节的分子机制。我们的初步研究提供的证据表明，尽管Gli2和Gli3被PKA、CKI和GSK3类似地磷酸化，但与Gli3不同，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。这个应用程序主要关注三个目标。1)阐明Gli2降解的分子机制；2)确定Shh信号在Gli2稳定性调控中的作用以及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。这项研究的完成将大大促进我们对Gli2转录因子如何调控及其如何介导Shh信号的分子机制的理解。这也可能使我们深入了解与异常Shh信号有关的人类出生缺陷和癌症的分子机制。此外，它可能揭示了β - trcp调节Gli2降解和Gli3加工的新机制。

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.