The molecular regulation of Gli2 in Hedgehog signaling

描述（由申请人提供）： Hedgehog（Hh）家族的分泌信号蛋白在脑和脊髓、肢体和许多其他结构的腹侧神经元细胞类型的图案化中起着重要作用。Hh信号通路活性的丧失或降低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类型的人类癌症相关，包括基底细胞癌和髓母细胞瘤。彻底了解这一途径是至关重要的预防或补救的异常所造成的缺陷或不受管制的Hh途径激活。在脊椎动物中，Hh信号由转录因子Gli/Ci家族的三个成员介导：Glil、Gli 2和Gli 3。遗传分析强调了这三个基因中每一个的生物学作用。Glil是Hh靶点和强转录激活因子，但不是小鼠中Hh信号转导所必需的。Gli 2是介导Hh信号所必需的正性信号。Gli 3在该通路中主要起负性作用。与此一致，大多数Gli 3蛋白在没有Hh信号的情况下被加工。与Gli 3相反，很少有人知道Gli 2蛋白的活性如何在分子水平上调节。本申请的目的是了解Gli 2调节的分子机制。我们的初步研究提供了证据，虽然Gli 2和Gli 3被PKA，CKI和GSK 3类似地磷酸化，但与Gli 3不同，Gli 2经历降解而不是加工。Gli 2的降解可能是由泛素和蛋白酶体系统通过B-TrCP介导的。本申请侧重于三个目标。1)阐明Gli 2降解的分子机制; 2）确定Shh信号在Gli 2稳定性调节中的作用以及Gli 2磷酸化和降解的意义; 3）理解Gli 2和Gli 3蛋白不同命运的分子基础。这项研究的完成将大大推进我们对Gli 2转录因子如何调节以及它如何介导Shh信号的分子机制的理解。这也可能使我们深入了解人类出生缺陷和癌症的分子机制与异常Shh信号。此外，它可能揭示了一种新的机制，β-TrCP调节Gli 2降解和可能的Gli 3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.