Mechanism of Hedgehog signal transduction

描述（由申请人提供）： Hedgehog（Hh）家族成员的信号传导介导局部细胞间通讯，这对于许多组织和结构的发育和维持是必不可少的。Hh信号的异常激活是基底细胞癌、髓母细胞瘤的基础，并可能导致许多其他癌症。Hh信号的转导知之甚少。Smoothened（Smo）是蛇形受体家族的一员，对Hh的细胞内反应的激活至关重要。应答通过包括Costal（趋异驱动蛋白）、Fused（S/T激酶）和Ci（锌指转录因子）的胞质复合物转导。根据Hh输入的水平，复合物可以将Ci以潜伏形式（Ci 155）保持在细胞质中，允许Ci 155进入细胞核，促进Ci的转录激活，或促进Ci的蛋白水解加工成其转录阻遏物形式（CiR）。我们最近发现，Smo结合细胞质调节复合物来调节其活性。这支持了我们从遗传分析中得出的模型。该模型表明，Smo可以采用三种不同的状态，这取决于Hh水平（OFF，LOW，HIGH），Smo直接接触Costal和Fused，Smo二聚体是HIGH信号传导所必需的。所提出的实验通过以下方式测试和扩展该模型：1）表征处于OFF、LOW和HIGH状态的Ci调节复合物，2）确定Smo二聚化/寡聚化在信号传导中的作用，以及3）使用对内源性Smo的信号传导具有显性效应的多种突变形式的Smo来鉴定和进一步剖析信号转导中的步骤。这些实验研究了三种不同的信号状态响应于不同水平的Hh的结构和机制基础。他们应该确定Hh信号转导途径三种状态之间转换的关键步骤。他们的成功完成将显着推进我们对这一基本信号转导途径的理解，并可能为基于Hh的病理学确定治疗靶点。

DESCRIPTION (provided by applicant): Signaling by Hedgehog (Hh) family members mediate local cell-cell communication that is essential for development and maintenance of many tissues and structures. Aberrant activation of Hh signaling underlies basal cell carcinoma, medulloblastoma, and may contribute to many other cancers. Transduction of the Hh signal is poorly understood. Smoothened (Smo), a member of the serpentine receptor family, is essential for activation of intracellular responses to Hh. Responses are transduced through a cyoplasmic complex including Costal (divergent kinesin), Fused (S/T kinase), and Ci (zinc finger transcription factor). Depending on the level of Hh input, the complex can hold Ci in the cytoplasm in a latent form (Ci155), allow Ci155 to enter the nucleus, promote transcriptional activation by Ci, or promote proteolytic processing of Ci to its transcriptional repressor form (CiR). We have recently shown that Smo binds the cytoplasmic regulatory complex to regulate its activity. This supports our model, derived from genetic analysis. The model suggests that Smo can adopt three distinct states depending on Hh levels (OFF, LOW, HIGH), that Smo directly contacts Costal and Fused, and that Smo dimers are necessary for HIGH signaling. The proposed experiments test and extend this model by 1) characterizing the Ci regulatory complex in the OFF, LOW, and HIGH states, 2) determining the role of Smo dimerization/oligomerization in signaling, and 3) using a variety of mutated forms of Smo with dominant effects on signaling by endogenous Smo to identify and further dissect the steps in signal transduction. These experiments investigate the structural and mechanistic basis for three distinct signaling states in response to different levels of Hh. They should identify the critical steps for transition between the three states of the Hh signal transduction pathway. Their successful completion would significantly advance our understanding of this fundamental signal transduction pathway and may pinpoint therapeutic targets for Hh-based pathologies.