Mechanism of Hedgehog signal transduction

描述(由申请人提供)：Hedgehog(HH)家族成员的信号调节局部细胞间的通讯，这对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，也可能与许多其他癌症有关。对HH信号的转导知之甚少。Smo是蛇纹石受体家族的一员，在激活细胞内对HH的反应中起着至关重要的作用。反应通过细胞质复合体传递，包括Costal(发散激动素)、融合(S/T激酶)和Ci(锌指转录因子)。根据HH输入水平的不同，该复合体可以将Ci以潜在的形式(CI155)保存在细胞质中，允许CI155进入细胞核，促进Ci的转录激活，或者促进Ci的蛋白水解性加工为其转录抑制形式(Cir)。我们最近发现，Smo与细胞质调节复合体结合，以调节其活性。这支持了我们的模型，该模型源自基因分析。该模型表明，根据HH水平的不同，Smo可以采取三种不同的状态(关、低、高)，Smo直接与Costal和Fused接触，Smo二聚体是高信号所必需的。所提出的实验通过1)表征处于关闭、低和高状态的Ci调节复合体，2)确定Smo二聚化/寡聚化在信号中的作用，以及3)利用内源Smo对信号转导具有显性作用的各种突变形式的Smo来识别和进一步剖析信号转导步骤来测试和扩展这一模型。这些实验研究了响应不同水平的HH的三种不同信号状态的结构和机制基础。他们应该确定在HH信号转导途径的三种状态之间转换的关键步骤。它们的成功完成将极大地促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.