Molecular mechanisms of Hedgehog receptor function

描述(由申请人提供)： Hedgehog(HH)信号通路在确定后生动物器官的胚胎模式中起着核心作用。胚胎后，HH信号介导成年组织的动态平衡再生，当不适当地活跃时，与许多癌症有关。尽管它在发育、生理和疾病中很重要，但我们从根本上不了解细胞外刺猬信号是如何跨膜传递的。核心问题是HH受体补丁(PTC；哺乳动物中的PTCH1)是一种转运蛋白样蛋白，通过什么机制调节Smoothens(Smo)，Smo是七个跨膜蛋白家族的成员。从扁虫到昆虫再到哺乳动物，PTC在没有HH的情况下抑制Smo的活性，当HH与PTC及其辅助受体结合时，这种抑制作用被解除，清华大学通过一系列下游事件释放Smo进行途径激活，并由此导致基因转录的变化。从机制上讲，ptch1被认为是跨膜Smo活性的脂质调节器的质子依赖的跨膜转运体，但这个调节器仍有待确定。此外，哺乳动物的HH信号转导与初级纤毛有关，但初级纤毛在信号转导中的实际作用尚不清楚。为了阐明纤毛HH受体功能的分子和细胞机制，我们建议定义ptch1/Smo纤毛运输和信号转导所需的内在序列要求和细胞因子，特别是HH途径活性调节的信号和因子。我们将确定介导ptch1调节Smo活性的内源性小分子，最初确定鞭毛衣藻是这种调节脂质的丰富来源。我们将测试ptch1是否发挥依赖于化学渗透梯度的跨膜转运蛋白的功能，并研究ptch1功能对血管纤毛运输动力学的影响。我们的发现将被整合到HH信号转导的详细细胞和分子描述中，并可能为改进HH途径依赖型癌症的治疗提供基础。 公共卫生相关性： 我们提出了一个多学科的方法来解决这个问题，即细胞外Hedgehog蛋白信号的存在是如何通过修补和光滑的成分传递到细胞膜上的。我们的发现将阐明与Hedgehog通路调节和活性紊乱相关的出生缺陷和肿瘤生长的原因和可能的治疗方法。

DESCRIPTION (provided by applicant): The Hedgehog (Hh) signaling pathway plays a central role in specifying the embryonic patterning of metazoan organs. Post-embryonically, Hh signaling mediates homeostatic regeneration of adult tissues and is associated with numerous cancers when inappropriately active. Despite its importance in development, physiology, and disease we fundamentally do not understand how the extracellular Hedgehog signal is transduced across the membrane. The central question is the mechanism by which the Hh receptor Patched (Ptc; Ptch1 in mammals), a transporter-like protein, acts to regulate Smoothened (Smo), a member of the seven transmembrane protein family. From flatworms to insects to mammals, Ptc inhibits Smo activity in the absence of Hh, and thisinhibition is lifted upon Hh binding to Ptc and its co-receptors, thu releasing Smo for pathway activation through a series of downstream events and consequent changes in gene transcription. Mechanistically, Ptch1 is thought to act as a proton-dependent transmembrane transporter of a lipidic modulator of Smo activity across the membrane, but this modulator remains to be identified. In addition, mammalian Hh signal transduction has been linked to the primary cilium, but the actual role of the primary cilium in transduction is not understood. To elucidate the molecular and cellular mechanisms of Hh receptor function in the cilium we propose to define intrinsic sequence requirements and cellular factors required for Ptch1/Smo ciliary trafficking and signal transduction, focusing in particular on signals and factors that are regulated by Hh pathway activity. We will identify endogenous small molecules that mediate Ptch1 regulation of Smo activity, having initially identified Chlamydomonas flagella as an enriched source of such a modulatory lipid. We will test whether Ptch1 functions as a transmembrane transporter that depends on a chemiosmotic gradient and investigate the effects of Ptch1 function on the dynamics of Smo ciliary trafficking. Our findings will be integrated into a detailed cellular and molecular account of Hh signal transduction, and may provide a basis for improvements in therapies for Hh pathway-dependent cancers. PUBLIC HEALTH RELEVANCE: We propose a multi-disciplinary approach to address the question of how presence of the extracellular Hedgehog protein signal is transmitted across the cell membrane by the Patched and Smoothened components. Our findings will illuminate the causes of and possible therapies for birth defects and neoplastic growth associated with derangements of Hedgehog pathway regulation and activity.