Molecular mechanisms of Hedgehog receptor function

描述（由申请人提供）： Hedgehog（Hh）信号通路在后生动物器官的胚胎发育中起着重要作用。胚胎后，Hh信号传导介导成体组织的稳态再生，并且当不适当地活跃时与许多癌症相关。尽管它在发育、生理和疾病中很重要，但我们根本不了解细胞外Hedgehog信号是如何跨膜转导的。核心问题是Hh受体Patched（Ptc;哺乳动物中的Ptch 1），一种转运蛋白样蛋白，用于调节Smoothened（Smo）的机制，Smo是七跨膜蛋白家族的成员。从扁形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，从而释放Smo，通过一系列下游事件激活通路，从而改变基因转录。 从机制上讲，Ptch 1被认为是跨膜Smo活性的质子依赖性跨膜转运蛋白，但这种调节剂仍有待鉴定。此外，哺乳动物的Hh信号转导已与初级纤毛，但初级纤毛在转导中的实际作用还不清楚。 为了阐明Hh受体在纤毛中的功能的分子和细胞机制，我们建议定义固有的序列要求和细胞因子所需的Ptch 1/Smo纤毛运输和信号转导，特别是集中在信号和因子，由Hh通路活性调节。我们将确定内源性小分子介导Ptch 1调节Smo活性，初步确定衣原体鞭毛作为这样的调制脂质的丰富来源。我们将测试Ptch 1是否作为依赖于化学渗透梯度的跨膜转运蛋白发挥作用，并研究Ptch 1功能对Smo纤毛运输动力学的影响。我们的研究结果将被整合到一个详细的细胞和分子帐户的Hh信号转导，并可能提供一个基础，改善治疗Hh通路依赖性癌症。

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.