Autophagic flux regulation by the cholesterol/H+ antiporter PTCH1

一个受精卵发育成一个正常形成的胚胎需要一系列的信号来完美地协调组织和器官的形成。其中一个重要的信号事件是所谓的“刺猬”通路，当它缺失时，会引发与生命不相容的非常严重的先天缺陷。相反，出生后Hedgehog通路的过度活性是儿童脑肿瘤和成人脑癌、皮肤癌、肺癌、前列腺癌和肠道癌的常见原因。我的团队在理解细胞如何感知Hedgehog信号并根据组织类型和环境传递不同结果方面做出了贡献。在这里，我们建议研究刺猬通路在调节自噬（细胞的“自噬”行为）方面的新功能。我们发现Hedgehog受体PTCH1，一种肿瘤抑制因子，可以抑制自噬。细胞通常从可用的营养物质中获取营养；然而，在饥饿的情况下，比如肿瘤细胞生长速度快于滋养它们的脉管系统，细胞会降解部分内容物以生存。自噬是癌细胞存活的必要条件。我们将研究Hedgehog途径如何在分子水平上调控自噬。我们将建立在我们最近发表的文章的基础上，表明PTCH1的c端结构域和ATG101之间的相互作用对于抑制自噬是必要的，自噬的特征是发生降解的酸性囊泡数量减少。我们提出PTCH1作为一种转运体，通过与胆固醇运输耦合的机制消散这些囊泡（自溶酶体）的质子梯度。我们将检验这一假设，并研究PTCH1的这一功能是否会因癌症中常见的c端结构域突变而丧失。我们希望我们的发现将增加对癌症治疗新靶点的认识，并将揭示细胞适应和生存于不同压力源的新方法。

Development of a fertilized egg into a properly formed embryo requires a number of signals that perfectly orchestrate the formation of tissues and organs. One of those important signalling events is the so-called "Hedgehog" pathway that when absent provokes very serious congenital defects incompatible with life. Conversely, excessive activity of the Hedgehog pathway after birth is a common cause of childhood brain tumours and adult brain, skin, lung, prostate, and gut cancers. My group has contributed to the understanding of how the Hedgehog signals are perceived by cells and transmitted into different outcomes, depending on the tissue type and the context. Here, we propose to investigate a novel function of the Hedgehog pathway in regulating autophagy, the "self-eating" behaviour of cells. We found that the Hedgehog receptor PTCH1, a tumour suppressor, inhibits autophagy. Cells normally feed themselves from available nutrients; however, in conditions of starvation like those encountered by tumour cells that grow faster that the vasculature that nourishes them, cells degrade part of their contents to survive. Autophagy is essential for cancer cells survival. We will investigate how the Hedgehog pathway regulates autophagy at the molecular level. We will build onto our recent publication that shows that interaction between the C-terminal domain of PTCH1 and ATG101 is necessary for inhibition of autophagy, characterised by reduced number of acidic vesicles where degradation occurs. We propose that PTCH1 acts as a transporter, dissipating the proton gradient of those vesicles (autolysosomes) by a mechanism coupled to cholesterol transport. We will test this hypothesis and will investigate if this function of PTCH1 is lost by mutations of the C-terminal domain frequently found in cancer. We hope that our findings will increase the knowledge on new targets for cancer therapy and will reveal new ways in which cells adapt and survive to different stressors.