溶酶体运输调节EGF信号通路的机制

Vesicle trafficking is a key feature of living cells and is important in modulating signaling transduction. In this proposal, we are focusing on how lysosomal trafficking regulates the EGF signaling pathway. It is known that several transport complexes, such as BLOC-1, BLOC-2, BLOC-3, AP-3, HOPS and ESCRT, are involved in the lysosomal trafficking pathway, but the underlying mechanism is largely unknown. In our preliminary data, BLOC-1 was involved in the EGFR lysosomal degradation, which is likely mediated through the interactions between blos1 (a subunit of BLOC-1) and sorting nexin-2 (SNX2), followed by the interaction between blos1 and Tsg101 (subunit of ESCRT-I). Knockdown of blos1 lead to the delayed EGFR degradation and upregulation of EGF signaling. In our proposal, we will take advantage of the mouse mutants of the above mentioned lysosomal transport complexes and live cell imaging techniques, to further define (1) the molecular and cellular mechanism of EGFR lysosomal trafficking in which BLOC-1 is involved, (2) the interactions between the lysosomal transport complexes in EGFR trafficking, (3) how the altered lysosomal function will affect the EGFR degradation and EGF signaling. This study aims to further dissect the lysosomal trafficking pathway in modulating signaling pathways.

细胞内物质运输对信号转导起着非常重要的调节作用。本项目在前期研究基础上，重点阐明溶酶体运输对EGF信号通路调节的分子细胞生物学机制。参与溶酶体运输的复合体有多个，例如BLOC-1/-2/-3，AP-3，HOPS, ESCRT等，但其作用的分子机制仍知之甚少。我们的初步结果表明, BLOC-1复合体的blos1亚基通过与分选蛋白SNX2及Tsg101（ESCRT-I复合体亚基）的互作，可能介导EGFR的溶酶体降解过程。Blos1亚基敲降时可导致EGFR的溶酶体降解延迟，从而上调EGF信号通路。本项目将以上述复合体的小鼠突变体为研究材料，利用活细胞成像等技术，重点研究1）BLOC-1参与EGFR溶酶体运输的分子机制；2）EGFR溶酶体运输中，BLOC-1与其它复合体的相互作用；3）溶酶体功能改变对EGFR降解的影响和信号通路的调节等内容，以进一步解析溶酶体运输参与信号转导调节的分子细胞机制。

本课题按原任务书的研究内容和目标组织实施，取得重要进展，已完成原任务书的各项考核指标。阐明了EGFR的溶酶体降解过程中，BLOC-1如何被招募到内体-溶酶体运输系统，以及如何与retromer, ESCRT-I, BLOC-2等复合体的亚基相互作用，协同完成EGFR的溶酶体运输的分子细胞机制。探讨了不同溶酶体运输复合体HPACs的突变体所导致的内体-溶酶体途径相关细胞器的结构和功能异常，及其与EGFR降解受阻的关系。并针对HPACs在内体-溶酶体运输、溶酶体相关细胞器发生和细胞自噬等三条通路中的功能进行了系统的研究，取得了重要进展。受本课题资助共发表相关SCI论文16篇，其中影响因子5.0以上的通讯作者论文8篇。此项研究加深了对EGFR溶酶体降解分子细胞机制和HPACs功能的认识，提出了一些新的观点或学说，为下一步有关溶酶体运输通路的分子细胞生物学研究奠定了重要基础。