PITP家族蛋白SEC14L2/Sec14l3在内质网-内吞体互作中的功能及机制研究

As the most widely distributed endomembrane system, endoplasmic reticulum (ER) has been demonstrated to contact with many other membrane-bound organelles in eukaryotic cells. It has been reported that ER-endosome membrane contact sites (MCS) contribute to lipid biosynthesis and exchange, endosome formation, fission and transport. Their defects are always related to numerous inherited or acquired diseases, including Niemann-Pick Type C, amyotrophic lateral sclerosis, obesity, coronary heart disease and pancreatic cancer progression. However, the regulatory clues for ER-endosome MCS establishment and maintenance are currently very limited. Our previous studies indicated that PITP family members SEC14L2/Sec14l3 accumulate at the ER-endosome contact sites and regulate the fission of RAB4+ endosomes. Using mammalian cell lines and zebrafish embryos as model systems, the proposed project aims to investigate the functions and underlying mechanisms of SEC14L2/Sec14l3 in regulating ER-endosome MCS formation. In addition, we will try to identify more potential factors that form ER-endosome tethering complexes with SEC14L2/Sec14l3, and explore their molecular mechanisms. The resultant data would deepen our understanding of the vital functions of ER-endosome MCS in regulating cellular process, organ formation and even the individual embryonic development, as well as provide knowledge for revealing molecular and pathological mechanisms of related human diseases.

内质网作为真核细胞中广泛分布的膜性细胞器，可与其它细胞器形成互作网络。它与内吞体的互作在脂质的合成与交换、内吞体的生成、裂变与迁移等过程中发挥重要作用，该互作的功能紊乱与C型尼曼匹克氏症、肌萎缩侧索硬化症、肥胖、冠心病及胰腺癌等疾病的发生发展密切相关。然而，对于该互作建立和维持的关键因子的鉴定及功能研究还处于起步阶段。申请人的前期工作发现PITP家族蛋白SEC14L2/Sec14l3可以定位于分选内吞体与管状内质网的内膜接触点，参与调控内质网与内吞体的互作，影响内吞体的裂变。在此基础之上，本项目拟利用哺乳动物细胞系和斑马鱼作为模式系统，深入研究SEC14L2/Sec14l3在内质网-内吞体互作发生中的功能及作用机制。同时，尝试鉴定与SEC14L2/Sec14l3共同发挥作用的新的调控因子，探讨其在细胞、器官、乃至个体水平上的生物学功能，为人类相关疾病的研究提供新的线索，具有重要的科学意义。

内质网与内吞体之间的互作在脂质的合成与交换、内吞体的生成、裂变与迁移等过程中发挥重要作用，对于该互作建立和维持的关键因子的鉴定及功能研究还处于起步阶段。本项目拟利用哺乳动物细胞系和斑马鱼作为模式系统，深入研究SEC14L2/Sec14l3在内质网-内吞体互作发生中的功能及作用机制，同时探讨其在细胞、器官、乃至个体水平上的生物学功能。本项目所取得的主要研究成果包括：发现SEC14L2/Sec14l3存在于高尔基来源的囊泡上，并且该Sec14l3+囊泡在内吞体与管状内质网的内膜接触点富集；SEC14L2/Sec14l3蛋白通过与PI3P、PI4P等磷脂分子的结合，介导磷脂分子在囊泡间的转运，进而影响ER所介导的内吞体分裂过程。Cos7细胞中，SEC14L2的敲除会导致ER所介导的内吞体分裂受阻，进而导致内吞体的数目变少、体积变大。此外，研究利用斑马鱼作为模式动物，构建了sec14l3突变体，发现该基因的合子突变体表现为动静脉管腔变小的血管缺陷表型。进一步的研究表明Sec14l3是通过调控VEGFR2的囊泡内吞及回收再利用过程，促进VEGF信号，进而影响斑马鱼血管的形成，揭示了其生理功能。该项目相关的研究成果发表于2019年的Nat Commun杂志。