Biozentrum der Universität Basel, Abteilung Zellbiologie, Basel, Switzerland.
PLoS One. 2010 Apr 21;5(4):e10245. doi: 10.1371/journal.pone.0010245.
Endocytosis is a key regulatory step of diverse signalling pathways, including receptor tyrosine kinase (RTK) signalling. Hrs and Stam constitute the ESCRT-0 complex that controls the initial selection of ubiquitinated proteins, which will subsequently be degraded in lysosomes. It has been well established ex vivo and during Drosophila embryogenesis that Hrs promotes EGFR down regulation. We have recently isolated the first mutations of stam in flies and shown that Stam is required for air sac morphogenesis, a larval respiratory structure whose formation critically depends on finely tuned levels of FGFR activity. This suggest that Stam, putatively within the ESCRT-0 complex, modulates FGF signalling, a possibility that has not been examined in Drosophila yet.
Here, we assessed the role of the Hrs/Stam complex in the regulation of signalling activity during Drosophila development. We show that stam and hrs are required for efficient FGFR signalling in the tracheal system, both during cell migration in the air sac primordium and during the formation of fine cytoplasmic extensions in terminal cells. We find that stam and hrs mutant cells display altered FGFR/Btl localisation, likely contributing to impaired signalling levels. Electron microscopy analyses indicate that endosome maturation is impaired at distinct steps by hrs and stam mutations. These somewhat unexpected results prompted us to further explore the function of stam and hrs in EGFR signalling. We show that while stam and hrs together downregulate EGFR signalling in the embryo, they are required for full activation of EGFR signalling during wing development.
CONCLUSIONS/SIGNIFICANCE: Our study shows that the ESCRT-0 complex differentially regulates RTK signalling, either positively or negatively depending on tissues and developmental stages, further highlighting the importance of endocytosis in modulating signalling pathways during development.
内吞作用是多种信号通路的关键调节步骤，包括受体酪氨酸激酶（RTK）信号通路。Hrs 和 Stam 构成了 ESCRT-0 复合物，该复合物控制着泛素化蛋白的初始选择，这些蛋白随后将在溶酶体中降解。已经在体外和果蝇胚胎发生过程中充分证实，Hrs 促进 EGFR 下调。我们最近在果蝇中分离到 stam 的第一个突变，并表明 Stam 是气囊形态发生所必需的，气囊是一种幼虫呼吸结构，其形成严重依赖于 FGFR 活性的精细调节。这表明 Stam（假定位于 ESCRT-0 复合物中）调节 FGF 信号转导，这一可能性尚未在果蝇中进行研究。
在这里，我们评估了 Hrs/Stam 复合物在果蝇发育过程中信号活性调节中的作用。我们表明，stam 和 hrs 是气管系统中 FGFR 信号有效传递所必需的，无论是在气囊原基细胞迁移过程中，还是在终末细胞中形成精细细胞质延伸过程中。我们发现 stam 和 hrs 突变细胞显示 FGFR/Btl 定位改变，可能导致信号水平受损。电子显微镜分析表明，内体成熟在 hrs 和 stam 突变的不同步骤受到影响。这些出乎意料的结果促使我们进一步探索 stam 和 hrs 在 EGFR 信号转导中的功能。我们表明，虽然 stam 和 hrs 共同下调胚胎中的 EGFR 信号，但它们在翅膀发育过程中完全激活 EGFR 信号是必需的。
结论/意义：我们的研究表明，ESCRT-0 复合物根据组织和发育阶段，以不同的方式调节 RTK 信号，无论是正向还是负向，进一步强调了内吞作用在发育过程中调节信号通路的重要性。
