Institut für Genetik, Heinrich-Heine-Universität Düsseldorf, Universitätsstr.1, 40225 Düsseldorf, Germany.
J Cell Sci. 2013 Jan 15;126(Pt 2):645-56. doi: 10.1242/jcs.116590. Epub 2012 Nov 23.
The tumour suppressor Lethal (2) giant discs (Lgd) is a regulator of endosomal trafficking of the Notch signalling receptor as well as other transmembrane proteins in Drosophila. The loss of its function results in an uncontrolled ligand-independent activation of the Notch signalling receptor. Here, we investigated the consequences of loss of lgd function and the requirements for the activation of Notch. We show that the activation of Notch in lgd cells is independent of Kuz and dependent on γ-secretase. We found that the lgd cells have a defect that delays degradation of transmembrane proteins, which are residents of the plasma membrane. Furthermore, our results show that the activation of Notch in lgd cells occurs in the lysosome. By contrast, the pathway is activated at an earlier phase in mutants of the gene that encodes the ESCRT-III component Shrub, which is an interaction partner of Lgd. We further show that activation of Notch appears to be a general consequence of loss of lgd function. In addition, electron microscopy of lgd cells revealed that they contain enlarged multi-vesicular bodies. The presented results further elucidate the mechanism of uncontrolled Notch activation upon derailed endocytosis.
肿瘤抑制因子 Lethal（2） giant discs（Lgd）是果蝇中 Notch 信号受体及其它跨膜蛋白的内体运输的调节剂。其功能丧失会导致 Notch 信号受体的无控配体非依赖性激活。在这里，我们研究了 lgd 功能丧失的后果以及 Notch 激活的要求。我们表明，lgd 细胞中 Notch 的激活不依赖于 Kuz，而依赖于γ-分泌酶。我们发现，lgd 细胞存在缺陷，延迟了跨膜蛋白的降解，这些蛋白是质膜的常驻蛋白。此外，我们的结果表明，Notch 在 lgd 细胞中的激活发生在溶酶体中。相比之下，在编码 ESCRT-III 成分 Shrub 的基因突变体中，该途径在更早的阶段被激活，而 Shrub 是 Lgd 的一个相互作用伙伴。我们进一步表明，Notch 的激活似乎是 lgd 功能丧失的普遍后果。此外，对 lgd 细胞的电子显微镜观察显示，它们含有扩大的多泡体。呈现的结果进一步阐明了在胞吞作用失控的情况下 Notch 激活不受控制的机制。
