Progida Cinzia, Malerød Lene, Stuffers Susanne, Brech Andreas, Bucci Cecilia, Stenmark Harald
Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Università del Salento, Via Provinciale Monteroni, 73100 Lecce, Italy.
J Cell Sci. 2007 Nov 1;120(Pt 21):3729-37. doi: 10.1242/jcs.017301.
Lysosomal degradation of signalling receptors such as the epidermal growth factor (EGF) receptor (EGFR) is an important mechanism for termination of cell signalling. Such degradation involves the endosomal sorting of ubiquitylated receptors into intralumenal vesicles (ILVs) of multivesicular endosomes (MVEs) that move along microtubules to fuse with perinuclear lysosomes. The Rab7-interacting lysosomal protein RILP is interesting in this context as it interacts with Vps22 (also known as EAP30) and Vps36 (also known as EAP45), subunits of the endosomal sorting complex required for transport II (ESCRT-II), as well as with the dynein-dynactin motor complex. Because previous functional studies of RILP have been based on its overexpression, we have asked here whether RILP is required for endocytic trafficking of receptors. Depletion of RILP caused elevated levels of four late-endosomal molecules, lyso-bisphosphatidic acid, Lamp1, CD63 and cation-independent mannose-6-phosphate receptors. Electron microscopy showed that endosomes of RILP-depleted cells were morphologically distinct from normal late endosomes and had a strongly reduced content of ILVs. As in Vps22-depleted cells, ligand-mediated degradation of EGFRs was strongly inhibited in RILP-depleted cells, in which endocytosed EGFRs were found to accumulate in early endosomes. By contrast, endocytosis and recycling of transferrin receptors occurred normally in RILP-depleted cells. These results establish that RILP, like the ESCRT proteins, is required for biogenesis of MVEs and degradative trafficking of EGFRs but not for trafficking of transferrin receptors through early endosomes. We propose that RILP might coordinate the biogenesis of MVEs with dynein-mediated motility.
溶酶体对信号受体（如表皮生长因子（EGF）受体（EGFR））的降解是终止细胞信号传导的重要机制。这种降解涉及将泛素化受体在内体中分拣到多囊泡内体（MVE）的腔内小泡（ILV）中，这些多囊泡内体沿着微管移动并与核周溶酶体融合。在这种情况下，与Rab7相互作用的溶酶体蛋白RILP很有意思，因为它与转运所需内体分拣复合体II（ESCRT-II）的亚基Vps22（也称为EAP30）和Vps36（也称为EAP45）相互作用，还与动力蛋白-动力蛋白激活蛋白运动复合体相互作用。由于之前对RILP的功能研究是基于其过表达，我们在此研究RILP是否是受体的内吞运输所必需的。RILP的缺失导致四种晚期内体分子（溶血双磷脂酸、Lamp1、CD63和不依赖阳离子的甘露糖-6-磷酸受体）水平升高。电子显微镜显示，RILP缺失细胞的内体在形态上与正常晚期内体不同，且ILV的含量大幅减少。与Vps22缺失细胞一样，在RILP缺失细胞中，配体介导的EGFR降解受到强烈抑制，在内吞的EGFR中发现其积聚在早期内体中。相比之下，转铁蛋白受体的内吞和循环在RILP缺失细胞中正常发生。这些结果表明，与ESCRT蛋白一样，RILP是MVE生物发生和EGFR降解运输所必需的，但不是转铁蛋白受体通过早期内体运输所必需的。我们提出，RILP可能将MVE的生物发生与动力蛋白介导的运动协调起来。
