抄録
Ligand-activated receptor tyrosine kinases (RTKs) undergo endocytosis and are transported via endosomes to lysosomes for degradation. This process, known as receptor downregulation, is crucial to terminate the cell proliferation signals produced by activated RTKs. During the process, ubiquitination of RTKs serves as a sorting signal for their trafficking from endosomes to lysosomes. The sorting of RTKs is executed by a complex of two ubiquitin-binding proteins, Hrs and STAM, which localizes on the early endosomal membrane. STAM has been shown to interact with a deubiquitinating enzyme UBPY, also known as USP8. Here we studied the role of UBPY in the downregulation of epidermal growth factor receptor (EGFR). Immunopurified UBPY deubiquitinated EGFR in vitro. Overexpression of UBPY in EGF-stimulated cells reduced the ubiquitination level of activated EGFR and delayed its degradation. Conversely, depletion of UBPY by RNA interference resulted in elevated ubiquitination and accelerated degradation of EGF-activated EGFR. Stimulation of cells with EGF induced the association of UBPY with endocytosed EGFR on Hrs-positive early endosomes, and this association required the interaction of UBPY with the Hrs-STAM complex. On the other hand, the endosomal localization of UBPY did not depend on the Hrs-STAM complex. Together, we conclude that UBPY deubiquitinates activated EGFR which is sorted by the Hrs-STAM complex on early endosomes, thereby removing its sorting signal and regulating its downregulation negatively. [J Physiol Sci. 2006;56 Suppl:S9]
