title: UBPY-mediated epidermal growth factor receptor (EGFR) de-ubiquitination promotes EGFR degradation.
abstract: Whereas poly-ubiquitination targets protein substrates for proteasomal degradation, mono-ubiquitination is known to regulate protein trafficking in the endosomal system and to target cargo proteins for lysosomal degradation. The role of the de-ubiquitinating enzymes AMSH and UBPY in endosomal trafficking of cargo proteins such as the epidermal growth factor receptor (EGFR) has only very recently been the subject of study and is already a matter of debate. Although one report (Mizuno, E., Iura, T., Mukai, A., Yoshimori, T., Kitamura, N., and Komada, M. (2005) Mol. Biol. Cell 16, 5163-5174) concludes that UBPY negatively regulates EGFR degradation by de-ubiquitinating the EGFR on endosomes, another report (Row, P. E., Prior, I. A., McCullough, J., Clague, M. J., and Urbe, S. (2006) J. Biol. Chem. 281, 12618-12624) concludes that UBPY-mediated EGFR de-ubiquitination is essential for EGFR degradation. Here, we demonstrate that Usp8/UBPY, the mammalian ortholog of budding yeast Ubp4/Doa4, constitutively co-precipitates in a bivalent manner with the EGFR. Moreover, UBPY is a substrate for Src-family tyrosine kinases that are activated after ligand-induced EGFR activation. Using overexpression of three different recombinant dominant negative UBPY mutants (UBPY C748A mutant, UBPY 1-505, and UBPY 640-1080) in NIH3T3 and HEK293 cells, we demonstrate that UBPY affects both constitutive and ligand-induced (i) EGFR ubiquitination, (ii) EGFR expression levels, and (iii) the appearance of intermediate EGFR degradation products as well as (iv) downstream mitogen-activated protein kinase signal transduction. Our findings provide further evidence in favor of the model that UBPY-mediated EGFR de-ubiquitination promotes EGFR degradation.
authors.affiliation: Department of Cell Biology, Institute for Neuroscience, Faculty of Natural Sciences, Mathematics and Informatics, Radboud University Nijmegen, 6525 ED Nijmegen, The Netherlands.
authors.forename: Husam A J
authors.initials: HA
authors.lastname: Alwan
authors.forename: Jeroen E M
authors.initials: JE
authors.lastname: van Leeuwen
mesh_terms: D000818:Animals; D010450:Endopeptidases / Q000502:physiology*; D056827:Endosomal Sorting Complexes Required for Transport; D011992:Endosomes / Q000378:metabolism; D066246:ErbB Receptors / Q000502:physiology*; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D009154:Mutation; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D014443:Tyrosine / Q000737:chemistry; D025801:Ubiquitin / Q000378:metabolism*; D043222:Ubiquitin Thiolesterase
chemical_list: D056827:Endosomal Sorting Complexes Required for Transport; D025801:Ubiquitin; D014443:Tyrosine; D066246:ErbB Receptors; D010450:Endopeptidases; C541534:USP8 protein, human; D043222:Ubiquitin Thiolesterase; C541536:Usp8 protein, mouse; C091939:ubiquitin isopeptidase