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Published 16 August 2004. doi:10.1083/jcb.200401141
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 166, Number 4, 487-492
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AMSH is an endosome-associated ubiquitin isopeptidase



John McCullough, Michael J. Clague, and Sylvie Urbé

Physiological Laboratory, University of Liverpool, Liverpool, L69 3BX, UK

Address correspondence to Sylvie Urbé, Physiological Laboratory, University of Liverpool, Crown St., Liverpool, L69 3BX, UK. Tel.: 44-141-794-5432. Fax: 44-151-794-4434. email urbe{at}liv.ac.uk


Abstract

The JAMM (JAB1/MPN/Mov34 metalloenzyme) motif has been proposed to provide the active site for isopeptidase activity associated with the Rpn11/POH1 subunit of the 19S-proteasome and the Csn5-subunit of the signalosome. We have looked for similar activity in associated molecule with the SH3 domain of STAM (AMSH), a JAMM domain–containing protein that associates with the SH3-domain of STAM, a protein, which regulates receptor sorting at the endosome. We demonstrate isopeptidase activity against K48-linked tetraubiquitin and K63-linked polyubiquitin chains to generate di-ubiquitin and free ubiquitin, respectively. An inactivating mutation (D348A) in AMSH leads to accumulation of ubiquitin on endosomes and the concomitant stabilization of a ubiquitinated form of STAM, which requires an intact ubiquitin interaction motif (UIM) within STAM. Short interfering RNA knockdown of AMSH enhances the degradation rate of EGF receptor (EGFR) following acute stimulation and ubiquitinated EGFR provides a substrate for AMSH in vitro. We propose that AMSH is a deubiquitinating enzyme with functions at the endosome, which oppose the ubiquitin-dependent sorting of receptors to lysosomes.

Key Words: JAMM domain; endocytosis; ubiquitin; AMSH; STAM


Abbreviations used in this paper: AMSH, associated molecule with the SH3 domain of STAM; DUB, deubiquitinating enzyme; EGFR, EGF receptor; Hrs, Hepatocyte growth factor regulated tyrosine kinase substrate; JAMM, JAB1/MPN/Mov34 metalloenzyme; NEM, N-ethylmaleimide; siRNA, short interfering RNA; STAM, signal transducing adaptor molecule; UBP, ubiquitin specific proteases; UIM, ubiquitin interaction motif.


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