Deconjugating enzymes (DCEs) are proteases that process ubiquitin or ubiquitin-like gene products, reverse the modification of proteins by a single ubiquitin or ubiquitin-like protein (UBL) and remodel polyubiquitin (or poly-UBL) chains on target proteins (Reyes-Turcu et al., 2009). The deubiquitylating - or deubiquitinating - enzymes (DUBs) represent the largest family of DCEs and regulate ubiquitin dependent signalling pathways. The activities of the DUBs include the generation of free ubiquitin from precursor molecules, the recycling of ubiquitin following substrate degradation to maintain cellular ubiquitin homeostasis and the removal of ubiquitin or ubiquitin-like proteins (UBL) modifications through chain editing to rescue proteins from proteasomal degradation or to influence cell signalling events (Komander et al., 2009). There are two main classes of DUB, cysteine proteases and metalloproteases. Ubiquitin specific protease 6 (USP6) is a member of the cysteine protease enzyme family and cloning of the gene was first described by Nakamura et al. (1992). USP6 was the first DUB to be identified as an oncogene (Oliveira and Chou, 2012). Multiple DUBs, including A20, CYLD, Cezanne, USP21 and USP15, have been shown to function as negative regulators of NFκB; however, only one DUB, USP6, induces NFκB activation (Pringle et al., 2012). USP6 is translocated and overexpressed in aneurysmal bone cyst (ABC), a paediatric tumour characterized by extensive bone degradation and inflammatory recruitment (Pringle et al., 2012). Recent work has shown that USP6 is part of a signalling pathway that contributes to ABC pathogenesis, raising the possibility that development of USP-specific inhibitors or NF-κB antagonists might be effective novel strategies for the treatment of these tumours (Ye et al., 2010).
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