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 carboxyl-terminal hydrolase 15 (Ubiquitin Specific Protease 15; USP15) is a member of the cysteine protease enzyme family and cloning of the human gene was first described by Baker et al. (1999). USP15 functions in COP9 signalosome mediated regulation of protein degradation and cellular signalling through catalysing the ubiquitin deconjugation reaction of a discrete number of substrates (Harper et al., 2011). USP15 plays a role in the downregulation of the NF-κB pathway through deubiquitylating the NF-κB inhibitor IκBα and also regulates human papillomavirus type 16 E6 oncoprotein stability. Among USPs, USP15 is most closely related to USP4 which has recently been implicated in mRNA splicing and more distantly to USP11 which has been linked to DNA damage repair pathways (Harper et al., 2011). It has recently been demonstrated that USP15 plays an essential role in the stabilisation and activity of caspase-3 during Paclitaxel-induced apoptosis. It has therefore been proposed that USP15 may be a candidate diagnostic marker and therapeutic target for Paclitaxel-resistant cancers (Xu et al., 2009).
Baker RT, Wang XW, Woollatt E, White JA, Sutherland GR (1999) Identification, functional characterization, and chromosomal localization of USP15, a novel human ubiquitin-specific protease related to the UNP oncoprotein, and a systematic nomenclature for human ubiquitin-specific proteases. Genomics 59, 264-274.
Harper S, Besong TM, Emsley J, Scott DJ, Dreveny I (2011) Structure of the USP15 N-terminal domains: a beta-hairpin mediates close association between the DUSP and UBL domains. Biochemistry 50, 7995-8004.
Komander D, Clague MJ, Urbe S (2009) Breaking the chains: structure and function of the deubiquitinases. Nat Rev Mol Cell Biol 10, 550-563.
Reyes-Turcu FE, Ventii KH, Wilkinson KD (2009) Regulation and cellular roles of ubiquitin-specific deubiquitinating enzymes. Ann Rev Biochem 78, 363-397.
Xu M, Takanashi M, Oikawa K, Tanaka M, Nishi H, Isaka K, Kudo M, Kuroda M (2009) USP15 plays an essential role for caspase-3 activation during Paclitaxel-induced apoptosis. Biochem Biophys Res Commun 388, 366-371.