De-ubiquitinating proteases USP2a and USP2c cause apoptosis by stabilising RIP1

Abstract

Dynamic ubiquitination impacts on the degradation of proteins by the proteasome as well as on their effects as signalling factors. Of the many cellular responses that are regulated by changes in ubiquitination, apoptosis has garnered special attention. We have found that USP2a and USP2c, two isoforms of the ubiquitin-specific protease USP2, cause cell death upon ectopic expression. We show that both USP2 isoforms can control the ubiquitination status of many proteins but from a panel of potential targets only the protein level of RIP1 was increased by these enzymes. This effect is responsible for the activity of USP2a and USP2c to cause cell death. Both enzymes likewise de-ubiquitinate TRAF2, a ubiquitin-ligase in the TNFR1 complex. Whilst this and the similar sub-cellular localisations of both enzyme isoforms indicate a substantial overlap of activities, inactivation by RNAi revealed that only the knock-down of USP2c resulted in apoptosis, whilst targeting USP2a did not have any consequence on the cells' survival. Consequently, we focussed our studies on USP2a and found that TRAF2 inhibits USP2a's effect on K48- but not on K63-linked ubiquitin chains. Hence, the ratio between USP2a and TRAF2 protein levels determines the cells' sensitivity to cell death.

The Molecular Mechanisms of Regulation on USP2's Alternative Splicing and the Significance of Its Products

“…Immunofluorescence analysis of HELA cells transfected with the plasmids of USP2-201 or USP2-202 showed that USP2-201 and USP2-202 proteins were both dispersed around nucleus and adjacent to the endoplasmic reticulum while didn't coincide with mitochondria and Golgi. The similar sub-cellular location of USP2-201 and USP2-202 protein was also observed in MCF7 cells transfected with the plasmids of them 26 . Further immunofluorescence localization of GFP-USP2-201 fusion protein in HELA cells proved that GFP-USP2-201 protein localized in early endosomes involved in EGFR degradation cycle 27 .…”

USP2a alters chemotherapeutic response by modulating redox

“…This is particularly evident following the recent publication by Mahul-Mellier on Hela and MCF7 breast cancer cells, where downregulation of USP2a by siRNA promotes NF-kB activation and protects cells against TNF-induced cell death, as a consequence of the impairment of the USP2a-TRAF protein ratio. 43, 44 …”

Deubiquitinating enzymes as oncotargets

“…Frequently the activity of deubiquitinating enzymes is regulated by interactions with various binding partners. TRAF2 can bind to Usp2a which inhibits its effect on K48 but not K63 linked poly-ubiquitin chains, consequently the ratio between TRAF2 and Usp2a determines cells sensitivity to cell death [ 76 ]. Usp10, alongside Usp13, is regulated by binding to Beclin-1 which affects their protein stability, activity and subsequent deubiquitination of target proteins [ 77 ].…”