WDR20 regulates shuttling of the USP12 deubiquitinase complex between the plasma membrane, cytoplasm and nucleus.

The human deubiquitinases USP12 and USP46 are very closely related paralogs with critical functions as tumor suppressors. The catalytic activity of these enzymes is regulated by two cofactors: UAF1 and WDR20. USP12 and USP46 show nearly 90% amino acid sequence identity and share some cellular activities, but have also evolved non-overlapping functions. We hypothesized that, correlating with their functional divergence, the subcellular localization of USP12 and USP46 might be differentially regulated by their cofactors. We used confocal and live microscopy analyses of epitope-tagged proteins to determine the effect of UAF1 and WDR20 on the localization of USP12 and USP46. We found that WDR20 differently modulated the localization of the DUBs, promoting recruitment of USP12, but not USP46, to the plasma membrane. Using site-directed mutagenesis, we generated a large set of USP12 and WDR20 mutants to characterize in detail the mechanisms and sequence determinants that modulate the subcellular localization of the USP12/UAF1/WDR20 complex. Our data suggest that the USP12/UAF1/WDR20 complex dynamically shuttles between the plasma membrane, cytoplasm and nucleus. This shuttling involved active nuclear export mediated by the CRM1 pathway, and required a short N-terminal motif (1MEIL4) in USP12, as well as a novel nuclear export sequence (450MDGAIASGVSKFATLSLHD468) in WDR20. In conclusion, USP12 and USP46 have evolved divergently in terms of cofactor binding-regulated subcellular localization. WDR20 plays a crucial role in as a "targeting subunit" that modulates CRM1-dependent shuttling of the USP12/UAF1/WDR20 complex between the plasma membrane, cytoplasm and nucleus.