MAZ Is a Substrate for the Deubiquitinating Enzyme DUB1

Abstract 3913

Ubiquitination is a fundamental mechanism of signal transduction that regulates immune responses and many other biological processes. Similar to phosphorylation, ubiquitination is a reversible process that is counter-regulated by ubiquitinating enzymes and deubiquitinating enzymes (DUBs).

DUB1 has been identified as a member of a subfamily of deubiquitinating enzymes that are induced by Interleukin-3 (IL-3) in Ba/F3 cells. Recently, we've known that DUB1 is expressed in some pro-B and pre-B cell lines and is differentially regulated during normal B cell differentiation with highest expression in small pre-B cells. To understand the functional role of DUB1 in early B cell development, we identified a transcription factor, MAZ, as an interacting partner or substrate of DUB1 in the Abelson-transformed 220-8 pro-B cell line by using a retrovirus-based protein-fragment complementation assay (RePCA) screen. MAZ has been identified as a critical regulator of p21 gene induction, which controls cell cycle progression in synovial fibroblast cells.

Immunoprecipitation and immunoblot analysis confirmed that MAZ and DUB1 interact with each other in cells. DUB1 expression significantly increased the steady-state cellular levels of MAZ. Notably, the half-life of MAZ in the pEGFP-DUB1-transfected cells was significantly increased by DUB1 expression, whereas the half-life of MAZ in the mock-transfected cells was less than 1 hr. These data therefore demonstrate that DUB1 specifically stabilizes MAZ in vivo.

We found that the overexpressed MAZ was polyubiquitinated and that the polyubiquitinated MAZ was the substrate for proteasome inhibitor MG132 caused a robust increase of MAZ polyubiquitination. Overexpression of DUB1 in 293T cells caused a decrease of MAZ polyubiquitination in a DUB1 dose-dependent manner. Taken together, these results indicate that DUB1 mediate the ubiquitination-dependent degradation of MAZ.

Other study shows that the DUB1 targets both K-48 and K-63 linked ubiquitination suggesting that it may be involved in both protein degradative and non-degradative functions during early B cell differentiation.