Monoubiquitination of ASXLs controls the deubiquitinase activity of the tumor suppressor BAP1

Salima Daou,Daméhan Tchelougou,Haining Yang,Jean-Yves Masson,Haithem Barbour,Oumaima Ahmed,Caroline Baril,Mika Tanji,Eric Bonneil,El Bachir Affar,Louis Masclef,Nazar Mashtalir,Pierre Thibault,Maxime Uriarte,Nadine Sen Nkwe,Frank Sicheri,Marc Therrien,Michele Carbone,Derek Ceccarelli

doi:10.1038/s41467-018-06854-2

Abstract

The tumor suppressor and deubiquitinase (DUB) BAP1 and its Drosophila ortholog Calypso assemble DUB complexes with the transcription regulators Additional sex combs-like (ASXL1, ASXL2, ASXL3) and Asx respectively. ASXLs and Asx use their DEUBiquitinase ADaptor (DEUBAD) domain to stimulate BAP1/Calypso DUB activity. Here we report that monoubiquitination of the DEUBAD is a general feature of ASXLs and Asx. BAP1 promotes DEUBAD monoubiquitination resulting in an increased stability of ASXL2, which in turn stimulates BAP1 DUB activity. ASXL2 monoubiquitination is directly catalyzed by UBE2E family of Ubiquitin-conjugating enzymes and regulates mammalian cell proliferation. Remarkably, Calypso also regulates Asx monoubiquitination and transgenic flies expressing monoubiquitination-defective Asx mutant exhibit developmental defects. Finally, the protein levels of ASXL2, BAP1 and UBE2E enzymes are highly correlated in mesothelioma tumors suggesting the importance of this signaling axis for tumor suppression. We propose that monoubiquitination orchestrates a molecular symbiosis relationship between ASXLs and BAP1.

Highlights

The tumor suppressor and deubiquitinase (DUB) BAP1 and its Drosophila ortholog Calypso assemble DUB complexes with the transcription regulators Additional sex combs-like (ASXL1, ASXL2, ASXL3) and Additional Sex Comb (Asx) respectively
Because the interaction between BAP1 and ASXL2 is important for their stability and tumor suppression[33], we sought to investigate the potential role of ubiquitination in coordinating BAP1/ASXL2 stability and function
Depletion of BAP1 by shRNA in U-2 OS cells resulted in reduced levels of endogenous ASXL2 with a noticeable band shift suggesting that the majority of ASXL2 is constitutively monoubiquitinated (Fig. 1e)

Summary

Introduction

The tumor suppressor and deubiquitinase (DUB) BAP1 and its Drosophila ortholog Calypso assemble DUB complexes with the transcription regulators Additional sex combs-like (ASXL1, ASXL2, ASXL3) and Asx respectively. ASXLs and Asx use their DEUBiquitinase ADaptor (DEUBAD) domain to stimulate BAP1/Calypso DUB activity. ASXLs use their respective DEUBAD domain to assemble distinct and mutually exclusive complexes with the CTD of BAP133,34 This interaction stimulates ubiquitin binding and DUB activity[16,33,34] (Fig. 1b). Monoubiquitination of the DEUBAD stabilizes ASXL2, stimulates BAP1 DUB activity and regulates mammalian cell proliferation. BAP1 promotes the ubiquitination of its co-factor ASXL2 regulating its stability, and this in turn regulates the enzymatic activity and function of the DUB complex

Methods

Results

Conclusion