Mass spectrometry-based 3X-FLAG-Ub-VS deubiquitinase (DUB) competition assay with cell extracts (DUB IP-MS) profiling MCF-7 cells with regard to specificity of WEHI-092, a selective inhibitor for USP9X. Sample key: #1-5 Untreated; #6-10 Ub-VS pre-treatment; #11-15 WEHI-092 treated (50 µM, 60 min).