Deubiquitinating enzyme that hydrolyzes ubiquitin moieties conjugated to substrates and thus, functions to process newly synthesized Ubiquitin, to recycle ubiquitin molecules or to edit polyubiquitin chains and prevents proteasomal degradation of substrates. Hydrolyzes both 'Lys-48'- and 'Lys-63'-linked tetraubiquitin chains. The muscle-specific isoform (USP25m) may have a role in the regulation of muscular differentiation and function. Thiol-dependent hydrolysis of ester, thioester, amide, peptide and isopeptide bonds formed by the C-terminal Gly of ubiquitin (a 76-residue protein attached to proteins as an intracellular targeting signal). Homodimer or oligomer. Interacts with ACTA1 (via its C-terminus); the interaction occurs for all isoforms but is strongest for isoform USP25m in muscle differentiating cells. Interacts (isoform USP25m only) with MYBPC1; the interaction prevents proteasomal degradation of MYBPC1. Interacts (isoform USP25m only) with FLNC (via filament repeats 17-18, 20-21 and 24). Interacts with GAPDH. Interacts with SUMO3; the interaction sumoylates efficiently USP25. Interacts with SUMO2; the interaction sumoylates efficiently USP25. Interacts with SUMO1; the interaction only weakly sumoylates USP25. Interacts with SYK; phosphorylates USP25 and regulates USP25 intracellular levels. Some transient punctuate nuclear location in myotubes during myocyte development. Isoform USP25a is found in most adult and fetal tissues; expression is moderately high in testis, pancreas, kidney, skeletal muscle, liver, lung, placenta, brain, heart, but very low in peripheral blood, colon, small intestine, ovary, prostate, thymus and spleen. Isoform USP25b is found in all tissues except heart and skeletal muscle. Isoform USP25m is heart and skeletal muscle specific. The muscle-specific isoform (USP25m) is up-regulated during myocyte differentiation. Levels increase up to 100-fold towards completion of differentiation. Acetylated. Sumoylation impairs binding to and hydrolysis of ubiquitin chains. Sumoylated preferentially with SUMO2 or SUMO3. Desumoylated by SENP1. Regulated by ubiquitination on the same residue. Preferentially monoubiquitinated but can also be polyubiquitinated. Autodeubiquitinated. Ubiquitination activates the enzymatic activity either by preventing sumoylation or by allowing novel interactions. Phosphorylation in the C-terminal by SYK regulates USP25 cellular levels. Belongs to the peptidase C19 family.