The function of ENSG00000166348 (USP54, ubiquitin specific peptidase 54) is as follows. Deubiquitinase that specifically mediates 'Lys-63'-linked deubiquitination of substrates with a polyubiquitin chain composed of at least 3 ubiquitins (PubMed:39587316). Specifically recognizes ubiquitin chain in position S2 and catalyzes cleavage of polyubiquitin within 'Lys-63'-linked chains (PubMed:39587316). Not able to deubiquitinate substrates with shorter ubiquitin chains (PubMed:39587316). Mediates deubiquitination of PLK4, maintaining PLK4 stability by reducing its ubiquitination-mediated degradation (PubMed:36590171). {ECO:0000269|PubMed:36590171, ECO:0000269|PubMed:39587316}.