Deubiquitinase involved in DNA damage response checkpoint and MYC proto-oncogene stability. Involved in DNA damage induced apoptosis by specifically deubiquitinating proteins of the DNA damage pathway such as CLSPN. Also involved in G2 DNA damage checkpoint, by deubiquitinating CLSPN, and preventing its degradation by the anaphase promoting complex/cyclosome (APC/C). In contrast, it does not deubiquitinate PLK1. Specifically deubiquitinates MYC in the nucleoplasm, leading to prevent MYC degradation by the proteasome: acts by specifically interacting with isoform 1 of FBXW7 (FBW7alpha) in the nucleoplasm and counteracting ubiquitination of MYC by the SCF(FBW7) complex. In contrast, it does not interact with isoform 4 of FBXW7 (FBW7gamma) in the nucleolus, allowing MYC degradation and explaining the selective MYC degradation in the nucleolus. Deubiquitinates ZNF304, hence preventing ZNF304 degradation by the proteasome and leading to the activated KRAS-mediated promoter hypermethylation and transcriptional silencing of tumor suppressor genes (TSGs) in a subset of colorectal cancers (CRC) cells (PubMed:24623306). 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). Interacts with ZNF304 (PubMed:24623306). Interacts with PRKD1 (PubMed:24623306). Interacts with TP53BP1 (PubMed:16901786). Interacts with isoform 1 of FBXW7; following DNA damage, dissociates from FBXW7 leading to degradation of MYC (PubMed:17873522, PubMed:17558397). Down-regulated upon hypoxia (PubMed:20046830). Up-regulated by the transcription factor c-Jun/JUN in a KRAS-dependent manner in colorectal cancer (CRC) cells (PubMed:24623306). Degraded upon nickel ion level or hypoxia exposure. Phosphorylated upon DNA damage at Ser-67 and Ser-714, by ATM or ATR (PubMed:16901786). Phosphorylated by PRKD1 (PubMed:24623306). Belongs to the peptidase C19 family. USP28 subfamily.