BRCC45 was initially suggested to be a housekeeping protein that is highly expressed in brain and reproductive organs. Later experiments indicated BRCC45 forms a complex with the breast and ovarian predisposition proteins BRCA1 and BRCA2 as well as RAD51 and BRCC36. This complex has a ubiquitin E3 ligase activity and is thought to enhance cellular survival following DNA damage. BRCC45 has also been suggested to function as a death receptor associated anti apoptotic protein by inhibiting the BID induced activation of the mitochondrial apoptotic pathway. Higher levels of BRCC45 were detected in the majority of hepatocellular carcinomas, suggesting that BRCC45 may promote tumorigenesis when overexpressed. At least three isoforms of BRCC45 are known to exist.