MTA1 and neoplasm: Mammalian COP1 functions as an E3 ubiquitin ligase targeting several substrates, including c‐Jun,[20] ETV1,[21] p53,[22] acetyl‐CoA carboxylase,[23] TORC2,[24] and MTA1.[25, 26] COP1 acts as an oncoprotein in tumorigenesis as it can suppress tumor suppressors: p53, p27, and 14‐3‐3 sigma activity,[22, 27, 28, 29] but COP1 knockout mouse model studies suggest that COP1 may also behave as a tumor suppressor via antagonizing proto‐oncogenic activity of c‐Jun and ETV1[20, 21, 30] in some tissues.