MDM2 and neoplasm: Biochemically, cyclin G1, serves as an activating and targeting subunit of its cognate cyclin-dependent kinase(s) (Cdk1, 2, or 5), which activates and stabilizes the c-Myc oncoprotein on the one hand; while cyclin G1 additionally recruits the phosphatase PP2A to selectively de-phosphorylate and activate Mdm2 (a p53 ubiquitin ligase), which thereby degrades p53 and its tumor suppressor function and leads to error-prone DNA replication and repair that is so often associated with progressive metastatic disease.