PRKN and Parkinson disease: Dysregulation of PHGDH, the key enzyme in serine synthesis, plays an important role in a variety of cancers.[34] PHGDH overexpression is involved in migration, drug resistance,[35] and metastasis.[36] Recent studies demonstrate that PHGDH ubiquitination is regulated by Parkin, an E3 ubiquitin ligase involved in Parkinson's disease, in human breast cancer and lung cancer,[37] RNF5 in breast cancer,[38] and RNF114 in liver or kidney.[38] Thus, three additional different E3 ligases can participate in PHGDH stability regulation.