Downregulation of p53 by phosphatase of regenerating liver 3 is mediated by MDM2 and PIRH2

Aims: The phosphatase of regenerating liver (PRL) family is related to tumorigenesis and metastasis in various cancer types. Its overexpression increases cell motility and proliferation via the downregulation of p21 expression. In a previous study, we reported that PRL-1 downregulates p53 and is a target gene of p53. In this study, we investigated whether a member of the PRL family, PRL-3, could regulate p53 like PRL-1 in cancer cells. Main methods: To elucidate the role of PRL-3 in regulating p53 in cancer cells, we used a cell culture system to measure protein level, transcriptional level, apoptosis or localization. Key findings: We determined that PRL-3 overexpression reduced the activity of the p21 and p53 reporters. Additionally, the levels of endogenous and exogenous p53 protein were reduced in cells transiently expressing PRL-3, whereas the ablation of PRL-3 by siRNA increased levels of the p53 protein. The downregulation of p53 by PRL-3 inhibited p53-mediated apoptosis. However, the phosphatase-dead mutant C104S, prenylated-site mutant C170S, and C104S/C170S PRL-3 evidenced minimal effects on the downregulation of p53 protein as compared with wild-type PRL-3. Further examinations revealed that PRL-3 expression reduced the stability of p53 by inducing the transcription of p53 induced protein with a RING-H2 domain (PIRH2) through early growth response (EGR) and by increasing the phosphorylation of mouse double minute 2 (MDM2), and then both negatively regulated p53. Significance: These findings demonstrated that PRL-3, like PRL-1, can negatively regulate p53 via the activation of PIRH2 and MDM2 in cancer cells.