The Zinc Finger Protein 106 Is A Novel Positive Regulator Of The P53 Tumor Suppressor

The tumor suppressor p53 serves as a cellular stress sentinel,responding to diverse cellular stresses,including DNA damage,oncogenic stress,hypoxia,and other stimuli.p53 is kept at very low levels in normal cells by mouse double minute 2(Mdm2),which functions primarily as an E3 ubiquitin ligase and promotes proteasomal-dependent degradation of p53.p53 is stabilized and activated in response to myriad stresses.On activation,p53 restricts cellular expansion by inducing cell cycle arrest,senescence,or apoptosis.Several lines of evidence suggest that a variety of stresses can activate different types of cellular signaling pathway leading to the suppression of Mdm2 activity and activation of p53.Many proteins regulate on the ubiquitination and proteasomal degradation of p53 by Mdm2,either enhancing or inhibiting its activity.In this study we identify a novel p53 binding protein the WD40 repeats containing zinc finger protein 106(ZFP106),which acts to stabilize and activate p53 by preventing Mdm2-mediated ubiquitination of p53.ZFP106 is a nucleolar protein,which was initially cloned as the polymorphic gene encoding the nine amino acid H3a minor histocompatibility transplantation antigen.However,the biological function of ZFP106 is largely unknown.Here we demonstrate that ZFP106 interacts with p53 both in vivo and in vitro.Yeast two-hybrid and GST-pulldown assays suggest a direct interaction between ZFP106 and p5 3.To determine the functional importance of the ZFP106-p53 interaction,we overexpressed ZFP106 in U20S cells and observed a significant increase in the p53 protein level.Overexpression of ZFP106 inhibits Mdm2-mediated ubiquitination of p53 and enhances the protein stability and activities of p53,resulting in up-regulation of p53 target genes,such as bax and p21.The half-life of endogenous p53 in the U2OS-ZFP106 cells is increased markedly from 0.5 to 1.6 h.In addition,knockdown of ZFP106 inhibits p53 induction and apoptosis after VP 16 treatments.Of interest,DNA damage appears to induce ZFP106 accumulation in the nucleoplasm where it interacts with and stabilizes p53.Thus our work identified a novel p53 binding protein ZFP106,which positively regulates p53 stability and activity.