期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：15
页码：4624-4629
DOI：10.1073/pnas.1420833112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceMDMX protein is a critical regulator of p53 and a novel drug target. The current generation of MDM2 inhibitors does not inhibit MDMX. Therefore, their therapeutic efficacy will be influenced by poorly characterized MDMX functional status in tumors. Efforts to develop MDMX inhibitors have been largely unsuccessful, indicating gaps in our understanding of the structure and regulation of MDMX. This study provides evidence that MDMX-p53 binding is regulated by an autoinhibitory mechanism that involves intramolecular interaction in MDMX through p53 mimicry. The results suggest a mechanism by which DNA damage signaling inhibits MDMX and activates p53. The p53 inhibitor MDMX is controlled by multiple stress signaling pathways. Using a proteolytic fragment release (PFR) assay, we detected an intramolecular interaction in MDMX that mechanistically mimics the interaction with p53, resulting in autoinhibition of MDMX. This mimicry is mediated by a hydrophobic peptide located in a long disordered central segment of MDMX that has sequence similarity to the p53 transactivation domain. NMR spectroscopy was used to show this hydrophobic peptide interacts with the N-terminal domain of MDMX in a structurally analogous manner to p53. Mutation of two critical tryptophan residues in the hydrophobic peptide disrupted the intramolecular interaction and increased p53 binding, providing further evidence for mechanistic mimicry. The PFR assay also revealed a second intramolecular interaction between the RING domain and central region that regulates MDMX nuclear import. These results establish the importance of intramolecular interactions in MDMX regulation, and validate a new assay for the study of intramolecular interactions in multidomain proteins with intrinsically disordered regions.
