MDMX Overexpression Prevents p53 Activation by the MDM2 Inhibitor Nutlin*

The p53 tumor suppressor plays a key role in maintaining genomic stability and protection against malignant transformation. MDM2 and MDMX are both p53-binding proteins that regulate p53 stability and activity. Recent development of the MDM2 inhibitor Nutlin 3 has greatly facilitated functional analysis of MDM2-p53 binding. We found that although MDMX is homologous to MDM2 and binds to the same region on p53 N terminus, Nutlin does not disrupt p53-MDMX interaction. The ability of Nutlin to activate p53 is compromised in tumor cells overexpressing MDMX. Combination of Nutlin with MDMX siRNA resulted in synergistic activation of p53 and growth arrest. These results suggest that MDMX is also a valid target for p53 activation in tumor cells. Development of novel compounds that are MDMX-specific or optimized for dual-inhibition of MDM2 and MDMX are necessary to achieve full activation of p53 in tumor cells.

[1]  A. Jochemsen,et al.  MDMX: a novel p53‐binding protein with some functional properties of MDM2. , 1996, The EMBO journal.

[2]  S. Francoz,et al.  Mdm4 and Mdm2 cooperate to inhibit p53 activity in proliferating and quiescent cells in vivo. , 2006, Proceedings of the National Academy of Sciences of the United States of America.

[3]  Yolande F M Ramos,et al.  Aberrant expression of HDMX proteins in tumor cells correlates with wild-type p53. , 2001, Cancer research.

[4]  Valerie Reinke,et al.  Rescue of embryonic lethality in Mdm4-null mice by loss of Trp53 suggests a nonoverlapping pathway with MDM2 to regulate p53 , 2001, Nature Genetics.

[5]  M. Dai,et al.  14‐3‐3γ binds to MDMX that is phosphorylated by UV‐activated Chk1, resulting in p53 activation , 2006, The EMBO journal.

[6]  L. Vassilev.  Small-Molecule Antagonists of p53-MDM2 Binding: Research Tools and Potential Therapeutics , 2004, Cell cycle.

[7]  A. Levine,et al.  Structure of the MDM2 Oncoprotein Bound to the p53 Tumor Suppressor Transactivation Domain , 1996, Science.

[8]  Kristian Helin,et al.  Amplification of Mdmx (or Mdm4) Directly Contributes to Tumor Formation by Inhibiting p53 Tumor Suppressor Activity , 2004, Molecular and Cellular Biology.

[9]  Yu Pan,et al.  Regulation of p53-MDMX Interaction by Casein Kinase 1 Alpha , 2005, Molecular and Cellular Biology.

[10]  K. Shirouzu,et al.  MDM2 interacts with MDMX through their RING finger domains , 1999, FEBS letters.

[11]  A. Jochemsen,et al.  Mutual Dependence of MDM2 and MDMX in Their Functional Inactivation of p53* , 2002, The Journal of Biological Chemistry.

[12]  S. Letteboer,et al.  Hdmx Protein Stability Is Regulated by the Ubiquitin Ligase Activity of Mdm2* , 2003, Journal of Biological Chemistry.

[13]  Jiandong Chen,et al.  Regulation of MDMX nuclear import and degradation by Chk2 and 14‐3‐3 , 2006, The EMBO journal.

[14]  William Arbuthnot Sir Lane,et al.  ATM and Chk2‐dependent phosphorylation of MDMX contribute to p53 activation after DNA damage , 2005, The EMBO journal.

[15]  Petra de Graaf,et al.  Phosphorylation of Hdmx mediates its Hdm2- and ATM-dependent degradation in response to DNA damage. , 2005, Proceedings of the National Academy of Sciences of the United States of America.

[16]  Yolande F M Ramos,et al.  Comparative study of the p53-mdm2 and p53-MDMX interfaces , 1999, Oncogene.

[17]  Hong Yang,et al.  Phosphorylation of p53 on Key Serines Is Dispensable for Transcriptional Activation and Apoptosis*♦ , 2004, Journal of Biological Chemistry.

[18]  Jiandong Chen,et al.  DNA Damage Induces MDMX Nuclear Translocation by p53-Dependent and -Independent Mechanisms , 2002, Molecular and Cellular Biology.

[19]  Jean-Christophe Marine,et al.  Mdmx as an essential regulator of p53 activity. , 2005, Biochemical and biophysical research communications.

[20]  Jiandong Chen,et al.  p53 α-Helix mimetics antagonize p53/MDM2 interaction and activate p53 , 2005, Molecular Cancer Therapeutics.

[21]  D. George,et al.  Stabilization of the MDM2 Oncoprotein by Interaction with the Structurally Related MDMX Protein* , 1999, The Journal of Biological Chemistry.

[22]  Y. Shiloh,et al.  DNA Damage-Induced Phosphorylation of MdmX at Serine 367 Activates p53 by Targeting MdmX for Mdm2-Dependent Degradation , 2005, Molecular and Cellular Biology.

[23]  Geng-Hung Liu,et al.  Synergistic roles of Mdm2 and Mdm4 for p53 inhibition in central nervous system development. , 2006, Proceedings of the National Academy of Sciences of the United States of America.

[24]  D. Lane,et al.  Identification of novel mdm2 binding peptides by phage display. , 1996, Oncogene.

[25]  A. Ciechanover,et al.  HdmX stimulates Hdm2-mediated ubiquitination and degradation of p53 , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[26]  Jeremy R Stuart,et al.  DNA Damage-induced MDMX Degradation Is Mediated by MDM2* , 2003, Journal of Biological Chemistry.

[27]  A. Levine,et al.  MDM2 is a central node in the p53 pathway: 12 years and counting. , 2005, Current cancer drug targets.

[28]  G. Stark,et al.  Levels of HdmX expression dictate the sensitivity of normal and transformed cells to Nutlin-3. , 2006, Cancer research.

[29]  Yu Pan,et al.  MDM2 Promotes Ubiquitination and Degradation of MDMX , 2003, Molecular and Cellular Biology.