Levels of HdmX expression dictate the sensitivity of normal and transformed cells to Nutlin-3.
Hdm2 and HdmX coordinately regulate the stability and function of p53. Each is overexpressed in subsets of many different types of malignancy, and most of these subsets maintain wild-type p53. Nutlins, newly discovered small-molecule inhibitors of the Hdm2-p53 interaction, offer a novel strategy for therapy of tumors with wild-type p53. We now show that Nutlin-3 efficiently induces apoptosis and diminishes long-term survival of human fibroblasts transformed in vitro by Hdm2 but not HdmX. The resistance of cells overexpressing HdmX to Nutlin-3 is due to its inability to disrupt the p53-HdmX interaction, resulting in continued suppression of p53 activity. Although HdmX overexpression yielded cells resistant to Nutlin-3, ablation of HdmX expression by short hairpin RNA sensitized tumor cells to Nutlin-3-mediated cell death or arrest. Furthermore, deletion of the COOH-terminal RING finger domain of HdmX completely reversed the resistance to Nutlin-3, probably reflecting the requirement of the RING finger for interaction with Hdm2. Thus, the relative abundance of Hdm2 and HdmX and the specificity of Nutlin-3 for Hdm2 influence the sensitivity of cells to p53-dependent apoptosis or arrest in response to Nutlin-3. Our findings establish Hdm2 and HdmX as independent therapeutic targets with respect to reactivating wild-type p53 as a means for cancer therapy.
Patton
John T
JT
Department of Molecular Genetics, Lerner Research Institute, Cleveland Clinic Foundation, Ohio 44195, USA.
Mayo
Lindsey D
LD
Singhi
Aatur D
AD
Gudkov
Andrei V
AV
Stark
George R
GR
Jackson
Mark W
MW
D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology; D018797:Cell Cycle Proteins; D002471:Cell Transformation, Neoplastic / Q000378:metabolism; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000378:metabolism; D004317:Doxorubicin / Q000008:administration & dosage; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D045325:HCT116 Cells; D006801:Humans; D007093:Imidazoles / Q000008:administration & dosage / Q000494:pharmacology*; D009687:Nuclear Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D010879:Piperazines / Q000008:administration & dosage / Q000494:pharmacology*; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
D018797:Cell Cycle Proteins; D007093:Imidazoles; C482775:MDM4 protein, human; D009687:Nuclear Proteins; D010879:Piperazines; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; C482205:nutlin 3; D004317:Doxorubicin; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2