Onzin, a c-Myc-repressed target, promotes survival and transformation by modulating the Akt-Mdm2-p53 pathway.
The c-Myc oncoprotein is a general transcription factor whose target genes dictate the c-Myc phenotype. One such target of c-Myc, 'onzin', is normally expressed at high levels in myeloid cells and is dramatically downregulated in response to c-Myc overexpression. We show here that short hairpin interfering RNA-mediated knockdown of endogenous onzin results in a reduced growth rate and a proapoptotic phenotype. In contrast, onzin overexpression in fibroblasts is associated with an increased growth rate, resistance to apoptotic stimuli, loss of the G2/M checkpoint, and tumorigenic conversion. Onzin-overexpressing cells fail to induce p53 in response to apoptotic stimuli and contain higher levels of the active, phosphorylated forms of Akt1 and, more strikingly, of Mdm2. Using yeast two-hybrid and coimmunoprecipitation assays, we show that onzin directly interacts with both proteins. Green fluorescent protein tagging also confirms directly that Akt1 and Mdm2 colocalize with onzin, although the precise subcellular distribution of each protein is dependent on its relative abundance. Collectively, our results identify onzin as a novel regulator of several p53-dependent aspects of the c-Myc phenotype via its dramatic effect on Mdm2. This is reminiscent of the c-Myc --> p19(ARF)--mid R: Mdm2 pathway and might function as a complementary arm to ensure the proper cellular response to oncogenic and/or apoptotic stimuli.
Rogulski
Kenneth
K
Section of Hematology/Oncology, Children's Hospital of Pittsburgh, Pittsburgh, PA 15213, USA.
Li
Youjun
Y
Rothermund
Kristi
K
Pu
Lixia
L
Watkins
Simon
S
Yi
Fenghua
F
Prochownik
Edward V
EV
D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D019556:COS Cells; D002453:Cell Cycle / Q000502:physiology; D002470:Cell Survival; D002522:Chlorocebus aethiops; D005347:Fibroblasts; D016158:Genes, p53; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D015513:Oncogene Proteins / Q000235:genetics / Q000502:physiology; D010641:Phenotype; D010766:Phosphorylation; D011506:Proteins / Q000235:genetics / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt / Q000096:biosynthesis* / Q000502:physiology; D051736:Proto-Oncogene Proteins c-mdm2 / Q000096:biosynthesis* / Q000502:physiology; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000502:physiology*; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis* / Q000502:physiology; D020798:Two-Hybrid System Techniques; D015854:Up-Regulation
C489427:MYC protein, human; D015513:Oncogene Proteins; C506004:PLAC8 protein, human; C475342:Plac8 protein, mouse; D011506:Proteins; D016271:Proto-Oncogene Proteins c-myc; D016159:Tumor Suppressor Protein p53; C506003:onzin protein, mouse; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; C494918:AKT1 protein, human; D051057:Proto-Oncogene Proteins c-akt