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J Biol Chem. 2016 May 6;291(19):10131-47. doi: 10.1074/jbc.M116.724781. Epub 2016 Mar 28.

Modeling the Etiology of p53-mutated Cancer Cells.

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From the Department of Anatomy and Cell Biology, Rush University Medical Center, Chicago, Illinois 60612 and.
The Shapiro Family Laboratory of Viral Oncology and Aging Research, UCLA School of Dentistry and David Geffen School of Medicine at UCLA, Los Angeles, California 90095.
From the Department of Anatomy and Cell Biology, Rush University Medical Center, Chicago, Illinois 60612 and


p53 gene mutations are among the most common alterations in cancer. In most cases, missense mutations in one TP53 allele are followed by loss-of-heterozygosity (LOH), so tumors express only mutant p53. TP53 mutations and LOH have been linked, in many cases, with poor therapy response and worse outcome. Despite this, remarkably little is known about how TP53 point mutations are acquired, how LOH occurs, or the cells involved. Nutlin-3a occupies the p53-binding site in MDM2 and blocks p53-MDM2 interaction, resulting in the stabilization and activation of p53 and subsequent growth arrest or apoptosis. We leveraged the powerful growth inhibitory activity of Nutlin-3a to select p53-mutated cells and examined how TP53 mutations arise and how the remaining wild-type allele is lost or inactivated. Mismatch repair (MMR)-deficient colorectal cancer cells formed heterozygote (p53 wild-type/mutant) colonies when cultured in low doses of Nutlin-3a, whereas MMR-corrected counterparts did not. Placing these heterozygotes in higher Nutlin-3a doses selected clones in which the remaining wild-type TP53 was silenced. Our data suggest silencing occurred through a novel mechanism that does not involve DNA methylation, histone methylation, or histone deacetylation. These data indicate MMR deficiency in colorectal cancer can give rise to initiating TP53 mutations and that TP53 silencing occurs via a copy-neutral mechanism. Moreover, the data highlight the use of MDM2 antagonists as tools to study mechanisms of TP53 mutation acquisition and wild-type allele loss or silencing in cells with defined genetic backgrounds.


cancer; cancer biology; mutagenesis in vitro; p53; tumor suppressor gene

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