p53 R172H/+ mice inherit a p53 mutation found in Li-Fraumeni syndrome and develop metastatic tumors at much higher frequency than p53 +/− mice. To explore the mutant p53 metastatic phenotype, we used expression arrays to compare primary osteosarcomas from p53 R172H/+ mice with metastasis to osteosarcomas from p53 +/− mice lacking metastasis. For this study, 213 genes were differentially expressed with a P value <0.05. Of particular interest, Pla2g16, which encodes a phospholipase that catalyzes phosphatidic acid into lysophosphatidic acid and free fatty acid (both implicated in metastasis), was increased in p53 R172H/+ osteosarcomas. Functional analyses showed that Pla2g16 knockdown decreased migration and invasion in mutant p53-expressing cells, and vice versa: overexpression of Pla2g16 increased the invasion of p53-null cells. Furthermore, Pla2g16 levels were increased upon expression of mutant p53 in both mouse and human osteosarcoma cell lines, indicating that Pla2g16 is a downstream target of the mutant p53 protein. ChIP analysis revealed that several mutant p53 proteins bind the Pla2g16 promoter at E26 transformationspecific (ETS) binding motifs and knockdown of ETS2 suppressed mutant p53 induction of Pla2g16. Thus, our study identifies a phospholipase as a transcriptional target of mutant p53 that is required for metastasis. mammary tumor | fatty acid metabolism T he p53 tumor suppressor pathway is inactivated in ∼50% of human cancers (http://p53.iarc.fr). Missense mutations in particular account for 80% of p53 alterations, suggesting that mutant p53 proteins provide additional advantages for tumor cell growth (1). Li-Fraumeni syndrome patients with p53 missense mutations have a higher cancer incidence and an earlier age of tumor onset than individuals with truncating or splicing mutations (2). p53 knockin mice show a gain-of-function (GOF) phenotype in vivo, with high metastatic capacity compared with mice inheriting a p53-null allele (3, 4). GOF activities of mutant p53 are mediated by suppression of the p53 family members, p63 and p73 (3-6). Other mechanisms of mutant p53 GOF include mutant-p53 complexes with Smad that fuel TGF-β-induced metastasis (7) and integrin recycling (8). Additionally, mutant p53 interacts with the vitamin D receptor and converts vitamin D into an antiapoptotic agent (9-14). More recently, mutant p53 was reported to form transcriptional complexes on promoters of genes encoding several enzymes of the Mevalonate pathway, which increases metastasis of breast cancer cells (9). These data suggest multiple pathways contribute to the GOF phenotypes of cells with mutant p53. Although mutant p53 lacks sequencespecific DNA binding activity, its interaction with other transcriptional factors or the components of basic transcriptional machinery allow it to modulate gene expression (15). ChIP-onchip and ChIP-sequencing techniques show that mutant p53 affects transcription of many genes (9, 13, 16, 17).In this study, expression array analyses identified gene differences between p53 R172H/+ m...

Mutant TP53 is an adverse risk factor in acute myeloid leukemia (AML), but large-scale integrated genomic-proteomic analyses of p53 alterations in AML patients remain limited. We analyzed TP53 mutational status, copy number (CN), and protein expression data in AML (N=528) and provide a compilation of mutation sites and types across disease subgroups among treated and untreated patients. Our analysis shows differential hotspots in subsets of AML and uncovered novel pathogenic variants involving TP53 splice sites. In addition, we identified TP53 CN loss in 70.2% of TP53-mutated AML, which had more deleterious TP53 mutations and copy neutral loss of heterozygosity in 5/32 (15.6%) AML patients who had intact TP53 CN. Importantly, we demonstrate that mutant p53 protein expression patterns by immunohistochemistry evaluated using digital image-assisted analysis provide a robust readout that integrates TP53 mutation and allelic states in patients with AML (sensitivity=94.49%, specificity=90.48%). Protein expression of p53 by immunohistochemistry informed mutation status irrespective of TP53 CN status. Genomic analysis of co-mutations in TP53-mutant AML showed a muted landscape that encompassed primarily mutations in genes involved in epigenetic regulation (DNMT3A and TET2), RAS/MAPK signaling (NF1, KRAS/NRAS, PTPN11), and RNA splicing (SRSF2). In summary, our data provides a rationale to refine risk stratification of AML patients on the basis of integrated molecular and protein-level TP53 analyses.

Mdm2, an E3 ubiquitin ligase, negatively regulates the tumor suppressor p53. In this study, we utilized a conditional Mdm2 allele, Mdm2FM, and a CreER Tamoxifen inducible recombination system to examine the effects of global Mdm2 loss in adult mice. Two different Tamoxifen injection regimens caused 100% lethality of Mdm2FM/−;CreER mice. Both radio-sensitive and radio-insensitive tissues were impaired. Strikingly, a large number of radio-insensitive tissues, including the kidney, liver, heart, retina and hippocampus, exhibited various pathological defects. Similar Tamoxifen injections in older (16–18 month old) Mdm2FM/−;CreER mice showed abnormalities only in the kidney. In addition, transcriptional activation of p21, Puma and multiple senescence markers in young (2–4 month old) mice following loss of Mdm2 was dampened in older mice. All phenotypes were p53-dependent as Mdm2FM/−;p53−/−;CreER mice subjected to the same Tamoxifen regimens were normal. Our findings implicate numerous possible toxicities in many normal tissues upon use of cancer therapies that aim to inhibit Mdm2 in tumors with wild type p53.

Although ~50% of acute myeloid leukemia (AML) patients have a normal diploid karyotype by conventional cytogenetics at diagnosis, this patient subset has a variable disease course and outcome. Aberrant overexpression of the p53 protein is usually associated with TP53 alterations and a complex karyotype, but the prevalence and impact of p53 overexpression in AML with diploid cytogenetics is unknown. We examined 100 newly diagnosed AML patients to evaluate the impact of p53 expression status quantified in bone marrow core biopsy samples using immunohistochemistry and computer-assisted image analysis. A total of 24 patients had p53 overexpression defined as 3+ staining intensity in ≥5% of cells; this finding correlated with lower platelet counts (P = .002), absence of CD34 expression in blasts (P = .009), higher bone marrow blast counts (P = .04), and a higher frequency of FLT3 internal tandem duplication (P = .007). Overexpression of p53 independently predicted for shorter leukemia-free survival in patients who underwent allogeneic stem cell transplantation by univariate (P = .021) and multivariate analyses (P = .004). There was no correlation between MDM2 and p53 protein expression in this cohort. We conclude that p53 expression evaluated by immunohistochemistry in bone marrow biopsy specimens at the time of AML diagnosis may indicate distinct clinical characteristics in patients with normal diploid cytogenetics and is a potentially valuable tool that can enhance risk-stratification.