p53R172H and p53R245W Hotspot Mutations Drive Distinct Transcriptomes in Mouse Mammary Tumors Through a Convergent Transcriptional Mediator.

Aggressive breast cancers harbor TP53 missense mutations. Tumor cells with TP53 missense mutations exhibit enhanced growth and survival through transcriptional rewiring. To delineate how TP53 mutations in breast cancer contribute to tumorigenesis and progression in vivo, we created a somatic mouse model driven by mammary epithelial cell-specific expression of Trp53 mutations. Mice developed primary mammary tumors reflecting the human molecular subtypes of Luminal A, Luminal B, HER2-enriched, and Triple Negative Breast Cancer with metastases. Transcriptomic analyses comparing MaPR172H/- or MaPR245W/- mammary tumors to MaP-/- tumors revealed (1) differences in cancer associated pathways activated in both p53 mutants and (2) Nr5a2 as a novel transcriptional mediator of distinct pathways in p53 mutants. Meta-analyses of human breast tumors corroborated these results. In vitro assays demonstrate mutant p53 upregulates specific target genes that are enriched for Nr5a2 response elements in their promoters. Co-immunoprecipitation studies revealed p53R172H and p53R245W interact with Nr5a2. These findings implicate NR5A2 as a novel mediator of mutant p53 transcriptional activity in breast cancer.

Mutant p53 protects triple-negative breast adenocarcinomas from ferroptosis in vivo.

The TP53 tumor suppressor gene is mutated early in most of the patients with triple-negative breast cancer (TNBC). The most frequent TP53 alterations are missense mutations that contribute to tumor aggressiveness. Here, we used an autochthonous somatic TNBC mouse model, in which mutant p53 can be toggled on and off genetically while leaving the tumor microenvironment intact and wild-type for p53 to identify physiological dependencies on mutant p53. In TNBCs that develop in this model, deletion of two different hotspot p53R172H and p53R245W mutants triggers ferroptosis in vivo, a cell death mechanism involving iron-dependent lipid peroxidation. Mutant p53 protects cells from ferroptosis inducers, and ferroptosis inhibitors reverse the effects of mutant p53 loss in vivo. Single-cell transcriptomic data revealed that mutant p53 protects cells from undergoing ferroptosis through NRF2-dependent regulation of Mgst3 and Prdx6, which encode two glutathione-dependent peroxidases that detoxify lipid peroxides. Thus, mutant p53 protects TNBCs from ferroptotic death.

Dimeric p53 Mutant Elicits Unique Tumor-Suppressive Activities through an Altered Metabolic Program.

Cancer-related alterations of the p53 tetramerization domain (TD) abrogate wild-type (WT) p53 function. They result in a protein that preferentially forms monomers or dimers, which are also normal p53 states under basal cellular conditions. However, their physiologic relevance is not well understood. We have established in vivo models for monomeric and dimeric p53, which model Li-Fraumeni syndrome patients with germline p53 TD alterations. p53 monomers are inactive forms of the protein. Unexpectedly, p53 dimers conferred some tumor suppression that is not mediated by canonical WT p53 activities. p53 dimers upregulate the PPAR pathway. These activities are associated with lower prevalence of thymic lymphomas and increased CD8+ T-cell differentiation. Lymphomas derived from dimeric p53 mice show cooperating alterations in the PPAR pathway, further implicating a role for these activities in tumor suppression. Our data reveal novel functions for p53 dimers and support the exploration of PPAR agonists as therapies. SIGNIFICANCE: New mouse models with TP53R342P (monomer) or TP53A347D (dimer) mutations mimic Li-Fraumeni syndrome. Although p53 monomers lack function, p53 dimers conferred noncanonical tumor-suppressive activities. We describe novel activities for p53 dimers facilitated by PPARs and propose these are "basal" p53 activities. See related commentary by Stieg et al., p. 1046. See related article by Choe et al., p. 1250. This article is highlighted in the In This Issue feature, p. 1027.

Integrative bioinformatic analysis of p53 and pathway alterations in two different lung cancer subtypes.

Whether p53, either wild type (WT) or mutant, plays cell-specific or uniform role remains controversial. Using The Cancer Genome Atlas, we examined p53 in the lung adenocarcinoma (LUAD) and lung squamous cell carcinoma (LUSC), two lung cancers with different cellular origins and frequent p53 mutation (52% and 83%, respectively). Mutant p53 more strongly correlates with different genomic alteration and protein expression profiles in LUAD than in LUSC. p53 mutation in LUAD and LUSC is associated with multiple exacerbated clinical outcomes. Although the presence of p53 mutation does not change the survival of LUAD patients, LUSC patients containing p53 mutation exhibit surprisingly prolonged survivals. Ingenuity Pathway Analyses with genes co-expressed with WT or mutant p53 in both LUAD and LUSC show that mutant p53 in these two cancers are correlated with different signaling. Additionally, WT p53 in LUAD are largely associated with activation of tumor suppressive pathways and suppression of the tumor promotive ones, a pattern different from what is observed for WT p53 in LUSC. Furthermore, pathway analyses of genes differentially expressed between cancers with mutant and WT p53 for both LUAD and LUSC revealed different pathway fashions for these two cancers. Our study indicates that both WT and mutant p53 may have cell-specific functions, which needs to be validated with future experimental investigations.

Omics analyses of a somatic Trp53R245W/+ breast cancer model identify cooperating driver events activating PI3K/AKT/mTOR signaling.

Alterations of the tumor suppressor TP53, one of the most common events in cancer, alone are insufficient for tumor development but serve as drivers of transformation. We sought to identify cooperating events through genomic analyses of a somatic Trp53R245W mouse model (equivalent to the TP53R248W hot spot mutation in human cancers) that recapitulates metastatic breast-cancer development. We identified cooperating lesions similar to those found in human breast cancers. Moreover, we identified activation of the Pi3k/Akt/mTOR pathway in most tumors via mutations in Pten, Erbb2, Kras, and/or a recurrent Pip5k1c mutation that stabilizes the Pip5k1c protein and activates Pi3k/Akt/mTOR signaling. Another PIP5K1C family member, PIP5K1A, is coamplified with PI4KB in 18% of human breast cancer patients; both encode kinases that are responsible for production of the PI3K substrate, phosphatidylinositol 4,5-bisphosphate. Thus, the TP53R248W mutation and PI3K/AKT/mTOR signaling are major cooperative events driving breast-cancer development. Additionally, a combination of two US Food and Drug Administration (FDA)-approved drugs, tigecycline and metformin, which target oxidative phosphorylation downstream of PI3K signaling, inhibited tumor cell growth and may be repurposed for breast-cancer treatment. These findings advance our understanding of how mutant p53 drives breast-tumor development and pinpoint the importance of PI3K/AKT/mTOR signaling, expanding combination therapies for breast-cancer treatment.

Differential Gain-of-Function Activity of Three p53 Hotspot Mutants In Vivo.

The majority of TP53 missense mutations identified in cancer patients are in the DNA-binding domain and are characterized as either structural or contact mutations. These missense mutations exhibit inhibitory effects on wild-type p53 activity. More importantly, these mutations also demonstrate gain-of-function (GOF) activities characterized by increased metastasis, poor prognosis, and drug resistance. To better understand the activities by which TP53 mutations, identified in Li-Fraumeni syndrome, contribute to tumorigenesis, we generated mice harboring a novel germline Trp53R245W allele (contact mutation) and compared them with existing models with Trp53R172H (structural mutation) and Trp53R270H (contact mutation) alleles. Thymocytes from heterozygous mice showed that all three hotspot mutations exhibited similar inhibitory effects on wild-type p53 transcription in vivo, and tumors from these mice had similar levels of loss of heterozygosity. However, the overall survival of Trp53R245W/+ and Trp53R270H/+ mice, but not Trp53R172H/+ mice, was significantly shorter than that of Trp53+/- mice, providing strong evidence for p53-mutant-specific GOF contributions to tumor development. Furthermore, Trp53R245W/+ and Trp53R270H/+ mice had more osteosarcoma metastases than Trp53R172H/+ mice, suggesting that these two contact mutants have stronger GOF in driving osteosarcoma metastasis. Transcriptomic analyses using RNA sequencing data from Trp53R172H/+, Trp53R245W/+, and Trp53R270H/+ primary osteosarcomas in comparison with Trp53+/- indicated that GOF of the three mutants was mediated by distinct pathways. Thus, both the inhibitory effect of mutant over wild-type p53 and GOF activities of mutant p53 contributed to tumorigenesis in vivo. Targeting p53 mutant-specific pathways may be important for therapeutic outcomes in osteosarcoma. SIGNIFICANCE: p53 hotspot mutants inhibit wild-type p53 similarly but differ in their GOF activities, with stronger tumor-promoting activity in contact mutants and distinct protein partners of each mutant driving tumorigenesis and metastasis.

In silico analysis of DND1 and its co-expressed genes in human cancers.

Dead-End (DND1) is an RNA-binding protein involved in translational regulation. Defects in DND1 gene causes germ cell tumors and sterility in rodents. Experimental studies with human somatic cancer cells indicate that DND1 has anti-proliferative and pro-apoptotic function in some while oncogenic function in other cells. We examined The Cancer Genome Atlas data for gene alterations and gene expression changes in DND1 in a variety of human cancers. We found that DND1 is amplified, deleted or mutated in multiple human cancers. In different cancers, DND1 alteration correlates with increased diagnosis age of patients, shift in tumor spectrum or change of tumor sites and in some cases is significantly associated with worse survival for cancer patients. For 15 cancers, we retrieved expression data of thousands of genes that co-expressed with DND1. We found that these cancers contain different percentage of genes that are positively or negatively co-expressed with DND1. Ingenuity Pathway Analysis was performed to explore the biological implications of these genes. More than 10 canonical pathways were identified and each cancer type exhibits unique pathway profiles. Comparison analysis across all 15 cancer types showed that some cancers exhibit strikingly similar profiles of DND1-correlated signaling pathway activation or suppression. Our data reinforce the notion that the biological role of DND1 is cell-type specific and suggest that DND1 may play opposing role by exerting anti-proliferative effects in some cancer cells while being pro-proliferative in others. Our study provides valuable insights to direct experimental investigations of DND1 function in somatic cancers.

Alterations of the Mdm2 C-Terminus Differentially Impact Its Function In Vivo.

Murine double minute 2 (Mdm2) is the principal E3-ubiquitin ligase for p53 and contains a C2H2C4 type RING domain wherein the last cysteine residue is followed by an evolutionarily conserved 13 amino acid C-terminal tail. Previous studies have indicated that integrity of the C-terminal tail is critical for Mdm2 function. Recently, a mutation extending the MDM2 length by five amino acids was identified and associated with enhanced p53 response in fibroblasts and premature aging in a human patient. To investigate the importance of the conserved Mdm2 C-terminal length on p53 regulatory function in vivo, we engineered three novel mouse alleles using CRISPR-Cas9 technology. Genetic studies with these murine models showed that curtailing Mdm2 C-terminal length by even a single amino acid leads to p53-dependent embryonic lethality. Extension of the Mdm2 C-terminal length by five amino acids (QLTCL) yielded viable mice that are smaller in size, exhibit fertility problems, and have a shortened life span. Analysis of early passage mouse embryonic fibroblasts indicated impaired Mdm2 function correlates with enhanced p53 activity under stress conditions. Furthermore, analysis in mice showed tissue-specific alterations in p53 target gene expression and enhanced radiosensitivity. These results confirm the physiological importance of the evolutionarily conserved Mdm2 C-terminus in regulating p53 functions. SIGNIFICANCE: This in vivo study highlights that alterations to the C-terminus of Mdm2 perturb its regulation of the tumor suppressor p53.

Wnt/ß-catenin-mediated p53 suppression is indispensable for osteogenesis of mesenchymal progenitor cells.

The developmental origins of mesenchymal progenitor cells (MPCs) and molecular machineries regulating their fate and differentiation are far from defined owing to their complexity. Osteoblasts and adipocytes are descended from common MPCs. Their fates are collectively determined by an orchestra of pathways in response to physiological and external cues. The canonical Wnt pathway signals MPCs to commit to osteogenic differentiation at the expense of adipogenic fate. In contrast to ß-catenin, p53's anti-osteogenic function is much less understood. Both activities are thought to be achieved through targeting Runx2 and/or Osterix (Osx, Sp7) transcription. Precisely, how Osx activity is dictated by ß-catenin or p53 is not clarified and represents a knowledge gap that, until now, has largely been taken for granted. Using conditional lineage-tracing mice, we demonstrated that chondrocytes gave rise to a sizable fraction of MPCs, which served as progenitors of chondrocyte-derived osteoblasts (Chon-ob). Wnt/ß-catenin activity was only required at the stage of chondrocyte-derived mesenchymal progenitor (C-MPC) to Chon-ob differentiation. ß-catenin- C-MPCs lost osteogenic ability and favored adipogenesis. Mechanistically, we discovered that p53 activity was elevated in ß-catenin- MPCs including ß-catenin- C-MPCs and deleting p53 from the ß-catenin- MPCs fully restored osteogenesis. While high levels of p53 were present in the nuclei of ß-catenin- MPCs, Osx was confined to the cytoplasm, implying a mechanism that did not involve direct p53-Osx interaction. Furthermore, we found that p53's anti-osteogenic activity was dependent on its DNA-binding ability. Our findings identify chondrocytes as an additional source for MPCs and indicate that Wnt/ß-catenin discretely regulates chondrocyte to C-MPC and the subsequent C-MPC to osteoblast developments. Most of all we unveil a previously unrecognized functional link between ß-catenin and p53, placing p53's negative role in the context of Wnt/ß-catenin signaling-induced MPC osteogenic differentiation.

Oncogenic KRAS Recruits an Expansive Transcriptional Network through Mutant p53 to Drive Pancreatic Cancer Metastasis.

Pancreatic ductal adenocarcinoma (PDAC) is almost uniformly fatal and characterized by early metastasis. Oncogenic KRAS mutations prevail in 95% of PDAC tumors and co-occur with genetic alterations in the TP53 tumor suppressor in nearly 70% of patients. Most TP53 alterations are missense mutations that exhibit gain-of-function phenotypes that include increased invasiveness and metastasis, yet the extent of direct cooperation between KRAS effectors and mutant p53 remains largely undefined. We show that oncogenic KRAS effectors activate CREB1 to allow physical interactions with mutant p53 that hyperactivate multiple prometastatic transcriptional networks. Specifically, mutant p53 and CREB1 upregulate the prometastatic, pioneer transcription factor FOXA1, activating its transcriptional network while promoting WNT/ß-catenin signaling, together driving PDAC metastasis. Pharmacologic CREB1 inhibition dramatically reduced FOXA1 and ß-catenin expression and dampened PDAC metastasis, identifying a new therapeutic strategy to disrupt cooperation between oncogenic KRAS and mutant p53 to mitigate metastasis. SIGNIFICANCE: Oncogenic KRAS and mutant p53 are the most commonly mutated oncogene and tumor suppressor gene in human cancers, yet direct interactions between these genetic drivers remain undefined. We identified a cooperative node between oncogenic KRAS effectors and mutant p53 that can be therapeutically targeted to undermine cooperation and mitigate metastasis.This article is highlighted in the In This Issue feature, p. 1861.

MDMX acts as a pervasive preleukemic-to-acute myeloid leukemia transition mechanism.

MDMX is overexpressed in the vast majority of patients with acute myeloid leukemia (AML). We report that MDMX overexpression increases preleukemic stem cell (pre-LSC) number and competitive advantage. Utilizing five newly generated murine models, we found that MDMX overexpression triggers progression of multiple chronic/asymptomatic preleukemic conditions to overt AML. Transcriptomic and proteomic studies revealed that MDMX overexpression exerts this function, unexpectedly, through activation of Wnt/ß-Catenin signaling in pre-LSCs. Mechanistically, MDMX binds CK1α and leads to accumulation of ß-Catenin in a p53-independent manner. Wnt/ß-Catenin inhibitors reverse MDMX-induced pre-LSC properties, and synergize with MDMX-p53 inhibitors. Wnt/ß-Catenin signaling correlates with MDMX expression in patients with preleukemic myelodysplastic syndromes and is associated with increased risk of progression to AML. Our work identifies MDMX overexpression as a pervasive preleukemic-to-AML transition mechanism in different genetically driven disease subtypes, and reveals Wnt/ß-Catenin as a non-canonical MDMX-driven pathway with therapeutic potential for progression prevention and cancer interception.

A Glance of p53 Functions in Brain Development, Neural Stem Cells, and Brain Cancer.

p53 is one of the most intensively studied tumor suppressors. It transcriptionally regulates a broad range of genes to modulate a series of cellular events, including DNA damage repair, cell cycle arrest, senescence, apoptosis, ferroptosis, autophagy, and metabolic remodeling, which are fundamental for both development and cancer. This review discusses the role of p53 in brain development, neural stem cell regulation and the mechanisms of inactivating p53 in gliomas. p53 null or p53 mutant mice show female biased exencephaly, potentially due to X chromosome inactivation failure and/or hormone-related gene expression. Oxidative cellular status, increased PI3K/Akt signaling, elevated ID1, and metabolism are all implicated in p53-loss induced neurogenesis. However, p53 has also been shown to promote neuronal differentiation. In addition, p53 mutations are frequently identified in brain tumors, especially glioblastomas. Mechanisms underlying p53 inactivation in brain tumor cells include disruption of p53 protein stability, gene expression and transactivation potential as well as p53 gene loss or mutation. Loss of p53 function and gain-of-function of mutant p53 are both implicated in brain development and tumor genesis. Further understanding of the role of p53 in the brain may provide therapeutic insights for brain developmental syndromes and cancer.

Transient enhancement of p53 activity protects from radiation-induced gastrointestinal toxicity.

Gastrointestinal (GI) syndrome is a serious side effect and dose-limiting toxicity observed in patients undergoing lower-abdominal radiotherapy. Previous mouse studies show that p53 gene dosage determines susceptibility to GI syndrome development. However, the translational relevance of p53 activity has not been addressed. Here, we used a knock-in mouse in which the p53-Mdm2 negative feedback loop is genetically disrupted. These mice retain biallelic p53 and thus, normal basal p53 levels and activity. However, due to the lack of p53-mediated Mdm2 transcription, irradiated Mdm2P2/P2 mice exhibit enhanced acute p53 activity, which protects them from GI failure. Intestinal crypt cells residing in the +4 and higher positions exhibit decreased apoptosis, increased p21 expression, and hyperproliferation to reinstate intestinal integrity. Correspondingly, pharmacological augmentation of p53 activity in wild-type mice with an Mdm2 inhibitor protects against GI toxicity without affecting therapeutic outcome. Our results suggest that transient disruption of the p53-Mdm2 interaction to enhance p53 activity could be a viable prophylactic strategy for alleviating GI syndrome in patients undergoing radiotherapy.

Nomogram based on homogeneous and heterogeneous associated factors for predicting bone metastases in patients with different histological types of lung cancer.

BACKGROUND: The purpose of the present study was to characterize the prevalence, associated factors, and to construct a nomogram for predicting bone metastasis (BM) with different histological types of lung cancer. PATIENTS AND METHODS: This study was a descriptive study that basing on the invasive lung cancer patients diagnosed between 2010 and 2014 in Surveillance, Epidemiology, and End Results program. A total of 125,652 adult patients were retrieved. Logistic regression analysis was conducted to investigate homogeneous and heterogeneous factors for BM occurrence. Nomogram was constructed to predict the risk for developing BM and the performance was evaluated by the receiver operating characteristics curve (ROC) and the calibration curve. The overall survival of the patients with BM was analyzed using the Kaplan-Meier method and the survival differences were tested by the log-rank test. RESULTS: A total of 25,645 (20.9%) were reported to have BM, and the prevalence in adenocarcinoma, squamous cell carcinoma, small cell lung cancer (SCLC), large cell lung cancer (LCLC), and non-small cell lung cancer/not otherwise specified lung cancer (NSCLC/NOS) were 24.4, 12.5, 24.7, 19.5 and 19.4%, respectively, with significant difference (P < 0.001). Male gender, more metastatic sites and lymphatic metastasis were positively associated with BM in all lung cancer subtypes. Larger tumor size was positively associated with BM in all the lung cancer subtypes except for NSCLC/NOS. Poorly differentiated histology was positively associated with adenocarcinoma, squamous cell carcinoma and NSCLC/NOS. The calibration curve and ROC curve exhibited good performance for predicting BM. The median survival of the bone metastatic lung cancer patients was 4.00 (95%CI: 3.89-4.11) months. With the increased number of the other metastatic sites (brain, lung and liver metastasis), the survival significantly decreased (p < 0.001). CONCLUSION: Different lung cancer histological subtypes exhibited distinct prevalence and homogeneity and heterogeneity associated factors for BM. The nomogram has good calibration and discrimination for predicting BM of lung cancer.

Advanced Hepatocellular Carcinoma with Bone Metastases: Prevalence, Associated Factors, and Survival Estimation.

BACKGROUND The objective of the present research was to explore the prevalence, risk, and prognostic factors associated with bone metastases (BM) in newly diagnosed hepatocellular carcinoma (HCC) patients. MATERIAL AND METHODS From 36 507 HCC patients who were registered in Surveillance, Epidemiology, and End Results (SEER) database, we enrolled 1263 with BM at the initial diagnosis of HCC from 2010 to 2014. Kaplan-Meier curves and log-rank tests were used to estimate overall survival for different subgroups. Univariate and multivariate logistic and Cox regression analyses were performed to identify risk factors and independent prognostic factors for BM. RESULTS A total of 1567 (4.29%) HCC patients were detected with BM at initial diagnosis. Male sex, unmarried status, higher T stage, lymph node involvement, intrahepatic metastases, and extrahepatic metastases (lung or brain) were positively associated with BM. The median survival of the patients was 3.00 months (95% CI: 2.77-3.24 months). Marital status and primary tumor surgery were independently associated with the better survival. CONCLUSIONS A list of factors associated with BM occurrence and the prognosis of the advanced HCC patients with BM were found. These associated factors may provide a reference for BM screening in HCC and guide prophylactic treatment in clinical settings.

Somatic Trp53 mutations differentially drive breast cancer and evolution of metastases.

TP53 mutations are the most frequent genetic alterations in breast cancer and are associated with more aggressive disease and worse overall survival. We have created two conditional mutant Trp53 alleles in the mouse that allow expression of Trp53R172H or Trp53R245W missense mutations in single cells surrounded by a normal stroma and immune system. Mice with Trp53 mutations in a few breast epithelial cells develop breast cancers with high similarity to human breast cancer including triple negative. p53R245W tumors are the most aggressive and exhibit metastases to lung and liver. Development of p53R172H breast tumors with some metastases requires additional hits. Sequencing of primary tumors and metastases shows p53R245W drives a parallel evolutionary pattern of metastases. These in vivo models most closely simulate the genesis of human breast cancer and will thus be invaluable in testing novel therapeutic options.

ONZIN Upregulation by Mutant p53 Contributes to Osteosarcoma Metastasis Through the CXCL5-MAPK Signaling Pathway.

BACKGROUND/AIMS: Gain-of-function of mutant p53 is associated with a high rate of lung metastasis in osteosarcoma. To investigate the mechanism of mutant p53-induced osteosarcoma metastasis, expression array analysis was performed, comparing non-metastatic osteosarcomas from p53+/- mice with metastatic osteosarcomas from p53R172H/+ mice. Onzin (Plac8) was identified as one of the genes upregulated in p53R172H/+ mouse metastatic osteosarcomas. Accordingly, we investigated the role of ONZIN in human osteosarcoma metastasis. METHODS: ONZIN function and its downstream targets were examined in osteosarcoma cell lines. Assays related to tumorigenesis and metastasis, including cell migration, invasion, clonogenic survival, and soft agar colony formation, were performed in osteosarcoma cells. Additionally, mouse xenograft models were used to examine the role of ONZIN overpression in tumorigenesis in vivo. Lastly, 87 osteosarcoma patients were recruited to investigate the clinical relevance of ONZIN overexpression in metastasis and prognosis. RESULTS: ONZIN overexpression enhanced osteosarcoma cell proliferation, clonogenic survival, migration, and invasion independent of p53 status. Furthermore, ONZIN overexpression induced CXCL5 upregulation and resulted in increased ERK phosphorylation, which contributed to more aggressive osteosarcoma metastatic phenotypes. More importantly, overexpression of ONZIN in human osteosarcoma patients was closely associated with lung metastasis, poor prognoses, and survival. CONCLUSIONS: Overexpression of ONZIN promotes osteosarcoma progression and metastasis, and can serve as a clinical biomarker for osteosarcoma metastasis and prognosis.

Integrative genome analysis of somatic p53 mutant osteosarcomas identifies Ets2-dependent regulation of small nucleolar RNAs by mutant p53 protein.

TP53 is the most frequently mutated gene in human cancer. Many mutant p53 proteins exert oncogenic gain-of-function (GOF) properties that contribute to metastasis, but the mechanisms mediating these functions remain poorly defined in vivo. To elucidate how mutant p53 GOF drives metastasis, we developed a traceable somatic osteosarcoma mouse model that is initiated with either a single p53 mutation (p53R172H) or p53 loss in osteoblasts. Our study confirmed that p53 mutant mice developed osteosarcomas with increased metastasis as compared with p53-null mice. Comprehensive transcriptome RNA sequencing (RNA-seq) analysis of 16 tumors identified a cluster of small nucleolar RNAs (snoRNAs) that are highly up-regulated in p53 mutant tumors. Regulatory element analysis of these deregulated snoRNA genes identified strong enrichment of a common Ets2 transcription factor-binding site. Homozygous deletion of Ets2 in p53 mutant mice resulted in strong down-regulation of snoRNAs and reversed the prometastatic phenotype of mutant p53 but had no effect on osteosarcoma development, which remained 100% penetrant. In summary, our studies identify Ets2 inhibition as a potential therapeutic vulnerability in p53 mutant osteosarcomas.

Tumorigenesis promotes Mdm4-S overexpression.

Disruption of the p53 tumor suppressor pathway is a primary cause of tumorigenesis. In addition to mutation of the p53 gene itself, overexpression of major negative regulators of p53, MDM2 and MDM4, also act as drivers for tumor development. Recent studies suggest that expression of splice variants of Mdm2 and Mdm4 may be similarly involved in tumor development. In particular, multiple studies show that expression of a splice variant of MDM4, MDM4-S correlates with tumor aggressiveness and can be used as a prognostic marker in different tumor types. However, in the absence of prospective studies, it is not clear whether expression of MDM4-S in itself is oncogenic or is simply an outcome of tumorigenesis. Here we have examined the role of Mdm4-S in tumor development in a transgenic mouse model. Our results suggest that splicing of Mdm4 does not promote tumor development and does not cooperate with other oncogenic insults to alter tumor latency or aggressiveness. We conclude that Mdm4-S overexpression is a consequence of splicing defects in tumor cells rather than a cause of tumor evolution.

High expression of PLA2G16 is associated with a better prognosis in HER2-positive breast cancer.

BACKGROUND: PLA2G16 functions as a phosphatase in metabolism and its abnormal expression is closely associated with tumor progression. The aim of this study is to investigate the prognosis value of PLA2G16 in breast cancer. METHODS: A tissue microarray including 200 invasive ductal carcinoma specimens was constructed. Immunohistochemistry was performed to determine the PLA2G16 expression status. The Kaplan-Meier analysis and log-rank test were used to evaluate the prognostic value of PLA2G16. The Multivariate Cox regression analysis was performed to identify whether PLA2G16 was an independent prognostic factor. RESULTS: In our retrospective study, Kaplan-Meier analysis showed that elevated PLA2G16 expression was correlated with improved DFS (P=0.032) in the whole breast cancer patients. In further subgroup analysis, PLA2G16 overexpression was found to be associated with prolonged DFS (P=0.018) in HER2-positive breast cancer patients. More importantly, Multivariate analysis suggested that PLA2G16 was a significant independent prognostic factor in HER2-enriched patients [hazard ratio (HR) =0.151; 95% confidence interval (CI) =0.034-0.672; P=0.013]. CONCLUSIONS: Our study evaluated the prognostic significance of PLA2G16 in patients with HER2-positive breast cancer and confirmed the relevance of this metabolism-related gene in patient outcome.