Trp53-null Mice Research Articles

P53 governs an AT1 differentiation programme in lung cancer suppression.

Lung cancer is the leading cause of cancer deaths worldwide1. Mutations in the tumour suppressor gene TP53 occur in 50% of lung adenocarcinomas (LUADs) and are linked to poor prognosis1-4, but how p53 suppresses LUAD development remains enigmatic. We show here that p53 suppresses LUAD by governing cell state, specifically by promoting alveolar type 1 (AT1) differentiation. Using mice that express oncogenic Kras and null, wild-type or hypermorphic Trp53 alleles in alveolar type 2 (AT2) cells, we observed graded effects of p53 on LUAD initiation and progression. RNA sequencing and ATAC sequencing of LUAD cells uncovered a p53-induced AT1 differentiation programme during tumour suppression in vivo through direct DNA binding, chromatin remodelling and inductionof genes characteristic of AT1 cells. Single-cell transcriptomics analyses revealed that during LUAD evolution, p53 promotes AT1 differentiation throughaction in a transitional cell state analogous to a transient intermediary seen during AT2-to-AT1 cell differentiation in alveolar injury repair. Notably, p53 inactivation results in the inappropriate persistence of these transitional cancer cells accompanied by upregulated growth signalling and divergence from lung lineage identity, characteristics associated with LUAD progression. Analysis of Trp53 wild-type and Trp53-null mice showed that p53 also directs alveolar regeneration after injury by regulating AT2 cell self-renewal and promoting transitional cell differentiation into AT1 cells. Collectively, these findings illuminate mechanisms of p53-mediated LUAD suppression, in which p53 governs alveolar differentiation, and suggest that tumour suppression reflects a fundamental role of p53 in orchestrating tissue repair after injury.

Synonymous alterations of cancer-associated Trp53 CpG mutational hotspots cause fatal developmental jaw malocclusions but no tumors in knock-in mice.

Intragenic CpG dinucleotides are tightly conserved in evolution yet are also vulnerable to methylation-dependent mutation, raising the question as to why these functionally critical sites have not been deselected by more stable coding sequences. We previously showed in cell lines that altered exonic CpG methylation can modify promoter start sites, and hence protein isoform expression, for the human TP53 tumor suppressor gene. Here we extend this work to the in vivo setting by testing whether synonymous germline modifications of exonic CpG sites affect murine development, fertility, longevity, or cancer incidence. We substituted the DNA-binding exons 5-8 of Trp53, the mouse ortholog of human TP53, with variant-CpG (either CpG-depleted or -enriched) sequences predicted to encode the normal p53 amino acid sequence; a control construct was also created in which all non-CpG sites were synonymously substituted. Homozygous Trp53-null mice were the only genotype to develop tumors. Mice with variant-CpG Trp53 sequences remained tumor-free, but were uniquely prone to dental anomalies causing jaw malocclusion (p < .0001). Since the latter phenotype also characterises murine Rett syndrome due to dysfunction of the trans-repressive MeCP2 methyl-CpG-binding protein, we hypothesise that CpG sites may exert non-coding phenotypic effects via pre-translational cis-interactions of 5-methylcytosine with methyl-binding proteins which regulate mRNA transcript initiation, expression or splicing, although direct effects on mRNA structure or translation are also possible.

Multifaceted role for p53 in pancreatic cancer suppression

The vast majority of human pancreatic ductal adenocarcinomas (PDACs) harbor TP53 mutations, underscoring p53's critical role in PDAC suppression. PDAC can arise when pancreatic acinar cells undergo acinar-to-ductal metaplasia (ADM), giving rise to premalignant pancreatic intraepithelial neoplasias (PanINs), which finally progress to PDAC. The occurrence of TP53 mutations in late-stage PanINs has led to the idea that p53 acts to suppress malignant transformation of PanINs to PDAC. However, the cellular basis for p53 action during PDAC development has not been explored in detail. Here, we leverage a hyperactive p53 variant-p5353,54-which we previously showed is a more robust PDAC suppressor than wild-type p53, to elucidate how p53 acts at the cellular level to dampen PDAC development. Using both inflammation-induced and KRASG12D-driven PDAC models, we find that p5353,54 both limits ADM accumulation and suppresses PanIN cell proliferation and does so more effectively than wild-type p53. Moreover, p5353,54 suppresses KRAS signaling in PanINs and limits effects on the extracellular matrix (ECM) remodeling. While p5353,54 has highlighted these functions, we find that pancreata in wild-type p53 mice similarly show less ADM, as well as reduced PanIN cell proliferation, KRAS signaling, and ECM remodeling relative to Trp53-null mice. We find further that p53 enhances chromatin accessibility at sites controlled by acinar cell identity transcription factors. These findings reveal that p53 acts at multiple stages to suppress PDAC, both by limiting metaplastic transformation of acini and by dampening KRAS signaling in PanINs, thus providing key new understanding of p53 function in PDAC.

73565 Defining tp53 tumor suppressor functions in zebrafish embryonal rhabdomyosarcoma

ABSTRACT IMPACT: By assessing function of mutant (patient-specific) tp53 in zebrafish embryonal rhabdomyosarcoma will inform clinicians of the severity of mutant tp53 alleles. OBJECTIVES/GOALS: This study aims to define loss- and gain-of-function TP53 mutations by comparing effects in tp53-null and wild-type tumors. In addition, it aims to generate a rapid in vivo analysis platform to assign function to patient specific TP53 mutations in the clinic METHODS/STUDY POPULATION: To define tp53 function in ERMS pathogenesis, we previously generated a new tp53-null mutant (tp53-/-) in zebrafish by deleting the entire tp53 genomic locus using TALEN mutagenesis. tp53-/- zebrafish spontaneously develop a spectrum of tumors including sarcomas, leukemia and germ cell tumors (Ignatius…Baxi et. al., eLife) reminiscent of tumors observed in Trp53-null mice. Using the tp53-/- mutants to generate kRASG12D-induced ERMS, we discovered that tp53 is a potent repressor of metastases but rather surprisingly had no effect on self-renewal (Ignatius…Baxi et. al., eLife). Here, using tp53-/- zebrafish, we assessed effects of wild-type and mutant (patient specific) tp53 on tumor initiation, proliferation and apoptosis. RESULTS/ANTICIPATED RESULTS: ERMS tumor initiation in the tp53-/- background is observed in &gt; 97% of animals whereas only &lt;40% of wild-type animals develop ERMS. Additionally, tp53 is a potent suppressor of ERMS proliferation and its effect on apoptosis is minor. Next, we expressed either WT zebrafish or human TP53 in tp53-/- animals along with kRASG12D and both genes suppressed tumor initiation and growth. We co-expressed TP53C176F (found in two ERMS patients) and TP53P153del (identified in a patient with osteosarcoma in our clinic) in zebrafish ERMS, and find that the TP53C176F allele significantly suppressed tumor initiation with effects predominantly on enhanced apoptosis. However, the TP53P153del allele initiated tumors at similar frequency compared to tp53-/- animals but increased the initiation of tumors in the head musculature. DISCUSSION/SIGNIFICANCE OF FINDINGS: Different TP53 alleles identified in patient tumors have very different effects on tumorigenesis in vivo and can respond differently to potentially therapeutic compounds. Thus, the type of precision modeling demonstrated here promises to help further define patient-specific TP53 biology and improve clinical strategies in the future.

Abstract B60: Pro-HGF and its activator confer a sustained transformation activity in ovulatory follicular fluid

Abstract The etiology of ovarian high-grade serous ovarian cancers (HGSC) originating from the epithelium of fallopian tube fimbriae is elusive. Based on the incessant ovulation hypothesis, our previous studies found that ROS released during ovulation, collaborated with hemoglobin from retrograde menstruation, caused oxidative damage and DNA breaks to the fimbrial epithelial cells. Repeated exposures of ovulatory follicular fluid could induce tumorigenesis of in Trp53-null mice and transform human fimbrial epithelial cells (FE25) immortalized by E6/E7. In addition to mutagenic ROS, we later identified IGF-axis proteins abundantly present in follicular fluid (FF) are largely responsible for the stemness activation and transformation of FE25 cells. However, FF-IGF signal does not confer other key phenotypes induced by FF, such as mitogenesis and cell migration. In this study, we further clarified the role of HGF, another growth factor abundantly present in FF. Treating FE25 cells with pure HGF and IGF2 could fully recapitulate the anchorage-independent growth (AIG) activity of FF with equal colony number of 55±12 and 60±6, respectively. Inhibitor of HGF cMET receptor, AMG337, greatly reduced the AIG activity to 8±5 colonies. HGF is known to be activated by a cascade of activation by cleavage of its precursor pro-HGF and the precursor (pro-HGFA) of its activating protein HGFA. We found FF contains a high level of these pro-form proteins and a low amount of the cleaved active forms. Interestingly, these pro-form HGF axis proteins are extremely stable in FF. After one-month incubation at 37 degrees Celsius, they could still be activated and exerted AIG of FE25 cells. Once encountering the cell surface, protease cleavage is initiated to activated pro-HGFA to HGFA, which then cleaves pro-HGF to HGF. Via the c-MET/AKT/ERK signaling, the activated HGF confers the mitogenic and transformation activity of FF. In FF, HGF seems to cooperate with IGF2 to sustain a long-term proliferation of fimbrial epithelial cells initiated by ROS-induced mutagenesis and clonally expanded by IGF axis signaling. A reservoir of durable pro-forms of HGFA and HGF are responsible for this sustained transformation activity. Thus, the mutagenic, clonogenic, and sustained mitogenic activities in FF strongly support the incessant ovulation theory with ovulatory carcinogens to be the culprit. Citation Format: Hsuan Shun Huang, Tang-Yuan Chu. Pro-HGF and its activator confer a sustained transformation activity in ovulatory follicular fluid [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr B60.

Combined MEK and PI3K/p110β Inhibition as a Novel Targeted Therapy for Malignant Mesothelioma Displaying Sarcomatoid Features.

Among malignant mesotheliomas (MM), the sarcomatoid subtype is associated with higher chemoresistance and worst survival. Due to its low incidence, there has been little progress in the knowledge of the molecular mechanisms associated with sarcomatoid MM, which might help to define novel therapeutic targets. In this work, we show that loss of PTEN expression is frequent in human sarcomatoid MM and PTEN expression levels are lower in sarcomatoid MM than in the biphasic and epithelioid subtypes. Combined Pten and Trp53 deletion in mouse mesothelium led to nonepithelioid MM development. In Pten;Trp53-null mice developing MM, the Gαi2-coupled receptor subunit activated MEK/ERK and PI3K, resulting in aggressive, immune-suppressed tumors. Combined inhibition of MEK and p110β/PI3K reduced mouse tumor cell growth in vitro. Therapeutic inhibition of MEK and p110β/PI3K using selumetinib (AZD6244, ARRY-142886) and AZD8186, two drugs that are currently in clinical trials, increased the survival of Pten;Trp53-null mice without major toxicity. This drug combination effectively reduced the proliferation of primary cultures of human pleural (Pl) MM, implicating nonepithelioid histology and high vimentin, AKT1/2, and Gαi2 expression levels as predictive markers of response to combined MEK and p110β/PI3K inhibition. Our findings provide a rationale for the use of selumetinib and AZD8186 in patients with MM with sarcomatoid features. This constitutes a novel targeted therapy for a poor prognosis and frequently chemoresistant group of patients with MM, for whom therapeutic options are currently lacking. SIGNIFICANCE: Mesothelioma is highly aggressive; its sarcomatoid variants have worse prognosis. Building on a genetic mouse model, a novel combination therapy is uncovered that is relevant to human tumors.

Loss of TRP53 (p53) accelerates tumorigenesis and changes the tumor spectrum of SJL/J mice.

Known as the guardian of the genome, transformation-related protein 53 (TRP53) is a well -known tumor suppressor. Here, we describe a novel TRP53 deficient mouse model on a tumor prone background—SJL/J mice. The absence of TRP53 (TRP53 nullizygosity) leads to a shift in the tumor spectrum from a non-Hodgkin’s-like disease to thymic lymphomas and testicular teratomas at a very rapid tumor onset averaging ~12 weeks of age. In haplotype studies, comparing tumor prone versus tumor resistant Trp53 null mouse strains, we found that other tumor suppressor, DNA repair and/or immune system genes modulate tumor incidence in TRP53 null strains, suggesting that even a strong tumor suppressor such as TRP53 is modulated by genetic background. Due to their rapid development of tumors, the SJL/J TRP53 null mice generated here can be used as an efficient chemotherapy or immunotherapy screening mouse model.

Abstract TMIM-074: IGF2 IN HUMAN FOLLICULAR FLUID PROMOTES LYMPHOMAGENESIS IN MAMMARY FAT PAD OF TRP53-NULL MICE, DEPENDING ON ESTROGEN IN MICROENVIRONMENT

Abstract Ovulation overdrive is the most important risk factor of ovarian cancer. In previous study we discovered that preovulatory follicular fluid (FF) collected from IVF women, upon weekly injections into the mammary fat pad of Trp53-null mice for 7 weeks, could induce early onset of B cell lymphomas. In subsequent studies (Abstract by Chu TY et al.), we disclosed the IGF-axis signaling conferred by FFs is responsible for the stemness, clonal expansion and transformation of fallopian tube fimbrial epithelial cells where IGF2 in FF bound IGF-1R on secretory cells to activate the downstream PI3K/Akt/mTOR and PI3K/Akt/NANOG signaling pathways for the transformation. In this study, we identified the same IGF2 is also responsible for the FF-induced lymphomagenesis in Trp53-null mice. When IGF2 was depleted from FF, the tumorigenesis rate reduced from 10/18 (56%) to 1/6 (17%). On the other hand, injections with pure IGF2 (100 mg/ml) grew tumors in 33% (2/6) of mice. The same injection to Trp53 wild type did not grow tumor. We also found a microenvironment of adipose tissue seemed to be important for the FF-induced lymphomagenesis. The same injections of FF into the subcutis and other sites did not grow tumor. Additionally, tumor development depends not only on the injection site but also on the female sex hormone and ER function. No tumor growth was observed in castrated female mice and in male mice. Adding fulvastrant to the injections resulted in complete shrinkage of tumor. Meanwhile, extended injection of FF from 7 weeks to 13 weeks promoted tumor progression but did not increase tumor incidence. The findings suggest a transformation activity of human preovulatory FF largely conferred by IGF2. In the context of germline Trp53 loss, this activity likely promotes expansion of the lymphocytic progenitors that have already been transformed. Meanwhile, we found ER is expressed in the tumor adjacent adipocytes but not in the lymphoma cells. Also, ER antagonist, although largely confined tumor growth, did not decrease the tumor incidence. In this tumorigenesis model conferred by Trp53 loss and FF-IGF2, estrogen seems to play an essential role in tumor progression but not in tumor initiation, and this promotion effect is through the adipocyte microenvironment. Citation Format: Hsuan-Shun Huang, Sung-Chao Chu, Tang-Yuan Chu. IGF2 IN HUMAN FOLLICULAR FLUID PROMOTES LYMPHOMAGENESIS IN MAMMARY FAT PAD OF TRP53-NULL MICE, DEPENDING ON ESTROGEN IN MICROENVIRONMENT [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr TMIM-074.

IGF-axis confers transformation and regeneration of fallopian tube fimbria epithelium upon ovulation.

BackgroundThe fallopian tube fimbria is regarded as the main tissue of origin and incessant ovulation as the main risk factor of ovarian high-grade serous carcinoma. Previously, we discovered the tumorigenesis activity of human ovulatory follicular fluid (FF) upon injection to the mammary fat pad of Trp53-null mice. We also found a mutagenesis activity of FF-ROS and a apoptosis-rescuing activity of Hb from retrograde menstruation. However, neither of them can explain the tumorigenesis activities of FF.MethodsFrom two cohorts of ovulatory FF retrieved from IVF patients, the main growth factor responsible for the transformation of human fimbrial epithelial cells was identified. Mechanism of activation, ways of signal transduction of the growth factor, as well as the cellular and genetic phenotypes of the malignant transformation was characterized.FindingsIn this study, we showed that insulin-like growth factor (IGF)-axis proteins, including IGFBP-bound IGF2 as well as the IGFBP-lytic enzyme PAPP-A, are abundantly present in FF. Upon engaging with glycosaminoglycans on the membrane of fimbrial epithelial cells, PAPP-A cleaves IGFBPs and releases IGF2 to bind with IGF-1R. Through the IGF-1R/AKT/mTOR and IGF-1R/AKT/NANOG pathways, FF-IGF leads to stemness and survival, and in the case of TP53/Rb or TP53/CCNE1 loss, to clonal expansion and malignant transformation of fimbrial epithelial cells. By depleting each IGF axis component from FF, we proved that IGF2, IGFBP2/6, and PAPP-A are all essential and confer the majority of the transformation and regeneration activities.InterpretationThis study revealed that the FF–IGF axis functions to regenerate tissue damage after ovulation and promote the transformation of fimbrial epithelial cells that have been initiated by p53- and Rb-pathway disruptions.FundThe study was supported by grants of the Ministry of Science and Technology, Taiwan (MOST 106-2314-B-303-001-MY2; MOST 105-2314-B-303-017-MY2; MOST 107-2314-B-303-013-MY3), and Buddhist Tzu Chi General Hospital, Taiwan (TCMMP104-04-01).

P53-mediated regulation of bile acid disposition attenuates cholic acid-induced cholestasis in mice.

The tumour suppressor p53 is traditionally recognized as a surveillance molecule to preserve genome integrity. Recent studies have demonstrated that it contributes to metabolic diseases. Here, we investigated the role of p53 in the regulation of bile acid disposition and cholestasis. The bile acid disposition-related gene expression profile affected by p53 activation was assessed in mouse primary hepatocytes with p53 depletion and in Trp53-null mice. Dual luciferase reporter assay was used to detect the transcriptional activities of target genes. Anticholestatic effects of p53 activator doxorubicin were investigated in a 0.5% cholic acid-fed mouse model of cholestasis. Changes in bile acids were evaluated using metabolomics analysis. Doxorubicin-mediated p53 activation induced Cyp2b10, Sult2a1 and Abcc2/3/4 expression in mice in vitro and in vivo. ABCC3 and CYP2B6 (human orthologue of Cyp2b10) were identified as direct p53 target genes. Doxorubicin attenuated cholic acid-induced cholestasis in mice, as demonstrated by shrunken gall bladder, decreased serum total bile acid and total bilirubin levels and alkaline phosphatase activity. Targeted metabolomics analysis revealed that doxorubicin enhanced the excretion of bile acid metabolites from serum and liver to intestine and faeces. Up-regulation of Cyp2b10, Sult2a1 and Abcc2/3/4 expression was further confirmed in cholestatic mice. Cholic acid-induced cholestatic injury was aggravated in p53-deficient mice and levels of bile acid in intestine and faeces were decreased. Our findings suggest a novel role of p53 in promoting bile acid disposition and alleviating cholestatic syndrome, which provides a potential therapeutic target for cholestasis.

Abstract DPOC-007: PROGESTERONE/PR ERADICATES p53–DEFECTIVE CELLS IN THE FALLOPIAN TUBE EPITHELIUM BY INDUCTION OF NECROPTOSIS

Abstract Cervical Cancer Prevention Center, Department of Research, Tzu Chi Medical Center, Hualien, Taiwan, Republic of China. Institute of Medical Sciences, Tzu Chi University, Taiwan, Republic of China. The fallopian tube (FT) fimbriae, which are regularly exposed to ovulatory carcinogens, have been identified as the origin of high–grade serous ovarian carcinoma (HGSOC), with loss of p53 determined to be a universal and the earliest step of carcinogenesis. In previous studies, we have identified ROS in ovarian follicle is highly mutagenic and toxic to the fallopian tube fimbria that bath in the ovulatory follicular fluid (FF) after ovulation. We also found that loss of p53 renders fimbrial epithelial cells less vulnerable to the ROS stress, and that hemoglobin in ovulated FF could rescue the ROS–stressed fimbrial epithelial cells from apoptosis. Given that both ovulation and retrograde menstruation, the two proven risk factors for HGSOC, are commonplace in menstrual cycles, and that occurrence of tubal p53 signature is frequent but HGSOC is rare, we hypothesize that luteal–phase progesterone (P4) is responsible for clearance of p53–defective epithelial lesions as a natural protection. Herein, we show that P4 and progesterone receptor (PR) induce necroptosis of tubal epithelial cells in p53–null mice and in immortalized p53–deficient human fimbria epithelial cells through the TNF–α/RIPK1/RIPK3/p–MLKL pathway. The clearance acts regularly in the luteal phase of the menstrual cycle, recovering shortly thereafter, and can be augmented with P4 supplementation. With the inhibition of PR, the oviduct epithelium of Trp53–null mice escapes the clearance and, upon repeated ovulation exposures, accumulates DNA double–strand breaks. Through the induction of necroptosis of p53–deficient epithelial cells, luteal phase P4 prevents the transformation of the FT epithelium after ovulation. This protection can be augmented with P4 supplementation. Citation Format: Tang–Yuan Chu, MD, PhD. PROGESTERONE/PR ERADICATES p53–DEFECTIVE CELLS IN THE FALLOPIAN TUBE EPITHELIUM BY INDUCTION OF NECROPTOSIS [abstract]. In: Proceedings of the 11th Biennial Ovarian Cancer Research Symposium; Sep 12-13, 2016; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(11 Suppl):Abstract nr DPOC-007.

Haemoglobin in pelvic fluid rescues Fallopian tube epithelial cells from reactive oxygen species stress and apoptosis.

Fallopian tube fimbrial epithelium is considered to be the major site of origin of ovarian high-grade serous carcinoma, with p53 loss being the earliest and universal change. We previously reported that reactive oxygen species (ROS) in the ovulatory follicular fluids (FFs) are mutagenic and cytotoxic to fimbrial epithelial cells, which are bathed in the peritoneal fluid mixed with FFs. Here, we observed that ferryl haemoglobin (Hb), which was abundantly present in ovulatory FFs and pelvic peritoneal fluids, could rescue p53-deficient immortalized fimbrial epithelial (FE25) cells and oviduct epithelial cells from Trp53-null mice from lethal ovulatory ROS stress. Ferryl Hb and FF containing high Hb levels protected FE25 cells from apoptosis, mainly by consuming extracellular ROS and reducing NADPH oxidase-mediated cell death. The remaining extracellular ROS could still induce DNA double-strand breaks in the fimbrial epithelial cells. Our study revealed that ferryl Hb in peritoneal fluid rescued ROS-stressed, DNA-damaged fimbrial epithelial cells from death, and suggested that peritoneal blood from various sources may contribute to the ovulation-induced transformation of Fallopian tube epithelium. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Abstract IA08: Developmental insights into breast cancer intratumoral heterogeneity

Abstract Breast cancer is no longer considered a single disease, but instead is made up of multiple subtypes with genetically and epigenetically heterogeneous tumors composed of numerous clones. Both the hierarchical cancer stem cell and clonal evolution models have been invoked to help explain this intratumoral heterogeneity. Several recent studies have helped define the functional interactions among the different cellular subpopulations necessary for the evolution of this complex ecosystem. These interactions involve paracrine interactions that include locally acting Wnt family members, reminiscent of the signaling pathways important for normal mammary gland development and stem cell self-renewal. For example, mammary gland stem cell self-renewal is regulated by paracrine signaling involving Wnt4 and RSPO1 secreted by differentiated mammary luminal cells under the influence of systemic steroid hormones. Furthermore, interactions between non-canonical and canonical Wnt pathways play an important role in mammary gland development and cell fate determination [1]. Using a genetically engineered p53 null triple negative breast cancer model, we described a novel feedback loop in which the breast cancer stem cells(CSC) function through the action of paracrine mediators secreted by the CSC progeny[2], similar to what is observed in the normal mammary gland. We demonstrated the existence of cross-talk between tumor cells via Wnt2, Cxcl12 and IL6 signaling, indicating the non-cell-autonomous properties and importance of cooperativity between tumor subpopulations in tumor initiation and progression. Ligands expressed in the mesenchymal progeny cells produced through the asymmetric division of CSCs interacted with receptors on the CSCs. Knockdown of the ligands in the mesenchymal cells and their respective receptors in the CSCs resulted in decreased mammosphere formation in co-cultures. Furthermore, knockdown of Wnt 2 in the mesenchymal cells resulted in increased tumor latency when limiting numbers of CSCs were transplanted into the cleared mammary fat pad. The functional interactions between CSCs and mesenchymal population of cells may provide an improved niche microenvironment, especially for those tumors initiated from extremely low numbers of the CSCs. These studies indicate that similar regulatory mechanisms may exist for the maintenance of both normal and tumor stem cells with respect to their symmetric and asymmetric division. A better understanding of these interactions, especially in the metastatic setting, will be important for the development of improved combinatorial therapies designed to prevent relapse and to ultimately decrease mortality.

Idh1 mutations contribute to the development of T-cell malignancies in genetically engineered mice

Gain-of-function mutations in isocitrate dehydrogenase 1 (IDH1) are key drivers of hematopoietic malignancies. Although these mutations are most commonly associated with myeloid diseases, they also occur in malignancies of the T-cell lineage. To investigate their role in these diseases and provide tractable disease models for further investigation, we analyzed the T-cell compartment in a conditional knock-in (KI) mouse model of mutant Idh1. We observed the development of a spontaneous T-cell acute lymphoblastic leukemia (T-ALL) in these animals. The disease was transplantable and maintained expression of mutant IDH1. Whole-exome sequencing revealed the presence of a spontaneous activating mutation in Notch1, one of the most common mutations in human T-ALL, suggesting Idh1 mutations may have the capacity to cooperate with Notch1 to drive T-ALL. To further investigate the Idh1 mutation as an oncogenic driver in the T-cell lineage, we crossed Idh1-KI mice with conditional Trp53 null mice, a well-characterized model of T-cell malignancy, and found that T-cell lymphomagenesis was accelerated in mice bearing both mutations. Because both IDH1 and p53 are known to affect cellular metabolism, we compared the requirements for glucose and glutamine in cells derived from these tumors and found that cells bearing the Idh1 mutation have an increased dependence on both glucose and glutamine. These data suggest that mutant IDH1 contributes to malignancy in the T-cell lineage and may alter the metabolic profile of malignant T cells.

Abstract B02: Oxidized hemoglobin promotes survival of ROS-stressed and DNA damaged fallopian tube epithelial cells with p53 loss, resulting in a copy number variation phenotype of HGSC.

Abstract Purpose: Ovulation is a strong risk factor for high grade serous carcinoma (HGSC) of ovary known to largely originate from the fallopian tube fimbriae. Previously, we have showed ROS in the mature follicular fluid (FF) is mutagenic and cytotoxic to fimbria epithelial cells, and induces DNA double strand breaks (DSB) in the context of p53 loss. We hypothesized that hemoglobin (Hb) in FF accumulated in cul-de-sac (CDS) after ovulatory bleeding may protect the bathed fimbria from cell death and enhance cancer initiation. Results: Peritoneal fluids collected from the CDS after ovulation contained high level of oxidized Hb and ROS, so did ovarian FFs retrieved from IVF patients. When treating E6/E7-immortalized fimbria secretory cells (FE25) with FFs with various ROS levels ranging from 100-1200 μM of H2O2 equivalence, a positive correlation of Hb levels (ranging from 100-1100 μg/ml) in FF and cell viability was observed. This was further confirmed in treating FE25 cells with H2O2 where Hb dose-dependently rescued cell death. As a consequence, FE25 cells treated with either Hb-high FF or with H2O2 plus Hb accumulated high level of DSB and showed an extensive DNA copy number variation compatible with the copy number variation (CNV) phenotype of HGSC. The resulted DNA aneuploidy rates were 50±5% and 65±7% in FE25 treated with 500 μM H2O2 supplemented with 100 μg/ml Hb or 3% Hb-hgih FF, respectively; as compared to 15±2% at baseline and 31±8% with H2O2 only. In the case of primary fimbria epithelial cells the figures were 2±0.3% and 1.3±0.2%, respectively. Finally, the p53 deficiency dependent rescuing effect of Hb on ROS-stressed tubal epithelial cells, and the consequent CNV phenotype were confirmed ex vivo with oviducts of wild type and Trp53-null mice. Conclusion: While ROS in FF induces DNA damage and cytotoxicity of p53-deficient fimbria epithelial cells, oxidized Hb in peritoneal fluid rescues cells from death and results in a CNV phenotype, a major characteristic of HGSC. Citation Format: Hsuan-Shun Huang, Che-Fang Hsu, Tang-Yuan Chu. Oxidized hemoglobin promotes survival of ROS-stressed and DNA damaged fallopian tube epithelial cells with p53 loss, resulting in a copy number variation phenotype of HGSC. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr B02.

The Trp53 delta proline (Trp53ΔP) mouse exhibits increased genome instability and susceptibility to radiation-induced, but not spontaneous, tumor development.

The tumor suppressor TP53 can initiate a plethora of anti-proliferative effects to maintain genomic integrity under conditions of genotoxic stress. The N-terminal proline-rich domain (PRD) of TP53 is important in the regulation of TP53 activity and stability. A common polymorphism at codon 72 in this region has been associated with altered cancer risk in humans. The Trp53ΔP mouse, which carries a germline homozygous deletion of a region of the PRD, does not develop spontaneous tumors in a mixed 129/Sv and C57BL/6 genetic background, but is highly susceptible to a broad range of tumor types following total body exposure to 4 Gy gamma (γ) radiation. This contrasts with the tumor spectrum in Trp53 null (-/-) mice, which mainly develop thymic lymphomas and osteosarcomas. Analysis of genomic instability in tissues and cells from Trp53ΔP mice demonstrated elevated basal levels of aneuploidy, but this is not sufficient to drive spontaneous tumorigenesis, which requires an additional DNA damage stimulus. Levels of genomic instability did not increase significantly in Trp53ΔP mice following irradiation exposure, suggesting that other radiation effects including tissue inflammation, altered metabolism or autophagy, may play an important role. The Trp53ΔP mouse is a novel model to dissect the mechanisms of tumor development induced by radiation exposure. © 2015 Wiley Periodicals, Inc.

Intratumoral heterogeneity in a Trp53-null mouse model of human breast cancer.

Intratumoral heterogeneity correlates with clinical outcome and reflects the cellular complexity and dynamics within a tumor. Such heterogeneity is thought to contribute to radio- and chemoresistance because many treatments may target only certain tumor cell subpopulations. A better understanding of the functional interactions between various subpopulations of cells, therefore, may help in the development of effective cancer treatments. We identified a unique subpopulation of tumor cells expressing mesenchymal-like markers in a Trp53-null mouse model of basal-like breast cancer using fluorescence-activated cell sorting and microarray analysis. Both in vitro and in vivo experiments revealed the existence of cross-talk between these "mesenchymal-like" cells and tumor-initiating cells. Knockdown of genes encoding ligands upregulated in the mesenchymal cells and their corresponding receptors in the tumor-initiating cells resulted in reduced tumorigenicity and increased tumor latency. These studies illustrate the non-cell-autonomous properties and importance of cooperativity between tumor subpopulations. Intratumoral heterogeneity has been considered one important factor in assessing a patient's initial response to treatment and selecting drug regimens to effectively increase tumor response rate. Elucidating the functional interactions between various subpopulations of tumor cells will help provide important new insights in understanding treatment response and tumor progression.

Intratumoral Heterogeneity in a Trp53-Null Mouse Model of Human Breast Cancer

Intratumoral Heterogeneity in a Trp53-Null Mouse Model of Human Breast Cancer

P2-25-1 - The Correlation Between Rb1 Loss Signatures Derived From Mouse and Breast Cancers Equipped with Clinical Information

Background: Inactivation of Retinoblastoma 1 (RB1) gene product is implicated in progression of breast, prostate and many other cancers. It has been shown that RB1 expression level is correlated with the subtypes and sensitivity to treatment in breast cancers. However, directly linking RB1 status to clinical behaviors in cancers has been hampered by heterogeneity in human cancers. To clarify the mechanism by which RB1 inactivation affects clinical courses, we obtained the gene expression profile by Rb1 depletion under genetically homogeneous conditions, and analyzed the correlation between Rb1 loss signatures and clinical behaviors in breast cancers.Methods: Trp53-null mouse derived tumor cells were transduced with shRNA of either control or Rb1, and whole RNA sequencing was performed. We compared the average between control samples and Rb1 knockdown samples. We extracted differentially expressed genes, and obtained Rb1 loss signatures by using homologous genes. Based on these signatures, we performed KEGG and GO analyses, detected overlapping genes using Mammaprit, OncotypeDX, and other reported breast cancer signatures. Also we investigated relevance to subtype, treatment sensitivity, and prognosis of breast cancer.Results: Some genes were found to be overlapped in Rb1 loss signatures and previously reported breast cancer signatures. Also the genes affected by Rb1 knockdown were included in signatures featuring high grade and poor prognosis in breast cancer. Conclusion:Rb1 depletion itself may associate clinical course in breast cancer.

Abstract 2977: Myc and Miz1 in medulloblastoma

Abstract Medulloblastoma (MB) is the most common malignant pediatric brain tumor, which arises in the cerebellum. Human MBs are classified into four subgroups: Wingless (WNT), Sonic Hedgehog (SHH), Group 3 (G3) and Group 4 (G4). In 2012, we developed a mouse model of the most aggressive and least curable G3 MB, by overexpressing MYC but not MYCN, in Trp53-null cerebellar granule neuron progenitors (GNPs), which were implanted into the cortices of recipient CD-1 nu/nu mice. Remarkably, enforced expression of MYCN in Trp53-null GNPs induced a SHH MB. This was unexpected since MYC and MYCN bind to the same E-box DNA binding sequences. We hypothesized that the difference between MYC- and MYCN-induced MBs might be due to their interaction with different partners in GNPs. Human G3 MBs are distinguished by MYC overexpression. The MYC proto-oncogene encodes a bHLH/leucine-zipper transcription factor that forms heterodimers with MAX to drive transcription. However, MYC can repress transcription when the MYC/MAX heterodimer is recruited to core promoter sequences by MIZ1, a member of the POZ-domain/zinc-finger transcription factor. MIZ1, ubiquitously expressed during embryonic development, can either be a transcription activator or repressor depending on its binding partners. To investigate whether the MYC/MIZ1 complex contributed to G3 MBs, we used a mutant of MYC which no longer binds to MIZ1 in which a Valine is substituted for an Aspartic acid amino acid at position 394 (MYCV394D). We enforced the expression of MYC or MYCV394D in GNPs purified from seven-day-old Trp53-null mouse pups using retroviral transduction, and implanted transduced GNPs into the cerebral cortices of recipient mice. MYCV394D-induced tumors developed later than MYC-induced G3 MBs. Histopathological analysis revealed that MYC-induced tumors exhibited a large cell/anaplastic (LCA) phenotype and were classified as G3 MBs; however, MYCV394D-induced tumors were described as unclassified primitive neuroectodermal tumors. In vitro, MYCV394D-induced tumors formed tumorspheres that were highly apoptotic and less proliferative compared to MYC tumorspheres. Global gene expression of MYCV394D tumors was distinct from murine G3 and SHH subgroup MBs. Particularly, genes needed for neuronal differentiation and which are strongly repressed by MYC in G3 MBs, were no longer repressed by the MYCV394D mutant, indicating that the MYC/MIZ1 complex was responsible for their repression. To analyze whether the MYC/MIZ1 complex was present on chromatin in G3 MBs, we performed ChIP-Seq for MYC and MIZ1. In contrast to Trp53-null GNPs, where MIZ1 only binds 140 promoters, 11.549 promoters were occupied by MIZ1 in G3 MBs, 9.353 of which were co-occupied by MYC (81%). Because as many of the joined binding sites neither contained a canonical E-box sequence nor a bona fide MIZ1 binding motif, we speculate that cooperative binding of oncogenic MYC with MIZ1 is necessary for binding. Our data suggest that the MYC-MIZ1 interaction is critical for the development of G3 MBs. Citation Format: BaoHan T. Vo, Elmar Wolf, Daisuke Kawauchi, Jerold Rehg, David Finkelstein, Brian Murphy, Martin Eilers, Martine F. Roussel. Myc and Miz1 in medulloblastoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2977. doi:10.1158/1538-7445.AM2014-2977