P53 Deficiency Research Articles

Inactivation of p27kip1 Promoted Nonspecific Inflammation by Enhancing Macrophage Proliferation in Islet Transplantation.

Islet transplantation suffers from low efficiency caused by nonspecific inflammation-induced graft loss after transplantation. This study reports increased islet loss and enhanced inflammatory response in p27-deficient mice (p27-/-) and proposes a possible mechanism. Compared with wild type, p27-/- mice showed more severe functional injury of islet, with increased serum levels of inflammatory cytokines IL-1 and TNF-α, inducing macrophage proliferation. Furthermore, the increased number, proapoptotic proteins, and nuclear factor-kappa b (NF-κB) phosphorylation status of the infiltrating macrophages were accompanied by increased TNF-α mRNA level of islet graft site in p27-/- mice. Moreover, in vitro, we found that macrophages were still activated and cocultured with islet and promoted islet loss even blocking the direct effect of TNF-α on islets. Malondialdehyde (MDA, an end product of lipid peroxidation) in islet and media were increased after cocultured with macrophages. p27 deficiency also increased macrophage proliferation and islet injury. Therefore, p27 inactivation promotes injury islet graft loss via the elevation of proliferation and inflammatory cytokines secretion in infiltrating macrophages which induced nonspecific inflammation independent of TNF-α/nuclear factor-kappa b pathway. This potentially represents a promising therapeutic target in improving islet graft survival.

Preclinical Study of Combination of Antifolate Agents with Palbociclib Isethionate to Treat Mantle Cell Lymphoma with or without P53 Deficiency

Preclinical Study of Combination of Antifolate Agents with Palbociclib Isethionate to Treat Mantle Cell Lymphoma with or without P53 Deficiency

Selenoprotein H is an essential regulator of redox homeostasis that cooperates with p53 in development and tumorigenesis

Selenium, an essential micronutrient known for its cancer prevention properties, is incorporated into a class of selenocysteine-containing proteins (selenoproteins). Selenoprotein H (SepH) is a recently identified nucleolar oxidoreductase whose function is not well understood. Here we report that seph is an essential gene regulating organ development in zebrafish. Metabolite profiling by targeted LC-MS/MS demonstrated that SepH deficiency impairs redox balance by reducing the levels of ascorbate and methionine, while increasing methionine sulfoxide. Transcriptome analysis revealed that SepH deficiency induces an inflammatory response and activates the p53 pathway. Consequently, loss of seph renders larvae susceptible to oxidative stress and DNA damage. Finally, we demonstrate that seph interacts with p53 deficiency in adulthood to accelerate gastrointestinal tumor development. Overall, our findings establish that seph regulates redox homeostasis and suppresses DNA damage. We hypothesize that SepH deficiency may contribute to the increased cancer risk observed in cohorts with low selenium levels.

Zbtb1 prevents default myeloid differentiation of lymphoid-primed multipotent progenitors.

Zbtb1 is a transcription factor that prevents DNA damage and p53-mediated apoptosis in replicating immune progenitors, affecting lymphoid as well as myeloid development when hematopoietic progenitors are in competition in mixed bone marrow chimeras. However, Zbtb1-deficient mice do not have an apparent myeloid deficiency. We report here that Zbtb1-deficient lymphoid-primed multipotent progenitors (LMPPs) are biased to develop towards the myeloid fate in detriment of lymphoid development, contributing to the apparent unaffected myeloid development. Zbtb1 expression was maintained during lymphoid development of LMPP cells but downregulated during myeloid development. Deficiency of Zbtb1 in LMPP cells was sufficient to direct a myeloid fate in lymphoid-inducing conditions and in the absence of myeloid cytokines as shown by upregulation of a myeloid gene signature and the generation of myeloid cells in vitro. Finally, biased myeloid differentiation of Zbtb1-deficient LMPP cells was not due to increased p53-dependent apoptosis as it was not reverted by transgenic Bcl2 expression or p53 deficiency. Altogether, our results show that Zbtb1 expression prevents activation of a default myeloid program in LMPP cells, ensuring the generation of lymphoid cells.

Zbtb1 Safeguards Genome Integrity and Prevents p53-Mediated Apoptosis in Proliferating Lymphoid Progenitors.

Expression of the transcription factor Zbtb1 is required for normal lymphoid development. We report in the present study that Zbtb1 maintains genome integrity in immune progenitors, without which cells undergo increased DNA damage and p53-mediated apoptosis during replication and differentiation. Increased DNA damage in Zbtb1-mutant (ScanT) progenitors was due to increased sensitivity to replication stress, which was a consequence of inefficient activation of the S-phase checkpoint response. Increased p53-mediated apoptosis affected not only lymphoid but also myeloid development in competitive bone marrow chimeras, and prevention of apoptosis by transgenic Bcl2 expression and p53 deficiency rescued lymphoid as well as myeloid development from Zbtb1-mutant progenitors. Interestingly, however, protection from apoptosis rescued only the early stages of T cell development, and thymocytes remained arrested at the double-negative 3 developmental stage, indicating a strict requirement of Zbtb1 at later T cell developmental stages. Collectively, these results indicate that Zbtb1 prevents DNA damage in replicating immune progenitors, allowing the generation of B cells, T cells, and myeloid cells.

P21 mediates macrophage reprogramming through regulation of p50-p50 NF-κB and IFN-β.

M1 and M2 macrophage phenotypes, which mediate proinflammatory and antiinflammatory functions, respectively, represent the extremes of immunoregulatory plasticity in the macrophage population. This plasticity can also result in intermediate macrophage states that support a balance between these opposing functions. In sepsis, M1 macrophages can compensate for hyperinflammation by acquiring an M2-like immunosuppressed status that increases the risk of secondary infection and death. The M1 to M2 macrophage reprogramming that develops during LPS tolerance resembles the pathological antiinflammatory response to sepsis. Here, we determined that p21 regulates macrophage reprogramming by shifting the balance between active p65-p50 and inhibitory p50-p50 NF-κB pathways. p21 deficiency reduced the DNA-binding affinity of the p50-p50 homodimer in LPS-primed and -rechallenged macrophages, impairing their ability to attenuate IFN-β production and acquire an M2-like hyporesponsive status. High p21 levels in sepsis patients correlated with low IFN-β expression, and p21 knockdown in human monocytes corroborated its role in IFN-β regulation. The data demonstrate that p21 adjusts the equilibrium between p65-p50 and p50-p50 NF-κB pathways to mediate macrophage plasticity in LPS tolerance. Identifying p21-related pathways involved in monocyte reprogramming may lead to potential targets for sepsis treatment.

Abstract 3073: Targeting chronic lymphocytic leukemia by interfering glutathione synthesis using a novel therapeutic enzyme cyst(e)inase (AEB3103)

Abstract Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in the Western countries. Despite recent advance in new therapeutic agents that have improved treatment outcomes, CLL remains incurable due in part to the inability to completely eradicate the leukemia cells in vivo. Previous studies showed that CLL cells have high intrinsic oxidative stress and are highly dependent on cellular antioxidant glutathione (GSH) to maintain redox balance and cell viability. One logical strategy to impact CLL cells would be to abrogate the glutathione protection of CLL cells in vivo. Recently we discovered that primary leukemia cells isolated from CLL patients were unable to effectively utilize cystine for GSH synthesis due to low expression of the cystine transporter Xc-, and that bone marrow stromal cells highly express Xc- and effectively take up cystine for conversion to cysteine (Zhang et al: Nature Cell Biology, 2012). These findings provide a biochemical basis to develop novel strategies to effectively target leukemia cells in the stromal microenvironment and improve in vivo therapeutic activity. In this study, we tested the depletion of extracellular cystine and cysteine using a novel therapeutic enzyme-cyst(e)inase (AEB3103), as a potential way to block GSH synthesis in CLL cells and abolish the stromal protection of the leukemia cells. Our study showed that AEB3103 was very effective in depleting GSH in CLL cells and caused massive CLL cell death even in the presence of stromal cells. Importantly, AEB3103 could also overcome drug resistance of CLL cells with p53 deficiency both in primary leukemia cells isolated from CLL patients with 17p deletion and mouse leukemic cells isolated from mouse model we recently reported (Liu et al: Leukemia, 2014). In addition, AEB3103 showed very low toxicity to normal cells. These promising in vitro data warrant further animal studies, which are currently on ongoing using the CLL mouse model with TCL1-Tg:p53-/- genotype. Our study suggests that AEB3103 and its combination with standard anti-CLL drugs may potentially be useful for clinical treatment of CLL, even for the more aggressive CLL subtypes with unfavorable cytogenetic alterations such as those with chromosome17p deletion and p53 mutations, and may improve in vivo therapeutic activity. Citation Format: Jinyun Liu, Li Feng, Everett M. Stone, Joseph Tyler, Scott W. Rowlinson, Michael J. Keating, Peng Huang. Targeting chronic lymphocytic leukemia by interfering glutathione synthesis using a novel therapeutic enzyme cyst(e)inase (AEB3103). [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3073.

Abstract 1012: Systems analysis of colon cancer cell metabolism rewired by p53 and KRAS mutations

Abstract Introduction. Somatic mutations in proto-oncogenes and tumour-suppressor genes contribute to rewire the already deregulated metabolic network in cancer cells, resulting in uncontrolled proliferation and oncogenesis. In this study, we set out to establish a dynamic mathematical model of bioenergetics and to exploit it to explore the multifaceted cross-talk between bioenergetics, somatic gene mutations in KRAS and p53, and cell proliferation and survival. Model Development. We have developed an ordinary differential equations-based model of central carbon metabolism in cancer cells which includes glycolysis, pentose phosphate pathway, citric acid cycle and respiratory chain, based on our previous work and published models. The model describes how nutrients (glucose, glutamine, lactate, pyruvate, serine and glycine) from the extracellular micro-environment affect bioenergetics parameters. The resulting model predictions are linked to cell proliferation via a heuristic function. Enzymatic activities regulated by p53 and KRAS mutations were obtained by mining publically available datasets and their regulation by the mutational status was modelled by adapting the corresponding kinetic parameters. To estimate the kinetic parameters, model simulation outputs were fitted to a portfolio of experimental data both generated de novo in house and gathered from the literature in HCT-116 colon cancer cells. Experiments were performed on parental HCT-116 (p53 competent; harbouring a KRAS mutation on exon 2 of codon G13) and three derived mutant cell lines covering all four combinations of p53 and KRAS mutational status to isolate their relative and joint effect on bioenergetics signatures. HCT-116-derived cell lines included: p53 proficient cells with the KRAS allelic mutation silenced by homologous recombination in the presence or absence of p53 knockout by lentiviral shRNA. Results. The model was calibrated against ATP concentrations measured via single-cell microscopy (ATeam probe and TMRM dye) following pharmacological inhibition of respiratory chain complexes (rotenone, sodium azide and oligomycin) as a function of nutrients availability (glucose, lactate, pyruvate). Modelling results revealed that p53 and KRAS mutations drive a shift in metabolic signatures and L-lactate emerged as a pivotal metabolite to stratify the different phenotypes. Systems analysis revealed that in KRAS mutated cells p53 deficiency leads to an increase in glucose uptake and flux through the pentose phosphate pathway and a decrease in lactate production. Indeed, p53 deficient HCT-116 cells showed a decrease in extracellular lactate with respect to p53 proficient cells in validation experiments. Conclusions. The computational model developed can be used to benchmark mechanistic hypotheses by which tumour suppressors and/or oncogenic mutations rewire metabolism and to identify putative targets for therapeutic intervention. Citation Format: Manuela Salvucci, Robert O’Byrne, Natalia Niewidok, Séan Kilbride, Caoimhín G. Concannon, Heiko Düssmann, Heinrich H. Huber, Jochen HM Prehn. Systems analysis of colon cancer cell metabolism rewired by p53 and KRAS mutations. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1012.

Abstract 1367: Intra-cerebral pharmacokinetic monitoring of a tyrosine kinase inhibitor (theranostic 18[F]-PET/NIRF labeled dasatinib) delivered via convection-enhanced delivery

Abstract Introduction: Convection enhanced delivery (CED) has been recently explored as an advantageous therapeutic strategy for central nervous system (CNS) tumors. One current limitation is the inability to quantitatively monitor distribution of chemotherapeutic agents. The use of surrogate tracers probably underestimates differences in distribution and clearance owing to discordant features between contrast molecules and therapeutic agents, including bioactivity, degradation, conductivity, and diffusivity. Ideally, direct labelling of a therapeutic compound would eliminate these concerns and afford a noninvasive method to monitor critical pharmacokinetic information. This ability would pave the way for designing infusion parameters and drug schedules that are expected to be unique for CED-based therapy. Methods: The small molecule kinase inhibitor dasatinib was modified with a dual-probe technology that utilizes a boronate trap to conjugate 18[F] with a near-infrared fluorophore into a single molecule, 1, allowing for visualization by positron emission tomography (PET) and near-infrared fluorescence (NIRF). The novel boronate trap allows for direct conjugation of 18[F] with minimal disruption of dasatinib's mechanism of action, resulting in a small, versatile probe with potential for other clinically relevant targets. Results: The modified drug was first tested in vitro in a PDGF-B driven p53 deficient DIPG tumor line from Nestin tv-a; p53 floxed mouse. 1 was shown to enter cells on fluorescence microscopy and inhibit cell proliferation. Antagonist drug potency of 1 as evaluated on pontine glioma in ATP-dependent luminescent cell viability, cell-permeant calcein AM, and an MTS cell proliferation assays show that the IC50, of 1 is ∼10nM. In addition, infusions of 1 were performed via CED and intravenous systemic delivery in a RCAS/tv-a PDGF-B driven with p53 deficiency Ntv-a mouse model of high-grade glioma. Compared to systemic delivery, CED was shown to be roughly 230 times more effective in delivery of the infusion to the tumor site. Maximal glioma delivery occurred at 115 min post a 20 min infusion, with clearance occurring with a half-life of 45 min after maximum delivery. Conclusion: Dasatinib was modified to give 1, an agent that can be imaged non-invasively by fluorescence and positron emission tomography (PET). The modified dasatinib showed little modification in biologic activity when compared to unmodified dasatinib and exhibited cytotoxic effects in vitro in glioma cell culture. CED shows a clear benefit to intravenous delivery when the target site is in the CNS. The dual-label probe technology's versatility and minimal biologic profile lends itself to various clinical uses, including the study of different therapeutic agents and delivery routes without the need to rely on surrogate tracers. Citation Format: Melinda Wang, Zhiping Zhou, Hari Krishna Kommidi, Melanie Schweitzer, Mark Chan, Yue Linda Wu, Ranjodh Singh, Richard Ting, Mark M. Souweidane. Intra-cerebral pharmacokinetic monitoring of a tyrosine kinase inhibitor (theranostic 18[F]-PET/NIRF labeled dasatinib) delivered via convection-enhanced delivery. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1367.

Telomere Replication Stress Induced by POT1 Inactivation Accelerates Tumorigenesis.

SUMMARYGenome sequencing studies have revealed a number of cancer-associated mutations in the telomerebinding factor POT1. Here, we show that when combined with p53 deficiency, depletion of murine POT1a in common lymphoid progenitor cells fosters genetic instability, accelerates the onset, and increases the severity of T cell lymphomas. In parallel, we examined human and mouse cells carrying POT1 mutations found in cutaneous T cell lymphoma (CTCL) patients. Inhibition of POT1 activates ATRdependent DNA damage signaling and induces telomere fragility, replication fork stalling, and telomere elongation. Our data suggest that these phenotypes are linked to impaired CST (CTC1-STN1-TEN1) function at telomeres. Lastly, we show that proliferation of cancer cells lacking POT1 is enabled by the attenuation of the ATR kinase pathway. These results uncover a role for defective telomere replication during tumorigenesis.

Radiosensitization of Non-Small Cell Lung Cancer Cells by Inhibition of TGF-β1 Signaling With SB431542 Is Dependent on p53 Status.

Although medically inoperable patients with stage I non-small cell lung cancer cells (NSCLC) are often treated with stereotactic body radiation therapy, its efficacy can be compromised due to poor radiosensitivity of cancer cells. Inhibition of transforming growth factor-β1 (TGF-β1) using LY364947 and LY2109761 has been demonstrated to radiosensitize cancer cells such as breast cancer, glioblastoma, and lung cancer. Our previous results have demonstrated that another potent and selective inhibitor of TGF-β1 receptor kinases, SB431542, could radiosensitize H460 cells both in vitro and in vivo. In the present study, we investigated whether SB431542 could radiosensitize other NSCLC cell lines, trying to explore the potential implication of this TGF-β1 inhibitor in radiotherapy for NSCLC patients. The results showed that A549 cells were significantly radiosensitized by SB431542, whereas no radiosensitizing effect was observed in H1299 cells. Interestingly, both H460 and A549 cells have wild-type p53, while H1299 cells have deficient p53. To study whether the radiosensitizing effect of SB431542 was associated with p53 status of cancer cells, the p53 of H460 cells was silenced using shRNA transfection. Then it was found that the radiosensitizing effect of SB431542 on H460 cells was not observed in H460 cells with silenced p53. Moreover, X-irradiation caused rapid Smad2 activation in H460 and A549 cells but not in H1299 and H460 cells with silenced p53. The Smad2 activation postirradiation could be abolished by SB431542. This may explain the lack of radiosensitizing effect of SB431542 in H1299 and H460 cells with silenced p53. Thus, we concluded that the radiosensitizing effect of inhibition of TGF-β1 signaling in NSCLC cells by SB431542 was p53 dependent, suggesting that using TGF-β1 inhibitor in radiotherapy may be more complicated than previously thought and may need further investigation.

The NAE inhibitor pevonedistat interacts with the HDAC inhibitor belinostat to target AML cells by disrupting the DDR

AbstractTwo classes of novel agents, NEDD8-activating enzyme (NAE) and histone deacetylase (HDAC) inhibitors, have shown single-agent activity in acute myelogenous leukemia (AML)/myelodysplastic syndrome (MDS). Here we examined mechanisms underlying interactions between the NAE inhibitor pevonedistat (MLN4924) and the approved HDAC inhibitor belinostat in AML/MDS cells. MLN4924/belinostat coadministration synergistically induced AML cell apoptosis with or without p53 deficiency or FLT3–internal tandem duplication (ITD), whereas p53 short hairpin RNA (shRNA) knockdown or enforced FLT3-ITD expression significantly sensitized cells to the regimen. MLN4924 blocked belinostat-induced antiapoptotic gene expression through nuclear factor–κB inactivation. Each agent upregulated Bim, and Bim knockdown significantly attenuated apoptosis. Microarrays revealed distinct DNA damage response (DDR) genetic profiles between individual vs combined MLN4924/belinostat exposure. Whereas belinostat abrogated the MLN4924-activated intra-S checkpoint through Chk1 and Wee1 inhibition/downregulation, cotreatment downregulated multiple homologous recombination and nonhomologous end-joining repair proteins, triggering robust double-stranded breaks, chromatin pulverization, and apoptosis. Consistently, Chk1 or Wee1 shRNA knockdown significantly sensitized AML cells to MLN4924. MLN4924/belinostat displayed activity against primary AML or MDS cells, including those carrying next-generation sequencing–defined poor-prognostic cancer hotspot mutations, and CD34+/CD38−/CD123+ populations, but not normal CD34+ progenitors. Finally, combined treatment markedly reduced tumor burden and significantly prolonged animal survival (P < .0001) in AML xenograft models with negligible toxicity, accompanied by pharmacodynamic effects observed in vitro. Collectively, these findings argue that MLN4924 and belinostat interact synergistically by reciprocally disabling the DDR in AML/MDS cells. This strategy warrants further consideration in AML/MDS, particularly in disease with unfavorable genetic aberrations.

Disruption of Folliculin interacting protein-1 results in loss of sIg+ B cells and inhibits autophagy

Abstract Folliculin interacting protein-1 (Fnip1) was discovered through its interaction with Folliculin (Flcn), a tumor suppressor mutated in the rare disorder Birt-Hogg Dubé syndrome. The Fnip1/Flcn complex interacts with the catabolic regulator AMP kinase. Previous studies have shown that Fnip1 is required for the development of B-cells past the late pre-B stage (Park et al Immunity 2012) and for the development of invariant natural killer T (iNKT) cells (Park et al PNAS 2014). We previously found Fnip1-deficient immune cells exhibited concurrently increased activation of mTORC1 and AMPK. In this study, we used a floxed Fnip1 allele combined with poly inosine:cytosine (poly I:C)-inducible Mx1-Cre to investigate the effects of conditional Fnip1 depletion on immature and mature B cells, and utilized genetic experiments to investigate the mechanism(s) of the B cell developmental block. We show loss of sIg+ B cells in the bone marrow and spleen after conditional Fnip1 depletion. Fnip1-deficient B cells exhibited significantly increased metabolism (oxidative phosphorylation and glycolysis) upon stimulation, possibly as a result of increased mitochondrial number and mTOR activation. Bcl-xL and c-Myc overexpression rescued a small fraction of sIg+ B cells in Fnip1-deficient mice, while p53 deficiency (Trp53−/−) and mTORC1 inactivation (Raptorfl/flmb1-cre) did not. Finally, we show that Fnip1-deficient B cells expressing LC3-GFP have lower mean GFP fluorescence and do not respond as robustly as wild type B cells to induction of autophagy. These results suggest that Fnip1 mediates autophagy in B cells, and that tight regulation of autophagic flux is necessary for development and survival of immature and mature B cells.

Mice with a Mutation in the Mdm2 Gene That Interferes with MDM2/Ribosomal Protein Binding Develop a Defect in Erythropoiesis.

MDM2, an E3 ubiquitin ligase, is an important negative regulator of tumor suppressor p53. In turn the Mdm2 gene is a transcriptional target of p53, forming a negative feedback loop that is important in cell cycle control. It has recently become apparent that the ubiquitination of p53 by MDM2 can be inhibited when certain ribosomal proteins, including RPL5 and RPL11, bind to MDM2. This inhibition, and the resulting increase in p53 levels has been proposed to be responsible for the red cell aplasia seen in Diamond-Blackfan anemia (DBA) and in 5q- myelodysplastic syndrome (MDS). DBA and 5q- MDS are associated with inherited (DBA) or acquired (5q- MDS) haploinsufficiency of ribosomal proteins. A mutation in Mdm2 causing a C305F amino acid substitution blocks the binding of ribosomal proteins. Mice harboring this mutation (Mdm2C305F), retain a normal p53 response to DNA damage, but lack the p53 response to perturbations in ribosome biogenesis. While studying the interaction between RP haploinsufficiency and the Mdm2C305F mutation we noticed that Mdm2C305F homozygous mice had altered hematopoiesis. These mice developed a mild macrocytic anemia with reticulocytosis. In the bone marrow (BM), these mice showed a significant decrease in Ter119hi cells compared to wild type (WT) littermates, while no decrease in the number of mature erythroid cells (Ter119hiCD71low) was found in the spleen, which showed compensated bone marrow hematopoiesis. In methylcellulose cultures, BFU-E colonies from the mutant mice were slightly reduced in number and there was a significant reduction in CFU-E colony numbers in mutant mice compared with WT controls (p < 0.01). This erythropoietic defect was abrogated by concomitant p53 deficiency (Trp53ko/ko). Further investigation revealed that in Mdm2C305F animals, there was a decrease in Lin-Sca-1+c-Kit+ (LSK) cells, accompanied by significant decreases in multipotent progenitor (MPP) cells (p < 0.01). Competitive BM repopulation experiments showed that donor BM harboring the Mdm2C305F mutation possessed decreased repopulation capacity compared to WT BM, suggesting a functional stem cell deficit. These results suggest that there is a fine tuned balance in the interaction of ribosomal proteins with the MDM2/p53 axis which is important in normal hematopoiesis.

P53 Maintains Genomic Stability by Preventing Interference between Transcription and Replication.

p53 tumor suppressor maintains genomic stability, typically acting through cell-cycle arrest, senescence, and apoptosis. We discovered a function of p53 in preventing conflicts between transcription and replication, independent of its canonical roles. p53 deficiency sensitizes cells to Topoisomerase (Topo) II inhibitors, resulting in DNA damage arising spontaneously during replication. Topoisomerase IIα (TOP2A)-DNA complexes preferentially accumulate in isogenic p53 mutant or knockout cells, reflecting an increased recruitment of TOP2A to regulate DNA topology. We propose that p53 acts to prevent DNA topological stress originating from transcription during the S phase and, therefore, promotes normal replication fork progression. Consequently, replication fork progression is impaired in the absence of p53, which is reversed by transcription inhibition. Pharmacologic inhibition of transcription also attenuates DNA damage and decreases Topo-II-DNA complexes, restoring cell viability in p53-deficient cells. Together, our results demonstrate a function of p53 that may underlie its role in tumor suppression.

P21 deficiency is susceptible to osteoarthritis with inflammation

P21 deficiency is susceptible to osteoarthritis with inflammation

P21 deficiency increases the regenerative capacity of bone and cartilage after injury

P21 deficiency increases the regenerative capacity of bone and cartilage after injury

Abstract P2-05-08: p53 deficiency enhances metastatic potential of triple negative breast cancer by promoting growth in primary and metastatic sites

Abstract TP53 is one of the most commonly mutated genes in human cancer. Mutation or loss of TP53 can occur during the early stages of oncogenesis or as a later event as tumors progress to more aggressive forms. We used a patient-derived xenograft (PDX) model of triple negative breast cancer (TNBC) to investigate how p53 deficiency contributes to metastasis. The PDX line was generated by engrafting the primary breast tumor of a patient with TP53 wild-type metastatic TNBC into the humanized mammary fat pad of NOD/SCID mice. Isogenic lines differing only in TP53 status were generated from this model by silencing p53. Here we demonstrate that the p53-proficient and -deficient tumors metastasized from the mouse mammary gland and colonized the lung, liver, bone, brain, and lymph nodes with similar frequency. p53-deficient tumors grew faster in both the primary and metastatic sites as a result of increased mitosis and decreased apoptosis. Circulating tumor cells (CTCs) are currently being evaluated in p53-proficient and –deficient PDX models. Gene expression profiling identified candidate genes with potential clinical relevance that may be responsible for increased tumor growth upon p53 loss in late stage tumors. This model is also being used to identify genes that promote breast cancer metastasis. To enrich for metastasis, metastatic subpopulations of tumor cells were isolated from lungs and serially passaged in vivo. This serial passaging enriched for metastasis to multiple secondary sites. A transcriptional signature of putative metastasis genes was generated and is being functionalized with high throughput screening in vivo. Citation Format: Powell E, Shao J, Mistry N, Yuan Y, Tieu T, Decker K, Chen H-C, Cai S, Do K-A, Heffernan TP, Edwards J, Piwnica-Worms D, Piwnica-Worms H. p53 deficiency enhances metastatic potential of triple negative breast cancer by promoting growth in primary and metastatic sites. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-05-08.

P53 deficiency linked to B cell translocation gene 2 (BTG2) loss enhances metastatic potential by promoting tumor growth in primary and metastatic sites in patient-derived xenograft (PDX) models of triple-negative breast cancer

BackgroundDespite advances in early diagnosis and treatment of cancer patients, metastasis remains the major cause of mortality. TP53 is one of the most frequently mutated genes in human cancer, and these alterations can occur during the early stages of oncogenesis or as later events as tumors progress to more aggressive forms. Previous studies have suggested that p53 plays a role in cellular pathways that govern metastasis. To investigate how p53 deficiency contributes to late-stage tumor growth and metastasis, we developed paired isogenic patient-derived xenograft (PDX) models of triple-negative breast cancer (TNBC) differing only in p53 status for longitudinal analysis.MethodsPatient-derived isogenic human tumor lines differing only in p53 status were implanted into mouse mammary glands. Tumor growth and metastasis were monitored with bioluminescence imaging, and circulating tumor cells (CTCs) were quantified by flow cytometry. RNA-Seq was performed on p53-deficient and p53 wild-type tumors, and functional validation of a lead candidate gene was performed in vivo.ResultsIsogenic p53 wild-type and p53-deficient tumors metastasized out of mammary glands and colonized distant sites with similar frequency. However, p53-deficient tumors metastasized earlier than p53 wild-type tumors and grew faster in both primary and metastatic sites as a result of increased proliferation and decreased apoptosis. In addition, greater numbers of CTCs were detected in the blood of mice engrafted with p53-deficient tumors. However, when normalized to tumor mass, the number of CTCs isolated from mice bearing parental and p53-deficient tumors was not significantly different. Gene expression profiling followed by functional validation identified B cell translocation gene 2 (BTG2), a downstream effector of p53, as a negative regulator of tumor growth both at primary and metastatic sites. BTG2 expression status correlated with survival of TNBC patients.ConclusionsUsing paired isogenic PDX-derived metastatic TNBC cells, loss of p53 promoted tumor growth and consequently increased tumor cell shedding into the blood, thus enhancing metastasis. Loss of BTG2 expression in p53-deficient tumors contributed to this metastatic potential by enhancing tumor growth in primary and metastatic sites. Furthermore, clinical data support conclusions generated from PDX models and indicate that BTG2 expression is a candidate prognostic biomarker for TNBC.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-016-0673-9) contains supplementary material, which is available to authorized users.

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.