Restoration of endogenous wild-type p53 activity in a glioblastoma cell line with intrinsic temperature-sensitive p53 induces growth arrest but not apoptosis

Germline Variants in Cancer Predisposition Genes in Pediatric Patients with Central Nervous System Tumors

Central nervous system (CNS) tumors comprise around 20% of childhood malignancies. Germline variants in cancer predisposition genes (CPGs) are found in approximately 10% of pediatric patients with CNS tumors. This study aimed to characterize variants in CPGs in pediatric patients with CNS tumors and correlate these findings with clinically relevant data. Genomic DNA was isolated from the peripheral blood of 51 pediatric patients and further analyzed by the next-generation sequencing approach. Bioinformatic analysis was done using an "in-house" gene list panel, which included 144 genes related to pediatric brain tumors, and the gene list panel Neoplasm (HP:0002664). Our study found that 27% of pediatric patients with CNS tumors have a germline variant in some of the known CPGs, like ALK, APC, CHEK2, ELP1, MLH1, MSH2, NF1, NF2 and TP53. This study represents the first comprehensive evaluation of germline variants in pediatric patients with CNS tumors in the Western Balkans region. Our results indicate the necessity of genomic research to reveal the genetic basis of pediatric CNS tumors, as well as to define targets for the application and development of innovative therapeutics that form the basis of the upcoming era of personalized medicine.

Dual specificity phosphatase (DUSP)-4 is induced by platelet-derived growth factor -BB in an Erk1/2-, STAT3- and p53-dependent manner

Dual specificity phosphatase (DUSP) 4 has been described as a negative regulator of MAP kinase signaling, in particular for the ERK1/2 and JNK pathways. We found that DUSP4 expression was upregulated in response to prolonged platelet-derived growth factor (PDGF)-BB stimulation. The PDGF-BB-induced DUSP4 expression was dependent on ERK1/2, STAT3 and p53. We found that inhibition of ERK1/2 effectively reduced DUSP4 mRNA levels, whereas STAT3 was necessary for maintaining p53 expression. p53 has binding sites in the DUSP4 promoter and was found to promote DUSP4 expression.

Use of synchrotron medical microbeam irradiation to investigate radiation-induced bystander and abscopal effects in vivo

The question of whether bystander and abscopal effects are the same is unclear. Our experimental system enables us to address this question by allowing irradiated organisms to partner with unexposed individuals. Organs from both animals and appropriate sham and scatter dose controls are tested for expression of several endpoints such as calcium flux, role of 5HT, reporter assay cell death and proteomic profile. The results show that membrane related functions of calcium and 5HT are critical for true bystander effect expression. Our original inter-animal experiments used fish species whole body irradiated with low doses of X-rays, which prevented us from addressing the abscopal effect question. Data which are much more relevant in radiotherapy are now available for rats which received high dose local irradiation to the implanted right brain glioma. The data were generated using quasi-parallel microbeams at the biomedical beamline at the European Synchrotron Radiation Facility in Grenoble France. This means we can directly compare abscopal and "true" bystander effects in a rodent tumour model. Analysis of right brain hemisphere, left brain and urinary bladder in the directly irradiated animals and their unirradiated partners strongly suggests that bystander effects (in partner animals) are not the same as abscopal effects (in the irradiated animal). Furthermore, the presence of a tumour in the right brain alters the magnitude of both abscopal and bystander effects in the tissues from the directly irradiated animal and in the unirradiated partners which did not contain tumours, meaning the type of signal was different.

IPH-926 lobular breast cancer cells harbor a p53 mutant with temperature-sensitive functional activity and allow for profiling of p53-responsive genes

Profiling of p53-responsive genes has been carried out in different cellular models, most of which involved genetic modifications or cytotoxic stimulation. We report on the utilization of IPH-926 human lobular breast cancer cells for the profiling of p53-responsive genes using a novel approach without such modifications. We discovered that IPH-926 cells harbor a homozygous TP53 missense mutation encoding for a rare p53 mutant (E285K) with temperature-sensitive (ts) loss of function characteristics. This mutation had evolved as a late, secondary genetic event during the natural clonal evolution of the corresponding lobular carcinoma. In vitro temperature shifts reconstituted endogenous wild-type p53 activity in IPH-926, as evidenced by induction of p21(Waf1). Transcriptional alterations associated with restored p53 function were profiled using Affymetrix microarrays and a new strategy to gate out non-specific temperature effects. At the P=0.0005 significance level, 60 genes were differentially expressed following reconstitution of p53 activity. These genes included CDKN1A, MDM2 and PHLDA3, a recently described p53-inducible inhibitor of AKT. Similar transcriptional alterations were observed upon reconstitution of p53 activity in BT-474 cells, which also harbor ts-p53 E285K, and in ASPC1 cells transduced with ts-p53 A138V. Consistent with these models, low PHLDA3 expression was associated with nuclear p53 accumulation, indicative of deleterious TP53 mutations, in primary breast cancers. From a molecular point of view, IPH-926 thus provides a new tool to study transcriptional programs controlled by p53. From a tumor pathology perspective, IPH-926 also provides the first direct evidence of a p53-related clonal evolutionary pathway in lobular breast cancer progression.

Novel Perspectives on p53 Function in Neural Stem Cells and Brain Tumors

Malignant glioma is the most common brain tumor in adults and is associated with a very poor prognosis. Mutations in the p53 tumor suppressor gene are frequently detected in gliomas. p53 is well-known for its ability to induce cell cycle arrest, apoptosis, senescence, or differentiation following cellular stress. That the guardian of the genome also controls stem cell self-renewal and suppresses pluripotency adds a novel level of complexity to p53. Exactly how p53 works in order to prevent malignant transformation of cells in the central nervous system remains unclear, and despite being one of the most studied proteins, there is a need to acquire further knowledge about p53 in neural stem cells. Importantly, the characterization of glioma cells with stem-like properties, also known as brain tumor stem cells, has opened up for the development of novel targeted therapies. Here, we give an overview of what is currently known about p53 in brain tumors and neural stem cells. Specifically, we review the literature regarding transformation of adult neural stem cells and, we discuss how the loss of p53 and deregulation of growth factor signaling pathways, such as increased PDGF signaling, lead to brain tumor development. Reactivation of p53 in brain tumor stem cell populations in combination with current treatments for glioma should be further explored and may become a viable future therapeutic approach.

The DU145 human prostate carcinoma cell line harbors a temperature-sensitive allele of p53

BACKGROUND

Some nuances of mutant and wild-type p53 activity have been uncovered utilizing temperature sensitive (TS) alleles. However, few human tumor derived cell lines possess a TS p53 mutant.

METHODS

The cell lines DU145 (heterozygous p53, P223L, and V274F) and PC3 (p53-null, where exogenous P223L and V274F were introduced individually or in combination) were examined for TS p53 activity as revealed by reporter construct and target gene activation.

RESULTS

TS p53 function was observed in DU145 and expression of the P223L allele in PC3 conferred a TS p53 profile. Activation of p21Waf1 demonstrated that P223L TS activity may have been influenced by cellular context.

CONCLUSIONS

The DU145 cell line harbors a TS mutant of p53 and, in addition to being a widely used model of human prostate carcinoma, may also reveal new insights into p53 function due to the unique transcriptional properties of its TS phenotype.

RB and RB2/p130 genes demonstrate both specific and overlapping functions during the early steps of in vitro neural differentiation of marrow stromal stem cells

Marrow stromal stem cells (MSCs) are stem-like cells that are currently being tested for their potential use in cell therapy for a number of human diseases. MSCs can differentiate into both mesenchymal and nonmesenchymal lineages. In fact, in addition to bone, cartilage and fat, it has been demonstrated that MSCs are capable of differentiating into neurons and astrocytes. RB and RB2/p130 genes are involved in the differentiation of several systems. For this reason, we evaluated the role of RB and RB2/p130 in the differentiation and apoptosis of MSCs under experimental conditions that allow for MSC differentiation toward the neuron-like phenotype. To this end, we ectopically expressed either RB or RB2/p130 and monitored proliferation, differentiation and apoptosis in rat primary MSC cultures induced to differentiate toward the neuron-like phenotype. Both RB and RB2/P130 decreased cell proliferation rate. In pRb-overexpressing cells, the arrest of cell growth was also observed in the presence of the HDAC-inhibitor TSA, suggesting that its antiproliferative activity does not rely upon the HDAC pathway, while the addition of TSA to pRb2/p130-overexpressing cells relieved growth inhibition. TUNEL reactions and studies on the expression of genes belonging to the Bcl-2 family showed that while RB protected differentiating MSCs from apoptosis, RB2/p130 induced an increase of apoptosis compared to controls. The effects of both RB and RB2/p130 on programmed cell death appeared to be HDAC- independent. Molecular analysis of neural differentiation markers and immunocytochemistry revealed that RB2/p130 contributes mainly to the induction of generic neural properties and RB triggers cholinergic differentiation. Moreover, the differentiation potentials of RB2/p130 and RB appear to rely, at least in part, on the activity of HDACs.

TRAIL triggers apoptosis in human malignant glioma cells through extrinsic and intrinsic pathways

Many malignant glioma cells express death receptors for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), yet some of these cells are resistant to TRAIL. Here, we examined signaling events in TRAIL-induced apoptosis and searched for therapeutic agents that could overcome TRAIL resistance in glioma cells. TRAIL induced apoptosis through death receptor 5 (DR5) and was mediated by caspase-8-initiated extrinsic and intrinsic mitochondrial pathways in sensitive glioma cell lines. TRAIL also triggered apoptosis in resistant glioma cell lines through the same pathways, but only if the cells were pretreated with chemotherapeutic agents, cisplatin, camptothecin and etoposide. Previous studies suggested that this was due to an increase in DR5 expression in wild-type TP53 cells, but this mechanism did not account for cells with mutant TP53. Here, we show that a more general effect of these agents is to downregulate caspase-8 inhibitor c-FLIP(S) (the short form of cellular Fas-associated death domain-fike interleukin-1-converting enzyme-inhibitory protein) and up-regulate Bak, a pro-apoptotic Bcl-2 family member, independently of cell's TP53 status. Furthermore, we showed that TRAIL alone or in combination with chemotherapeutic agents, induced apoptosis in primary tumor cultures from patients with malignant gliomas, reinforcing the potential of TRAIL as an effective therapeutic agent for malignant gliomas.

Migration and differentiation of nuclear fluorescence-labeled bone marrow stromal cells after transplantation into cerebral infarct and spinal cord injury in mice

There is increasing evidence that bone marrow stromal cells (BMSC) have the potential to migrate into the injured neural tissue and to differentiate into the CNS cells, indicating the possibility of autograft transplantation therapy. The present study was aimed to clarify whether the mouse BMSC can migrate into the lesion and differentiate into the CNS cells when transplanted into the mice subjected to focal cerebral infarct or spinal cord injury. The BMSC were harvested from mice and characterized by flow cytometry. Then, the BMSC were labeled by bis-benzimide, a nuclear fluorescence dye, over 24 h, and were stereotactically transplanted into the brain or spinal cord of the mice. The cultured BMSC expressed low levels of CD45 and high levels of CD90 and Sca-1 on flow cytometry. A large number of grafted cells survived in the normal brain 4 weeks after transplantation, many of which were located close to the transplanted sites. They expressed the neuronal marker including NeuN, MAP2, and doublecortin on fluorescent immunohistochemistry. However, when the BMSC were transplanted into the ipsilateral striatum of the mice subjected to middle cerebral artery occlusion, many of the grafted cells migrated into the corpus callosum and injured cortex, and also expressed the neuronal markers 4 weeks after transplantation. In particular, NeuN was very useful to validate the differentiation of the grafted cells, because the marker was expressed in the nuclei and was overlapped with bis-benzimide. Similar results were obtained in the mice subjected to spinal cord injury. However, many of the transplanted BMSC expressed GFAP, an astrocytic protein, in injured spinal cord. The present results indicate that the mouse BMSC can migrate into the CNS lesion and differentiate into the neurons or astrocytes, and that bis-benzimide is a simple and useful marker to label the donor cells and to evaluate their migration and differentiation in the host neural tissues over a long period.

Isolation of temperature-sensitive p53 mutations from a comprehensive missense mutation library

Temperature-sensitive (ts) mutations have been used as a genetic and molecular tool to study the functions of many gene products. Each ts mutant protein may contain a temperature-dependent intramolecular mechanism such as ts conformational change. To identify key ts structural elements controlling the protein function, we screened ts p53 mutants from a comprehensive mutation library consisting of 2,314 p53 missense mutations for their sequence-specific transactivity through p53-binding sequences in Saccharomyces cerevisiae. We isolated 142 ts p53 mutants, including 131 unreported ts mutants. These mutants clustered in beta-strands in the DNA-binding domain, particularly in one of the two beta-sheets of the protein, and 15 residues (Thr155, Arg158, Met160, Ala161, Val172, His214, Ser215, Pro223, Thr231, Thr253, Ile254, Thr256, Ser269, Glu271, and Glu285) were ts hot spots. Among the 142 mutants, 54 were examined further in human osteosarcoma Saos-2 cells, and it was confirmed that 89% of the mutants were also ts in mammalian cells. The ts mutants represented distinct ts transactivities for the p53 binding sequences and a distinct epitope expression pattern for conformation-specific anti-p53 antibodies. These results indicated that the intramolecular beta-sheet in the core DNA-binding domain of p53 was a key structural element controlling the protein function and provided a clue for finding a molecular mechanism that enables the rescue of the mutant p53 function.

Brain angiogenesis inhibitor 1 is differentially expressed in normal brain and glioblastoma independently of p53 expression

Brain angiogenesis inhibitors (BAI) are putative transmembrane proteins containing an extracellular domain with thrombospondin type-1 repeats which can exhibit anti-angiogenic activity. BAI1 mRNA is expressed mainly in the brain, while BAI2 and BAI3 mRNAs are more widely expressed. We hypothesized that the BAI family might have anti-tumoral properties and studied the expression of BAI1 protein in normal human brain and in glioblastoma multiforme. We generated an anti-BAI1 antibody and showed that BAI1 was widely expressed in normal brain but was absent in 28 glioma cell lines and in the majority of human glioblastoma investigated. BAI1 expression did not correlate with TP53 status and we did not confirm previous findings that p53 regulates BAI1 mRNA expression in glioma cells. The finding that expression of BAI proteins may be lost during tumor formation is of special interest as restoration of their function in tumors may be of therapeutic benefit.

Tumor suppressor p53 mediates apoptotic cell death triggered by cyclosporin A

The tumor suppressor p53 can induce growth arrest and cell death via apoptosis in response to a number of cellular stresses. We have shown previously that the immunosuppressant cyclosporin A (CsA) induces programmed cell death with typical features of apoptosis in rat glioma cells. We report that CsA treatment results in increased level of the p53 tumor suppressor, its nuclear accumulation, and transcriptional activation of p53-dependent genes. The increase of p53 correlates with the elevation of p21(Waf1) and Bax protein expression. The increased level of Bax protein was accompanied with changes in its subcellular localization and association with mitochondria. Importantly, we demonstrate that glioma cells stably transfected with a mutant p53 (p53Val135) fail to increase p21 and Bax protein levels and are less sensitive to CsA-induced apoptosis. Furthermore, primary fibroblasts from p53-/- knockout mice are significantly more resistant to CsA-induced apoptosis compared with their corresponding counterparts containing functional p53. Together, our results suggest that the apoptotic program activated by CsA can be mediated by activation of p53 tumor suppressor and potentiation of its ability to initiate apoptosis.