Ella Kim - Academia.edu (original) (raw)

Papers by Ella Kim

Oncogene, 2007

Since the very early days of p53 research, the gain of oncogenic activities by some mutant p53 pr... more Since the very early days of p53 research, the gain of oncogenic activities by some mutant p53 proteins had been suspected as an important factor contributing to cancer progression. Considerable progress towards understanding the biology of mutant p53 has been made during the last years, the quintessence being the realization that the impact of mutant p53 proteins on the transcriptome of a tumor cell is much more global than previously thought. The emerging role of mutant p53 proteins in coordinating oncogenic signaling and chromatin modifying activities reveals an until now unsuspected function of these proteins as important modifiers of the oncogenic transcriptional response. Notwithstanding the fact that the sequencespecific DNA binding activity of mutant p53 proteins is impaired, they are still able to associate with specific loci on DNA by utilizing different mechanisms. The ability to associate with DNA appears to be crucial for the master role of mutant p53 proteins in coordinating oncogenic transcriptional responses.

Acta Neurochirurgica, 2004

Previous studies have demonstrated that inhibitors of the arachidonic acid metabolism block migra... more Previous studies have demonstrated that inhibitors of the arachidonic acid metabolism block migration and sensitise human glioma cells to treatment inducing apoptosis. This paradigm may provide a new concept for anti-invasive treatment strategies targeting invasive glioma cells. However, the effect of such treatment on other cellular elements in glial tumours such as endothelial cells is unknown. In this study we have analysed the expression of metabolites of the arachidonic acid pathway in endothelial cells in vitro and in vivo and we have assessed the influence of inhibitors of this pathway on motility, capillary like tube formation, and apoptosis in human endothelial cells. Human endothelial cells (HUVEC) in culture showed expression for thromboxane synthase and both isoforms of cyclo-oxygenase, COX-1 and COX-2. Immunostaining demonstrated low levels of COX-1 expression in capillaries and larger vessels of normal brain and moderately elevated levels of this enzyme in small vessels of brain tumours of various grades. Both thromboxane synthase and COX-2 expression was limited to endothelial cells found in anaplastic gliomas and glioblastomas. Thromboxane synthase inhibitors strongly decreased endothelial cell migration in HUVEC in vitro and capillary like tube formation was strongly inhibited by the compound at a similar dose range. The non-selective cyclo-oxygenase inhibitor ASA and the selective COX-2 inhibitor sulindac only had a minor effect on endothelial cell migration, however, the COX-2 inhibitor sulindac showed a synergistic effect with the thromboxane synthase inhibitor. Thromboxane synthase inhibitors induced apoptosis in endothelial cells as demonstrated by intracellular histone-complexed DNA fragmentation. These data suggest that inhibitors of thromboxane synthase influence migration and apoptosis in both human glioma cells and human endothelial cells. An anti-invasive treatment strategy using this class of compounds may therefore not only sensitise glioma cells to conventional treatments inducing apoptosis but may also be supported by an anti-angiogenic effect.

Cell Death and Differentiation, 2008

Journal of Biological Chemistry, 2002

Transcriptional activation of p53-regulated genes is initiated by sequence-specific DNA binding o... more Transcriptional activation of p53-regulated genes is initiated by sequence-specific DNA binding of p53 to target binding sites. Regulation of sequence-specific DNA binding is complex and occurs at various levels. We demonstrate that DNA topology is an important parameter for regulating the selective and highly specific interaction of p53 with its target binding sites. Specific binding of wild-type p53 is greatly enhanced when cognate binding sites are present in a non-linear stem-loop conformation. The C-terminal domain plays a key role in regulating the specific interactions of p53 with target binding sites in a DNA conformation-dependent manner. The C-terminal domain is required for binding to target sites in a non-linear DNA conformation in contrast to the strong inhibitory effects of the C terminus on p53 interaction with linear DNA. We propose that selective binding of p53 to various promoters may be determined by the DNA conformation within p53 cognate sites.

Nucleic Acids Research - NAR, 2005

Despite the loss of sequence-specific DNA binding, mutant p53 (mutp53) proteins can induce or rep... more Despite the loss of sequence-specific DNA binding, mutant p53 (mutp53) proteins can induce or repress transcription of mutp53-specific target genes. To date, the molecular basis for transcriptional modulation by mutp53 is not understood, but increasing evidence points to the possibility that specific interactions of mutp53 with DNA play an important role. So far, the lack of a common denominator for mutp53 DNA binding, i.e. the existence of common sequence elements, has hampered further characterization of mutp53 DNA binding. Emanating from our previous discovery that DNA structure is an important determinant of wildtype p53 (wtp53) DNA binding, we analyzed the binding of various mutp53 proteins to oligonucleotides mimicking non-B DNA structures. Using various DNA-binding assays we show that mutp53 proteins bind selectively and with high affinity to non-B DNA. In contrast to sequence-specific and DNA structuredependent binding of wtp53, mutp53 DNA binding to non-B DNA is solely dependent on the stereo-specific configuration of the DNA, and not on DNA sequence. We propose that DNA structure-selective binding of mutp53 proteins is the basis for the well-documented interaction of mutp53 with MAR elements and for transcriptional activities mediates by mutp53.

Oncogene, 2005

Sequence-specific DNA binding is a major activity of the tumor suppressor p53 and a prerequisite ... more Sequence-specific DNA binding is a major activity of the tumor suppressor p53 and a prerequisite for the transactivating potential of the protein. p53 interaction with target DNA is tightly regulated by various mechanisms, including binding of different components of the transcription machinery, post-translational modifications, and interactions with other factors that modulate p53 transactivation in a cell context-and promoter-specific manner. The bifunctional redox factor 1 (Ref-1/APE1) has been identified as one of the factors, which can stimulate p53 DNA binding by redox-dependent as well as redoxindependent mechanisms. Whereas stimulation of p53 DNA binding by the redox activities of Ref-1 is understood quite well, little is known about mechanisms that underlie the redox-independent effects of Ref-1. We report in this study a previously unknown activity of Ref-1 as a factor promoting tetramerization of p53. We demonstrate that Ref-1 promotes association of dimers into tetramers, and de-stacking of higher oligomeric forms into the tetrameric form in vitro, thereby enhancing p53 binding to target DNA.

Oncogene, 1997

Sequence-speci®c transactivation of target genes is one of the most important molecular propertie... more Sequence-speci®c transactivation of target genes is one of the most important molecular properties of the tumor suppressor p53. Binding of p53 to its target DNAs is tightly regulated, with modi®cations in the carboxyterminal regulatory domain of the p53 protein playing an important role. In this study we examined the possible in¯uence of DNA structure on sequence-speci®c DNA binding by p53, by analysing its binding to p53 consensus elements adopting dierent conformations. We found that p53 has the ability to bind to consensus elements which are present in a double-helical form, as well as to consensus elements which are located within alternative non-B-DNA structures. The ability of a consensus element to adopt either one of these conformations is dependent on its sequence symmetry, and is strongly in¯uenced by its sequence environment. Our data suggest a model according to which the conformational status of the target DNA is an important determinant for sequence-speci®c DNA binding by p53. Modi®cations in the carboxy-terminal regulatory region of p53 possibly determine the preference of p53 for a given DNA conformation.

Oncogene, 2003

Cancer formation and progression is a complex process determined by several mechanisms that promo... more Cancer formation and progression is a complex process determined by several mechanisms that promote cell growth, invasiveness, neo-angiogenesis, and render neoplastic cells resistant to apoptosis. The tumor suppressor p53 and the proto-oncogenic factor ets-1 are important regulators of such mechanisms. While it is well established that p53 and ets-1 influence various aspects of cell behavior by regulating the transcription of specific genes, little is known about the functional relationship between these transcription factors. We found that the gene encoding thromboxane synthase (TXSA), which we recently identified as a factor promoting invasion and resistance to apoptosis in gliomas, is a novel target gene for both p53 and ets-1. We demonstrate that p53 and ets-1 coregulate TXSA in an antagonistic and interrelated manner, with ets-1 being a potent transcriptional activator and p53 inhibiting ets-1-dependent transcription. Negative interference with ets-1 transcription requires functional p53 and is lost in mutant p53 proteins. We show that ets-1 and p53 associate physically in vitro and in vivo and that their interaction, rather than a direct binding of p53 to the TXSA promoter, is required for transcriptional repression of TXSA by wild-type p53. An important implication of our findings is that the loss of p53-mediated negative control over ets-1-dependent transcription may lead to the acquisition of an invasive phenotype in tumor cells.

Oncogene, 1999

promote or prohibit sequence speci®c DNA binding of p53, are an important feature in orchestratin... more promote or prohibit sequence speci®c DNA binding of p53, are an important feature in orchestrating the activation of dierent p53 responsive promoters.

Neuro-Oncology, 1999

The capacity of glial tumor cells to migrate and diffusely in ltrate normal brain compromises sur... more The capacity of glial tumor cells to migrate and diffusely in ltrate normal brain compromises surgical eradication of the disease. Identi cation of genes associated with invasion may offer novel strategies for anti-invasive therapies. The gene for TXsyn, an enzyme of the arachidonic acid pathway, has been identi ed by differential mRNA display as being overexpressed in a glioma cell line selected for migration. In this study TXsyn mRNA expression was found in a large panel of glioma cell lines but not in a strain of human astrocytes. Immunohistochemistry demonstrated TXsyn in the parenchyma of glial tumors and in reactive astrocytes, whereas it could not be detected in quiescent astrocytes and oligodendroglia of normal brain. Glioma cell lines showed a wide range of thromboxane B 2 formation, the relative expression of which correlated with migration rates of these cells. Migration was effectively blocked by speci c inhibitors of TXsyn, such as furegrelate and dazmegrel. Other TXsyn inhibitors and cyclooxygenase inhibitors were less effective. Treatment with speci c inhibitors also resulted in a decrease of intercellular adhesion in glioma cells. These data indicate that TXsyn plays a crucial role in the signal transduction of migration in glial tumors and may offer a novel strategy for anti-invasive therapies.

Journal of Neuropathology & Experimental Neurology, 2013

Glioma-initiating cells (GICs) represent a potential important therapeutic target because they ar... more Glioma-initiating cells (GICs) represent a potential important therapeutic target because they are likely to account for the frequent recurrence of malignant gliomas; however, their identity remains unsolved. Here, we characterized the cellular lineage fingerprint of GICs through a combination of electrophysiology, lineage marker expression, and differentiation assays of 5 human patient-derived primary GIC lines. Most GICs coexpressed nestin, NG2 proteoglycan, platelet-derived growth factor receptor->, and glial fibrillary acidic protein. Glioma-initiating cells could be partially differentiated into astrocytic but not oligodendroglial or neural lineages. We also demonstrate that GICs have a characteristic electrophysiologic profile distinct from that of well-characterized tumor bulk cells. Together, our results suggest that GICs represent a unique type of cells reminiscent of an immature phenotype that closely resembles but is not identical to NG2 glia with respect to marker expression and functional membrane properties. FIGURE 3. The differentiation potential of glioma-initiating cells (GICs) is restricted to the astroglial lineage. (A) Percentage of glioma cells with marked glial fibrillary acidic protein (GFAP) expression (GFAP + ) in response to distinct differentiation stimuli: modified SATO medium (mSATO), ciliary neurotrophic factor (CNTF), forskolin (FORS), or fetal calf serum (FCS). Cells grown in neurobasal medium (NB) were used as a control (one-way ANOVA with Dunnet test, n Q 3 independent experiments). (B) Glial fibrillary acidic protein immunofluorescence of GICs. Glial fibrillary acidic protein expression increases, and the morphology changes in response to FCS (middle row) and on growth factor removal (lower row) as compared with the control condition (NB, upper row). Scale bar = 40 Km.

Journal of Neuro-Oncology, 2009

The invasion-and apoptosis-associated thromboxane synthase gene encoding an enzyme of the arachid... more The invasion-and apoptosis-associated thromboxane synthase gene encoding an enzyme of the arachidonic acid pathway has been implicated in glioma progression. Furegrelate, a specific inhibitor of thromboxane synthase, blocks cell motility, induces apoptosis and increases sensitivity to drug induced apoptosis in human glioma cells in vitro. The impact of furegrelate on the sensitivity of human glioma cells to c-irradiation was analyzed using colony formation assay in vitro and an orthotopic mouse model in vivo. Pre-treatment of glioma cells with furegrelate increases radiation sensitivity of cultured glioma cells. Treatment of experimental gliomas with suboptimal doses of radiation and furegrelate results in a significant decrease in tumor volumes compared to untreated controls. Thus, the specific thromboxane synthase inhibitor furegrelate increases death response induced by c-radiation in glioma cells in vitro and sensitizes experimental gliomas to radiation treatment in vivo.

Journal of Neurochemistry, 2002

The c/s elements mediating activation of the tyrosine hydroxylase gene by angiotensin II were exa... more The c/s elements mediating activation of the tyrosine hydroxylase gene by angiotensin II were examined by transfecting tyrosine hydroxylase promoter-luciferase constructs into cultured bovine adrenal medullary cells. Angiotensin li-responsive elements are located within -54/+25-bp and -269/-55-bp promoter regions and were identified, respectively, as cyclic AMP (ORE)and 1 2-O-tetradecanoylphorbol 1 3-acetate responsive element (TRE)-like sequences. Unlike ORE, TRE also supports basal promoter activity. Mutations of TRE or ORE that reduced angiotensin II stimulation abolished in vitro binding of nuclear proteins to those elements, suggesting that proteins forming ORE-and TRE-inducible complexes may mediate angiotensin II stimulation. The TRE is adjacent to a dyad symmetry element. Those two sites form a common regulatory unit in which the dyad symmetry element acts as a repressor of the TRE site. Isolated dyad symmetry element did not bind nuclear proteins in vitro. In supercoiled DNA it exhibited Si nuclease sensitivity and was recognized by a DNA cruciform-specific antibody consistent with the extrusion of a cruciform structure that overlaps with the TRE. A mutation that abolished formation of the cruciform correlated with a loss of repressor activity. We propose a novel model of tyrosine hydroxylase gene regulation in which functions of the TRE are modulated via structural transition in the adjacent DNA.

International Journal of Radiation Oncology*Biology*Physics, 2008

Purpose: Despite beneficial effects of irradiation/chemotherapy on survival of glioblastoma (GBM)... more Purpose: Despite beneficial effects of irradiation/chemotherapy on survival of glioblastoma (GBM) patients, collateral damage to intact neural tissue leads to ''radiochemobrain'' and reduced quality of life in survivors. For prophylactic neuroprotection, erythropoietin (EPO) is a promising candidate, provided that concerns regarding potential tumor promoting effects are alleviated. Methods and Materials: Human GBM-derived cell lines U87, G44, G112, and the gliosarcoma-derived line G28 were treated with EPO, with and without combinations of irradiation or temozolomide (TMZ). Responsiveness of glioma cells to EPO was measured by cell migration from spheroids, cell proliferation, and clonogenic survival. Implantation of U87 cells into brains of nude mice, followed 5 days later by EPO treatment (5,000 U/kg intraperitoneal every other day for 2 weeks) should reveal effects of EPO on tumor growth in vivo. Reverse transcriptasepolymerase chain reaction was performed for EPOR, HIF-1a, and epidermal growth factor receptor (EGFR)vIII in cell lines and 22 human GBM specimens. Results: EPO did not modulate basal glioma cell migration and stimulated proliferation in only one of four cell lines. Importantly, EPO did not enhance tumor growth in mouse brains. Preincubation of glioma cells with EPO for 3 h, followed by irradiation and TMZ for another 24 h, resulted in protection against chemoradiationinduced cytotoxicity in three cell lines. Conversely, EPO induced a dose-dependent decrease in survival of G28 gliosarcoma cells. In GBM specimens, expression of HIF-1a correlated positively with expression of EPOR and EGFRvIII. EPOR and EGFRvIII expression did not correlate. Conclusions: EPO is unlikely to appreciably influence basal glioma growth. However, concomitant use of EPO with irradiation/chemotherapy in GBM patients is not advisable. Ó

FEBS Letters, 1989

An S-adenosyl-L-methionine:DNA-methyltransferase, termed M. hd, was purified from Bacillus natto ... more An S-adenosyl-L-methionine:DNA-methyltransferase, termed M. hd, was purified from Bacillus natto B3364 strain by successive column chromatography. The molecular weight determined by gel liltration was 37 kDa for M. BnaI. Analysis of methyltransferase by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed correspondence of the M.BnaI activity with one protein band at a molecular weight of 35 kDa. Sequencing of pUCl9 DNA methylated with M.&a1 showed the cytosine-5 methylation in the BnaI recognition sequence GGAT]CC at the position indicated by the arrow.

Journal of Cellular …, 2000

Mutant p53 not simply is an inactivated tumor suppressor, as at least some mutant p53 proteins ex... more Mutant p53 not simply is an inactivated tumor suppressor, as at least some mutant p53 proteins exhibit oncogenic properties. Mutant p53 thus is the most commonly expressed oncogene in human cancer. Accordingly, the expression of mutant p53 in tumors often correlates with bad prognosis, and expression of mutant p53 in p53-negative tumor cells enhances their transformed phenotype. The molecular basis for this "gain of function" is not yet understood. However, the finding that mutant p53 tightly associates with the nuclear matrix in vivo, and with high affinity binds to nuclear matrix attachment region (MAR) DNA in vitro, suggests that these activities are connected and may result in perturbation of nuclear structure and function in tumor cells. MAR-binding of mutant p53 most likely is due to conformation-selective DNA binding by mutant p53, i.e. the specific interaction of a given mutant p53 protein with regulatory or structural genomic DNA elements that are able to adopt specific non-B-DNA conformations. In support to this assumption, human mutant p53 (Gly(245)-->Ser) was shown to bind to repetitive DNA elements in vivo that might be part of MAR elements. This further supports a model according to which mutant p53, by interacting with key structural components of the nucleus, exerts its oncogenic activities through perturbation of nuclear structure and function. J. Cell. Biochem. Suppl. 35:115-122, 2000.

Biochemistry and Cell Biology, 2003

The most import biological function of the tumor suppressor p53 is that of a sequence-specific tr... more The most import biological function of the tumor suppressor p53 is that of a sequence-specific transactivator. In response to a variety of cellular stress stimuli, p53 induces the transcription of an ever-increasing number of target genes, leading to growth arrest and repair, or to apoptosis. Long considered as a &amp;amp;amp;quot;latent&amp;amp;amp;quot; DNA binder that requires prior activation by C-terminal modification, recent data provide strong evidence that the DNA binding activity of p53 is strongly dependent on structural features within the target DNA and is latent only if the target DNA lacks a certain structural signal code. In this review we discuss evidence for complex interactions of p53 with DNA, which are strongly dependent on the dynamics of DNA structure, especially in the context of chromatin. We provide a model of how this complexity may serve to achieve selectivity of target gene regulation by p53 and how DNA structure in the context of chromatin may serve to modulate p53 functions.

Biochemical Pharmacology, 2009

W. Deppert). Abbreviations: wtp53, wild-type p53; mutp53, mutant p53; CNS, central nervous system... more W. Deppert). Abbreviations: wtp53, wild-type p53; mutp53, mutant p53; CNS, central nervous system; BTISC, brain tumor initiating stem-like cells; GBM, glioblastoma multiforme; ClQ, chloroquine. a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / b i o c h e m p h a r m 0006-2952/$ -see front matter #

Analytical Biochemistry, 2013