PubMed İndeksli Yayınlar Koleksiyonu / PubMed Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7645
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Article Citation - WoS: 37Mechanisms of Cellular Resistance To Imatinib in Human Chronic Myeloid Leukemia Cells(Taylor and Francis Ltd., 2007) Baran, Yusuf; Ural, Ali Uğur; Gündüz, UfukA major advancement in the treatment of chronic myeloid leukemia (CML) has been the development of imatinib, which has shown striking activity in the chronic phase and the accelerated phase, but less so in the blast phase of the disease. Despite high rates of hematologic and cytogenetic responses to therapy, the emergence of resistance to imatinib has been recognized as a major problem in the treatment of patients with CML. Various cellular mechanisms may be involved in the nature of cellular resistance. Increased amount of target, alteration in structure of target proteins, decreased drug uptake and increased detoxification are well-known mechanisms of resistance. On the other hand, in some cases, even if anticancer drugs reach their sites of action, bypassing drug efflux system of the cells, some cells still may survive via the dysregulation of apoptotic signalling. In this study, mechanisms of resistance to imatinib-induced apoptosis in human Meg-01 CML cells were examined. Continuous exposure of cells to step-wise increasing concentrations of imatinib resulted in the selection of 200- and 1000 nM imatinib-resistant sub-lines referred to as Meg-01/IMA-0,2 and Meg-01/1MA-1, respectively. MTT cell proliferation, cell cycle analyses and trypan blue dye exclusion analyses showed that Meg-0l/IMA-1 cells were resistant to imatinib-induced apoptosis as compared to parental sensitive cells. There was an increased expression of BCR/ABL, Bcl-2 and an increase in mitochondrial membrane potential (MMP) detected in resistant cells comparing to parental sensitive cells. There was no mutation detected in imatinib binding site of ABL kinase region. Various diverse mechanisms have been reported for their involvement in the multidrug resistance. In this study, it has been shown that the degree of BCR/ABL expression appears to be directly proportional to the levels of imatinib resistance. In addition, there have been BCR/ABL-independent mechanisms reported for deriving resistance against imatinib. Our results revealed that besides BCR/ABL overexpression, imatinib resistance also depends on the inhibition of apoptosis as a result of up-regulation of anti-apoptotic stimuli and down-regulation of pro-apoptotic stimuli through MMP but does not depend on any mutation on imatinib binding site of ABL kinase.Article Citation - WoS: 16Citation - Scopus: 16Multidrug Resistance Mediated by Mrp1 Gene Overexpression in Breast Cancer Patients(Taylor and Francis Ltd., 2009) Abaan, Ogan Demir; Mutlu, Pelin Kaya; Baran, Yusuf; Atalay, Can; Gündüz, UfukMultidrug resistance (MDR) is a serious handicap towards the effective treatment of breast cancer patients. One of the most prevalent MDR mechanisms is through the overexpression of genes coding the proteins called Multidrug Resistance-associated Proteins (MRPs). The aim of this study was to investigate the expression of MRP1 in tumor tissues from breast cancer patients. In this study, a semi-quantitative RT-PCR approach was utilized. Our results suggest that MRP1 overexpression can mediate MDR in patients. Pre-evaluation of the level of such MDR mediators before chemotherapy can increase the efficacy of the treatment.Article Citation - WoS: 6Citation - Scopus: 6Docetaxel Enhances the Cytotoxic Effects of Imatinib on Philadelphia Positive Human Chronic Myeloid Leukemia Cells(Taylor and Francis Ltd., 2009) Güçlüler, Gözde; Baran, YusufChronic myelogenous leukemia (CML) results from a translocation between chromosomes 9 and 22 which generates BCR/ABL fusion protein and characterized by uncontrolled proliferation of immature white blood cells. Imatinib, a molecularly targeting anticancer agent, is used widely for the treatment of CML and showed significant activity in chronic and accelerated phases but much less in blast crisis phase. The resistance to imatinib especially in blast crisis phase is recognized as a major problem in the treatment of CML patients. Docetaxel is shown to arrest cells in G2/M phase of the cell cycle which makes cells more sensitive to chemo- and radiotherapy. In this study, we aimed to increase chemosensitivity of human K562 CML cells to imatinib in combination with docetaxel. Taken together, our results showed that the combination of imatinib and docetaxel decreased cellular proliferation and increased apoptosis in human K562 chronic myeloid leukemia cells as compared to any agent alone. Imatinib and docetaxel induced apoptosis through caspase-3 enzyme activity and mitochondrial membrane potential.Article Citation - WoS: 55Citation - Scopus: 64Identification of a Novel System for Boron Transport: Atr1 Is a Main Boron Exporter in Yeast(American Society for Microbiology, 2009) Kaya, Alaattin; Karakaya, Hüseyin Çağlar; Fomenko, Dmitri E.; Gladyshev, Vadim N.; Koç, AhmetBoron is a micronutrient in plants and animals, but its specific roles in cellular processes are not known. To understand boron transport and functions, we screened a yeast genomic DNA library for genes that confer resistance to the element in Saccharomyces cerevisiae. Thirty boron-resistant transformants were isolated, and they all contained the ATR1 (YML116w) gene. Atr1 is a multidrug resistance transport protein belonging to the major facilitator superfamily. C-terminal green fluorescent protein-tagged Atr1 localized to the cell membrane and vacuole, and ATR1 gene expression was upregulated by boron and several stress conditions. We found that atr1△ mutants were highly sensitive to boron treatment, whereas cells overexpressing ATR1 were boron resistant. In addition, atr1△ cells accumulated boron, whereas ATR1-overexpressing cells had low intracellular levels of the element. Furthermore, atr1△ cells showed stronger boron-dependent phenotypes than mutants deficient in genes previously reported to be implicated in boron metabolism. ATR1 is widely distributed in bacteria, archaea, and lower eukaryotes. Our data suggest that Atr1 functions as a boron efflux pump and is required for boron tolerance.Article Citation - WoS: 11Citation - Scopus: 16Bisphosphonate Treatment and Radiotherapy in Metastatic Breast Cancer(Humana Press, 2008) Ural, Ali Uğur; Avcu, Ferit; Baran, YusufPatients with advanced breast cancer frequently develop metastasis to bone. Bone metastasis results in intractable pain and high risk of pathologic fractures due to osteolysis. The treatment of breast cancer patients with bone metastases requires a multidisciplinary approach. Radiotherapy is an established treatment for metastatic bone pain. It may be delivered either as a localized low dose treatment for localized bone pain or systemically for more widespread symptoms. Bisphosphonates have been shown to reduce morbidity and bone pain from bone metastases when given to patients with metastatic bone disease. In vivo studies indicate that early bisphosphonates administration in combination with radiotherapy improves remineralization and restabilization of osteolytic bone metastases in animal tumor models. This review focused on a brief discussion about biology of bone metastases, the effects of radiotherapy and bisphosphonate therapy, and possible mechanisms of combination therapy in metastatic breast cancer patients.Article Citation - WoS: 17Citation - Scopus: 19Effect of Thioredoxin Deletion and P53 Cysteine Replacement on Human P53 Activity in Wild-Type and Thioredoxin Reductase Null Yeast(American Chemical Society, 2009) Stoner, Christopher S.; Pearson, George D.; Koç, Ahmet; Merwin, Jason R.; Lopez, Nathan I.; Merrill, Gary FredericReporter gene transactivation by human p53 is inhibited in budding yeast lacking the TRR1 gene encoding thioredoxin reductase. To investigate the role of thioredoxin in controlling p53 activity, the level of reporter gene transactivation by p53 was determined in yeast lacking the TRX1 and TRX2 genes encoding cytosolic thioredoxin. Surprisingly, p53 activity was unimpaired in yeast lacking thioredoxin. Subsequent analyses showed that thioredoxin deletion suppressed the inhibitory effect of thioredoxin reductase deletion, suggesting that accumulation of oxidized thioredoxin in mutant yeast was necessary for p53 inhibition. Purified human thioredoxin and p53 interacted in vitro (K d = 0.9 μM thioredoxin). To test the idea that dithio-disulfide exchange reactions between p53 and thioredoxin were responsible for p53 inhibition in mutant yeast, each p53 cysteine was changed to serine, and the effect of the substitution on p53 activity in TRR1 and Δtrr1 yeast was determined. Substitutions at Zn-coordinating cysteines C176, C238, or C242 resulted in p53 inactivation. Unexpectedly, substitution at cysteine C275 also inactivated p53, which was the first evidence for a non-zinc-coordinating cysteine being essential for p53 function. Cysteine substitutions at six positions (C124, C135, C141, C182, C229, and C277) neither inactivated p53 nor relieved the requirement for thioredoxin reductase. Furthermore, no tested combination of these six cysteine substitutions relieved thioredoxin reductase dependence. The results suggested that p53 dependence on thioredoxin reductase either was indirect, perhaps mediated by an upstream activator of p53, or was due to oxidation of one or more of the four essential cysteines.Article Citation - WoS: 7Citation - Scopus: 8Checkpoint Deficient Rad53-11 Yeast Cannot Accumulate Dntps in Response To Dna Damage(Elsevier Ltd., 2007) Koç, Ahmet; Merrill, Gary F.Deoxyribonucleotide pools are maintained at levels that support efficient and yet accurate DNA replication and repair. Rad53 is part of a protein kinase regulatory cascade that, conceptually, promotes dNTP accumulation in four ways: (1) it activates the transcription of ribonucleotide reductase subunits by inhibiting the Crt1 repressor; (2) it plays a role in relocalization of ribonucleotide reductase subunits RNR2 and RNR4 from nucleus to cytoplasm; (3) it antagonizes the action of Sml1, a protein that binds and inhibits ribonucleotide reductase; and (4) it blocks cell-cycle progression in response to DNA damage, thus preventing dNTP consumption through replication forks. Although several lines of evidence support the above modes of Rad53 action, an effect of a rad53 mutation on dNTP levels has not been directly demonstrated. In fact, in a previous study, a rad53-11 mutation did not result in lower dNTP levels in asynchronous cells or in synchronized cells that entered the S-phase in the presence of the RNR inhibitor hydroxyurea. These anomalies prompted us to investigate whether the rad53-11 mutation affected dNTP levels in cells exposed to a DNA-damaging dose of ethylmethyl sulfonate (EMS). Although dNTP levels increased by 2- to 3-fold in EMS treated wild-type cells, rad53-11 cells showed no such change. Thus, the results indicate that Rad53 checkpoint function is not required for dNTP pool maintenance in normally growing cells, but is required for dNTP pool expansion in cells exposed to DNA-damaging agents.Article Citation - WoS: 33Citation - Scopus: 35Upregulation of Multi Drug Resistance Genes in Doxorubicin Resistant Human Acute Myelogeneous Leukemia Cells and Reversal of the Resistance(Taylor and Francis Ltd., 2007) Baran, Yusuf; Gür, Bala; Kaya, Pelin; Ural, Ali Uğur; Avcu, Ferit; Gündüz, UfukThe major problem in the treatment of acute myeloid leukemia (AML) patients results from multidrug resistance to administered anticancer agents. Drug resistance proteins, MDR1 and MRP1, which work as drug efflux pumps, can mediate the multidrug resistance of human leukemia cells. In this study, the mechanisms of resistance to doxorubicin-induced cell death in human HL60 AML cells were examined. Continuous exposure of cells to step-wise increasing concentrations of doxorubicin resulted in the selection of HL60/DOX cells, which expressed about 10.7-fold resistance as compared to parental sensitive cells. The expression analyses of MRP1 and MDR1 drug efflux proteins in doxorubicin-sensitive and -resistant HL60 cells revealed that there was an upregulation of MRP1 gene in HL60/DOX cells as compared to parental sensitive cells. On the other hand, while there was no expression of MDR1 gene in parental cells, the expression of MDR1 gene was upregulated in HL60/DOX cells. HL60/DOX cells also showed cross-resistance to cytosine arabinoside (Ara-c). This resistance was reversed by a combination therapy of Ara-c and cyclosporine A. However, the expression levels of CD15 and CD16 surface markers were significantly decreased in HL60/DOX cells.Article Citation - WoS: 16Citation - Scopus: 14Identification of Staphylococci by 16s Internal Transcribed Spacer Rrna Gene Restriction Fragment Length Polymorphism(Microbiology Society, 2005) Sudağıdan, Mert; Yenidünya, Ali Fazıl; Güneş, HaticeThe capacity of 16S internal transcribed spacer (16S-ITS) rRNA gene RFLP to differentiate 16 type strains and nine clinical isolates of staphylococci was evaluated. The 16S rRNA gene was amplified together with the ITS region and the amplification products were digested with TaqI restriction enzyme. Analysis of the 16S-ITS rRNA gene RFLP profiles differentiated each of the 16 type strains into distinct RFLP haplotypes.Article Citation - WoS: 28Citation - Scopus: 27Determination of Thiamine Hcl and Pyridoxine Hcl in Pharmaceutical Preparations Using Uv-Visible Spectrophotometry and Genetic Algorithm Based Multivariate Calibration Methods(Pharmaceutical Society of Japan, 2004) Özdemir, Durmuş; Dinç, ErdalSimultaneous determination of binary mixtures pyridoxine hydrochloride and thiamine hydrochloride in a vitamin combination using UV-visible spectrophotometry and classical least squares (CLS) and three newly developed genetic algorithm (GA) based multivariate calibration methods was demonstrated. The three genetic multivariate calibration methods are Genetic Classical Least Squares (GCLS), Genetic Inverse Least Squares (GILS) and Genetic Regression (GR). The sample data set contains the UV-visible spectra of 30 synthetic mixtures (8 to 40 μg/ml) of these vitamins and 10 tablets containing 250 mg from each vitamin. The spectra cover the range from 200 to 330 nm in 0.1 nm intervals. Several calibration models were built with the four methods for the two components. Overall, the standard error of calibration (SEC) and the standard error of prediction (SEP) for the synthetic data were in the range of <0.01 and 0.43 μg/ml for all the four methods. The SEP values for the tablets were in the range of 2.91 and 11.51 mg/tablets. A comparison of genetic algorithm selected wavelengths for each component using GR method was also included