Chronic myeloid leukemia (CML) cells express the active BCR-ABL1 protein, which

Chronic myeloid leukemia (CML) cells express the active BCR-ABL1 protein, which has been targeted by imatinib in CML therapy, but resistance to this drug is usually an emerging problem. These cells experienced lower native mitochondrial membrane potential than imatinib-sensitive cells, but UV-irradiation reversed that relationship. We observed a significant lowering of the manifestation of the succinate dehydrogenase (gene, and secondary or acquired resistance following imatinib treatment. Several mechanisms associated with the gene can underline imatinib-resistance, including amplification, its mutations and Narlaprevir epigenetic modifications as well as interference with BCR-ABL1-signaling [4]. However, detailed pathways leading to imatinib-resistance are not exactly known. CML, similarly to other cancers, is characterized by genomic instability, which, at least in part, is induced by the BCR-ABL1 kinase. The kinase can stimulate the production of reactive oxygen species (ROS), which damage DNA and induce cellular redox imbalance [5]. Such endogenous oxidative stress may promote increased susceptibility to exogenous oxidative stress induced by environmental factors, including UV light. ROS-induced DNA lesions can be misrepaired by mechanisms with the involvement of BCR-ABL1 [6,7]. Therefore, BCR-ABL1 may induce DNA damage, contributing to genomic instability, which is then further increased Gdf6 by the BCR-ABL1-dependent mechanism of these damages. We previously showed that BCR-ABL1-induced genomic instability might be associated not only with cancer phenotype of BCR-ABL+ cells, but also with imatinib-resistance [8]. Genomic instability is mainly determined by cellular DNA damage response (DDR), in which DNA repair plays a pivotal role. We showed that BCR-ABL1 modulated DNA repair in many kinds of cells [9,10,11,12,13]. As BCR-ABL1 contains redox-sensitive cysteine residues, exogenous ROS can change the structure of this protein leading to alterations in its interaction with small molecules, Narlaprevir which may eventually result in imatinib resistance [14]. Main UV-induced DNA damages are 2,3-cyclobutane pyrimidine dimer and pyrimidine (6-4) pyrimidone photoproduct, which in humans are processed by nucleotide excision repair [15]. However, UV may induce a variety of other damages, which can result from its stimulation of ROS production and lead to apoptosis [16]. It was shown that UV-induced ROS production was associated with decreased mitochondrial potential [17]. Therefore, cellular reaction to UV damage may involve essentially the same components, which may be associated with imatinib-resistance in CML cells: nucleotide excision repair as the most versatile system of DNA repair, playing a pivotal role in the maintenance of genomic stability, ROS neutralization, apoptosis and mitochondrial functioning. Therefore, in searching for the mechanism underlying difference between imatinib-resistant and -sensitive cells, it is reasonable to check some components of DNA damage response (DDR) in these cells. In the present work, we investigated UV-induced DNA damage and its repair, apoptosis, ROS production and the expression of (succinate dehydrogenase complex, subunit B), (myeloid cell leukemia sequence Narlaprevir 1), mitochondrial (cytochrome c oxidase subunit I), (NADH dehydrogenase subunit 3) and (cytochrome B) genes in cells sensitive and resistant to imatinib. These genes are mainly involved in metabolic/respiratory processes, which are associated with ROS production and they all can be associated with apoptosis, although they are not key players in this process. 2. Results 2.1. Cell Viability after Imatinib Treatment All cell lines were incubated for 24 h with various imatinib concentrations. The viability of imatinib-resistant cells harboring the Y253H (253) mutation and with acquired resistance (AR) cells did not change after the incubation, but the subline with non-mutated (S) decreased its viability to about 17% (Figure 1). Therefore, we considered further the S subline as imatinib-sensitive, whereas 253 and AR sublines were considered as imatinib-resistant. Figure 1 Relative mean viability of mouse 32D cells transfected with the gene: sensitive (S, white circles) and resistant to imatinib as evaluated by the Cell Counting Kit-8 assay. Imatinib resistance Narlaprevir resulted from the Y253H mutation in the gene … 2.2. Cells Primary Resistant to Imatinib Produce More ROS both Endogenously and Following UV Exposure Endogenous ROS levels in 253 imatinib-resistant cells were higher than in their sensitive counterparts (< 0.001) (Figure 2). UV radiation induced an evident increase in ROS level in all cell lines, but ROS production in 253 cells was still higher than in S line (< 0.001). Therefore, primary imatinib-resistant cells accommodated more ROS than cells with acquired imatinib resistance, which might contribute to genome instability of these cells. Figure 2 Mean intracellular reactive oxygen species levels in mouse 32D cells transfected with the gene: sensitive (S) and resistant to imatinib expressed as the fluorescence of 2,7-dichlorofluorescein (DCF) oxidatively converted from ... 2.3. Imatinib-Resistant Cells Have More Pyrimidine Dimers and Oxidative DNA Damage Induced by UV UV light induced DNA.

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