Characterization of an etoposide-resistant human K562 cell line, K/eto

Monitoring the Expression Profiles of Doxorubicin-Resistant K562 Human Leukemia Cells by Serial Analysis of Gene Expression

We examined the expression profiles of doxorubicin-resistant K562 cells by serial analysis of gene expression (SAGE) to identify novel and/or partially characterized genes that might be related to drug resistance in human leukemia. SAGE complementary DNA (cDNA) libraries were constructed from K562 and doxorubicin-resistant K562 (K562/ADM) cells, and concatamer sequences were analyzed with SAGE 2000 software. We used 9792 tags in the identification of 1076 different transcripts, 296 of which were similarly expressed in K562 and K562/ADM cells. There were 343 genes more actively expressed in K562/ADM than in parental K562 cells and 437 genes expressed less often in K562/ADM cells. K562/ADM cells showed increased expression of well-known genes, including the genes for spectrin beta, eukaryotic translation initiation factor 1A (EIF1A), RAD23 homolog B, laminin receptor 1, and polyA-, RAN-, and PAI-1 messenger RNA-binding proteins. K562/ADM cells showed decreased expression of the genes for fatty acid desaturase 1 (FADS1), hemoglobin epsilon 1, N-myristoyltransferase 1, hemoglobin alpha 2, NADH dehydrogenase Fe-S protein 6, heat shock 90-kDa protein, and karyopherin beta 1. Quantitative reverse transcription-polymerase chain reaction analysis confirmed the increased expression of EIF1A and the decreased expression of FADS1 in K562/ADM cells. Prior to this investigation, such differences in the expression of these genes in doxorubicin-resistant leukemia cells were unknown. Although we do not provide any evidence in the present report for the potential roles of these genes in drug resistance, SAGE may provide a perspective into our understanding of drug resistance in human leukemia that is different from that provided by cDNA microarray analysis.

Altered expression of DNA-topoisomerase IIalpha is associated with increased rate of spontaneous polyploidization in etoposide resistant K562 cells

Molecular mechanisms of drug resistance and alterations in chromosome number were studied in two independently etoposide selected clonal cell lines, K562-VP16-1 and K562-W16-2, and in bulk cell line K562-VPI6. In all cell lines was observed down-regulation of topo IIalpha gene expression, while topo IIbeta mRNA content was unchanged compared to parental cell line. Antiapoptotic bcl-2 mRNA content was decreased in all drug resistant cell variants, the level of bcl-X(L) mRNA was greatly diminished only in one of cell lines, K562-VP16-1. Proapoptotic bax mRNA was down regulated to an undetectable level in all resistant cell lines analysed. These data indicate that abrogation of bax-mediated apoptosis can be implicated in development of etoposide resisance. Cytogenetic analysis revealed increased rate of spontaneous polyploidization in K562-VPI6 bulk and K562-VP-16-2 cells, while in K562-VP-16-1 cells was observed only moderate accumulation of polyploid cells. The degree of changes in topo IIa but not bcl-2 family members expression correlated positively with dynamics of accumulation of polyploid cells. Our findings suggest that down regulation of topo IIalpha in association with p53 deficiency can confer chromosomal instability in etoposide-resistant K562 cells.

Volume changes of isolated human K562 leukemia cells induced by electric field pulses

Electropermeabilization of immobilized human leukemia K562 cells was studied by measuring changes in cell volume. Such changes reflect mass transfer between the cell and external medium. Electropermeabilization was carried out in an isosmotic water-sorbitol medium with a range of electric field strengths from 500 to 800 V. cm(-1), corresponding to low-energy levels. Electroporation of the K562 cell membrane was found to provoke an inflow of sorbitol and a corresponding osmotic inflow of water and/or an outflow of intracellular solutes due to Fick diffusion. Such flows were found to involve the shrinkage, swelling, or rupture of K562 cells, depending on the characteristics of the electric field and of the physiological state of cells. The behavior of immobilized cells was observed during their exposure to the electric field. The response in immobilized cell volume corresponded with the theoretical pore size and pore opening time, permitting an explanation of the behavior of cell suspensions subject to electrical fields.

Lack of a point mutation of human DNA topoisomerase II in multidrug-resistant anaplastic thyroid carcinoma cell lines

DNA topoisomerases are major defined targets for a large variety of clinically important anticancer agents, including etoposide, adriamycin, and mitoxantrone. Mutations at amino acids 439, 450 and 803 of DNA topoisomerase II were examined in multiple anticancer drug-resistant anaplastic thyroid carcinomas (ten cell lines and three cancerous tissues) by reverse transcriptase-polymerase chain reaction (RT-PCR) and subsequent DNA sequencing. No mutation was found in these cell lines and tissues, but mdr1, mrp and/or lrp mRNA were expressed to a varying degree, and there was no significant difference in DNA topoisomerase IIalpha content among the cell lines and tissues as evaluated by Western blotting. Our experimental data indicate that overexpression of multidrug resistance-related mRNA is sufficient to confer drug resistance.

Altered stability of etoposide-induced topoisomerase II-DNA complexes in resistant human leukaemia K562 cells

K562 leukaemia cells were selected for resistance using 0.5 microM etoposide (VP-16). Cloned K/VP.5 cells were 30-fold resistant to growth inhibition by VP-16 and 5- to 13-fold resistant to m-AMSA, adriamycin and mitoxantrone. K/VP.5 cells did not overexpress P-glycoprotein; VP-16 accumulation was similar to that in K562 cells. VP-16-induced DNA damage was reduced in cells and nuclei from K/VP.5 cells compared with K562 cells. Topoisomerase II protein was reduced 3- to 7-fold and topoisomerase II alpha and topoisomerase II beta mRNAs were each reduced 3-fold in resistant cells. After drug removal, VP-16-induced DNA damage disappeared 1.7 times more rapidly and VP-16-induced DNA-topoisomerase II adducts dissociated 1.5 times more rapidly in K/VP.5 cells than in K562 cells. ATP (1 mM) was more effective in enhancing VP-16-induced DNA damage in nuclei isolated from sensitive cells than in nuclei from resistant cells. In addition, ATP (0.3-5 mM) stimulated VP-16-induced DNA-topoisomerase II adducts to a greater extent in K562 nuclei than in K/VP.5 nuclei. Taken together, these results indicate that resistance to VP-16 in a K562 subline is associated with a quantitative reduction in topoisomerase II protein and, in addition, a distinct qualitative alteration in topoisomerase II affecting the stability of drug-induced DNA-topoisomerase II complexes.

Mutational inactivation of the p53 gene in the human erythroid leukemic K562 cell line

The K562 human chronic myelogenous leukemia (CML) cell line has attained widespread use as a model for studying hematologic malignancy and erythroid differentiation. Sequencing of the p53 gene in the K562 cell line demonstrated a mutation in exon 5 characterized by a single base insertion (cytosine) between codons 135 and 136. This frameshift mutation leads to an N-terminal truncated protein of 147 amino acids. Only the mutated sequence was present suggesting that the normal allele has been lost. Reverse transcription PCR (RT-PCR) detected a p53 transcript but Western blotting and immunohistochemical staining of cells failed to detect p53 protein. The identification of an inactivation mutation of p53 in the K562 cell line further supports the argument that p53 mutations play a role in myeloid blast transformation of CML.

Differing patterns of cross-resistance resulting from exposures to specific antitumour drugs or to radiation in vitro

This article reviews the patterns of cross-resistance identified in various P-glycoprotein-mediated and non-P-glycoprotein-mediated drug resistant mammalian tumour cell lines. The differing patterns of cross-resistance and the variable levels of resistance expressed are summarised and discussed. Although the mechanism by which P-glycoprotein can recognise and transport a large group of structurally-unrelated substrates remains to be defined, the recent evidence indicating that membrane associated domains participate in substrate recognition and binding is summarised, and other possible explanations for these variable cross-resistance patterns are considered. Amongst the non-P-glycoprotein-overexpressing multidrug resistant cell lines, two subsets are clearly identifiable, one lacking and the other expressing cross-resistance to the Vinca alkaloids. Resistance mechanisms implicated in these various sublines and possible explanations for their differing levels and patterns of cross-resistance are summarised. Clinical resistance is identified in patients following treatment not only with antitumour drugs, but also after radiotherapy. Experimental data providing a biological basis for this observation are summarised. A distinctive multiple drug resistance phenotype has been identified in tumour cells following exposure in vitro to fractionated X-irradiation characterised by: the expression of resistance to the Vinca alkaloids and the epipodophyllotoxins but not the anthracyclines and overexpression of P-glycoprotein which is post-translationally regulated, but without any concomitant overexpression of P-glycoprotein mRNA. Finally, the possible clinical relevance of these variable patterns of cross-resistance to the antitumour drugs commonly used in the clinic is considered.

Primer-dependent amplification of mdr1 mRNA by polymerase chain reaction

We have developed a sensitive reverse transcription (RT)-polymerase chain reaction (PCR) to evaluate multidrug resistance in various tissues, using seven mdr-specific primer sets. mdr1 mRNA expression was noted in 16/197 samples. However, the apparent degree of mdr1 mRNA expression depended on the sequence of the primers employed. These findings suggest that more than two sets of primers should be used for effective RT-PCR.