Expression of phenotypic traits following modulation of colchicine resistance in J774.2 cells

Molecular cytogenetics of multiple drug resistance

The refractory nature of many human cancers to multi-agent chemotherapy is termed multidrug resistance (MDR). In the past several decades, a major focus of clinical and basic research has been to characterize the genetic and biochemical mechanisms mediating this phenomenon. To provide model systems in which to study mechanisms of multidrug resistance, in vitro studies have established MDR cultured cell lines expressing resistance to a broad spectrum of unrelated drugs. In many of these cell lines, the expression of high levels of multidrug resistance developed in parallel to the appearance of cytogenetically-detectable chromosomal anomalies resulting from gene amplification. This review describes cytogenetic and molecular-based studies that have characterized DNA amplification structures in MDR cell lines and describes the important role gene amplification played in the cloning and characterization of the mammalian multidrug resistance genes (mdr). In addition, this review discusses the genetic selection generally used to establish the MDR cell lines, and how drug selections performed in transformed cell lines generally favor the genetic process of gene amplification, which is still exploited to identify drug resistance genes that may play an important role in clinical MDR.

P-glycoprotein as multidrug transporter: a critical review of current multidrug resistant cell lines

MDR has been studied extensively in mammalian cell lines. According to usual practice, the MDR phenotype is characterized by the following features: cross resistance to multiple chemotherapeutic agents (lipophilic cations), defective intracellular drug accumulation and retention, overexpression of P-gp (often accompanied by gene amplification), and reversal of the phenotype by addition of calcium channel blockers. An hypothesis for the function of P-gp has been proposed in which P-gp acts as a carrier protein that actively extrudes MDR compounds out of the cells. However, basic questions, such as what defines the specificity of the pump and how is energy for active efflux transduced, remain to be answered. Furthermore, assuming that P-gp acts as a drug transporter, one will expect a relationship between P-gp expression and accumulation defects in MDR cell lines. A review of papers reporting 97 cell lines selected for resistance to the classical MDR compounds has revealed that a connection exists in most of the reported cell lines. However, several exceptions can be pointed out. Furthermore, only a limited number of well characterized series of sublines with different degrees of resistance to a single agent have been reported. In many of these, a correlation between P-gp expression and transport properties can not be established. Co-amplification of genes adjacent to the mdr1 gene, mutations [122], splicing of mdr1 RNA [123], modulation of P-gp by phosphorylation [124] or glycosylation [127], or experimental conditions [26,78] could account for some of the complexity of the phenotype and the absence of correlation in some of the cell lines. However, both cell lines with overexpression of P-gp without increased efflux [i.e., 67,75] and cell lines without P-gp expression and accumulation defects/increased efflux [i.e., 25,107] have been reported. Thus, current results from MDR cell lines contradict--but do not exclude--that P-gp acts as multidrug transporter. Other models for the mechanism of resistance have been proposed: (1) An energy-dependent permeability barrier working with greater efficacy in resistant cells. This hypothesis is supported by studies of influx which, although few, all except one demonstrate decreased influx in resistant cells; (2) Resistant cells have a greater endosomal volume, and a greater exocytotic activity accounts for the efflux.(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for linear extrachromosomal elements mediating gene amplification in the multidrug-resistant J774.2 murine cell line

Previous studies from our laboratory have demonstrated specific cytogenetic alterations accompanying development of colchicine resistance in the J774.2 murine cell line and in two sublines (J7.Cl-30 and J7.Cl-100). Although gene amplification is not observed in the parental J774.2 cell line, a approximately 35-fold amplification of the gene for p-glycoprotein (mdr) was noted in the J7.Cl-30 subline (770-fold CLCR) and a approximately 70-fold amplification in the J7.Cl-100 subline (2500-fold CLCR). In this study, we analyzed the localization and organization of the mdr gene. In the colchicine-resistant (CLCR) J7.Cl-30 subline, the p-glycoprotein domain was observed to reside on differently sized extrachromosomal elements. Our results indicate not only circular extrachromosomal elements but also linear extrachromosomal elements. By means of pulsed-field gel electrophoresis (PFGE), the sizes of the extrachromosomal elements were shown to be greater than 2,500 kilobase-pairs (kb), 800 kb, and 400 kb. In contrast, the J7.Cl-100 subline was characterized by the presence of homogeneously staining regions (HSRs). We have noted that with increasing colchicine resistance the extrachromosomal elements are replaced by HSRs. Our findings of linear elements that appear to be precursors of HSRs may offer a new way to interpret different theories of extrachromosomal gene amplification. The J7.Cl-30 cell line presents a unique system to analyze further the formation and structure of extrachromosomal elements.

Amplification and expression of a multidrug resistance gene in human glioma cell lines

Two human glioma cell lines were examined for multidrug resistance (MDR). A vincristine (VCR)-resistant glioma cell line showed a cross resistance to Adriamycin (doxorubicin, ADR) and etoposide (VP-16) to varying extents, suggesting the presence of MDR; the resistance to VCR was considerably decreased by calcium entry blockers. On the other hand, another VCR-sensitive glioma cell line exhibited no cross resistance to ADR or VP-16. Double minute chromosomes and homogeneously staining regions as well as clonal aberrations of chromosome 7 were not observed in cytogenetic studies of multidrug-resistant and multidrug-sensitive glioma cell lines. In Northern and Southern blot analyses, MDR gene 1 (MDR1) messenger ribonucleic acid (mRNA) was shown to be overexpressed without any amplification of the MDR1 gene in multidrug-resistant glioma cell lines as compared to multidrug-sensitive glioma cell lines. It would be reasonable to suggest that amplification of the MDR1 gene may not be a sine qua non for acquisition of MDR and that the MDR1 mRNA level may be correlated with the extent of MDR.

Initial and early effects of adriamycin in murine sarcoma 180 cannot be restored in a resistant subline by increasing the uptake and external concentration of the drug

We demonstrate the early effects (1 day) of Adriamycin (ADM) on proliferation-stimulated and quiescent sensitive, and ADM-resistant cells of the murine tumor sarcoma 180 (S 180). By investigating cell-cycle distribution and thymidine labeling, it can be shown that sensitive cells are strongly affected by the drug, even in a proliferationarrested state. A remarkable but slow DNA synthesis is the prominent effect of this drug treatment on sensitive cells, even under nonstimulating conditions. In resistant cells, neither an increase in concentration nor a variation in drug uptake can induce effects that could be compared with those observed in the sensitive line. From these results we conclude that the early effects of ADM are not modulated by drug uptake.

Distinct P-glycoprotein precursors are overproduced in independently isolated drug-resistant cell lines

A family of P-glycoproteins are overproduced in multidrug-resistant cells derived from the murine macrophage-like line J774.2. To determine whether individual family members are overproduced in response to different drugs, the P-glycoprotein precursors in several independently isolated cell lines, which were selected for resistance to vinblastine or taxol, were compared. Individual cell lines selected with vinblastine overproduced P-glycoprotein precursors of either 120 or 125 kDa. Taxol-selected cell lines overproduced either the 125-kDa precursor or both precursors simultaneously. Two similar but distinct peptide maps for the mature P-glycoproteins were observed. These maps corresponded to each precursor regardless of the drug used for selection. One vinblastine-resistant cell line switched from the 125- to the 120-kDa precursor when grown in increasing concentrations of drug. This change coincided with the overexpression of a distinct subset of mRNA species that code for P-glycoprotein. It is concluded that precursor expression is not drug-specific. These data suggest that individual overproduced P-glycoprotein family members are translated as distinct polypeptides. The results may help to explain the diversity in the multidrug-resistant phenotype.

Use of fluorescent dyes as molecular probes for the study of multidrug resistance

Fluorescence microscopy has shown that 18 different fluorescent dyes, staining various intracellular structures in transformed hamster fibroblasts (DM-15), did not stain or stained weakly multidrug-resistant cells selected from DM-15 by colchicine. Reduced staining by fluorescent dyes was characteristic also of five other tested multidrug-resistant cell lines of hamster and mouse origin, selected by actinomycin D, colcemid, rubomycin, and ruboxyl. The intensity of staining of two revertant cell lines was similar to that of parental sensitive cells. All tested inhibitors of multidrug resistance, including weak detergent, metabolic inhibitors, calcium channel blockers, calmodulin inhibitors, and reserpine, restored normal staining of multidrug-resistant cells. The dyes accumulated in resistant cells in presence of these inhibitors left the cells several minutes after the removal of the inhibitor from the incubation medium. Sensitive cells retained the dyes for several hours. The efflux of the dyes from resistant cells is an active process since it occurred even in the presence of the dyes in the incubation medium. The efflux could be blocked by all tested inhibitors of multidrug resistance and it is possibly a basic mechanism of the reduced staining of resistant cells. These data support the idea that multidrug resistance is based on active nonspecific efflux of the drugs and indicate that the simple procedure of cell staining can be used for the detection of resistant cells and further study of the phenomenon of multidrug resistance.

Use of antibodies to probe membrane glycoproteins associated with drug-resistant J774.2 cells

Three drug-resistant sublines of the murine macrophage-like cell line J774.2 were selected in vitro for their ability to grow in high concentrations of either taxol, vinblastine, or colchicine. Each contains a major plasma membrane glycoprotein (130-150 kDa), which is barely seen in the drug-sensitive parental cell line. Polyclonal antibodies, raised against the glycoproteins present in the colchicine- and vinblastine-resistant cells, were used to probe for relationships among the three glycoproteins. Our observations suggest that the glycoproteins from the different drug-resistant cell lines share many common domains but are not identical.