Recombinant glutathione S-transferase (GST) expressing cells purified by flow cytometry on the basis of a GST-catalyzed intracellular conjugation of glutathione to monochlorobimane

Treatment with a JNK inhibitor increases, whereas treatment with a p38 inhibitor decreases, H2O2-induced calf pulmonary arterial endothelial cell death

Oxidative stress induces apoptosis in endothelial cells (ECs). Reactive oxygen species (ROS) promote cell death by regulating the activity of various mitogen-activated protein kinases (MAPKs) in ECs. The present study investigated the effects of MAPK inhibitors on cell survival and glutathione (GSH) levels upon H₂O₂ treatment in calf pulmonary artery ECs (CPAECs). H₂O₂ treatment inhibited the growth and induced the death of CPAECs, as well as causing GSH depletion and the loss of mitochondrial membrane potential (MMP). While treatment with the MEK or JNK inhibitor impaired the growth of H₂O₂-treated CPAECs, treatment with the p38 inhibitor attenuated this inhibition of growth. Additionally, JNK inhibitor treatment increased the proportion of sub-G₁ phase cells in H₂O₂-treated CPAECs and further decreased the MMP. However, treatment with a p38 inhibitor reversed the effects of H₂O₂ treatment on cell growth and the MMP. Similarly, JNK inhibitor treatment further increased, whereas p38 inhibitor treatment decreased, the proportion of GSH-depleted cells in H₂O₂-treated CPAECs. Each of the MAPK inhibitors affected cell survival, and ROS or GSH levels differently in H₂O₂-untreated, control CPAECs. The data suggest that the exposure of CPAECs to H₂O₂ caused the cell growth inhibition and cell death through GSH depletion. Furthermore, JNK inhibitor treatment further enhanced, whereas p38 inhibitors attenuated, these effects. Thus, the results of the present study suggest a specific protective role for the p38 inhibitor, and not the JNK inhibitor, against H₂O₂-induced cell growth inhibition and cell death.

Screening for recombinant glutathione transferases active with monochlorobimane

A rapid and facile colony assay has been developed for catalytically active enzymes in combinatorial cDNA libraries of mutated glutathione transferases (GST), expressed in Escherichia coli. The basis of the method is the conjugation of glutathione (GSH) with the fluorogenic substrate monochlorobimane (MCB). This screening method makes it possible to isolate and characterize one recombinant clone that is active with MCB among thousands of inactive variants. Colonies containing GSTs that catalyze the conjugation of GSH with MCB display fluorescence under long-wavelength UV light. The fluorescence is visible instantly. One rat and 11 human GSTs representing four distinct enzyme classes were studied, and all except human GST T1-1 gave rise to fluorescent colonies. The colony assay based on MCB can consequently be broadly applied for identifying active GSTs both after subcloning of wild-type enzymes and in the screening of mutant libraries. Populations of bacteria expressing GSTs can also be analyzed by flow cytometry.

Kinetic analysis of the intracellular conjugation of monochlorobimane by IC-21 murine macrophage glutathione-S-transferase

Monochlorobimane (MCB) reacts with glutathione (GSH) in a reaction catalyzed by the glutathione-S-transferase (GST) isozymes. The diffusion of MCB through cell membranes is rapid and the fluorescence conjugates are relatively insensitive to quenching and to pH effects, and are expelled slowly from the cell, allowing the rate of fluorescence increase to be used to probe the dynamics of the intracellular reaction. Using low-light microscopic cytometry to monitor the initial rates of fluorescence increase for the GST-catalyzed reaction within IC-21 macrophages yields Vmax = 8.4 x 10(-16) mol s-1 cell-1 and KMCBm = 65 microM. Combining these data with an integrated Michaelis analysis of the reaction course yields KIP approximately 1.5 x 10(-5) M, and KmGSH approximately 3.0 x 10(-4) M (at [MCB] = 50 microM). The values of Vmax and KMCBm for the cell-free (extracellular) GST-catalyzed conjugation reaction are 1.2 x 10(-18) mol s-1 cell-1 and 3.1 microM, respectively. The values of Vmax for the intra- and extracellular conjugation reactions differ by 700-fold, suggesting the presence of an intracellular activator for this enzyme system.

Glutathione S-transferases and P-glycoprotein in normal rat hepatocytes and hepatoma cells: analysis using flow cytometry

Using indirect immunofluorescence with fluorescein isothiocyanate-conjugated antibodies, in combination with flow cytometry (FCM), we have developed a technique to detect the alpha, mu and pi isozymes of GST in cell suspensions from normal rat liver, and in H4IIE cells, a rat hepatoma cell line. Cell suspensions fixed in 1% paraformaldehyde were observed to require cell membrane permeation with lysolecithin to allow access and binding of antibodies to immunoreactive proteins within the cytoplasm. FCM analysis indicated normal rat hepatocytes to be positive for GST alpha and mu, but not GST pi, and the H4IIE cells to be positive for all three GST isozymes. Further analysis by FCM for the expression of P-glycoprotein (mdr), a membrane-associated protein product of the multidrug resistance gene, showed an association between the presence of GST pi and mdr in the two cell types. Thus, mdr was detected in significant amounts in H4IIE cells, but not in rat hepatocytes. The method described here has potential applications in screening, sorting and further characterisation for GST pi-positive hepatocytes for mechanistic studies during sequential rat liver carcinogenesis, as well as for characterisation of human tumors for the expression of different GST isozymes and P-glycoprotein during therapeutic management.

Gene transfer by electroporation, lipofection, and DEAE-dextran transfection: compatibility with cell-sorting by flow cytometry

The aim of this work was to define a transfection procedure that is compatible with the sorting and propagation of cells that transiently express a heterologous gene. Three requirements were established for the procedure and were met with COS monkey kidney cells that express a recombinant glutathione S-transferase (GST) gene. The transfection procedure used had to generate (i) populations in which at least 10% of the cells expressed recombinant GST, (ii) cellular morphological homogeneity throughout the population, and (iii) viable cells with at least a 5% colony-forming ability. Of the transfection techniques tested, only electroporation satisfied all three requirements. Usually 20-22% of the cells that survived electroporation expressed recombinant GST 3 days after electroporation as measured by flow cytometry, and 25% of the cells that survived electroporation formed colonies in cloning assays. Transfection with DEAE-dextran and chloroquine did enable 40% of the surviving cells to express GST, but only 0.01% of the cells that survived transfection formed colonies in cloning assays. Finally, with lipofection, only 1% of the surviving cells expressed recombinant GST, although 25-40% of the cells that survived transfection formed colonies. These studies define the merits and limitations of transfection techniques relative to the analysis and sorting of transfected cells by flow cytometry.