Cultured proximal cells derived from transgenic mouse provide a model to study drug toxicity

Transimmortalized proximal tubule and collecting duct cell lines derived from the kidneys of transgenic mice

This review summarizes the strategy of cellular immortalization based on the principle of targeted oncogenesis in transgenic mice, used to establish models of transimmortalized renal proximal tubule cells, referred to as PKSV-PCT and PKSV-PR-cells, and collecting duct principal cells, referred to as mpkCCD(cl4) cells. These cell lines have maintained for long-term passages the main biochemical and functional properties of the parental cells from which they were derived. Proximal tubule PKSV-PCT and PKSV-PR cells have been proved to be suitable cell systems for toxicological and pharmacological studies. They also permitted the establishment of a model of multidrug-resistant (MDR) renal epithelial tubule cells, PKSV-PR(col50), which have served for the study of both MDR-dependent extrusion of chemotherapeutic drugs and inappropriate accumulation of weak base anthracyclines in intracellular acidic organelles. The novel collecting duct cell line mpkCCD(cl4), which has maintained the characteristics of tight epithelial cells, in particular Na(+) absorption stimulated by aldosterone, has been extensively used for pharmacological studies related to the regulation of ion transport. These cells have permitted the identification of several aldosterone-induced proteins playing a key role in the regulation of Na(+) absorption mediated by the epithelial Na(+) channel ENaC. Recent studies have also provided evidence that these cell lines represent valuable cell systems for the study of host-pathogen interactions and the analysis of the role of renal tubule epithelial cells in the induction of inflammatory response caused by uropathogens that may lead to severe renal damage.

Regulation of NaCl transport in the renal collecting duct: lessons from cultured cells

The fine control of NaCl absorption regulated by hormones takes place in the distal nephron of the kidney. In collecting duct principal cells, the epithelial sodium channel (ENaC) mediates the apical entry of Na(+), which is extruded by the basolateral Na(+),K(+)-ATPase. Simian virus 40-transformed and "transimmortalized" collecting duct cell lines, derived from transgenic mice carrying a constitutive, conditionally, or tissue-specific promoter-regulated large T antigen, have been proven to be valuable tools for studying the mechanisms controlling the cell surface expression and trafficking of ENaC and Na(+),K(+)-ATPase. These cell lines have made it possible to identify sets of aldosterone- and vasopressin-stimulated proteins, and have provided new insights into the concerted mechanism of action of serum- and glucocorticoid-inducible kinase 1 (Sgk1), ubiquitin ligase Nedd4-2 (neural precursor cell-expressed, developmentally down-regulated protein 4-2), and 14-3-3 regulatory proteins in modulating ENaC-mediated Na(+) currents. Epidermal growth factor and induced leucine zipper protein have also been shown to repress and stimulate ENaC-dependent Na(+) absorption, respectively, by activating or repressing the mitogen-activated protein kinase externally regulated kinase(1/2). Overall, these findings have provided evidence suggesting that multiple pathways are involved in regulating NaCl absorption in the distal nephron.

Inhibitors of vacuolar H+-ATPase impair the preferential accumulation of daunomycin in lysosomes and reverse the resistance to anthracyclines in drug-resistant renal epithelial cells

It has been suggested that the inappropriate sequestration of weak-base chemotherapeutic drugs in acidic vesicles by multidrug-resistance (MDR) cells contributes to the mechanisms of drug resistance. The function of the acidic lysosomes can be altered in MDR cells, and so we investigated the effects of lysosomotropic agents on the secretion of lysosomal enzymes and on the intracellular distribution of the weak-base anthracycline daunomycin in drug-resistant renal proximal tubule PKSV-PR(col50) cells and their drug-sensitive PKSV-PR cell counterparts. Imaging studies using pH-dependent lysosomotropic dyes revealed that drug-sensitive and drug-resistant cells exhibited a similar acidic lysosomal pH (around 5.6-5.7), but that PKSV-PR(col50) cells contained more acidic lysosomes and secreted more of the lysosomal enzymes N -acetyl-beta-hexosaminidase and beta-glucuronidase than their parent PKSV-PR cells. Concanamycin A (CCM A), a potent inhibitor of the vacuolar H(+)-ATPase, but not the P-glycoprotein modulator verapamil, stimulated the secretion of N -acetyl-beta-hexosaminidase in both drug-sensitive and drug-resistant cells. Fluorescent studies and Percoll density gradient fractionation studies revealed that daunomycin accumulated predominantly in the lysosomes of PKSV-PR(col50) cells, whereas in PKSV-PR cells the drug was distributed evenly throughout the nucleo-cytoplasmic compartments. CCM A did not impair the cellular efflux of daunomycin, but induced the rapid nucleo-cytoplasmic redistribution of the drug in PKSV-PR(col50) cells. In addition, CCM A and bafilomycin A1 almost completely restored the sensitivity of these drug-resistant cells to daunomycin, doxorubicin and epirubicin. These findings indicate that lysosomotropic agents that impair the acidic-pH-dependent accumulation of weak-base chemotherapeutic drugs may reverse anthracycline resistance in MDR cells with an expanded acidic lysosomal compartment.

Different sensitivity to nephrotoxic agents and osmotic stress in proximal tubular and collecting duct cell lines derived from transgenic mice

We established six renal tubular cell lines from definite tubular areas of the kidney of transgenic mice harboring tsSV40 large T-antigen gene. Three are proximal tubular cell lines prepared from the S(1), S(2) and S(3) segments of the proximal tubule and the others are collecting duct cell lines obtained from cortical, outer medullary and inner medullary collecting ducts (CCD, OMCD and IMCD, respectively). To verify the growth properties of these cell lines under different temperature conditions (33 and 39 degrees C), two representative cells were chosen from the proximal tubule (S(1) cells) and from the collecting duct (IMCD cells). From these cells, a daily change in cell number was evaluated as a parameter of cell growth. As might be expected, cell numbers of these cells increased only at 33 degrees C. Similar patterns were also observed with the other cell lines. To observe the different sensitivity to nephrotoxic agents in proximal tubular cell lines, the cells were exposed to nephrotoxic agent, gentamicin, ochratoxin A or cisplatin. Gentamicin (1 mg/ml) dose-dependently decreased cellular ATP levels of the S(1) cells only. In contrast, the effect of ochratoxin A (10(-6) M) was most pronounced in the S(2) cells, and that of cisplatin (10 microg/ml) in the S(3) cells. To characterize collecting duct cell lines, a hyperosmotic challenge of 700 or 1100 mOsm/l was applied to the cells. At an isoosmotic condition of 300 mOsm/l, the number of cells from the collecting ducts, regardless of their origin, increased continuously during the culture period of 4 days. At an osmotic concentration of 700 mOsm/l, the number of CCD cells decreased, while OMCD cells showed a gradual but a significant increase in cell numbers throughout the culture period. IMCD cells, however, proliferated even at a concentration as high as 1100 mOsm/l, although an initial decrease in cell number was noted on the first day of culture. For confirmation of intracellular free calcium ([Ca(2+)](i)) mobilization, cells were treated with ATP and bradykinin. The [Ca(2+)](i) was increased significantly and immediately by ATP (10(-4) M) in S(1) cells and bradykinin (10(-7) M) in IMCD cells. From the results obtained, it is indicated that renal tubular cell lines from transgenic mice have different sensitivities to nephrotoxic or osmotic stress showing the conservation of the functional characters of the definite part it originated from.

Stimulated secretion of lysosomal enzymes induced by drugs in transimmortalized proximal tubule mouse kidney cells

We summarize the results of study of the properties of two models of transimmortalized proximal tubule epithelial cells derived from the kidneys of transgenic mice harboring the SV40 large T and little t antigens/L-pyruvate kinase hybrid gene. The two cell lines, referred to as PKSV-PCT and PKSV-PR cells, maintained for long-term passages the main biochemical and functional properties from the convoluted and terminal parts of the proximal tubule, respectively, from which they were derived. In PKSV-PCT cells, gentamicin induced lysosomal alkalinization, decreased the cellular N-acetyl-beta-D-glucuronidase, and stimulated its secretion in a dose-dependent manner. The results indicate that these models of mouse proximal cultured cells could be suitable models for the study of the cellular action of drugs.