Tumor Necrosis factor- and Expression of the Multidrug Resistance-Associated Genes LRP and MRP

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Abstract
Background and Purpose: Cancer cells that express P-glycoprotein, multidrug resistance-associated protein (MRP), or lung resistance protein (LRP) have demonstrated resistance to a wide variety of chemotherapeutic drugs. Recently, we reported that human colon carcinoma cells that express all three proteins exhibit reduced P-glycoprotein gene expression and a loss of multidrug resistance after exposure to tumor necrosis factor-α, a hormone-like protein produced by cells of the immune system. In this study, we examined the effects of tumor necrosis factor- a on MRP and LRP gene expression in the same colon carcinoma cells. Methods: HCT15 and HCT116 colon carcinoma cells were incubated with tumor necrosis factor-α at 100 U/mL for 2, 12, 24, 48, or 72 hours; alternatively, cells transfected with an expression vector containing a human tumor necrosis factor-α complementary DNA were studied. The effects of tumor necrosis factor-α on MRP and LRP messenger RNA expression were evaluated by means of reverse transcription and the polymerase chain reaction; effects on MRP and LRP protein expression were examined by use of specific monoclonal antibodies and flow cytometry. The flow cytometry data were analyzed by use of the twosided, nonparametric Mann-Whitney rank sum test. Results: Treatment with exogenous tumor necrosis factor-α reduced the level of LRP messenger RNA in both cell types in an apparently timedependent fashion; in HCT15 cells, almost no LRP messenger RNA was detected after 48 hours of treatment. In contrast, the level of MRP messenger RNA was increased in HCT116 cells by such treatment, but the level in HCT15 cells was unchanged. Treatment with exogenous tumor necrosis factor-α induced changes in LRP and MRP protein expression in the two cell types that paralleled the changes found for messenger RNA. In transfected cells, the endogenous production of tumor necrosis factor-α reduced LRP gene expression (both messenger RNA and protein) and increased MRP gene expression (both messenger RNA and protein), regardless of cell type. Conclusion: In human colon carcinoma cells, tumor necrosis factor-α influences MRP and LRP gene expression in opposite ways. The findings for LRP gene expression parallel our earlier findings for P-glycoprotein expression in these cells. Implication: In developing strategies for overcoming multidrug resistance in tumor cells, the possibility that an agent can suppress one or more mechanisms of drug resistance and enhance others should be considered.

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