Co-expression of cytokeratin 8 and breast cancer resistant protein indicates a multifactorial drug-resistant phenotype in human breast cancer cell line

AimsThe aim was to determine whether increased CK8 and BCRP expression cooperatively contribute to multidrug resistance (MDR) in MCF-7/MX cells.Accumulating evidence suggests that the development and maintenance of cancer MDR involves complex multimodal mechanisms that interact concomitantly and complementarily. In this report, we observed elevated expression of cytokeratin 8 (CK8) in MCF-7/MX, a mitoxantrone (MX)-selected human breast tumor cell line with the MDR phenotype known as overexpression of breast cancer resistant protein (BCRP).Main methodsGene transfection methods were used to express CK8 and BCRP in NIH3T3 fibroblasts, individually or in combination.Key findingsTaken together, our present study suggests that CK8 together with BCRP may play significant roles in conferring the multifactorial MDR phenotype of MCF-7/MX cells, but may act independently via potentially different mechanisms.Although expressing either CK8 or BCRP alone was able to confer resistance to mitoxantrone, cells co-expressing both proteins demonstrated significantly increased drug resistance. Furthermore, RNAi knockdown of CK8 and BCRP, alone and in combination, in MCF-7/MX cells significantly attenuated their resistance to chemotherapeutic agents. Interestingly, in contrast to inhibition of BCRP expression via anti-BCRP shRNA vector transfection, reversal of mitoxantrone resistance by transfection with anti-CK8 shRNA was not accompanied by an increase in intracellular drug accumulation.SignificanceCombinational approaches that target multiple drug-resistance-related molecules/pathways in cancer cells may represent more efficacious strategies to overcome MDR.