[Synergic effect of Na(+)-K(+) ATPaseB1 and adriamycin on inhibition of cell proliferation and reversal of drug resistance in breast cancer MCF-7 cells].

Background and objective: Na(+)-K(+)ATPase (Na(+)-K(+) pump) is an important cell energy conversion system which is probably associated with tumor metastasis. Expression of its B1 subunit gene-ATP1B1 is high in well differentiated and low in poorly differentiated tumor cells. This study was to investigate the synergic effect of Na(+)-K(+) ATPaseB1 and adriamycin (ADM) on inhibition of cell proliferation and reversal of drug resistance in MCF-7 and MCF-7/ADM cells.

Methods: Growth of MCF-7 and MCF-7/ADM cells transfected with PEGFP-ATP1B1 and shATP1B1 were measured by MTT. Intracellular fluorescence intensity of ADM was analyzed by inverted fluorescence microscopy and flow cytometry. ATP enzyme activity was measured by ultramicro-ATP enzyme, and mRNA expression of multi-drug resistance gene MDR1 was detected by RT-PCR and real-time PCR. The expression of P-glycoprotein (P-gp) was analyzed by western blot.

Results: The sensitivity of MCF-7 and MCF-7/ADM cells transfected with pEGFP-ATP1B1 to ADM was higher in comparing to the negative control ADM-C3 (transfected with vector pEGFP-C3) and the control ADM-RPMI-1640 (cultured with RPMI-1640), and the differences between ADM-ATP1B1 and ADM-RPMI-1640 groups were statistically significant at different concentrations of adriamycin (P<0.05). After the B1 subunit was silenced, the sensitivity of cells to ADM in the ADM-shNC group was higher than that in the shATP and ADM-RPMI-1640 groups. The mean fluorescence intensity of ADM in the ADM-ATP1B1 group was higher than that in the ADM-C3 and ADM-RPMI-1640 groups (P<0.05). ATP enzyme activity was significantly higher in ADM-ATP1B1 group comparing to the ADM-RPMI-1640 group (P<0.05). mRNA expression of MDR1 gene and protein expression of P-gp were not significantly different among the ADM-ATP1B1 group and two control groups (P>0.05).

Conclusion: Na(+)-K(+) ATPase B1 can synergize with ADM and reverse drug resistance to ADM in the MCF-7/ADM cell line. This may be related to ATP enzyme activity, but not to influencing the expression of MDR1 gene.