Cytoplasmic Macrophage Colony-stimulating Factor Induces Adriamycin-resistance By Translocating The ABCG2 From Cytoplasm To Cell Membrane Mediated Via PI3K Signaling In MCF-7 Cells.

OBJECTIVE: To explore the possible mechanism of drug-resistance induced by cytoplasmic macrophage colony-stimulating factor in Human breast cancer MCF-7 cell .METHODS: Human breast cancer MCF-7 cell, MCF-7-M cell (pCMV/cyto/myc-M-CSF transfected-MCF-7 cell that highly expresses nuclear M-CSF, referred as to MCF-7-M cell) and MCF-7-C cell (vector pCMV/cyto/myc transfected MCF-7 cell, referred as to MCF-7-C cell) were cultured. The total and cell membrane levels of ABCG2 were assayed by Western blot. The mRNA expression of ABCG2 was detected by RT-PCR.The sub-cellular distribution of ABCG2 was detected by Immunofluorescence. The drug concentrations were analysed by Fluorospectrophotometry within the three types of cells.The detection of doxorubicin resistance was assayed by MTT.RESULTS: The results from RT-PCR and western blot indicate that there is little significant difference in total protein and mRNA of ABCG2 between MCF-7, MCF-7-C and MCF-7-M, but that the levels of ABCG2 protein in the cell membrane of MCF-7-M cells are markedly higher than that of either MCF-7-C cells or MCF-7 cells (p<0.05); The results from Fluorospectrophotometry show that the concentration of adriamycin within MCF-7-M cells is lower than that of both MCF-7-C cells and MCF-7 cells (p<0.05). The adriamycin sensitivity of MCF-7-M cells is decreased compared with either MCF-7-C cells or MCF-7 cells (p<0.05) and IC₅₀ of MCF-7-M cells, MCF-7-C cells and MCF-7 cells is 7.87±0.43,8.06±0.31,121.47±0.39μg/mL, respectively. The pretreatment of both PI3K inhibitor LY294002 and ABCG2 inhibitor Fumitremorgin C significantly increases the adriamycin sensitivity (IC₅₀ is 11.47±1.42and32.79±1.73μg/mL,respectively. p=0.007 and0.013<0.05) and intracellular concentration of MCF-7-M cells. LY294002 increases membrane ABCG2 protein in MCF-7-M cells.CONCLUSION: Cytoplasmic M-CSF induces the adriamycin-resistance. Both PI3K signalings and ABCG2 is involved in the adriamycin–resistance mediated by cytoplasmic M-CSF. Cytoplasmic M-CSF induces adriamycin-resistance by translocating the ABCG2 from Cytoplasm to cell membrae mediated via PI3K signalings in MCF-7 cells.