Expression of glucosylceramide synthase, converting ceramide to glucosylceramide, confers adriamycin resistance in human breast cancer cells

Multidrug-resistant cancer cells display elevated levels of glucosylceramid e (Lavie, Y., Cao, H. T., Volner, A. Lucci, A. Han, T. Y., Geffen, V., Giul iano, A. E., and Cabot, M. C. (1997) J. Biol. Chem. 272, 1682-1687). In thi s study, we have introduced glucosylceramide synthase (GCS) into wild type MCF-7 breast cancer cells using a retroviral tetracycline-on expression sys tem, and we developed a cell line, MCF-7/GCS. MCF-7/GCS cells expressed an 11-fold higher level of GCS activity compared with the parental cell line. Interestingly, the transfected cells demonstrated strong resistance to adri amycin and to ceramide, whereas both agents were highly cytotoxic to MCF-7 cells. The EC50 values of adriamycin and ceramide were 11-fold (p < 0.0005) and 5-fold (p < 0.005) higher, respectively, in MCF-7/GCS cells compared w ith MCF-7 cells. Ceramide resistance displayed by MCF-7/GCS cells closely p aralleled the activity of expressed GCS with a correlation coefficient of 0 .99. In turn, cellular resistance and GCS activity were dependent upon the concentration of the expression mediator doxycycline. Adriamycin resistance in MCF-7/GCS cells was related to the hyperglycosylation of ceramide and w as not related to shifts in the levels of either P-glycoprotein or Bcl-2. T his work demonstrates that overexpression of GCS, which catalyzes ceramide glycosylation, induces resistance to adriamycin and ceramide in MCF-7 breas t cancer cells.