title: Glucosylceramide synthase blockade down-regulates P-glycoprotein and resensitizes multidrug-resistant breast cancer cells to anticancer drugs.
abstract: Overexpression of glucosylceramide synthase (GCS), a pivotal enzyme in glycolipid biosynthesis, contributes to cancer cell resistance to chemotherapy. We previously showed that transfection of doxorubicin-resistant MCF-7-AdrR cells with GCS antisense restored cell sensitivity to doxorubicin and greatly enhanced sensitivity to vinblastine and paclitaxel. In that study, doxorubicin promoted generation of ceramide in MCF-7-AdrR/GCS antisense cells; the present study implicates factors in addition to ceramide that augment sensitivity to chemotherapy. Although GCS antisense cells showed enhanced ceramide formation compared with MCF-7-AdrR when challenged with paclitaxel, GCS antisense cells also showed a 10-fold increase in levels of intracellular drug (paclitaxel and vinblastine). In addition, transfected cells had dramatically decreased expression (80%) of P-glycoprotein and a 4-fold decrease in the level of cellular gangliosides. Chemical inhibition of GCS produced the same effects as antisense transfection: exposure of MCF-7-AdrR cells to the GCS inhibitor 1-phenyl-2-palmitoylamino-3-morpholino-1-propanol (PPMP, 5.0 micromol/L, 4 days) decreased ganglioside levels, restored sensitivity to vinblastine, enhanced vinblastine uptake 3-fold, and diminished expression of MDR1 by 58%, compared with untreated controls. A similar effect was shown in vinblastin-resistant KB-V0.01 cells; after 7 days with PPMP (10 micromol/L), MDR1 expression fell by 84% and P-glycoprotein protein levels decreased by 50%. MCF-7-AdrR cells treated with small interfering RNAs to specifically block GCS also showed a dramatic decrease in MDR1 expression. This work shows that limiting GCS activity down-regulates the expression of MDR1, a phenomenon that may drive the chemosensitization associated with blocking ceramide metabolism. The data suggest that lipids play a role in the expression of multidrug resistance.
authors.affiliation: John Wayne Cancer Institute at Saint John's Health Center, Santa Monica, California 90404, USA.
authors.forename: Valérie
authors.initials: V
authors.lastname: Gouazé
authors.forename: Yong-Yu
authors.initials: YY
authors.lastname: Liu
authors.forename: Carlton S
authors.initials: CS
authors.lastname: Prickett
authors.forename: Jing Y
authors.initials: JY
authors.lastname: Yu
authors.forename: Armando E
authors.initials: AE
authors.lastname: Giuliano
authors.forename: Myles C
authors.initials: MC
authors.lastname: Cabot
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D000230:Adenocarcinoma / Q000188:drug therapy* / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D015536:Down-Regulation; D004317:Doxorubicin / Q000494:pharmacology; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D005732:Gangliosides / Q000378:metabolism; D005964:Glucosyltransferases / Q000037:antagonists & inhibitors* / Q000235:genetics; D006801:Humans; D009025:Morpholines / Q000494:pharmacology; D016376:Oligonucleotides, Antisense / Q000235:genetics; D017239:Paclitaxel / Q000494:pharmacology; D013107:Sphingolipids / Q000494:pharmacology; D014162:Transfection; D014747:Vinblastine / Q000494:pharmacology
chemical_list: C095823:1-phenyl-2-palmitoylamino-3-morpholino-1-propanol; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D005732:Gangliosides; D009025:Morpholines; D016376:Oligonucleotides, Antisense; D013107:Sphingolipids; D014747:Vinblastine; D004317:Doxorubicin; D005964:Glucosyltransferases; C023246:ceramide glucosyltransferase; D017239:Paclitaxel