Globo Series GSLs Mediate MDR1 Transactivation. (A) Glycosphingolipids. Cells were cultured in 10% FBS RPMI-1640 medium and harvested by trypsin-EDTA. Extracted lipids (5 μl aliquot of 100 μl) were resolve by TLC and GSLs were visualized by spraying with diphenylamine-aniline phosphoric acid reagent. GlcCer, glucosylceramide. (B) Gb3, a receptor of verocytotoxin on GCS transfectants. Cells were incubated with increasing concentrations of verocytotoxin in 5% FBS RPMI-1640 medium for 72 hr. *, p < 0.001 compared to ADR-RES. (C) GEM GSLs. GEMs of cells were prepared with gradient sucrose and extracted lipids (100 μg of GEM protein) were applied to HPTLC plates. (D) cSrc phosphorylation in GEMs. Equal amounts of GEM protein (50 μg/lane) were resolved by 4-12% gradient SDS-PAGE and immunoblotted with antibodies. p-cSRc/cSrc represents optical densities of the bands; *, p < 0.001 compared with mock.