MGr1-Ag is associated with multidrug-resistant phenotype of gastric cancer cells

BACKGROUND: MGr1-antigen (Ag) was previously reported as an upregulated protein in multidrug-resistant (MDR) gastric cancer cells. The aim of this study was to characterize the role of MGr1-Ag in the multidrug resistance of gastric cancer cells. METHODS: Laser scanning confocal microscopy (LSCM), two-dimensional electrophoresis, and Western blot were used to detect MGr1-Ag in gastric cancer cells. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay was used to determine the sensitivity of the MDR gastric cancer cells, SGC7901/VCR, to chemotherapeutic drugs. Adriamycin accumulation and retention in SGC7901/VCR cells were analyzed using flow cytometry. RESULTS: LSCM showed that MGr1-Ag localized mainly on the membrane and partly in the cytoplasm of SGC7901/VCR cells. Western blot showed that the expression level of MGr1-Ag in SGC7901/VCR cells was higher than that in its parental cells, SGC7901, and that the apparent molecular weight and isoelectric point of MGr1-Ag were 42 kDa and pH 4.8, respectively. After incubation with MGr1 antibody, SGC7901/VCR cells showed significantly decreased IC(50) values for adriamycin (from 0.887 +/- 0.081 mg/l to 0.607 +/- 0.084 mg/l; P, 0.05), vincristine (from 0.707 +/- 0.055 mg/l to 0.557 +/- 0.042 mg/l; P, 0.05), and 5-fluorouracil (from 4.367 +/- 0.407 mg/l to 2.630 +/- 0.644 mg/l; P, 0.05), as well as slightly increased IC(50) values for mitomycin (from 0.183 +/- 0.045 mg/l to 0.198 +/- 0.048 mg/l; P. 0.05). In addition, incubation with MGr1 significantly enhanced adriamycin accumulation and retention in SGC7901/VCR cells. CONCLUSION: Overexpression of MGr1-Ag is associated with the MDR phenotype of gastric cancer cells.