Fig. 1

Thioredoxin is upregulated in adaptive bortezomib-resistant multiple myeloma cells. a and b Generation of adaptive bortezomib-resistant myeloma cell lines: MM.1R cells (a) and RPMI8226/Dox cells (b) were cultured with serially increased concentrations of bortezomib over a period of 1.5 years. The parental and bortezomib-resistant myeloma cells were treated with various concentration of bortezomib for 48 h and the IC₅₀ for parental and bortezomib-resistant myeloma cells were calculated and shown. c and d Thioredoxin mRNA expression is upregulated in bortezomib (BTZ)-resistant MM.1R cells (c) and in RPMI8226/Dox cells (d). Parental cells and BTZ-resistant MM.1R cells and BTZ-resistant RPMI8226/Dox cells at the highest bortezomib concentration were harvested and mRNA expression measured by RT-PCR. Error bars, standard error of the mean (SEM) (e and f). Thioredoxin protein expression increased in parallel to increased bortezomib drug resistance. Serial MM.1R (e) and RPMI8226/Dox (f) cells that were cultured with increased concentrations of bortezomib were harvested and protein expression measured by western blot analysis. The intensity of expression was semi-quantitated using Image-Pro Plus 6.0 software and adjusted to β-actin. Error bars, standard error of the mean (SEM); *p < 0.05, **p < 0.01, ***p < 0.005, ****p < 0.001