Effects of Ub on the growth of hematopoietic cells.

(A) Dose-response of HL-60 and KT-3 to Ub. Triplicate aliquots of the cells were cultured in serum-free ASF103 medium with various concentrations of Ub for 48 hours, followed by measurement of cell proliferation with an MTT assay. (B) Effects of Ub on various types of hematopoietic cells. The cells were cultured in ASF103 medium in the presence or the absence of 100 μg/mL Ub for 48 hours and were subjected to an MTT assay. (C) Effects of proteasome inhibitors PSI, MG132, and methylated Ub (Met-Ub) on Ub-induced growth suppression. KT-3 cells were resuspended in ASF103 medium containing 1 ng/mL rhIL-6 with or without 100 μg/mL Ub and various concentrations of PSI or MG132 as indicated, cultured for 48 hours, and subjected to an MTT assay. In addition, KT-3 cells were preincubated with 100 μg/mL Met-Ub for 3 hours, cultured with or without Ub for 48 hours, and subjected to an MTT assay. The results are shown as the mean ± SD of triplicate cultures.