CK2 activity downstream from growth factors. (A) Effects of CK2 inhibition on MM cell growth (▪) were not reversed by the addition of survival stimuli such as IL-6 (20 ng/mL) (□) or IGF-I (100 ng/mL) (). OPM2 cells were cultured with the indicated stimuli in the absence or in the presence of TBB, K27, or both and then were subjected to MTT-based viability assay 48 hours later. Data are the mean ± SD. (B) Western blot analysis of the IL-6/STAT3 cascade in MM cells on CK2 inhibition. MM cells were serum starved for 4 hours (cell lines OPM2) or 2 hours (freshly isolated MM plasma cells from patients), incubated for 2 hours with 0.1% DMSO, (5 μM) K27, or 20 μM TBB and then stimulated for the indicated time points with 10 ng/mL IL-6. For MM cell lines, the levels of phospho-Tyr702 STAT3, phospho-Ser727 STAT3, and total STAT3, and for MM cells from patients the levels of phospho-Tyr702 STAT3 and total STAT3 were assessed, as indicated. β-Actin was used to measure protein loading.