CT26/NIS-cODC CSCs have intrinsically low proteasome activity with high NIS accumulation and radioiodine uptake. (A) CT26 /NIS-cODC cells efficiently form tumorspheres (TS; left top); and TS of CT26/ZsGreen cells display increased fluorescence (left bottom). Western blots for CD133 and NIS in CT26/NIS-cODC cells grown as monolayers (non-TS) or as TS. Blots are cropped with single blot parts separated by space. For full length blot pictures, see supplement Fig. 2. Bars are the mean ± SD of band intensities normalized to β-actin from triplicate samples expressed as fold of non-TS controls. (B) Fluorometric assays of proteasome activity in CT26/NIS-cODC cells at baseline (left); and radioiodine uptake in cells at baseline or under BTZ exposure (16 h at 200 nM; right). Bars are the mean ± SD of uptake from triplicate samples expressed as % controls. **P < 0.01, ‡P < 0.001 compared to non-TS controls. CSC: cancer stem cell; BTZ: bortezomib; N.S.: not significant.