The proteasome inhibitor bortezomib inhibits the constitutive activation of NF-κB in CTCL cells in a dose- and time-dependent fashion. CTCL cell lines SeAx and MyLa (A) and CTCL cells from 5 patients with Sézary syndrome (B) were cultured in the presence of bortezomib (10, 20, and 40 nM) during 24 and 48 hours as indicated above each lane or group of lanes. Nuclear extracts were prepared and subjected to EMSA. The data are representative of 2 independent sets of experiments. (C) Confocal microscopy analysis. Confocal images of PBLs from one patient with Sézary syndrome (top panels), SeAx cells (middle panels), and MyLa cells (bottom panels) show the localization of p65 (green) and p50 (red) in untreated cells (left column), cells treated with 20 nM bortezomib for 24 (middle column) or 48 hours (right column). DAPI was used for nuclear staining. Images were acquired as described in Figure 1D.