Bortezomib down-regulates IκBα expression. (A) MM.1S, RPMI 8226, and U266 cells were cultured with bortezomib (10 nM and 20 nM) for 8 hours. (B) RPMI 8226 cells were cultured with bortezomib (20 nM) for the indicated time periods. (C) Primary tumor cells from MM patients were cultured with bortezomib (20 nM) for 8 hours. Whole-cell lysates (A-C) were immunoblotted with indicated Abs.