Bortezomib reduces XIAP expression. (A) HL B-cell lines were treated for 48 hours with increasing concentrations of bortezomib. cIAP2, cIAP1, XIAP, actin, Bcl2, Bax, Mcl1, and cytochrome c were detected in total cell extracts by Western blotting using specific antibodies. (B) Quantitative analysis of Western blot of XIAP expression. Graphs of mean band intensity of XIAP from Western blot images were acquired on an Alpha Innotech documentation station (Biozym; Hess, Oldendorf, Germany). All values were normalized to the actin expression levels and are presented as percentage of the mean levels in untreated cells (100%). The SD was calculated from up to 3 individual experiments. (C) HL B-cell lines were treated for 48 hours with increasing concentrations of Bay. cIAP2, cIAP1, XIAP, and actin were detected in total cell extracts by specific antibodies. (D) Quantitative analysis of XIAP mRNA. Total mRNA of HL B-cell lines was prepared and analyzed by Northern blotting using XIAP and β-actin probes. The quantification of XIAP mRNA was performed using a phosphoimager (molecular imager; Bio-Rad) by measurement of signal intensities normalized for β-actin mRNA content and is presented as percentage of the mean levels in untreated cells (100%). The data show 1 representative of 3 independent experiments. (E) HeLa and HeLa-myc-XIAP cell lines were treated for 48 hours with increasing concentrations of bortezomib. XIAP, myc-XIAP, and actin were detected in total cell extracts by Western blotting using specific antibodies.