Elevated stress response and proteasome-related gene expression in MM cells versus healthy twin PCs. Normalized gene expression values in CD138⁺ and CD138^– cells from BM from the patient with MM and the healthy twin were detected by gene chip Hu95av2 microarray profiling for heat shock proteins hsp 90, hsp 70, and hsp 40 transcripts (A); and proteasome-related genes CDC34, proteasome alpha and beta subunits (B). Cell lysates were prepared from MM cells and normal twin PCs, resolved by 10% SDS-PAGE, transferred onto nitrocellulose membranes, and then probed with (A) anti–hsp 70 and anti-actin Abs; or (B) anti-CDC34 and anti-actin Abs. Blots were developed by enhanced chemiluminescence, and relative protein expression in patient MM cells compared with normal twin PCs was calculated using densitometry.