Multiple myeloma cell lines constitutively express high levels of physiologic UPR components. Five different multiple myeloma cell lines were treated for 12 and 24 hours with 50 μM tunicamycin (TM), 1 μM brefeldin A (BfA), 30 μM melphalan (Mel), 250 nM staurosporine (STS), or the indicated concentration of the proteasome inhibitors epoxomycin (EPOX), PSI, or bortezomib (BZ). Whole-cell lysates were isolated, subjected to sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE), and transferred to nitrocellulose membranes. The membranes were sequentially probed for GRP94, GRP78, and actin. The relative induction (Rel. Ind.) is the amount of protein present in treated samples relative to untreated cells after normalizing protein loading to actin using densitometry. Cell viability was assessed from an aliquot of the treated cells by Annexin V–FITC and propidium iodide staining. Representative blots from at least 3 independent experiments are shown.