Drugs capable of inducing ER stress have contrasting effects on Hsp70 expression. (A) Alterations in expression levels of BiP and Grp94 transcripts occur in response to all drugs (■, TM; □, TG; , 17-AAG; , Radicicol; , Bortezomib). (B) Upregulation of Hsp70 occurs in response to Hsp90 and proteasome inhibitors but not in response to inhibitors of protein glycosylation (TM) or the SERCA pump (TG). U266 cells treated, as indicated, with the Ic50 doses of drugs were lysed and analyzed by immunoblotting.