Influence of proteasome and redox state on heat shock-induced activation of stress kinases, AP-1 and HSF

We studied the pattern of activation of stress kinases and of transcription factors activator protein-1 (AP-1) and heat shock factor (HSF) in FAO cell s by combining two treatments, i.e. heating (42 degreesC for 1 h) and prote asome inhibition, each known to cause cellular heat shock response. The co- treatment heat shock (NS) and proteasome inhibitor (a peptidyl aldehyde or lactacystin) showed cumulative effects on the intensity and duration of act ivation of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) at the end of the HS period and during recovery. Similarly, t he thiol-reducing agents N-(2-mercaptoethyl)-1,3-diaminopropane and dithiot hreitol strongly activated both JNK and p38 MAPK in cells undergoing HS. AP -1 DNA binding activity in response to proteasome inhibitors was so strong that it shadowed the stimulatory effect of HS in the combined treatment, bu t lactacystin, which is the most potent and specific proteasome inhibitor, decreased the binding late during recovery from IIS. Thiol-reducing agents prevented AP-1 DNA binding induced by HS. The combined HS/proteasome inhibi tors or HS/thiol-reducing agents treatments cooperatively activated HSF DNA binding. Expression of collagenase I and hsp 70 mRNAs reflects the differe nt behavior of AP-1 and HSF transcription factors in cells exposed to HS an d proteasome inhibition. The data seem to indicate that JNK and p38 MAPK ac tivations are not necessarily coupled to DNA binding of AP-1, which can be either. increased or inhibited when these kinases are activated. AP-1 and H SF show opposite patterns of response to IIS in the presence of proteasome inhibitors or reducing agents. (C) 2001 Elsevier Science B.V. All rights re served.