title: Proteasome inhibitors lactacystin and MG132 inhibit the dephosphorylation of HSF1 after heat shock and suppress thermal induction of heat shock gene expression.
abstract: Recently, we have shown that two proteasome inhibitors, MG132 and lactacystin, induce hyperphosphorylation and trimerization of HSF1, and transactivate heat shock genes at 37 degrees C. Here, we examined the effects of these proteasome inhibitors and, in addition, a phosphatase inhibitor calyculin A (CCA) on the activation of HSF1 upon heat shock and during post-heat-shock recovery, with emphasis on HSF1 hyperphosphorylation and the ability of HSF1 to transactivate heat shock genes. When lactacystin, MG132, or CCA was present after heat shock, HSF1 remained hyperphosphorylated during post-heat-shock recovery at 37 degrees C. Failure of HSF1 to recover to its preheated dephosphorylated state correlated well with the suppression of the heat-induced hsp70 expression. In vitro, HSF1 from heat-shocked cells, when dephosphorylated, showed an increase in HSE-binding affinity. Taken together, these data suggest that phosphorylation of HSF1 plays an important role in the negative regulation of heat-shock response. Specifically, during post-heat-shock recovery phase, prolonged hyperphosphorylation of HSF1 suppresses heat-induced expression of heat shock genes.
authors.affiliation: Departments of Medical Physics and Radiation Oncology, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York, 10021, USA.
authors.forename: D
authors.initials: D
authors.lastname: Kim
authors.forename: G C
authors.initials: GC
authors.lastname: Li
mesh_terms: D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D015536:Down-Regulation; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics; D000076249:Heat Shock Transcription Factors; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics*; D006358:Hot Temperature; D048031:JNK Mitogen-Activated Protein Kinases; D007976:Leupeptins / Q000494:pharmacology*; D008387:Marine Toxins; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010080:Oxazoles / Q000494:pharmacology; D010766:Phosphorylation; D014157:Transcription Factors
chemical_list: D015853:Cysteine Proteinase Inhibitors; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D018840:HSP70 Heat-Shock Proteins; D000076249:Heat Shock Transcription Factors; D006360:Heat-Shock Proteins; D007976:Leupeptins; D008387:Marine Toxins; D010080:Oxazoles; D014157:Transcription Factors; C067713:lactacystin; C059041:calyculin A; D004247:DNA; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; D000111:Acetylcysteine