title: Heat-induced proteolysis of HSF causes premature deactivation of the heat shock response in Nb2 lymphoma cells.
abstract: Nb2-11 cells, a prolactin (PRL)-dependent T-lymphoma cell line, display an unusual response to heat stress characterized by the lack of expression of inducible hsp70 mRNA transcripts and a reduction in the levels of constitutively expressed heat shock protein (HSP) genes. This aberrant heat shock response appears to result from heat-induced proteolytic fragmentation of heat shock factor (HSF). In this report, we have investigated processes that promote HSF fragmentation and identified characteristics of a protease that may be responsible for this effect. Cycloheximide did not affect HSF fragmentation of heat-shocked Nb2-11 cells suggesting that proteases responsible for this proteolysis are constitutively expressed and become activated by the heat shock conditions. PRL protected Nb2-11 cells from heat-induced fragmentation whereas sodium butyrate (NaBT) rendered a fragmentation-resistant cell line (Nb2-SFJCD1 cells) sensitive to HSF proteolysis. Heat-induced HSF fragmentation in Nb2-11 cells was not affected by pretreating cultures with several serine protease inhibitors. However, a dose-dependent decrease in HSF fragmentation was achieved by pretreating cultures with iodoacetamide, a cysteine protease inhibitor that is active in apoptosis. Apparently, the heat shock response in Nb2 cells is attenuated by a mechanism that involves the premature deactivation of HSF by its selective proteolysis. Attenuation of this critical cellular stress response may be an important contributor to the progression of hormone-dependent tumors possibly by influencing apoptotic processes known to regulate the activity of these cells.
authors.affiliation: Department of Pharmacology and Toxicology, University of North Dakota School of Medicine, Grand Forks 58202, USA.
authors.forename: M
authors.initials: M
authors.lastname: Zhang
authors.forename: D J
authors.initials: DJ
authors.lastname: Buckley
authors.forename: K P
authors.initials: KP
authors.lastname: Lavoi
authors.forename: A R
authors.initials: AR
authors.lastname: Buckley
authors.forename: M J
authors.initials: MJ
authors.lastname: Blake
mesh_terms: D000818:Animals; D002087:Butyrates / Q000494:pharmacology; D020148:Butyric Acid; D003513:Cycloheximide / Q000494:pharmacology; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism*; D010450:Endopeptidases / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics; D006360:Heat-Shock Proteins / Q000378:metabolism*; D018869:Heat-Shock Response / Q000276:immunology*; D007460:Iodoacetamide / Q000494:pharmacology; D016399:Lymphoma, T-Cell / Q000503:physiopathology*; D008894:Milk Proteins; D011388:Prolactin / Q000494:pharmacology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D050794:STAT1 Transcription Factor; D050799:STAT5 Transcription Factor; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D015534:Trans-Activators / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D002087:Butyrates; D015853:Cysteine Proteinase Inhibitors; D004268:DNA-Binding Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D008894:Milk Proteins; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D050794:STAT1 Transcription Factor; D050799:STAT5 Transcription Factor; D015842:Serine Proteinase Inhibitors; D015534:Trans-Activators; D020148:Butyric Acid; D011388:Prolactin; D003513:Cycloheximide; D010450:Endopeptidases; D007460:Iodoacetamide