title: RhoA Activation Sensitizes Cells to Proteotoxic Stimuli by Abrogating the HSF1-Dependent Heat Shock Response.
abstract: BACKGROUND
  The heat shock response (HSR) is an ancient and highly conserved program of stress-induced gene expression, aimed at reestablishing protein homeostasis to preserve cellular fitness. Cells that fail to activate or maintain this protective response are hypersensitive to proteotoxic stress. The HSR is mediated by the heat shock transcription factor 1 (HSF1), which binds to conserved heat shock elements (HSE) in the promoter region of heat shock genes, resulting in the expression of heat shock proteins (HSP). Recently, we observed that hyperactivation of RhoA conditions cardiomyocytes for the cardiac arrhythmia atrial fibrillation. Also, the HSR is annihilated in atrial fibrillation, and induction of HSR mitigates sensitization of cells to this disease. Therefore, we hypothesized active RhoA to suppress the HSR resulting in sensitization of cells for proteotoxic stimuli.
  
  
  RESULTS
  Stimulation of RhoA activity significantly suppressed the proteotoxic stress-induced HSR in HL-1 atrial cardiomyocytes as determined with a luciferase reporter construct driven by the HSF1 regulated human HSP70 (HSPA1A) promoter and HSP protein expression by Western Blot analysis. Inversely, RhoA inhibition boosted the proteotoxic stress-induced HSR. While active RhoA did not preclude HSF1 nuclear accumulation, phosphorylation, acetylation, or sumoylation, it did impair binding of HSF1 to the hsp genes promoter element HSE. Impaired binding results in suppression of HSP expression and sensitized cells to proteotoxic stress.
  
  
  CONCLUSIONS
  These results reveal that active RhoA negatively regulates the HSR via attenuation of the HSF1-HSE binding and thus may play a role in sensitizing cells to proteotoxic stimuli.
authors.affiliation: Department of Clinical Pharmacy and Pharmacology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Roelien A M
authors.initials: RA
authors.lastname: Meijering
authors.affiliation: Department of Clinical Pharmacy and Pharmacology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Marit
authors.initials: M
authors.lastname: Wiersma
authors.affiliation: Department of Clinical Pharmacy and Pharmacology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Denise M S
authors.initials: DM
authors.lastname: van Marion
authors.affiliation: Department of Clinical Pharmacy and Pharmacology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Deli
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Department of Clinical Pharmacy and Pharmacology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Femke
authors.initials: F
authors.lastname: Hoogstra-Berends
authors.affiliation: Department of Cell Biology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Anne-Jan
authors.initials: AJ
authors.lastname: Dijkhuis
authors.affiliation: Department of Molecular Pharmacology, University of Groningen, Groningen, The Netherlands.
authors.forename: Martina
authors.initials: M
authors.lastname: Schmidt
authors.affiliation: Institute of Experimental and Clinical Pharmacology and Toxicology, Mannheim Medical Faculty, University of Heidelberg, Mannheim, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Wieland
authors.affiliation: Department of Cell Biology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Harm H
authors.initials: HH
authors.lastname: Kampinga
authors.affiliation: Department of Clinical Pharmacy and Pharmacology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Henning
authors.affiliation: Department of Clinical Pharmacy and Pharmacology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands; Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Bianca J J M
authors.initials: BJ
authors.lastname: Brundel
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004151:Dipeptides / Q000494:pharmacology; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D000076249:Heat Shock Transcription Factors; D006358:Hot Temperature; D006801:Humans; D018613:Microscopy, Confocal; D010766:Phosphorylation / Q000187:drug effects; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D020218:Response Elements / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D004151:Dipeptides; D015852:Eukaryotic Initiation Factor-2; C000619706:HSF1 protein, human; D018840:HSP70 Heat-Shock Proteins; C490786:HSPA1A protein, human; D000076249:Heat Shock Transcription Factors; D014157:Transcription Factors; C071482:calpeptin; D053148:Caspase 3; D020742:rhoA GTP-Binding Protein