Modulation of the arsenite-induced expression of stress proteins by reducing agents.
We examined the effects of reducing agents on the expression of heat shock protein 27 (hsp27), alpha B crystallin, and hsp70 in C6 rat glioma cells in response to stress. Cells were exposed to arsenite (100 microM for 1 h) in the presence of dithiothreitol at various concentrations (0.03-2 mM), and the accumulation of all three proteins was markedly stimulated in cells that had been exposed to arsenite in the presence of a low concentration (0.03-0.1 mM) of dithiothreitol. Stimulation of these arsenite-induced responses was also observed in the presence of 0.1 mM 2-mercaptoethanol or 0.05 mM dithioerythritol. The enhanced expression of mRNAs for hsp27, alpha B crystallin and hsp70, as well as the prolonged activation of heat shock transcription factor 1 (HSF1), were also observed in cells that had been treated with arsenite in the presence of 0.05 mM dithiothreitol. The arsenite-inducible expression of the three proteins was completely suppressed when dithiothreitol was present at concentrations above 1 mM during the stress period, although delayed activation of the binding to a heat shock element (HSE) by phosphorylated HSF was observed in these cells. Exposure of cells first to arsenite for 1 h and then to dithiothreitol resulted in a very effective suppression of the arsenite-inducible responses, and the responses were inhibited even by a low concentration of dithiothreitol. These results suggest that the signal transduction pathway for the arsenite-induced expression of hsps involves at least two redox-sensitive steps: (i) a process that is stimulated by mild reducing power during the stress period; and (ii) a process that is followed by the activation of HSF and is very sensitive to suppression by a reducing agent.
Kato
K
K
Department of Biochemistry, Aichi Human Service Center, Japan.
Ito
H
H
Okamoto
K
K
D000818:Animals; D018053:Arsenites / Q000494:pharmacology*; D015153:Blotting, Western; D019256:Cadmium Chloride / Q000494:pharmacology; D003459:Crystallins / Q000187:drug effects / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000187:drug effects; D003864:Depression, Chemical; D004229:Dithiothreitol / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D018840:HSP70 Heat-Shock Proteins / Q000187:drug effects / Q000378:metabolism; D000076249:Heat Shock Transcription Factors; D006360:Heat-Shock Proteins / Q000096:biosynthesis* / Q000187:drug effects* / Q000378:metabolism; D006358:Hot Temperature; D051381:Rats; D019163:Reducing Agents / Q000494:pharmacology*; D013997:Time Factors; D014157:Transcription Factors; D014407:Tumor Cells, Cultured
D018053:Arsenites; D003459:Crystallins; D004268:DNA-Binding Proteins; D018840:HSP70 Heat-Shock Proteins; D000076249:Heat Shock Transcription Factors; D006360:Heat-Shock Proteins; C000619709:Hsf1 protein, rat; D019163:Reducing Agents; D014157:Transcription Factors; D019256:Cadmium Chloride; C015001:arsenite; D004229:Dithiothreitol