Modulation of the arsenite-induced expression of stress proteins by reducing agents

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Cell Stress Society International

RESUMO

We examined the effects of reducing agents on the expression of heat shock protein 27 (hsp27), αB crystallin, and hsp70 in C6 rat glioma cells in response to stress. Cells were exposed to arsenite (100 µM 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, αB crystalling 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 completly supressed 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 supression 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 expreesion 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 supression by a reducing agent.

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