Enhancement of expression of stress proteins by agents that lower the levels of glutathione in cells.

The effects of diethyl maleate and buthionine sulfoximine, agents that lower cellular levels of glutathione, on expression of hsp27 and alphaB crystallin in response to stress were studied. When C6 rat glioma cells were treated with 100 microM arsenite for 1 h, accumulation of the two proteins, estimated by specific immunoassays, was markedly enhanced by additional exposure to 1 mM diethyl maleate or 2.5 mM buthionine sulfoximine. The latter also increased heat- and CdCl2-induced accumulation of hsp27 and alphaB crystallin. Stress-induced accumulation of hsp70, estimated by Western blotting analysis, was also enhanced by these agents. Northern blotting analysis revealed increase in levels of mRNAs for hsp27, alphaB crystallin and hsp70. The period of heat shock element (HSE)-binding activity of heat shock factor (HSF) stimulated by arsenite was extended by addition of diethyl maleate and buthionine sulfoximine. The induced phosphorylated state of HSF1 was also prolonged by diethyl maleate. Although exposure of cells to diethyl maleate alone for 1 h caused neither accumulation of hsp27, alphaB crystallin and hsp70 nor expression of mRNAs for these proteins, HSE-binding activity of HSF was stimulated. However, the activated HSF was not phosphorylated. These results suggest that diethyl maleate induces an intermediate state of HSF that binds to HSE but is transcriptionally inert. The mechanism is unclear but the levels of glutathione in cells that were exposed to diethyl maleate or buthionine sulfoximine were markedly decreased.