Synthesis of hsp-70 Is Enhanced in Glutathione-Depleted Hep G2 Cells

The question of whether depletion of glutathione (GSH) could affect the synthesis of stress proteins was investigated in Hep G2 cells. Cells were exposed to BSO/DEM at 37°C to deplete glutathione. When 95% of the glutathione was depleted cells were washed, and BSO was added to cells previously exposed to BSO/DEM; then the cells were incubated at 37, 38.5, or 39°C for 4 h. Two-dimensional PAGE analysis of GSH-depleted cells incubated at 37°C indicated increased synthesis of heme oxygenase and a polypeptide tentatively identified as hsp-70B′. Depletion of GSH did not affect the cellular concentration of hsp-70 as assessed by Western immunoblotting, yet Northern blot analysis indicated that hsp-70 mRNA was increased in GSH-depleted cells. Incubation of GSH-replete cells at 38.5°C did not appear to enhance the amount of hsp-70 mRNA or the relative rate of hsp-70 synthesis. In contrast, incubation of GSH-depleted cells at 38.5°C elevated steady-state hsp-70 mRNA levels and the rate of hsp-70 synthesis relative to total protein synthesis. Depletion of GSH also increased the relative rate of hsp-70 synthesis at 39°C. These results suggest that the synthesis of stress proteins can be affected by glutathione concentrations.