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 degrees 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 degrees C for 4 h. Two-dimensional PAGE analysis of GSH-depleted cells incubated at 37 degrees 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 degrees 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 degrees 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 degrees C. These results suggest that the synthesis of stress proteins can be affected by glutathione concentrations.