gamma-Glutamylcysteine synthetase and active transport of glutathione S-conjugate are responsive to heat shock in K562 erythroid cells.

Effect of heat shock on a glutathione-synthesizing enzyme, gamma-glutamylcysteine synthetase (gamma-GCS), and ATP-dependent outward transport of glutathione S-conjugate was characterized using K562 erythroid cells. When K562 cells grown at 37 degrees C were shifted to 42 degrees C for 2 h, an approximate 1.7-fold increase in the activity of gamma-GCS was observed. Treatment of K562 cells with erythropoietin (EP) for 12 h resulted in a decrease in the activity of gamma-GCS to 64% of the control. However, responsiveness of this enzyme activity in the cells treated with EP to heat shock was similar to that in untreated cells. Changes in the immunological activity of gamma-GCS were also observed in parallel with those in the enzymatic activity. On Northern blot analysis of total RNAs isolated from the cells with human cDNA for gamma-GCS, a substantial induction of mRNA level was found by heat shock and a reduction of EP. These changes were modest but correlated to the mRNA expression of a heat shock protein, HSP 70. Heat shock also had an effect of 1.8-fold stimulation on glutathione S-conjugate transport in K562 cells previously incubated with 1-chloro-2,4-dinitrobenzene. Treatment of the cells with EP resulted in a decrease in this transport by 62%. Similarly, the levels of glutathione S-conjugate-stimulated Mg(2+)-ATPase, which enzyme is thought to be involved in the transport of glutathione S-conjugate, were responsive to heat shock and EP. These results suggest that glutathione synthesis and transport process of glutathione metabolites are responsive to heat shock and play a role in the defense system against stresses. It is also suggested that the regulatory site of the expression of these enzymes by heat shock is independent of that by EP.