Granzyme A mediates glucocorticoid-induced apoptosis in leukemia cells

To identify the genes responsible for mediating apoptotic effects of glucocorticoid on leukemia cells, changes in gene expression were analyzed during dexamethasone-induced apoptosis of glucocorticoid-sensitive human acute lymphocytic leukemia 697 cells by using cDNA microarrays containing more than 4000 named genes. The microarray analysis showed that 26 genes had markedly differential expression after treatment with 100 nM dexamethasone; 17 genes were up-regulated, including granzyme A, glucocorticoid receptor, and suppressor of cytokine signaling-2; and nine genes were down-regulated, including early growth response 1 and acute myeloid leukemia 1. To circumvent the problem of recovering mRNA from dying cells, 697 cells that were stably transfected with the death inhibitor Bcl-2 were also used, and the expression of selected genes was examined by RT-PCR analysis, which confirmed the expression profile obtained by microarray analysis. The granzyme A protein accumulated in 697 cells and its enzymatic activity increased after dexamethasone treatment in a time-dependent manner, in accordance with the increase in caspase-3 activity. Furthermore, the granzyme inhibitor 3,4-dichloroisocoumarin inhibited the dexamethasone-induced apoptosis of 697 cells in a concentration-dependent manner. These results showed that granzyme A is critically involved in mediating the apoptotic effect of glucocorticoid on leukemia cells.