Hydrogen peroxide signaling is required for glucocorticoid-induced apoptosis in lymphoma cells

Glucocorticoid-induced apoptosis is exploited clinically for the treatment of hematologic malignancies. Determining the required molecular events for glucocorticoid-induced apoptosis will identify resistance mechanisms and suggest strategies for overcoming resistance. In this study, we found that glucocorticoid treatment of WEHI7.2 murine thymic lymphoma cells increased the steady-state [H2O2] and oxidized the intracellular redox environment before cytochrome c release. Removal of glucocorticoids after the H2O2 increase resulted in a 30% clonogenicity; treatment with PEG–CAT increased clonogenicity to 65%. Human leukemia cell lines also showed increased H2O2 in response to glucocorticoids and attenuated apoptosis after PEG–CAT treatment. WEHI7.2 cells that overexpress catalase (CAT2, CAT38) or were selected for resistance to H2O2 (200R) removed enough of the H2O2 generated by glucocorticoids to prevent oxidation of the intracellular redox environment. CAT2, CAT38, and 200R cells showed a 90–100% clonogenicity. The resistant cells maintained pERK survival signaling in response to glucocorticoids, whereas the sensitive cells did not. Treating the resistant cells with a MEK inhibitor sensitized them to glucocorticoids. These data indicate that: (1) an increase in H2O2 is necessary for glucocorticoid-induced apoptosis in lymphoid cells, (2) increased H2O2 removal causes glucocorticoid resistance, and (3) MEK inhibition can sensitize oxidative stress-resistant cells to glucocorticoids.

► Glucocorticoids cause apoptosis in lymphoma cells.
► Glucocorticoid treatment increases intracellular H2O2.
► Removal of the excess H2O2 causes glucocorticoid resistance.
► H2O2 is a necessary signal for glucocorticoid-induced apoptosis.
► MEK inhibitors overcome glucocorticoid resistance in ROS-resistant cells.