Aim: The phosphorylation of histone H2AX, a novel tumor suppressor protein, is involved in regulation of cancer cell apoptosis. The aim of this study was to examine whether H2AX phosphorylation was required for resveratrol-induced apoptosis of human chronic myelogenous leukemia (CML) cells in vitro.Methods: K562 cells were tested. Cell apoptosis was analyzed using flow cytometry, and the phosphorylation of H2AX and other signaling proteins was examined with Western blotting. To analyze the signaling pathways, the cells were transfected with lentiviral vectors encoding H2AX-wt or specific siRNAs. Results: Treatment of K562 cells with resveratrol (20-100 µmol/L) induced apoptosis and phosphorylation of H2AX at Ser139 in time-and dose-dependent manners, but reduced phosphorylation of histone H3 at Ser10. Resveratrol treatment activated two MAPK family members p38 and JNK, and blocked the activation of another MAPK family member ERK. Pretreatment with the p38 inhibitor SB202190 or the JNK inhibitor SP600125 dose-dependently reduced resveratrol-induced phosphorylation of H2AX, which were also observed when the cells were transfected with p38-or JNK-specific siRNAs. Overexpression of H2AX in K562 cells markedly increased resveratrol-induced apoptosis, whereas overexpression of H2AX-139m (Ser139 was mutated to block phosphorylation) inhibited resveratrol-induced apoptosis. K562 cells transfected with H2AX-specific siRNAs were resistant to resveratrol-induced apoptosis. Conclusion: H2AX phosphorylation at Ser139 in human CML cells, which is regulated by p38 and JNK, is essential for resveratrolinduced apoptosis.

Increasing evidence suggests that histone H2AX plays a critical role in regulation of tumor cell apoptosis and acts as a novel human tumor suppressor protein. However, the action of H2AX in chronic myelogenous leukemia (CML) cells is unknown. The detailed mechanism and epigenetic regulation by H2AX remain elusive in cancer cells. Here, we report that H2AX was involved in apoptosis of CML cells. Overexpression of H2AX increased apoptotic sensitivity of CML cells (K562) induced by imatinib. However, overexpression of Ser139-mutated H2AX (blocking phosphorylation) decreased sensitivity of K562 cells to apoptosis. Similarly, knockdown of H2AX made K562 cells resistant to apoptotic induction. These results revealed that the function of H2AX involved in apoptosis is strictly related to its phosphorylation (Ser139). Our data further indicated that imatinib may stimulate mitogen-activated protein kinase (MAPK) family member p38, and H2AX phosphorylation followed a similar time course, suggesting a parallel response. H2AX phosphorylation can be blocked by p38 siRNA or its inhibitor. These data demonstrated that H2AX phosphorylation was regulated by p38 MAPK pathway in K562 cells. However, the p38 MAPK downstream, mitogen- and stress-activated protein kinase-1 and -2, which phosphorylated histone H3, were not required for H2AX phosphorylation during apoptosis. Finally, we provided epigenetic evidence that H2AX phosphorylation regulated apoptosis-related gene Bim expression. Blocking of H2AX phosphorylation inhibited Bim gene expression. Taken together, these data demonstrated that H2AX phosphorylation regulated by p38 is involved in Bim expression and apoptosis in CML cells induced by imatinib.