Indexed on: 16 Mar '10Published on: 16 Mar '10Published in: Cell and Tissue Biology
In this study, we examined the role of JAK/STAT signaling in the regulation of chronic leukemia K562 cell proliferation. STAT3 and STAT5 tyrosine phosphorylation was used as a marker of the activation status of STAT proteins. We demonstrated that, in growing cultures of K562 cells, both STAT3 and STAT5 are constitutively activated. To determine the significance of STAT activity in maintaining the high level of K562 proliferation, we tested two JAK inhibitors, AG-490 (JAK2 and JAK3 inhibitor) and WHI-P131 (a new specific JAK3 inhibitor). We showed that, during the prolonged cultivation (48 h) of K562 cells with AG-490 or WHI-P131, the cells remained viable. It was found that treatment with WHI-P131 (30–100 μM) decreased tyrosine phosphorylation of STAT5 and did not affect the high level of STAT3 phosphorylation. In proliferating K562 cells, AG-490 (25–50 μM) did not influence on STAT3 and STAT5 phosphorylation. The flow cytometry analysis revealed a dose-dependent decrease in G1 and S phases and an increase in G2/M phases in WHI-P131-treated K562 cells and no changes in cell cycle structure in AG-490-treated cultures. Thus, our findings indicate the preferential role of STAT5 (not constitutively active STAT3) in the proliferation of leukemia K562 cells and demonstrate the specificity of WHI-P131 inhibitory effect; unlike other JAK drugs that stimulate apoptosis and decrease proliferation, WHI-P131 prevents K562 cells growth by arresting in G2/M phases of the cell cycle.