STAT5A regulates DNMT3A in CD34(+)/CD38(-) AML cells.

Signal transducer and activator of transcription 5 (STAT5) is activated in CD34(+)/CD38(-) acute myelogenous leukemia (AML) cells. Inhibition of STAT5 induced apoptosis and sensitized these cells to the growth inhibition mediated by conventional chemotherapeutic agents. The present study attempted to identify molecules that are regulated by STAT5 in CD34(+)/CD38(-) AML cells by utilizing cDNA microarrays, comparing the gene expression profiles of control and STAT5A shRNA-transduced CD34(+)/CD38(-) AML cells. Interestingly, DNA methyltransferase (DNMT) 3A was downregulated after depletion of STAT5A in CD34(+)/CD38(-) AML cells. Reporter gene assays found that an increase in activity of DNMT3A occurred in response to activation of STAT5A in leukemia cells. On the other hand, dephosphorylation of STAT5A by AZ960 decreased this transcriptional activity. Further studies utilizing a chromatin immunoprecipitation assay identified a STAT5A-binding site on the promoter region of DNMT3A gene. Forced expression of STAT5A in leukemia cells caused hypermethylation on the promoter region of the tumor suppressor gene, PTEN, and downregulated its mRNA levels, as measured by methylation-specific and real-time polymerase chain reaction, respectively. Taken together, these data suggest that STAT5A positively regulates levels of DNMT3A, resulting in inactivation of tumor suppressor genes by epigenetic mechanisms in AML cells.