HoxA10 is a homeodomain transcription factor which is frequently overexpressed in human acute myeloid leukemia (AML). In murine bone marrow transplantation studies, HoxA10-overexpression induces a myeloproliferative disorder with accumulation of mature phagocytes in the peripheral blood and tissues. Over time, differentiation block develops in these animals, resulting in AML. In immature myeloid cells, HoxA10 represses transcription of some genes which confer the mature phagocyte phenotype. Therefore, overexpressed HoxA10 blocks differentiation by repressing myeloid-specific gene transcription in differentiating myeloid cells. In contrast, target-genes involved in myeloproliferation due to HoxA10-overexpression have not been identified. To identify such genes, we screened a CpG island microarray with HoxA10 co-immuno-precipitating chromatin. We identified the DUSP4 gene, which encodes mitogen activated protein kinase phosphatase 2 (Mkp2), as a HoxA10 target-gene. We analyzed the DUSP4 5’ flank and identified two proximal-promoter cis elements which are activated by HoxA10. We find that DUSP4-transcription and Mkp2-expression decrease during normal myelopoiesis. However, this down regulation is impaired in myeloid cells overexpressing HoxA10. In hematopoietic cells, c-Jun n-terminal kinases (Jnk) are the preferred substrates for Mkp2. Therefore Mkp2 inhibits apoptosis by de-phosphorylating (inactivating) Jnk. Consistent with this, HoxA10-overexpression decreases apoptosis in differentiating myeloid cells. Therefore, our studies identify a mechanism by which overexpressed HoxA10 contributes to inappropriate cell survival during myelopoiesis.