STAT5-dependent regulation of CDC25A by miR-16 controls proliferation and differentiation in FLT3-ITD acute myeloid leukemia

We recently identified the CDC25A phosphatase as a key actor in proliferation and differentiation in acute myeloid leukemia which expresses the FLT3-ITD mutation. In this paper we demonstrate that CDC25A level is controlled by a complex STAT5/miR-16 transcription and translation pathway working downstream of this receptor. First, we established by CHIP analysis that STAT5 is directly involved in FLT3-ITD-dependent CDC25A gene transcription. In addition, we determined that miR-16 expression is repressed by FLT3-ITD activity, and that STAT5 participates in this repression. In accordance with these results, miR-16 expression was significantly reduced in a panel of AML primary samples carrying the FLT3-ITD mutation when compared with FLT3wt cells. The expression of a miR-16 mimic reduced CDC25A protein and mRNA levels, and RNA interference-mediated down modulation of miR-16 restored CDC25A expression in response to FLT3-ITD inhibition. Finally, decreasing miR-16 expression partially restored the proliferation of cells treated with the FLT3 inhibitor AC220, while the expression of miR-16 mimic stopped this proliferation and induced monocytic differentiation of AML cells. In summary, we identified a FLT3-ITD/STAT5/miR-16/CDC25A axis essential for AML cell proliferation and differentiation.

The cell cycle regulator CDC25A is a target for JAK2V617F oncogene

The JAK2V617F mutation is present in the majority of patients with polycythemia vera and one-half of those with essential thrombocythemia and primary myelofibrosis. JAK2V617F is a gain-of-function mutation resulting in constitutive JAK2 signaling involved in the pathogenesis of these diseases. JAK2V617F has been shown to promote S-phase entry. Here, we demonstrate that the CDC25A phosphatase, a key regulator of the G1/S cell-cycle transition, is constitutively overexpressed in JAK2V617F-positive cell lines, JAK2-mutated patient CD36+ progenitors, and in vitro–differentiated proerythroblasts. Accordingly, CDC25A is overexpressed in BM and spleen of Jak2V617F knock-in mice compared with wild-type littermates. By using murine FDC-P1–EPOR and human HEL and SET-2 cell lines, we found that JAK2V617F-induced CDC25A up-regulation was caused neither by increased CDC25A transcription or stability nor by the involvement of its upstream regulators Akt and MAPK. Instead, our results suggest that CDC25A is regulated at the translational level through STAT5 and the translational initiation factor eIF2α. CDC25A inhibition reduces the clonogenic and proliferative potential of JAK2V617F-expressing cell lines and erythroid progenitors while moderately affecting normal erythroid differentiation. These results suggest that CDC25A deregulation may be involved in hematopoietic cells expansion in JAK2V617F patients, making this protein an attracting potential therapeutic target.