THE REGULATORY ROLE OF THE TRANSCRIPTION FACTOR ZNF224 IN CHRONIC MYELOGENOUS LEUKEMIA

The transcription factor ZNF224 was recently identified as a proapoptotic factor in chronic myelogenous leukemia (CML), mediating ara-C drug- induced apoptosis. Most recently, we demonstrated that the fusion protein Bcr-Abl negatively regulates ZNF224 expression in CML, while Bcr-Abl inhibition by the tyrosine kinase inhibitor (TKI) Imatinib, used as first-line treatment in CML, triggers ZNF224 up-regulation in CML cells. On the other hand, Bcr-Abl via Jak2 activation increases the expression of c-Myc gene, which is required for Bcr-Abl oncogenic transformation in CML. Coherently, Bcr-Abl inhibition by Imatinib results in c-Myc reduction, which represents a key step for Imatinib and new generation TKIs responsiveness in CML. In this work, we demonstrated that ZNF224 is a novel transcriptional repressor of c-Myc oncogene in CML and coherently, hampers c-Myc proliferative network, reducing CML cells proliferation and DNA synthesis. Intriguingly, our data describe a crucial role for ZNF224 induction in Imatinib repression on c-Myc in CML and subsequently demonstrate that alterations in ZNF224 binding sites on c-Myc promoter significantly affect Imatinib transcriptional repression of c-Myc gene in CML cells, thus suggesting a potential implication of this region in Imatinib responsiveness. In addition, we further reveal that AG490, a potent Jak2 inhibitor, negatively regulate c-Myc, at least in part via ZNF224 up-regulation. A crucial problem linked to TKIs treatment in CML is the possibility to develop resistance towards these drugs. Here we demonstrate that ZNF224 expression is lower in Imatinib-resistant CML cells and that its induction by Imatinib is impaired, but can be restored by AG490. Consistently, AG490 treatment or ZNF224 induction in Imatinib-resistant CML cells results in c- Myc reduction and apoptosis induction. Moreover, enforcing ZNF224 implications in Imatinib responsiveness, we further demonstrate that ZNF224 is a transcriptional repressor of AXL tyrosine kinase in CML, which plays a crucial role in Imatinib resistance in CML. Taken together, our results identify new mechanisms by which ZNF224 transcription factor exerts an anti-oncogenic effect in CML and highlight the crucial role of ZNF224 in Imatinib responsiveness, thus providing convincing evidence that ZNF224 induction could play a role in overcoming Imatinib resistance in CML cells.