Abstract
Aberrant expression of EVI1 has been frequently found in myeloid malignancies as well as in cancers of the ovary, lung, head and neck, cervix, and breast, and is associated with a poor patient survival. Targeted degradation of oncoproteins is an effective strategy for cancer therapy. The AML1/MDS1/EVI1 (AME) transcription factor fusion protein is a product of the human t(3;21)(q26;q22) translocation found as a secondary mutation in some cases of CML during the blast phase (CML-BP) and in patients with de novo and therapy-related myelodysplastic syndrome (MDS) and acute myelogenous leukemia (AML). Expression of AME in mouse bone marrow cells by retroviral transduction impairs hematopoiesis and eventually induces an acute myeloid leukemia (AML)-like disease in mice. Arsenic Trioxide (ATO) has been found to be an effective treatment for patients suffering from acute promyelocytic leukemia (APL). This is, at least in part, mediated by degradation of the PML/RARα oncoprotein that is associated with over 90% of APL. We have recently shown that ATO used at therapeutic levels also degrades AME. The ATO treatment induces differentiation and apoptosis in AME leukemic cells in vitro and causes decrease in peripheral leukemic cells and splenomegaly in vivo. ATO appears to target AME at both the EVI1 and MDS moieties of the protein for degradation via the ubiquitin-proteasome pathway and proteasome-independent mechanism, respectively. To investigate the mechanism of ATO induced degradation of EVI1 oncoproteins, we examined the effect of reactive oxygen species (ROS), on EVII expression, one of the downstream effectors of ATO-induced apoptosis. We found that EVI1 degradation correlates with the amount of ROS generated in cells. EVI1 can also be targeted for degradation by doxorubicin, a chemotherapeutic agent that is effective in treating AML and ovarian cancer and a strong ROS inducer. Interestingly, the antioxidant N-acetyl cysteine (NAC) abrogates the degradation of the EVI1 protein in the presence of doxorubicin. These results demonstrate that EVI1 can be targeted for degradation by ROS. ROS inducing agents could be used as a part of targeted therapy for EVI1-positive malignancies.