Physical Interaction of the Proto-Oncogene EVI1 with Hypermethylated in Cancer 1 (HIC1) Deregulates EVI1 Mediated Apoptosis in Cancer Cells

Abstract 2449

The ecotropic viral integration site I (EVII) gene has attracted considerable attention in recent years because of its reported involvement in chronic myeloid leukemia, high risk myelodysplastic syndrome and a very high percentage of acute myeloid leukemias. The most recent World Health Organization classification has designated AML with inv (3) or t(3;3) and associated RPN1/EVI1 fusion, as a distinct AML subgroup associated with an unfavorable prognosis. Studies also indicate that EVI1 may be overexpressed in a subset of human colon cancers, and that EVI1 might affect disease progression and/or sensitivity to chemotherapy. The presence of zinc finger domains that are able to bind to specific sequences of DNA suggests that EVI1 is a transcriptional regulator; however, few target genes of EVI1 have been functionally identified. In the present study, we demonstrate by co-immunoprecipitation assay that the proximal zinc finger domain of EVI1 binds to HIC1, which abolishes the ability of EVI1 to induce expression of Bcl-xL. HIC1, is an epigenetically regulated transcriptional repressor that functionally cooperates with p53 to suppress age dependent development of cancer in mice. Inactivation of HIC1 results in up regulation of SIRT1, which deacetylate and inactivates p53; allowing cells to bypass apoptosis and DNA damage survival., Our study also demonstrates via indirect immuno fluorescence analysis that EVI1 and HIC1 proteins are colocalized in speckles in the nucleus. We recently reported that EVI1 not only binds the Bcl-xL promoter but also up regulates its transcriptional activity and protein expression. We now demonstrate by EMSA and luciferase assays that physical interaction between EVI1 and HIC1 releases the binding of EVI1 from the Bcl-xL promoter, and hence promotes apoptosis. Thus by directly binding to EVI1, HIC1 displaces EVI1 from its DNA consensus site leading to down regulation of Bcl-xL. Also we observed that posttranslational modification of EVI1, mainly acetylation plays a critical role in this EVI1-HIC1 protein-protein interaction. Further elucidation of the counteracting effects of HIC1 and EVI1 on Bcl-xL expression may provide new insights in EVI1 mediated disease progression.