Abstract 5376: Requirement of TET2 in MLL-AF9 mediated leukemogenesis

Abstract

Abstract TET methylcytosine dioxygenase 2 (TET2) catalyzes the conversion of 5-methylcytosine to 5-hydroxymethylcytosine resulting in DNA demethylation. Loss-of-function mutations or deletions of TET2 have been found in several myeloid malignancies including myelodysplastic syndrome (MDS), myeloproliferative neoplasms (MPN), chronic myelomonocytic leukemia (CMML) and acute myeloid leukemia (AML). Moreover, deletion of TET2 leads to myeloid malignancies in mice. Therefore, TET2 has been suggested to play a tumor suppressor role in myeloid malignancies. In this study, unexpectedly, we have uncovered a tumor promoter function for TET2 in MLL rearranged leukemia. Chromosomal rearrangements of the Mixed Lineage Leukemia (MLL) gene have been found in ~10% of acute leukemia and are associated with poor prognosis. We observed that depletion of TET2 significantly inhibited the proliferation of MLL-AF9 positive MOLM14 leukemia cells. Similarly, knockdown of TET2 markedly reduced proliferation in murine Ba/F3 cells stably expressing MLL-AF9. Conversely, overexpression of TET2 significantly increased proliferation in MLL-AF9 expressing MOLM14 and Ba/F3 cells. In addition, deletion of TET2 significantly inhibited MLL-AF9 mediated myeloid colony formation in the bone marrow (BM) cells ex vivo. Next, we assessed the in vivo effects of TET2 deletion in MLL-AF9-mediated leukemogenesis using retroviral bone marrow transduction and transplantation assays. Whereas recipients of MLL-AF9-transduced wild type BM exhibited marked increase in white blood cells (WBC) and neutrophils in their peripheral blood and significant increase in the spleen size, recipients of MLL-AF9-transduced TET2-deficient BM showed significantly reduced WBC and neutrophil counts and reduced spleen size. Flow cytometric analysis showed significantly increased myeloid precursors (Gr-1+/Mac1+) and granulocyte macrophage progenitors (GMP) in the BM of transplanted animals receiving MLL-AF9 expressing wild type BM compared with recipients of MLL-AF9 expressing TET2-deficient BM. Furthermore, transplanted animals receiving MLL-AF9-transduced wild type BM showed marked increase in hematopoietic stem/progenitor cells (LSK; Lin-Sca-1+c-kit+), which was significantly reduced upon TET2 deletion. Deficiency of TET2 also significantly reduced MLL-AF9-mediated increase in hematopoietic progenitor colony formation in the BM. In addition, deletion of TET2 resulted in increased overall survival in mice expressing MLL-AF9. Together, these data indicate that TET2 is required for leukemic transformation mediated by MLL-AF9. Our results suggest a novel tumor promoter function for TET2 in MLL rearranged leukemia. Citation Format: Dipmoy Nath, Golam Mohi. Requirement of TET2 in MLL-AF9 mediated leukemogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5376. doi:10.1158/1538-7445.AM2017-5376