ABSTRACT: Aberrant expression of the homeodomain transcription factor CDX2 occurs in most cases of acute myeloid leukemia (AML) and promotes leukemogenesis, making CDX2, in principle, an attractive therapeutic target. Conversely, CDX2 acts as a tumor suppressor in colonic epithelium. The effectors mediating the leukemogenic activity of CDX2 and the mechanism underlying its context-dependent properties are poorly characterized, and strategies for interfering with CDX2 function in AML remain elusive. We report data implicating repression of the transcription factor KLF4 as important for the oncogenic activity of CDX2, and demonstrate that CDX2 differentially regulates KLF4 in AML versus colon cancer cells through a mechanism that involves tissue-specific patterns of promoter binding and epigenetic modifications. Furthermore, we identified deregulation of the PPARγ signaling pathway as a feature of AML expressing CDX2, and observed that PPARγ agonists derepress KLF4 and are preferentially toxic to CDX2-positive leukemic cells. These data delineate transcriptional programs associated with CDX2 expression in hematopoietic cells; provide insight into the antagonistic duality of CDX2 function in AML versus colon cancer; and suggest reactivation of KLF4 expression, through modulation of PPARγ signaling, as a new therapeutic modality in a large proportion of AML patients. Experiment 1 (Samples 1-6): The transcriptional changes induced by Cdx2 were assessed ex vivo in primary murine hematopoietic stem and progenitor cells. Bone marrow cells were harvested from 3x15 C57BL/6 mice, and differentiated cells were removed by incubation with rat antibodies against lineage antigens (CD3, CD4, CD8, Gr-1, B220, CD19, IL-7R, Ter119) followed by depletion with magnetic beads (Dynabeads, Invitrogen). Lineage-depleted cells were stained with APC-conjugated anti-c-Kit and PE-Cy5-conjugated goat anti-rat antibodies, and c-Kit+ Lin– cells were sorted using a BD FACSAria cell sorter (BD Biosciences). Cells were plated in RetroNectin-coated tissue culture dishes (Takara Bio) and transduced twice with pMSCV-Cdx2-IRES-GFP or pMSCV-IRES-GFP retroviral constructs. After 48 hours, GFP-positive cells were sorted using a BD FACSAria cell sorter. Experiment 2 (Samples 7-10): The transcriptional changes induced by Cdx2 were assessed in vivo in Cdx2-initiated murine leukemias and compared with those of leukemias initiated by 5 different MLL fusion oncogenes (previously published data, available at GSE13690). Bone marrow cells isolated from C57BL/6 mice were transduced with pMSCV-Cdx2-IRES-GFP, and 8x10e5 GFP-positive cells were injected into lethally irradiated syngeneic recipient mice after 48 hours, followed by injection of 1x10e6 spleen cells from primary leukemic animals into sublethally irradiated secondary recipients. Spleen cells from secondary leukemic animals were harvested.
