Myeloid Leukemogenesis Driven by Aberrant CDX2 Expression Involves Transcriptional Repression of KLF4 and Deregulated PPARγ Signaling

Aberrant expression of the developmental regulatory gene CDX2 in the adult hematopoietic compartment occurs in 90% of acute myeloid leukemia (AML) cases and promotes leukemogenesis. In contrast, CDX2 acts as a tumor suppressor in the colon and rectum. The effectors that mediate the leukemogenic activity of CDX2, as well as the mechanistic basis for the disparate functions of CDX2 in AML and colorectal cancer, remain largely unknown. Methods: DNA microarrays were used to characterize a gene signature that was activated in mouse hematopoetic stem and progenitor cells in response to enforced Cdx2 expression, in a murine model of Cdx2-induced leukemia, and in human AML associated with aberrant CDX2 expression. The functional role of candidate CDX2 effectors was evaluated by lentiviral gene knockdown and overexpression in myeloid leukemia and colon cancer cell lines. The interaction of CDX2 with putative target genes was examined by chromatin immunoprecipitation. A chemical-genomic analysis based on the Connectivity Map was used to identify drugs that may reverse CDX2-induced transcriptional changes. Results: A cross-species analysis of murine and human transcriptome data identified repression of the zinc-finger transcription factor KLF4 as an essential component of the CDX2 signature. KLF4 was silenced by CDX2, and restoration of KLF4 expression induced cell cycle arrest and apoptosis selectively in myeloid leukemia cells expressing CDX2. In contrast to AML, KLF4 is positively regulated by CDX2 in colonic epithelial cells, and consistent with its tissue-specific properties, CDX2 was found to bind to distinct sites in the KLF4 upstream regulatory region in AML versus colon cancer cells, which induced antagonistic changes in histone methylation patterns at the KLF4 promoter. A Connectivity Map analysis revealed that the transcriptional changes induced by CDX2 in hematopoietic cells are counteracted by drugs that stimulate the nuclear receptor PPARγ. Of potential therapeutic value, PPARγ agonists upregulate KLF4 expression and are preferentially toxic to CDX2-expressing myeloid leukemia cells, which were found to display altered PPARγ signaling both in vitro and in vivo. Conclusions: These data delineate the transcriptional program associated with CDX2 expression in hematopoietic cells, identify KLF4 as a reciprocally controlled AML suppressor gene, and uncover reactivation of KLF4 expression, through modulation of PPARγ signaling, as a novel therapeutic modality in CDX2-driven AML. Furthermore, these observations indicate that transcriptional regulators like CDX2 may have opposing effects on carcinogenesis in different tissues due to differential regulation of their downstream targets.

No relevant conflicts of interest to declare.