KLF4-mediated upregulation of the NKG2D ligand MICA in acute myeloid leukemia: a novel therapeutic target identified by enChIP.

The immunoreceptor NKG2D, which is expressed on NK cells and T cell subsets is critically involved in tumor immune surveillance. This applies in particular to acute myeloid leukemia (AML), which evades immune detection by downregulation of NKG2D ligands (NKG2D-L), including MICA. The absence of NKG2D-L on AML cells is moreover associated with leukemia stem cell characteristics. The NKG2D/NKG2D-L system thus qualifies as an interesting and promising therapeutic target.Here we aimed to identify transcription factors susceptible to pharmacological stimulation resulting in the expression of the NKG2D-L MICA in AML cells to restore anti-tumor activity. Using a CRISPR-based engineered ChIP (enChIP) assay for the MICA promoter region and readout by mass spectrometry-based proteomics, we identified the transcription factor krüppel-like factor 4 (KLF4) as associated with the promoter. We demonstrated that the MICA promoter comprises functional binding sites for KLF4 and genetic as well as pharmacological gain- and loss-of-function experiments revealed inducible MICA expression to be mediated by KLF4.Furthermore, induction in AML cells was achieved with the small compound APTO253, a KLF4 activator, which also inhibits MYC expression and causes DNA damage. This induction in turn yielded increased expression and cell surface presentation of MICA, thus rendering AML cells more susceptible to NK cell-mediated killing. These data unravel a novel link between APTO253 and the innate anti-tumor immune response providing a rationale for targeting AML cells via APTO253-dependent KFL4/MICA induction to allow elimination by endogenous or transplanted NK and T cells in vivo. Video Abstract.