Validation of the MLL-LEDGF/P75 interaction as a therapeutic target for mixed lineage leukemia

Mixed-lineage leukemia (MLL)-rearrangements induce a genetically distinct and aggressive subset of human acute leukemia. N-terminal MLL fusions form a complex with the lens epithelium-derived growth factor (LEDGF/p75) and MENIN. This complex contributes to the association of MLL-fusion multiprotein complexes to chromatin. Knockdown and transdominant experiments have shown that both LEDGF/p75 and MENIN are required for efficient MLL fusion-mediated transformation and for the expression of downstream MLL regulated genes like HOXA9 and MEIS1. LEDGF/p75 interacts with MLL-MENIN via its integrase binding domain (IBD). Through X-ray crystallography, NMR spectroscopy and mutational studies we and others resolved the MLL-MENIN-LEDGF/p75 complex. Colony forming assays with primary murine MLL-AF9 immortalized cells expressing MLL interaction-defective LEDGF/p75 mutants confirmed that the complex is crucial for leukemic transformation. Next to MLL, LEDGF/p75 is known to interact with several other proteins including JPO2, PogZ, and HIV-1 integrase. We analysed the IBD interaction with JPO2 and PogZ by NMR. Mutational analysis and competition experiments showed that the interaction of MLL, Jpo2 and PogZ with the IBD is mutual exclusive and maintained by an intrinsically unstructured consensus motif. The newly defined interface overlaps with the binding site of HIV-1 integrase. Overexpression of a LEDGF/p75 binding peptide, known to inhibit the LEDGF/p75-HIV-1 integrase interaction, also impaired growth of primary murine MLL-AF9 expressing leukemic blasts providing a direct rationale for the design of small molecules targeting the LEDGF/p75-MLL interaction.