FEBS Workshop on Chromatin Proteomics location:Heraklion, Crete, Greece date:3-8 October 2016
The Lens Epithelium Derived Growth Factor/p75 (LEDGF/p75) is a chromatin reader recognising H3K36me2 and me3 marks through its N-terminal PWWP domain. Through its C-terminal domain (IBD), LEDGF/p75 targets different non-related proteins and protein complexes to the chromatin. This function is hijacked by the Human Immunodeficiency Virus (HIV) to guide viral integration into active chromatin. Our group developed the first-in-class small molecules inhibiting the LEDGF/p75 – HIV interaction which are currently in early clinical development (Christ et al., 2010). LEDGF/p75 also tethers the Mixed-lineage leukemia protein (MLL) to the chromatin. MLL translocations induce a genetically distinct subset of acute leukemias with poor prognosis and the interaction with LEDGF/p75 has been shown to be essential for cellular transformation, making LEDGF/p75 an interesting therapeutic target. Until now it was however not clear how the IBD can interact with at least 7 structurally unrelated proteins and how a single HIV virus can compete with these cellular proteins to bind LEDGF/p75. Using NMR spectroscopy, we mapped the interaction of LEDGF/p75 with its cellular binding partners MLL, JPO2 and PogZ. These data revealed that the interaction of LEDGF/p75 is maintained by a conserved intrinsically disordered IBD binding motif (IBM). The importance of this motif was verified in vitro through mutational analysis. Mutants and inhibitory peptides also revealed that this interface is essential for MLL-rearranged leukemia. In addition, based on IBM conservation, we identify and validate IWS1 as a novel LEDGF/p75 interaction partner. Our results also reveal how HIV integrase efficiently displaces cellular binding partners from LEDGF/p75.