The structural basis of the p50:p50:HDAC1 anti-inflammatory corepressor complex

Abstract

Protein-protein interactions between NF-κB subunits and many transcriptional regulatory proteins have been discussed and in some cases well understood, however, the structural basis of the previously described p50:p50- Histone Deacetylase 1 (HDAC1) inflammatory repressor complex is poorly characterized. Understanding the mechanism of this interaction will be invaluable in the search for therapeutics that exploit this complex to attenuate inflammation in a potentially IKK-independent manner. We have combined in silico analysis along with in vitro peptide arrays, coexpression and co-immunoprecipitation assays to verify potential sites of interaction between the p50 homodimer and HDAC1. Multiple sites of interest on the p50 structure determined from in silico predictions were combined with peptide array data to reveal clear regions of potential interaction between p50 and HDAC1. Detailed directed mutagenesis of one such region (the nuclear localization sequence) resulted in a loss of the interaction between p50 and HDAC1 in coimmunoprecipitation experiments. Additionally, loss of this HDAC1 interaction appears to induce a greater pro-inflammatory response in both resting and stimulated conditions. These results provide the first structural evidence of a direct interaction and points to a specific region of p50 as the key region for p50 proteinprotein interaction. Establishing the rules governing this critical complex will undoubtedly assist in further exploration of its properties in vivo and shed light on the complex interactions of NF-κB transcription factors and their co-regulators. Further studies have the potential to identify novel tailored therapeutic targets in diseases characterized by both acute and chronic inflammation unencumbered by the drawbacks associated with the ubiquitous actions of therapeutic kinase inhibitors.