Biochemical and Structural Studies of the Sin3L/HDAC Complex

Histone deacetylases (HDACs) have emerged as promising targets for treating a variety of pathological conditions including cancers, inflammatory disorders, cardiovascular, neurodegenerative, and infectious diseases. Nuclear HDACs – and HDAC2 in particular – have been implicated in promoting cardiac hypertrophy, thus making them attractive targets for selective inhibition. However, little is known at the molecular level regarding how these HDACs are recruited and incorporated into giant multi-protein corepressor complexes and how their activity and substrate specificity are modulated by other subunits and small molecules. This proposal seeks to fill these critical gaps in knowledge by characterizing the interactions involving the paralogous HDAC1 and HDAC2 enzymes with the core subunits of the 1.2-2 MDa Sin3L corepressor complex including Sin3A, SAP30, Sds3 and RBBP4/7 that each have been implicated in important roles in cardiac biology. Our goals in this proposal are (i) to characterize the enzymology of HDAC1/2 including elucidating its substrate specificity and modulation of its enzyme activity by core subunits of the Sin3L complex as well as by small molecules including those that enhance and inhibit its activity and (ii) to structurally characterize using crystallographic approaches and/or electron cryomicroscopy the binary and higher-order HDAC1/2 complexes involving one or more core subunits and evaluate the functional consequences of mutant subunits in vitro and in cells. These studies will provide a structural and mechanistic understanding of HDAC regulation and corepressor complex assembly which has implications in the design and development of isozyme- and/or corepressor complex-selective HDAC inhibitors for treating cardiovascular diseases.