Resolving the deceptive isoform and complex selectivity of HDAC1/2 inhibitors

The histone deacetylase paralogs HDAC1/2/3 and their corepressor complexes serve as epigenetic master regulators of chromatin function. Over the past decades, HDACs have been widely pursued as pharmacological targets, and considerable efforts have been invested in the development of small molecule drugs. Specifically, ortho-aminoanilide-derived inhibitors, including CI-994 and Cpd-60, stand out with their attractive selectivity profiles and have been used extensively as tools to delineate the biological roles of specific HDAC isoforms and complexes. Here, we apply a suite of activity-independent strategies to investigate how dynamic processes that regulate HDAC complexes govern the isoform and complex selectivity of HDAC inhibitors. Importantly, we find that overreliance on static and simplified biochemical activity assays has confounded the determination of the biological selectivity of these ligands. Our data urge a comprehensive reinterpretation of numerous studies utilizing these tool compounds for the interrogation of epigenetic and other cellular processes.

Towards an understanding of the structure and function of MTA1

Gene expression is controlled through the recruitment of large coregulator complexes to specific gene loci to regulate chromatin structure by modifying epigenetic marks on DNA and histones. Metastasis-associated protein 1 (MTA1) is an essential component of the nucleosome remodelling and deacetylase (NuRD) complex that acts as a scaffold protein to assemble enzymatic activity and nucleosome targeting proteins. MTA1 consists of four characterised domains, a number of interaction motifs, and regions that are predicted to be intrinsically disordered. The ELM2-SANT domain is one of the best-characterised regions of MTA1, which recruits histone deacetylase 1 (HDAC1) and activates the enzyme in the presence of inositol phosphate. MTA1 is highly upregulated in several types of aggressive tumours and is therefore a possible target for cancer therapy. In this review, we summarise the structure and function of the four domains of MTA1 and discuss the possible functions of less well-characterised regions of the protein.