Divergent JNK Phosphorylation of HDAC3 in Triple-Negative Breast Cancer Cells Determines HDAC Inhibitor Binding and Selectivity

Histone deacetylase (HDAC) catalytic activity is regulated by formation of co-regulator complexes and post-translational modification. Whether these mechanisms are transformed in cancer and how this affects the binding and selectivity of HDAC inhibitors (HDACis) is unclear. In this study, we developed a method that identified a 3- to 16-fold increase in HDACi selectivity for HDAC3 in triple-negative breast cancer (TNBC) cells in comparison with luminal subtypes that was not predicted by current practice measurements with recombinant proteins. We found this increase was caused by c-Jun N-terminal kinase (JNK) phosphorylation of HDAC3, was independent of HDAC3 complex composition or subcellular localization, and was associated with a 5-fold increase in HDAC3 enzymatic activity. This study points to HDAC3 and the JNK axes as targets in TNBC, highlights how HDAC phosphorylation affects HDACi binding and selectivity, and outlines a method to identify changes in individual HDAC isoforms catalytic activity, applicable to any disease state.