Inhibitors of zinc-dependent histone deacetylases (HDACs) profoundly impact cellular function by altering gene expression via changes in nucleosomal histone tail acetylation. Historically, investigators have employed pan-HDAC inhibitors, such as the hydroxamate trichostatin A (TSA), which simultaneously targets members of each of the three zinc-dependent HDAC classes (classes I, II and IV). More recently, class- and isoform-selective HDAC inhibitors have been developed, providing invaluable chemical biology probes for dissecting the roles of distinct HDACs in the control of various physiological and pathophysiological processes. For example, the benzamide class I HDAC-selective inhibitor, MGCD0103, was shown to block cardiac fibrosis, a process involving excess extracellular matrix (ECM) deposition, which often results in heart dysfunction. Here, we compare the mechanisms of action of structurally distinct HDAC inhibitors in isolated primary cardiac fibroblasts, which are the major ECM-producing cells of the heart. TSA, MGCD0103, and the cyclic peptide class I HDAC inhibitor, apicidin, exhibited a common ability to enhance histone acetylation, and all potently blocked cardiac fibroblast cell cycle progression. In contrast, MGCD0103, but not TSA or apicidin, paradoxically increased expression of a subset of fibrosis-associated genes. Using the cellular thermal shift assay (CETSA), we provide evidence that the divergent effects of the HDAC inhibitors on cardiac fibroblast gene expression relates to differential engagement of HDAC1 and HDAC2-containing complexes. These findings illustrate the importance of employing multiple compounds when pharmacologically assessing HDAC function in a cellular context, and during HDAC inhibitor drug development.
- The American Society for Pharmacology and Experimental Therapeutics