Histone deacetylases (HDACs), enzymes involved in chromatin remodeling, are promising targets for anticancer drug development. Several HDAC inhibitors (HDACi) are in clinical trials. One limitation of present HDACi is their nonspecificity, affecting many HDACs with similar effectiveness. We have identified a small molecule, the sesquiterpene lactone parthenolide (PN), which specifically depletes HDAC1 protein without affecting other class I/II HDACs. HDAC1 depletion occurred through proteasomal degradation and resulted in transcriptional consequences comparable to those observed with pan-HDACi. Surprisingly, HDAC1 depletion did not occur through the inflammation mediator IKK2, a known PN target and regulator of HDAC1. Rather, PN promoted HDAC1 depletion and cell death through the DNA-damage-transducer ataxia telangiectasia mutated. Our study suggests that modulating cellular HDAC protein levels with small molecules provides an alternative approach to specific HDAC inhibition and effective cancer treatment.

Class I histone deacetylases (HDACs) are ubiquitous enzymes that repress gene expression by deacetylating histone tails and promoting chromatin compaction. Pro-inflammatory agents activate programmes of gene expression through transcription factors such as nuclear factor-jB (NF-jB), even in the context of ubiquitous HDAC activity. How this is accomplished remains unknown. We found that cells treated with the pro-inflammatory cytokine tumour necrosis factor-a rapidly and substantially reduced HDAC1 protein levels without affecting other class I HDACs. In addition, HDAC1 depletion occurred through protein degradation, required IKK2 activity and resulted in increased transcription from both NF-jB-associated and unassociated gene promoters. Our study suggests that the activation of programmes of gene expression by pro-inflammatory agents requires global changes in specific critical epigenetic regulators such as HDAC1.