Inhibition of histone deacetylases permits lipopolysaccharide-mediated secretion of bioactive IL-1b via a caspase-1-independent mechanism

Histone deacetylase (HDAC) inhibitors (HDACi) are clinically approved anticancer drugs that have important immunemodulatory properties. We report the surprising finding that HDACi promote LPS-induced IL-1 beta processing and secretion in human and murine dendritic cells and murine macrophages. HDACi/LPS-induced IL-1 beta maturation and secretion kinetics differed completely from those observed upon inflammasome activation. Moreover, this pathway of IL-1 beta secretion was dependent on caspase-8 but was independent of the inflammasome components NACHT, LRR, and PYD domains-containing protein 3, apoptosis-associated speck-like protein containing a carboxyl-terminal caspase-recruitment domain, and caspase-1. Genetic studies excluded HDAC6 and HDAC10 as relevant HDAC targets in this pathway, whereas pharmacological inhibitor studies implicated the involvement of HDAC11. Treatment of mice with HDACi in a dextran sodium sulfate-induced colitis model resulted in a strong increase in intestinal IL-1 beta, confirming that this pathway is also operative in vivo. Thus, in addition to the conventional inflammasome-dependent IL-1 beta cleavage pathway, dendritic cells and macrophages are capable of generating, secreting, and processing bioactive IL-1 beta by a novel, caspase-8-dependent mechanism. Given the widespread interest in the therapeutic targeting of IL-1 beta, as well as the use of HDACi for anti-inflammatory applications, these findings have substantial clinical implications