Premature activation of the inflammatory processes that mediate human parturition leads to preterm birth, a major clinical problem associated with neonatal morbidity and mortality. Histone deacetylase inhibitors (HDACi) are currently in clinical trials for the treatment of inflammatory disorders. Recent evidence suggests that there may be a therapeutic use for HDACi in the management of preterm birth, with administration of HDACi to pregnant mice shown to delay delivery. Because NF-B is a key orchestrator of the inflammatory response and plays a pivotal role in parturition, it is important to understand how administration of HDACi might affect NF-B activity in human uterine tissues. We show here that the effects of HDACi on nuclear factor-B (NF-B) in human myometrial cells are time-dependent. Short-term exposure to HDACi enhanced interleukin (IL)-1-induced NF-B activity as a result of potentiating IB kinase (IKK) activity, thereby leading to persistent turnover of IB␣/ proteins and prolonging NF-B phosphorylation, nuclear localization, and DNA binding. Conversely, longterm HDACi treatments resulted in repression of NF-B DNA binding. Nevertheless, both short-and long-term HDACi treatments inhibited the expression of four labor-associated proinflammatory genes (COX-2, IL-8, IL-6, and RANTES), and this was associated with repression of the proinflammatory transcription factor c-Jun. Together, our data indicate that HDACi exert anti-inflammatory effects in human myometrium and may thus be useful in achieving a myometrial gene expression profile that favors uterine quiescence. However, coadministration of an IKK inhibitor may be both necessary and sufficient to circumvent potential induction of labor-associated pathways that could result from HDACi-induced augmentation of NF-B activity.During parturition, myometrium undergoes a transition from a state of quiescence to one of contractility, resulting in delivery of the neonate. Although the molecular mechanisms that underpin this transition are poorly understood, it is widely accepted that parturition is an inflammatory process, involving the up-regulation of multiple proinflammatory genes (Romero et al., 2006). Premature activation of uterine proinflammatory pathways can lead to preterm birth, a major clinical problem that occurs in 5 to 10% of pregnancies and is associated with 70 to 75% of neonatal morbidity/ mortality (Wen et al., 2004).Histone acetylation plays a major role in gene transcription, enabling the partial unraveling of local chromatin structure that is required to make the DNA accessible for binding by transcription factors and the basal transcription machinery (Li et al., 2004). Acetylation is reversible and reflects a dynamic balance between the activities of histone acetyltransferases (HATs) and histone deacetylases (HDACs). Aberrant recruitment of HDACs to promoters and/or overexpression of HDACs are observed in cancer cells, and This work was supported by Tommy's Campaign. Article, publication date, and citation information can be foun...