Placental CRH may be part of a clock that governs the length of human gestation. The mechanism underlying differential regulation of CRH in the human placenta is poorly understood. We report here that constitutively activated RelB/nuclear factor-κB2 (NF-κB)-2 (p100/p52) acts as an endogenous stimulatory signal to regulate CRH by binding to an NF-κB enhancer of CRH gene promoter in the human placenta. Nuclear staining of NF-κB2 and RelB in villous syncytiotrophoblasts and cytotrophoblasts was coupled with cytoplasmic CRH in syncytial knots of cytotrophoblasts. Chromatin immunoprecipitation identified that CRH gene associated with both RelB and NF-κB2 (p52). Dexamethasone increased synthesis and nuclear translocation of RelB and NF-κB2 (p52) and their association with the CRH gene. In contrast, progesterone, a down-regulator of placental CRH, repressed NF-κB2 (p100) processing, nuclear translocation of RelB and NF-κB2 (p52), and their association with the CRH gene. Luciferase reporter assay determined that the NF-κB enhancer of CRH was sufficient to regulate transcriptional activity of a heterologous promoter in primary cytotrophoblasts. RNA interference-mediated repression of RelB or NF-κB2 resulted in significant inhibition of CRH at both transcriptional and translational levels and prevented the dexamethasone-mediated up-regulation of CRH transcription and translation. These results suggest that the noncanonical NF-κB pathway regulates CRH production in the human placenta and is responsible for the positive regulation of CRH by glucocorticoids.

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Corticotropin-releasing hormone (CRH) produced in the placenta may be part of a clock that regulates the length of human gestation. Maternal plasma CRH abundance exponentially increases as pregnancy advances. Glucocorticoid stimulates CRH expression in full-term human placenta by promoting noncanonical (RelB/p52 heterodimer-mediated) nuclear factor κB (NF-κB) pathway activity. Using dexamethasone to mimic glucocorticoid exposure, we found that an epigenetic switch mediated the glucocorticoid-induced expression of CRH as gestation advances. The amount of acetylated histone H3 lysine 9 (H3K9) associated with the CRH promoter was greater in cytotrophoblasts from full-term placenta than in those from midterm placenta. Knocking down the lysine acetyltransferase CBP reduced H3K9 histone acetylation and prevented dexamethasone-induced CRH expression. Unexpectedly, knocking down the histone deacetylase HDAC1 or pharmacologically inhibiting type I and II HDACs also decreased the expression of CRH yet increased the acetylation of H3K9 and other histone regions. Both CBP and HDAC1 bound at the CRH promoter in a complex with the RelB/p52 heterodimer in a mutually dependent manner; knocking down any one factor in the complex prevented binding of the others as well as the dexamethasone-induced CRH expression. Our results suggest that glucocorticoids induce a transcription complex consisting of RelB/p52, CBP, and HDAC1 that triggers a dynamic acetylation-mediated epigenetic change to induce CRH expression in full-term human placenta.