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Human placental CRH is part of a clock that governs the length of pregnancy. CRH is upregulated by glucocorticoid (GC) in the placenta, but is down regulated by GC in other human tissues. We hypothesized that epigenetic regulation is responsible for this difference in CRH regulation in the placenta.
Human midtrimester (MT) and term placentas were collected and cytotrophoblasts were cultured. Histone lysine acetylation was determined by electrophoresis and Western blot. Chromatin immunoprecipitation (ChIP) assay was used for analysis of acetylated histone lysines on the CRH gene. CRH RNA and protein levels were determined by RT-PCR and Western blot. Trophoblasts were exposed to Trichostatin A (TSA), an inhibitor of HDAC1 (histone deacetylation), or dexamethasone (DEX), Experiments were repeated 3 times. Statistical analysis was performed.
Screening of lysine residues identified that acetylation of H3-lysine 9 (H3K9) was highly accumulated in term placenta (Fig.1A). None of N-terminal tail lysine residues of either H3 and H4 were acetylated in the MT placenta 2) In ChIP assays, acetylated-H3K9 (ac-H3K9) showed 5∼6 fold increased association with CRH gene compared with control in term placenta, but not in the MT placenta. In the term placenta, CBP and HDAC1 showed ∼6 and ∼4 fold increased association with the CRH promoter, respectively (Fig.1B). 3) Knockdown of CBP or HDAC1 inhibited CRH mRNA level (Fig.1B). 4) Knockdown of CBP or HDAC1 inhibited association of RelB or p52 with CRH gene promoter (Fig.1C). 5) DEX promoted CRH expression and 2∼3 fold increased association of ac-H3K9 with CRH gene promoter in term placenta. 6) TSA reduced CRH expression.
Association of H3-K9 with the CRH gene increases as pregnancy advances, is increased by GC, and depends upon CBP and HDAC1. This may be the mechanism for an epigenetic switch responsible for upregulation of CRH by GC.