title: Term myometrium is characterized by increased activating epigenetic modifications at the progesterone receptor-A promoter.
abstract: Term human myometrial expression of progesterone receptor (PR)-A is increased relative to PR-B, and as PR-A is a repressor of progesterone action mediated through PR-B, this increase may mediate the withdrawal of progesterone action and precipitate the onset of labour. PR-A and PR-B expression is regulated by two separate promoters of the PR gene. We hypothesized that epigenetic histone modifications at the two promoters contribute to the labour-associated regulation of PR-A and PR-B expression in term myometrium. PR total, PR-B and PR-A mRNA levels were determined using quantitative real-time PCR, and chromatin immunoprecipitation was used to determine the levels of activating and repressive histone modifications at the PR-A and PR-B promoters in human myometrial samples not in labour (n = 4) and in labour (n = 4). Chromatin extracts were immunoprecipitated with antibodies against activating (histone H3 and H4 acetylation and histone H3 lysine 4 trimethylation), and repressive (histone H3 lysine 9 trimethylation, histone H3 lysine 27 trimethylation and asymmetrical histone H3 arginine 2 dimethylation) histone modifications. PR-A mRNA levels increased during labour, while PR-B mRNA levels remained constant resulting in an increase of PR-A/PR-B mRNA ratio, as expected. Regardless of labour status, significantly higher levels of the activating histone modifications were found at the PR-A promoter compared with the PR-B promoter (P <0.001). H3K4me3 increased significantly at both promoters with labour onset (P =0.001). Low levels of the repressive histone modifications were also present at both promoters, with no labour-associated changes observed. Our data indicate that the PR-A promoter is epigenetically marked for activation in term myometrium more extensively than the PR-B promoter, and that labour is associated with an increase in H3K4me3 activating modification, consistent with the previously described increase in PR protein at this time.
authors.affiliation: Mothers and Babies Research Centre,  Hunter Medical Research Institute, University of Newcastle, Newcastle, NSW 2310,  Australia.
authors.forename: S Y
authors.initials: SY
authors.lastname: Chai
authors.forename: R
authors.initials: R
authors.lastname: Smith
authors.forename: T
authors.initials: T
authors.lastname: Zakar
authors.forename: C
authors.initials: C
authors.lastname: Mitchell
authors.forename: G
authors.initials: G
authors.lastname: Madsen
mesh_terms: D044127:Epigenesis, Genetic; D005260:Female; D006657:Histones / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D007745:Labor Onset / Q000378:metabolism*; D009215:Myometrium / Q000378:metabolism*; D011247:Pregnancy; D011263:Pregnancy Trimester, Third; D011374:Progesterone / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011980:Receptors, Progesterone / Q000235:genetics* / Q000378:metabolism
chemical_list: D006657:Histones; D012333:RNA, Messenger; D011980:Receptors, Progesterone; C101118:progesterone receptor A; C097314:progesterone receptor B; D011374:Progesterone