Dexamethasone Regulates IGF-1 Expression And Affects Proliferation And Nutrient Transport After Syncytialazation In BeWo Cells

Prenatal exposure to excessive glucocorticoids(GCs)leads to impaired placental growth and functions,which contributes to intrauterine growth retardation and fetal programming of adult health and disease.Placental secretion of IGF-I plays a critical role in the regulation of placental growth and function in autocrine,paracrine or endocrine manners.GCs-induced reduction in placenta weight was associated with down-regulation of IGF-1 expression in placenta.However,the mechanism by which Dex inhibits IGF-1 expression in placenta remains elusive.Placenta contains cytotrophoblasts and syncytiotrophoblasts.During placentation,mononuclear cytotrophoblasts,which can mitosis and participate in the growth of the placenta,fuse to form a multinucleated syncytia ensuring hormonal production and nutrient exchanges between the maternal and fetal circulation.In this study,human placental choriocarcinoma(BeWo)cells before and after syncytialization were used as cytotrophoblasts and syncytiotrophoblasts models,respectively,to explore the effects of dexamethasone(Dex)on transcriptional regulation of IGF-1 gene and the placental growth and function.1 Dex affects proliferation of Be Wo cells via GR-mediated IGF-1 transcriptional regulationIn this study,human choriocarcinoma(BeWo)cells were used as models to investigate the effect of Dex on transcriptinal regulation of IGF-1 at cytrotrophoblast stage.We treated Be Wo cells with Dex(10-7 M)for 24 h.Dex significantly inhibited cell viability(P<0.05),decreased the proliferation rate as indicated by BrdU staining(P<0.05).Moreover,Dex induced cell cycle arrest at G0/G1 phase(P<0.05)testedby FACS.RT-PCR analysis showed a significant decrease(P<0.05)of mRNA expression for IGF-1 and its transcript variants,together with reduced IGF-1 level in the culture media(P<0.05).At the same time,Dex reduced the protein content of glucocorticoid receptor(GR)and its phoshorylated active form.Dex stimulated nucleus translocation of GR as shown by immunofluorescence staining.RU486,a glucocorticoid receptor.antagonist,completely prevented Dex-induced down-regulation of Be Wo cell proliferation and IGF-1 mRNA expression(P<0.05),indicating that Dex-regulated IGF-1 gene repression is mediated through GR.Two potential GREs were predicted in the IGF-1 gene promoter region.In order to elucidate the mechanisms by which GR regulates IGF-1 transcription,chromatin immunoprecipitation analysis was performed.GR binding to the GRE1 of the IGF1 gene promoter was significantly lower(P<0.05),yet that to the GRE2 was significantly higher(P<0.05)in Dex-treated cells.In addition,IGF-1 supplementation effectively restored Dex-induced inhibition of BeWo cell proliferation(P<0.05),indicating that Dex affects BeWo cell proliferation via GR-mediated IGF-1 transcriptional regulation.2 Dex regulates IGF-1 and SLC7A5 expression in syncytiotrophoblast via GR-mediated mechanismIn this study,forskolin-induced syncytialized BeWo cells were used as a model of syncytiotrophoblast to investigate the effect of Dex on the expression of IGF-1 and nutrients transporters in syncytiotrophoblasts.Cells were treated with Dex(10-7 M)for 24 h.Dex significantly down-regulated(P<0.05)the mRNA expression of amino acid transportor SLC7A5.Concurrently,the mRNA abundance of IGF-1 and its transcript variants was(P<0.05)down-regulated in Dex-treated syncytiotrophoblasts,together with significantly lower IGF-1 level in the media.Dex significantly descreased(P<0.05)the protein content of GR and its phoshorylated active form.RU486 was able to diminish Dex-induced GR phosphorylation and IGF-1 transrepression.ChIP analysis revealed significangtly decreased(P<0.05)binding of GR to GRE1 but not GRE2.IGF-1 supplementation was not able to reverse Dex-induced downregulation of SLC7A5,indicating that IGF-1 is unlikely involved in De-induced inhibition of SLC7A5 expression in syncytiotrophoblast.