title: Involvement of Epac1/Rap1/CaMKI/HDAC5 signaling cascade in the regulation of placental cell fusion.
abstract: The placental transcription factor glial cell missing 1 (GCM1) and its target gene syncytin-1 are involved in cAMP-stimulated trophoblastic fusion for syncytiotrophoblast formation. GCM1 DNA-binding activity is inhibited by sumoylation, whereas GCM1 stability is decreased by deacetylation. cAMP enhances GCM1 desumoylation through the Epac1/Rap1/CaMKI signaling cascade and CaMKI is known to down-regulate class IIa HDAC activity. In this paper, we study whether the Epac1/Rap1/CaMKI signaling cascade regulates GCM1 activity and placental cell fusion through class IIa HDACs. Interaction and co-localization of GCM1 and HDAC5 were characterized by co-immunoprecipitation analysis and immunofluorescence microscopy (IFM). Regulation of GCM1 transcription activity and syncytin-1 expression by HDAC5 was studied by transient expression. Phospho-specific antibodies against HDAC5, RNA interference and IFM were used to examine the de-repression of GCM1 activity, syncytin-1 expression and cell-cell fusion by Epac1/Rap1/CaMKI signaling cascade in placental BeWo cells expressing constitutively active Epac1 and CaMKI. We demonstrate that both GCM1 and HDAC5 are expressed in the syncytiotrophoblast layer of full-term placenta and the nuclei of BeWo cells. The interaction between HDAC5 and GCM1 facilitates GCM1 deacetylation and suppresses its transcriptional activity. In contrast, Epac1 stimulates HDAC5 phosphorylation on Ser259 and Ser498 in a Rap1- and CaMKI-dependent manner leading to nuclear export of HDAC5 and thereby de-repression of GCM1 transcriptional activity. Importantly, HDAC5 suppresses syncytin-1 expression and cell-cell fusion in BeWo cells, which is counteracted by Epac1 and CaMKI. Our results reveal a new layer of regulation of GCM1 activity and placental cell fusion through the Epac1/Rap1/CaMKI signaling cascade by restraining HDAC5 from interacting with and mediating GCM1 deacetylation.
authors.affiliation: Institute of Biological Chemistry, Academia Sinica, Nankang, Taipei 115, Taiwan.
authors.forename: Ching-Wen
authors.initials: CW
authors.lastname: Chang
authors.forename: Mei-Leng
authors.initials: ML
authors.lastname: Cheong
authors.forename: Geen-Dong
authors.initials: GD
authors.lastname: Chang
authors.forename: Ming-Song
authors.initials: MS
authors.lastname: Tsai
authors.forename: Hungwen
authors.initials: H
authors.lastname: Chen
mesh_terms: D021581:Active Transport, Cell Nucleus; D054729:Calcium-Calmodulin-Dependent Protein Kinase Type 1 / Q000378:metabolism*; D002459:Cell Fusion; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D004268:DNA-Binding Proteins; D005260:Female; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D057809:HEK293 Cells; D006655:Histone Deacetylases / Q000378:metabolism*; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism; D010920:Placenta / Q000166:cytology* / Q000378:metabolism; D011247:Pregnancy; D011485:Protein Binding; D015398:Signal Transduction / Q000502:physiology; D014157:Transcription Factors / Q000378:metabolism; D014327:Trophoblasts / Q000166:cytology* / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; C491089:GCM1 protein, human; D020662:Guanine Nucleotide Exchange Factors; D009687:Nuclear Proteins; C116122:RAPGEF3 protein, human; D014157:Transcription Factors; C517596:CAMK1 protein, human; D054729:Calcium-Calmodulin-Dependent Protein Kinase Type 1; C404500:HDAC5 protein, human; D006655:Histone Deacetylases
keywords: Epac1; GCM1; HDAC5; cell–cell fusion; placenta