Methylation status and transcriptional expression of the MHC class I loci in human trophoblast cells from term placenta.
Of the various molecular regulatory mechanisms that may be used by human trophoblast cells to down-regulate expression of HLA class I genes, we chose to investigate the methylation of DNA, generally associated with inhibition of transcription. We analyzed the methylation status of different HLA class I loci in villous and extravillous cytotrophoblast cells and in vitro-differentiated syncytiotrophoblast, purified from human term placenta, as well as in the human trophoblast-derived JAR and JEG-3 cell lines. We then compared methylation status and transcriptional activity. An inverse relationship was established between JAR and JEG-3: HLA-A, -B, and -G are methylated and repressed in JAR, whereas in JEG-3, HLA-A is methylated and repressed but HLA-B and -G are partially methylated and transcribed. HLA-E is unmethylated and transcribed in both cell lines. Apart from HLA-E, which is always unmethylated and transcribed, no such relationship exists for the other class I loci in trophoblast cells. Whereas nonclassical HLA-G and classical HLA-A and -B class I genes are undermethylated in both cytotrophoblast and syncytiotrophoblast, they are clearly transcribed in the former but minimally transcribed in the latter subpopulation. Thus, the down-regulation of class I gene expression in the in vitro-differentiated syncytiotrophoblast is unlikely to be caused by DNA methylation. Furthermore, there is no detectable expression of any class I molecule at the cell surface of either trophoblast cell subpopulation, suggesting a negative control on translation and/or on the secretory pathway to the plasma membrane.
Guillaudeux
T
T
Unité INSERM U395, University Hospital Center Purpan, Toulouse, France.
Rodriguez
A M
AM
Girr
M
M
Mallet
V
V
Ellis
S A
SA
Sargent
I L
IL
Fauchet
R
R
Alsat
E
E
Le Bouteiller
P
P
D001483:Base Sequence; D015152:Blotting, Northern; D015139:Blotting, Southern; D002460:Cell Line; D005434:Flow Cytometry; D005786:Gene Expression Regulation / Q000276:immunology; D006680:HLA Antigens / Q000235:genetics*; D015395:Histocompatibility Antigens Class I / Q000235:genetics*; D006801:Humans; D007124:Immunoenzyme Techniques; D008745:Methylation; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D014158:Transcription, Genetic / Q000235:genetics*; D014327:Trophoblasts / Q000276:immunology*
D006680:HLA Antigens; D015395:Histocompatibility Antigens Class I