The miscarriage-associated HLA-G –725G allele influences transcription rates in JEG-3 cells

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Abstract
BACKGROUND: HLA-G is a non-classical HLA with important immunomodulatory roles in pregnancy. A polymorphism in the promoter region, –725G, was previously associated with sporadic miscarriage in women who were unselected with respect to reproductive history. In this study, the transcription levels of different HLA-G promoter haplotypes were examined to determine whether the miscarriage-associated –725G allele influences transcription. METHODS: Five naturally occurring promoter haplotypes and three variant haplotypes created by site-directed mutagenesis were sub-cloned into luciferase expression vectors and transfected into JEG-3 cells. Expression levels of these eight haplotypes were examined in cultured cells before and after treatment with interferon-β (IFN-β), cytosine-5-DNA methyltransferase (M. SssI) and 5-aza-2′-deoxycytidine. Differences in expression levels between haplotypes were determined by analysis of variance (ANOVA). RESULT: Promoter haplotypes with the miscarriage-associated –725G allele were expressed at significantly higher levels in all culture conditions compared with otherwise identical haplotypes that had a –725C or –725T allele. CONCLUSION: Variation in the HLA-G promoter region influences transcription rates. Contrary to expectations, increased expression of HLA-G may be disadvantageous in some pregnancies.