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

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-beta (IFN-beta), 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.