The genetic diversity within the 1.4 kb HLA-G 5′ upstream regulatory region moderately impacts on cellular microenvironment responses
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The HLA-G 5'URR extending 1.4 kb from the ATG presents a unique set of regulatory elements among HLA genes. Several variable sites have been described that coincide with or are close to these elements, thus HLA-G 5′URR polymorphism might influence the HLA-G expression level. We cloned the ten most frequent HLA-G 5′URR haplotypes to evaluate their activity on a luciferase reporter gene in HLA-G+ cell lines (JEG-3/choriocarcinoma and FON+/melanoma). We also investigated associations between the plasma HLA-G (sHLA-G) levels and the HLA-G 5′URR variability in 157 healthy individuals. Cell lines were transfected with pGL3-Basic vector constructions containing HLA-G 5′URR sequences. The G010101a (in JEG-3) and G010101b (in FON+) haplotypes exhibited higher promoter activity, whereas the G010101d (in JEG-3) and G010102a (in FON+) haplotypes exhibited lower promoter activity. In the presence of HLA-G inducers (interferon-β and progesterone) or repressors (cyclopamine) HLA-G promoter activity was modulated, but certain haplotypes exhibited differential responses. No strict association was observed between plasma sHLA-G levels and the 5′URR haplotypes or genotypes; however, the G010101b haplotype was underrepresented among HLA-G-negative plasmas. Therefore, the HLA-G 5′URR polymorphism may have an impact on the modulation of HLA-G gene expression, but alone provides a limited predictive value for sHLA-G levels in vivo.