Cellular distribution of proteasome subunit Lmp7 mRNA and protein in human placentas

Abstract

Human leucocyte antigen (HLA) class I antigen expression is closely controlled in placental trophoblast cells, which interface directly with genetically disparate maternal blood and tissues during pregnancy. In this study, the possibility that LMP7, a proteasome component that may be required for processing of class I-associated peptides, might be lacking or refractory to cytokine induction in trophoblast cells that fail to display HLA class I antigens was investigated. Analysis of Lmp7 mRNA and protein in paraformaldehyde-fixed placentas by in situ hybridization and immunohistochemistry revealed that both HLA class I-positive and HLA class I-negative trophoblast cells contain Lmp7 gene products. Consistent with these results, northern blot hybridization studies showed that HLA class I-positive (JEG-3) and HLA null (Jar) trophoblast-derived cell lines contain Lmp7 mRNA. After 48 hr of exposure to HLA class I-modulating cytokines, Lmp7 mRNA levels in JEG-3 cells were markedly increased by two interferons (IFN-beta, IFN-gamma) and tumour necrosis factor (TNF) whereas at the same time point, Jar cell Lmp7 mRNA was modestly enhanced by IFN-gamma. Collectively, the findings indicate that expression of HLA class I antigens in trophoblast cells is unlikely to be restricted by lack of Lmp7 gene products and suggest that endogenous placental cytokines may have different influences on Lmp7 mRNA levels in phenotypically distinct trophoblast subpopulations.