Histone deacetylases inhibit IFN-gamma-inducible gene expression in mouse trophoblast cells

Trophoblast cells are the first cells to differentiate from the developing mammalian embryo, and they subsequently form the blastocyst-derived component of the placenta. IFN-gamma plays critical roles in activating innate and adaptive immunity, as well as apoptosis. In mice, IFN-gamma is produced in the pregnant uterus, and is essential for formation of the decidual layer of the placenta and remodeling of the uterine vasculature. Responses of mouse trophoblast cells to IFN-gamma appear to be selective, for IFN-gamma activates MHC class I expression and enhances phagocytosis, but fails to activate either MHC class II expression or apoptosis in these cells. To investigate the molecular basis for the selective IFN-gamma responsiveness of mouse trophoblast cells, IFN-gamma-inducible gene expression was examined in the trophoblast cell lines SM9 and M-11, trophoblast stem cells, and trophoblast stem cell-derived giant cells. IFN-gamma-inducible expression of multiple genes, including IFN regulatory factor-1 (IRF-1), was significantly reduced in trophoblast cells compared with fibroblast cells. Decreased IRF-1 mRNA expression in trophoblast cells was due to a reduced rate of IRF-1 transcription relative to fibroblast cells. However, no impairment of STAT-1 tyrosine phosphorylation or DNA-binding capacity was observed in IFN-gamma-treated mouse trophoblast cells. Importantly, histone deacetylase (HDAC) inhibitors significantly enhanced IFN-gamma-inducible gene expression in trophoblast cells, but not fibroblasts. Our collective studies demonstrate that IFN-gamma-inducible gene expression is repressed in mouse trophoblast cells by HDACs. We propose that HDAC-mediated inhibition of IFN-gamma-inducible gene expression in mouse trophoblast cells may contribute to successful pregnancy by preventing activation of IFN-gamma responses that might otherwise facilitate the destruction of the placenta.