Atypical mechanisms regulate the PMA-induced expression of IFN-γ in a porcine trophectoderm cell line (original) (raw)

2003, Veterinary Immunology and Immunopathology

Interferon-g (IFN-g) is a major effector cytokine of the immune system with an expression pattern strictly restricted to cells of the lymphoid lineage. Several years ago, we reported that, during early pregnancy, the trophectoderm of the pig blastocyst, which represents a monolayer of polarized epithelial cells secretes high amount of IFN-g in a transient and developmentally regulated manner. In an effort to study the molecular basis of this atypical IFN-g gene expression, a pig trophectoderm cell line, TBA B4-3, was established in our laboratory. These cells developed a polarized phenotype with high transepithelial electrical resistance (TER) when grown on a microporous membrane. We found that treatment of polarized TBA B4-3 cells with the strong PKC agonist PMA induced, 3-4 days later, a transient IFN-g mRNA expression and vectorial IFN-g protein secretion. In order to better understand IFN-g gene regulation in TBA B4-3 cells, we examined in this system the effect of several drugs and factors known to affect the inducibility of this cytokine in T lymphocytes, the main source of IFN-g in the immunocompetent animal. We found that cyclosporine A (CsA) treatment of TBA B4-3 cells induces a partial inhibition of IFN-g secretion, thus indicating a minor role for the calcineurin signaling pathway in IFN-g expression. In addition, we found that although PMA alone can induce IFN-g secretion, the calcium ionophore A23187 synergizes with PMA for induction. We also analyzed by Southern blot the methylation status of a CpG dinucleotide in the 5 0 flanking region of IFN-g promoter and found that it was unmethylated in TBA B4-3 cells and in several pig epithelial cell lines that do not express IFN-g thus indicating the absence of correlation between demethylation and the ability to express IFN-g. Taken together, these results indicate that the mechanisms involved in IFN-g induction in TBA B4-3 cells are atypical compared to those presently known to operate in the T cell lineage.