IFN- γ Gene Expression in Epithelial Trophectoderm Cells Is Linked to Downregulation of the p44/p42 MAP Kinase Pathway

Abstract

We previously stated that interferon-γ (IFN-γ) is highly expressed in a transient and developmentally regulated manner by the trophectoderm of the pig blastocyst, which represents a monolayer of polarized epithelial cells, during early pregnancy. In order to study the molecular mechanisms of this atypical IFN-γ gene expression, we established the pig trophectoderm cell line TBA B4-3. These cells develop a polarized phenotype with high transepithelial electrical resistance (TER) when grown on a microporous membrane. We previously showed that treatment of polarized TBA B4-3 cells with the strong protein kinase C (PKC) agonist phorbol 12-myristate-13-acetate (PMA) induced 3-4 days later a transient IFN-γ mRNA expression and apical IFN-γ protein secretion. In the present paper, we report that after PMA removal, a transient phase of p44/p42 mitogen-activated protein (MAP) kinase activation occurs, followed by a strong downregulation preceding the phase of IFN-γ expression. Surprisingly, we found that inhibition of this surge of p44/p42 MAP kinase activation with MEK inhibitors (U0126 and PD98059) triggers earlier IFN-γ mRNA and protein expression, correlated with earlier TER rising and restoration of epithelial phenotype. These results indicate that in the TBA B4-3 cell system, activation of this signaling pathway has a negative effect on IFN-γ gene expression. These observations reinforce the hypothesis of a link between establishment of cell polarity and induction of IFN-γ that could be mediated by signaling from intercellular junctions.