Induction of the IFN-gamma gene and protein is linked to the establishment of cell polarity in a porcine epithelial cell line

We report here original properties of a porcine trophectoderm cell line, TBA B4-3, that developed a polarized phenotype with high transepithelial electrical resistance (TER) values and functional tight junctions (TJs) when grown on a microporous membrane. We found that treatment of polarized TBA B4-3 cells with a strong protein kinase C (PKC) agonist, phorbol 12-myristate-13-acetate (PMA), induced 3-4 days later a transient interferon-gamma (IFN-gamma) mRNA expression and vectorial IFN-gamma protein secretion toward the apical side of the monolayer. Exposure of TBA B4-3 cells to PMA first resulted in a rapid and profound disorganization of the monolayer structure mainly characterized by the appearance of multilayered polyp-like foci structures, a strong decrease of the TER, and a increase of permeability correlated with changes in the organization and localization of the TJ-associated proteins (ZO-1 and occludin) and filamentous actin (f-actin). After PMA removal, spontaneous return to the initial polarized monolayer state occurred, characterized by TER rising to prestimulation values, TJ protein relocalization, and multilayered cell structures fading. This return was strictly correlated with transient IFN-gamma gene induction. Our report represents the first example of an inducible expression of IFN-gamma by a polarized epithelial cell. After PMA treatment, the close correlation between establishment of cell polarity and IFN-gamma gene expression suggests a link between these phenomena. This also suggests a novel biological mechanism by which transient and reversible disorganization of a polarized monolayer of epithelial cells could trigger regulated expression of a cytokine gene by these cells.