Effects of PMA and transcription factors on ovine interferon-τ transactivation in various cell lines

Interferon-tau (IFNτ) is produced by the trophectoderm of ruminant ungulates and its gene transactivation in vitro has so far been achieved only in human choriocarcinoma cells, JAR and JEG3. To examine if ovine IFNτ gene transactivation could be induced in cells other than JAR or JEG3 cells and its activation could be aided by the expression of a protooncogene(s), a transient transfection system was developed with the upstream region of ovine IFNτ gene that had been inserted into the chloramphenicol acetyltransferase (CAT) reporter plasmid (IFNτCAT). The effect of a protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate (PMA), on IFNτ-CAT transcriptional activity was examined in JEG3, human embryonic kidney (293), HeLa and Vero cells. Upon transfection and PMA treatment, ovine IFNτ gene was transactivated in two unrelated cell lines, JEG3 and 293 cells. Since IFNτ-CAT was not induced in HeLa or Vero cells, HeLa and JEG3 cells were further examined for their ability to support IFNτ-CAT transactivation in a co-transfection system. While the expression of c-myc, interferon regulatory factor 1 or 2 (IRF-1 or IRF-2) was not effective, CAT activity was strongly enhanced in both JEG3 and HeLa cells with the co-transfection of c-Jun or c- Jun plus c-Fos. These data suggest that ovine IFNτ gene transcription induced by PMA is not specific for trophoblast cells and a protooncogene, c- jun, is a downstream effector of PMA activated nuclear factors in its signal transduction cascade resulting in IFNτ gene transactivation.