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

Interferon-tau (IFNtau) 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 IFNtau 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 IFNtau gene that had been inserted into the chloramphenicol acetyltransferase (CAT) reporter plasmid (IFNtau-CAT). The effect of a protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate (PMA), on IFNtau-CAT transcriptional activity was examined in JEG3, human embryonic kidney (293), HeLa and Vero cells. Upon transfection and PMA treatment, ovine IFNtau gene was transactivated in two unrelated cell lines, JEG3 and 293 cells. Since IFNtau-CAT was not induced in HeLa or Vero cells, HeLa and JEG3 cells were further examined for their ability to support IFNtau-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 IFNtau 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 IFNtau gene transactivaion.