Characterization of interleukin 2 and phorbol myristate acetate augmentation of expression of transfected human interferon-gamma genomic DNA.

We have reported that human interferon-gamma (IFN-gamma) genomic DNA is expressed after transfection into a mouse T-lymphoblastoid cell line and expression can be enhanced by both interleukin 2 (IL2) and phorbol myristate acetate (PMA). It can now be shown that PMA rapidly induces new transcription of the IFN-gamma gene and that increased human (Hu) IFN-gamma can be detected by 2 h after the addition of PMA to the mouse cells. Enhancement of IFN-gamma production by IL2 takes place with similar kinetics with increased IFN-gamma production observed at 4-6 h after IL2 addition, although the maximum amount of IFN-gamma produced in response to IL2 was significantly lower than that produced in response to PMA. Furthermore, along with increased levels of cytoplasmic IFN-gamma RNA, we were able to demonstrate increased nuclear transcription at 4 h after IL2 treatment. Stimulation of IFN-gamma mRNA by both PMA and IL2 could occur in the presence of cycloheximide, indicating that protein synthesis was not required for the initial stimulation to occur. However, the functional half-life of IFN-gamma mRNA after actinomycin D treatment was higher in cells that had been treated with PMA when compared with untreated or IL2-treated cells. This data indicates that there are quantitative differences in the ability of PMA or IL2 to augment IFN-gamma production, and that PMA may increase IFN-gamma production in the transfected cell by additional mechanisms, such as increasing mRNA stability.