Characterization of Interleukin 2 and Phorbol Myristate Acetate Augmentation of Expression of Transfected Human Interferon-γ Genomic DNA

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Abstract
We have reported that human interferon-γ (IFN-γ) 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 my ris ta te acetate (PMA).(1) It can now be shown that PMA rapidly induces new transcription of the IFN-γ gene and that increased human (Hu) IFN-γ can be detected by 2 h after the addition of PMA to the mouse cells. Enhancement of IFN-γ production by IL2 takes place with similar kinetics with increased IFN-γ production observed at 4-6 h after IL2 addition, although the maximum amount of IFN-γ produced in response to IL2 was significantly lower than that produced in response to PMA. Furthermore, along with increased levels of cytoplasmic IFN-γ RNA, we were able to demonstrate increased nuclear transcription at 4 h after IL2 treatment. Stimulation of IFN-γ 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-γ 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-γ production, and that PMA may increase IFN-γ production in the transfected cell by additional mechanisms, such as increasing mRNA stability.