Abstract
We have examined the mechanism of synergistic action occurring between interferon (lFN)-y and 12-0-tetradecanoylphorbol-13-acetate (TPA) with respect to the reduction of 125I-epidermal growth factor (125I-EGF) binding to human amnion (WISH) cells [Karasaki Y et al (1989) J Biol Chem 264: 6158-6163]. The cells were treated with protein kinase C (PKC) inhibitors (H7, staurosporine) to investigate the role of PKC in the synergism between IFN-γ and TPA, since TPA is a strong activator of PKC. The combined effect of IFN-γ and TPA was blocked by the PKC inhibitor, suggesting that PKC plays an important role in the synergistic action of TPA and IFN-y on the inhibition of EGF binding to the cells. The prolonged incubation (24 h) of the cells with TPA resulted in the restoration of EGF binding to the cells. A 24 h treatment of WISH cells with both IFN-γ and TPA, however, still exhibited greater than 50% inhibition of EGF binding No PKC activity however was observed in the WISH cells treated with both IFN-γ and TPA for 24 h as well as with TPA alone for 24 h, indicating that IFN-γ may synergize with the second mediator induced by PKC rather than PKC itself in the reduction of EGF binding to WISH cells. In addition, IFN-y showed the synergistic action with calcium ionophores on the reduction of EGF binding to the cells, suggesting that Ca2+ may be one of the second mediators which was induced by TPA and which cooperated with IFN-γ.
