Interferon-γ down-regulates membrane adenylate cyclase activity of a murine macrophage-like cell line (P388D1)

Effects of recombinant murine interferon-γ (rIFN-γ) on the membrane adenylate cyclase of a murine macrophage cell line (P388D₁) were investigated in order to explore the nature of a signal transmitted by IFN-γ receptor. Following the incubation of P388D₁ cells with 40 U/ml of rIFN-γ, the intracellular level of cAMP gradually increased about twofold over the control level within 60 min, and then began to gradually decline to about half the control level by 24 h incubation. The initial rise in cAMP level appeared to be due to the modest activation of adenylate cyclase and not due to the inhibition of cAMP-phosphodiesterase. Later decrease of intracellular cAMP may be due to quantitative down-regulation of the adenylate cyclase system. The basal enzymatic activity of the membrane prepared from P388D₁ cells exposed to IFN-γ for 24 h was found to be reduced to about 20% of that of the control membrane. However, the quality of the adenylate cyclase system appeared unchanged, because the relative degree of the response of the down-regulated membrane adenylate cyclase to prostaglandin PGE₂, NaF, guanylimidodiphosphate (GppNHp), cholera toxin (CT), or forskolin was found to remain unchanged. This quantitative down-regulation of adenylate cyclase must be due to the action of rIFN-γ, since the prior treatment of rIFN-γ with either acid (pH 2) or monoclonal anti-IFN-γ antibody inhibited the ability of IFN-γ to induce the down-regulation. The rIFN-γ-induced down-regulation is a reversible process, since the adenylate cyclase activity of the membrane was found to be restored when the rIFN-γ-exposed cells were cultured for 72 h in the absence of rIFN-γ. In addition, the 48 h-incubation of P388D₁ cells with rIFN-β or IFN-α was found not to significantly affect the membrane adenylate cyclase system.