Protein kinase (pp67-IFN) in plasma and tissues of mice with high levels of circulating interferon

Abstract

Summary Interferon-treated mouse cells show an enhanced protein kinase activity which is manifested by the phosphorylation of an endogenous 67,000-MW phosphoprotein (pp67-IFN). This kinase activity can be assayed conveniently and efficiently after its partial purification on poly(I)poly(C)-Sepharose. Here we show that besides cell tissue cultures, the pp67-IFN kinase is also detectable in the liver, spleen and plasma of mice injected with Newcastle disease virus (NDV), encephalomyocarditis virus (EMCV), poly(I)poly(C) or poly(A)poly(U), all of which induce interferon. In addition to the pp67-IFN kinase, we studied the level of pppA(2′p5′A)n synthetase (2–5A synthetase) in the spleen and liver of mice in order to monitor the action of circulating interferon. In contrast to a previously published work, no 2-5A synthetase was detectable in the plasma or in the serum of mice which showed high levels of 2–5A synthetase in their liver and spleen. The kinetics of enhancement of pp67-IFN kinase in the plasma and in the spleen followed that of circulating interferon. The maximum levels of this enzyme in mice were 15–18 h after the peak of circulating interferon. The pp67-IFN from the plasma and spleen of mice and from interferon-treated mouse cells were phosphorylated in their serine and threonine residues. The function of the kinase in the plasma of mice with high levels of circulating interferon remains to be investigated. Its detection, however, may serve as a marker for the presence and action of interferon since the pp67-IFN kinase could be detectable at a time when the level of circulating interferon is diminished.