Inhibitors of serine/threonine phosphatases enhance phosphorylation of the interferon-gamma receptor while selectively attenuating interferon-gamma-induced gene expression in human peripheral-blood monocytes

Interferon gamma activation of Raf-1 is Jak1-dependent and p21ras-independent

Signal transduction through the interferongamma (IFNgamma) receptor involves the formation of a ligand-dependent multimolecular association of receptor chains (alpha and beta), Janus tyrosine kinases (Jak1 and Jak2), and the transcription factor (signal transducers and activators of transcription 1alpha (STAT1alpha)) in addition to activation of mitogen-activated protein kinases (MAPK). Interactions between components of the Jak/STAT cascade and the p21(ras)/Raf-1/MAPK cascade are unexplored. Treatment of HeLa cells with IFNgamma resulted in the rapid and transient activation of Raf-1 and MAPK. Parallel activation of cells resulted in essentially no enhancement of p21(ras) activation despite marked enhancement after treatment with epidermal growth factor. In HeLa (E1C3) and fibrosarcoma (U4A) cell lines, both of which are deficient in Jak1 kinase, Raf-1 activation by IFNgamma was absent. Reconstitution of Raf-1 activity was observed only with kinase active Jak1 in both cell lines. In COS cells, transient expression of wild type or kinase-inactive Jak1 coimmunoprecipitated with Raf-1, but activation of Raf-1 activity was only observed in cells expressing kinase-active Jak1. These observations suggest that a kinase-active Jak1 is required for IFNgamma activation of Raf-1 that is p21(ras)-independent.

The immunobiology of interferon-gamma inducible protein 10 kD (IP-10): a novel, pleiotropic member of the C-X-C chemokine superfamily

Interferon-gamma inducible protein 10 kD (IP-10) is a highly inducible, primary response gene that belongs to the C-X-C chemokine superfamily. Despite the original cloning of IP-10 in 1985, its biological functions are still unclear although accumulating reports indicate that it is a pleiotropic molecule capable of eliciting potent biological effects, including stimulation of monocytes, natural killer and T-cell migration, regulation of T-cell and bone marrow progenitor maturation, modulation of adhesion molecule expression as well as inhibition of angiogenesis. More interest is now likely to be focused on IP-10 due to the recent cloning of an IP-10 receptor. This paper aims to highlight our current knowledge of IP-10 and its homologues as well as defining its likely involvement in regulating fibroproliferation following inflammatory lung injury.

Interferon-gamma affects protein kinase C activity in human neutrophils

Interferon-gamma (IFN-gamma) is a priming agent of polymorphonuclear neutrophilic granulocyte (PMN) oxygen metabolism, and protein kinase C (PKC) is traditionally believed to play a central role in activation of this oxygen metabolism. In the present study, we have shown that the PKC activity in PMN is affected by IFN-gamma. After only 2 minutes exposure to IFN-gamma (100 U/ml), PKC activity was significantly increased in the noncytosolic fraction of the cells. This increase was transient, but toward the end of the priming period of 2 h, the membrane-associated PKC activity increased again to about 152% of control. In the cytosolic fraction, a small and hardly detectable decrease in PKC activity was observed. Treatment of PMN with granulocyte-macrophage colony-stimulating factor (GM-CSF), another PMN priming agent, showed no significant effects on the PKC activity. When the cells were stimulated with the bacterial peptide fMLP after a priming period with IFN-gamma or GM-CSF for 2 h, no significant difference between treated and control cells could be observed. PMN oxygen metabolism, measured by flow cytometry as an accumulation of the fluorescent compound dichlorofluorescein, was in these experiments significantly primed by IFN-gamma, both at baseline and when stimulated with fMLP. The protein kinase C inhibitors H7 and Ro31-8220 blocked the fMLP responses to some extent, but not completely. However, no significant difference between fMLP responses in control and IFN-gamma-treated cells could be detected after administration of inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)