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.
Since many events following ligand-induced receptor clustering are controlled by serine and threonine (Ser/Thr) phosphorylation, we initiated an investigation into the role of Ser/Thr phosphatases in both phosphorylation of the interferon-gamma (IFN-gamma) receptor and IFN gamma-induced gene expression in human peripheral-blood monocytes. Whereas IFN gamma alone did not enhance phosphorylation of the IFN gamma receptor, treatment of monocytes with the Ser/Thr phosphatase inhibitors, okadaic acid and calyculin A, resulted in increased phosphorylation of the IFN gamma receptor. However, when these cells were analysed for IFN gamma-induced IP-10 gene expression, there was profound inhibition. Using three IFN gamma-induced early-response genes, IP-10, the Fc gamma receptor type I (Fc gamma RI) and ISG-54, we found selective sensitivity to pretreatment with okadaic acid and calyculin A. Whereas IFN gamma induction of IP-10 was blocked by both inhibitors, only calyculin A prevented Fc gamma RI-gene expression. Neither inhibitor prevented ISG-54 induction by IFN gamma. IFN-gamma-activated formation of the DNA-binding-protein complex FcRF gamma (which binds to the promoter of the Fc gamma RI gene) remained unaffected by okadaic acid or calyculin A. Therefore these data suggest that Ser/Thr phosphatases have no major part in IFN gamma-initiated signal transduction across the membrane, but selectively control the ultimate transcription of a set of early-response genes.
Luong
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Division of Cytokine Biology, Food and Drug Administration, Bethesda, MD 20892.
Winestock
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Finbloom
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D001483:Base Sequence; D004988:Ethers, Cyclic / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects*; D017781:Genes, Immediate-Early; D006801:Humans; D066298:In Vitro Techniques; D007371:Interferon-gamma / Q000378:metabolism*; D008387:Marine Toxins; D008969:Molecular Sequence Data; D009000:Monocytes / Q000187:drug effects* / Q000378:metabolism; D019319:Okadaic Acid; D009838:Oligodeoxyribonucleotides; D010080:Oxazoles / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D010766:Phosphorylation; D017471:Receptors, Interferon / Q000187:drug effects / Q000378:metabolism*; D000096743:Interferon gamma Receptor
D004988:Ethers, Cyclic; D007371:Interferon-gamma; D008387:Marine Toxins; D019319:Okadaic Acid; D009838:Oligodeoxyribonucleotides; D010080:Oxazoles; D010749:Phosphoprotein Phosphatases; D017471:Receptors, Interferon; D000096743:Interferon gamma Receptor; C059041:calyculin A