STAT3 AS AN ADAPTER TO COUPLE PHOSPHATIDYLINOSITOL 3-KINASE TO THE IFNAR1 CHAIN OF THE TYPE-I INTERFERON RECEPTOR

STAT (signal transducers and activators of transcription) proteins und ergo cytokine-dependent phosphorylation on serine and tyrosine, STAT3, a transcription factor for acute phase response genes, was found to a ct as an adapter molecule in signal transduction from the type I inter feron receptor. STAT3 bound to a conserved sequence in the cytoplasmic tail of the IFNAR1 chain of the receptor and underwent interferon-dep endent tyrosine phosphorylation. The p85 regulatory subunit of phospha tidylinositol S-kinase, which activates a series of serine kinases, bo und to phosphorylated STAT3 and subsequently underwent tyrosine phosph orylation, Thus, STAT3 acts as an adapter to couple another signaling pathway to the interferon receptor.