Constitutive association of JAK1 and STAT5 in pro-B cells is dissolved by interleukin-4-induced tyrosine phosphorylation of both proteins

Abstract

The bipartite human interleukin-4 (IL-4) receptor was functionally expressed in murine pro-B cells and activated by human IL-4 to evoke intracellular signaling. Mutual association of signal transducing proteins within the receptor complex was then studied in dependence of ligand stimulation. Besides ligand-induced receptor heterodimerization and contacts of the two IL-4 receptor subunits α and γ with Janus kinases JAK1 and JAK3 a prominent constitutive binding between JAK1 and signal transducer and activator of transcription STAT5 was detected. Since both these proteins become phosphorylated in response to IL-4 receptor stimulation, the influence of tyrosine phosphorylation on their mutual contact was analyzed. Association of JAK1 and STAT5 was found to occur exclusively between unphosphorylated proteins. Copyright (C) 1998 Federation of European Biochemical Societies.