Suppressor of cytokine signaling-3 preferentially binds to the SHP-2-binding site on the shared cytokine receptor subunit gp130

Suppressor of cytokine signaling-3 (SOCS-3) is one member of a family of in tracellular inhibitors of signaling pathways initiated by cytokines that us e, among others, the common receptor subunit gp130. The SH2 domain of SOCS- 3 has been shown to be essential for this inhibitory activity, and we have used a quantitative binding analysis of SOCS-3 to synthetic phosphopeptides to map the potential sites of interaction of SOCS-3 with different compone nts of the gp130 signaling pathway. The only high-affinity ligand found cor responded to the region of gp130 centered around phosphotyrosine-757 (pY757 ), previously shown to be a docking site for the tyrosine phosphatase sHP-2 . By contrast, phosphopeptides corresponding to other regions within gp130, Janus kinase, or signal transducer and activator of transcription proteins bound to SOCS-3 with weak or undetectable affinity. The significance of pY 757 in gp130 as a biologically relevant SOCS-3 docking site was investigate d by using transfected 2937 fibroblasts. Although SOCs-3 inhibited signalin g in cells transfected with a chimeric receptor containing the wild-type gp 130 intracellular domain, inhibition was considerably impaired for a recept or carrying a Y-->F point mutation at residue 757. Taken together, these da ta suggest that the mechanism by which SOCS-3 inhibits the gp130 signaling pathway depends on recruitment to the phosphorylated gp130 receptor, and th at some of the negative regulatory roles previously attributed to the phosp hatase SHP-2 might in fact be caused by the action of SOCS-3.