title: Identification of critical residues required for suppressor of cytokine signaling-specific regulation of interleukin-4 signaling.
abstract: Suppressor of cytokine signaling (SOCS) family proteins were originally identified as cytokine-induced negative regulators of cytokine signaling. We show that SOCS-1 and SOCS-3 inhibit interleukin (IL)-4-dependent signal transducer and activator of transcription 6 (Stat6) activation of and subsequent gene induction. By contrast, SOCS-2 and cytokine-inducible Src homology domain 2 (SH2)-containing protein up-regulate these processes. IL-4 initiates transmembrane signaling through two types of receptor complexes comprising the IL-4Ralpha subunit and the associated Janus kinase 1 (Jak1) as common essential components. We demonstrate that both SOCS-1- and SOCS-3-mediated down-regulation of IL-4 signaling is due to an inhibition of the receptor associated Jak1 activity. The SOCS proteins contain an amino-terminal region of variable length and primary structure, a central SH2 domain, and a carboxyl-terminal conserved motif termed SOCS-box. We show that the SH2 domains of SOCS-2, SOCS-3, and cytokine-inducible SH2-containing protein are functionally redundant in regulating the IL-4-dependent Jak-Stat signaling. The Pre-SH2 domains of SOCS-2 and SOCS-3 confer the specificity of their regulatory function. Importantly, the Pre-SH2 domain of SOCS-3 alone can inhibit IL-4 signaling. The SH2-proximal 25 amino acids of SOCS-3 are sufficient for this inhibition, and the Thr residue at position 24 and the Phe residue at position 25 are individually indispensable for its inhibitory function. Thus, the Thr-Phe motif in the Pre-SH2 domain plays a critical role in SOCS-3-mediated inhibition of the IL-4-dependent Jak-Stat signaling, likely by regulating the mode of SOCS-Jak interaction.
authors.affiliation: Department of Cancer Biology, Lerner Research Institute and the Department of Pulmonary and Critical Care Medicine, Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA. haquej@ccf.org
authors.forename: S J
authors.initials: SJ
authors.lastname: Haque
authors.forename: P C
authors.initials: PC
authors.lastname: Harbor
authors.forename: B R
authors.initials: BR
authors.lastname: Williams
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D002478:Cells, Cultured; D004268:DNA-Binding Proteins; D015847:Interleukin-4 / Q000502:physiology*; D053613:Janus Kinase 1; D051379:Mice; D016297:Mutagenesis, Site-Directed; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011506:Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D019948:Receptors, Interleukin-4 / Q000378:metabolism; D012097:Repressor Proteins; D050800:STAT6 Transcription Factor; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors; D018909:src Homology Domains
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D011506:Proteins; D019948:Receptors, Interleukin-4; D012097:Repressor Proteins; C106644:SOCS3 protein, human; D050800:STAT6 Transcription Factor; C491590:Socs1 protein, mouse; C491409:Socs2 protein, mouse; C491411:Socs3 protein, mouse; C485811:Socs5 protein, mouse; C494100:Stat6 protein, mouse; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D015847:Interleukin-4; D011505:Protein-Tyrosine Kinases; C507904:JAK1 protein, human; C507905:Jak1 protein, mouse; D053613:Janus Kinase 1