title: Both the suppressor of cytokine signaling 1 (SOCS-1) kinase inhibitory region and SOCS-1 mimetic bind to JAK2 autophosphorylation site: implications for the development of a SOCS-1 antagonist.
abstract: Suppressor of cytokine signaling (SOCS)-1 protein modulates signaling by IFN-gamma by binding to the autophosphorylation site of JAK2 and by targeting bound JAK2 to the proteosome for degradation. We have developed a small tyrosine kinase inhibitor peptide (Tkip) that is a SOCS-1 mimetic. Tkip is compared in this study with the kinase inhibitory region (KIR) of SOCS-1 for JAK2 recognition, inhibition of kinase activity, and regulation of IFN-gamma-induced biological activity. Tkip and a peptide corresponding to the KIR of SOCS-1, ((53))DTHFRTFRSHSDYRRI((68)) (SOCS1-KIR), both bound similarly to the autophosphorylation site of JAK2, JAK2(1001-1013). The peptides also bound to JAK2 peptide phosphorylated at Tyr(1007), pJAK2(1001-1013). Dose-response competitions suggest that Tkip and SOCS1-KIR similarly recognize the autophosphorylation site of JAK2, but probably not precisely the same way. Although Tkip inhibited JAK2 autophosphorylation as well as IFN-gamma-induced STAT1-alpha phosphorylation, SOCS1-KIR, like SOCS-1, did not inhibit JAK2 autophosphorylation but inhibited STAT1-alpha activation. Both Tkip and SOCS1-KIR inhibited IFN-gamma activation of Raw 264.7 murine macrophages and inhibited Ag-specific splenocyte proliferation. The fact that SOCS1-KIR binds to pJAK2(1001-1013) suggests that the JAK2 peptide could function as an antagonist of SOCS-1. Thus, pJAK2(1001-1013) enhanced suboptimal IFN-gamma activity, blocked SOCS-1-induced inhibition of STAT3 phosphorylation in IL-6-treated cells, enhanced IFN-gamma activation site promoter activity, and enhanced Ag-specific proliferation. Furthermore, SOCS-1 competed with SOCS1-KIR for pJAK2(1001-1013). Thus, the KIR region of SOCS-1 binds directly to the autophosphorylation site of JAK2 and a peptide corresponding to this site can function as an antagonist of SOCS-1.
authors.affiliation: Department of Microbiology and Cell Science, University of Florida, Gainesville, FL 32611, USA.
authors.forename: Lilian W
authors.initials: LW
authors.lastname: Waiboci
authors.forename: Chulbul M
authors.initials: CM
authors.lastname: Ahmed
authors.forename: Mustafa G
authors.initials: MG
authors.lastname: Mujtaba
authors.forename: Lawrence O
authors.initials: LO
authors.lastname: Flowers
authors.forename: James P
authors.initials: JP
authors.lastname: Martin
authors.forename: Mohammed I
authors.initials: MI
authors.lastname: Haider
authors.forename: Howard M
authors.initials: HM
authors.lastname: Johnson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D006801:Humans; D050832:Interferon-Stimulated Gene Factor 3 / Q000378:metabolism; D007371:Interferon-gamma / Q000494:pharmacology; D053614:Janus Kinase 2 / Q000378:metabolism*; D008213:Lymphocyte Activation / Q000187:drug effects; D008262:Macrophage Activation / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000494:pharmacology; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000378:metabolism / Q000494:pharmacology*; D050796:STAT3 Transcription Factor / Q000378:metabolism; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D018909:src Homology Domains
chemical_list: D050832:Interferon-Stimulated Gene Factor 3; D010446:Peptide Fragments; D047428:Protein Kinase Inhibitors; C108944:SOCS1 protein, human; D050796:STAT3 Transcription Factor; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; C079868:gamma interferon activation factor; D007371:Interferon-gamma; D053614:Janus Kinase 2