Waiboci Lilian W, Ahmed Chulbul M, Mujtaba Mustafa G, Flowers Lawrence O, Martin James P, Haider Mohammed I, Johnson Howard M
Department of Microbiology and Cell Science, University of Florida, Gainesville, FL 32611, USA.
J Immunol. 2007 Apr 15;178(8):5058-68. doi: 10.4049/jimmunol.178.8.5058.
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.
细胞因子信号转导抑制因子（SOCS）-1蛋白通过与JAK2的自磷酸化位点结合，并将结合的JAK2靶向蛋白酶体进行降解，从而调节γ干扰素的信号传导。我们开发了一种小的酪氨酸激酶抑制肽（Tkip），它是SOCS-1的模拟物。在本研究中，将Tkip与SOCS-1的激酶抑制区域（KIR）进行比较，以研究其对JAK2的识别、激酶活性抑制以及对γ干扰素诱导的生物学活性的调节。Tkip和对应于SOCS-1的KIR的肽（(53)DTHFRTFRSHSDYRRI(68)，SOCS1-KIR）与JAK2的自磷酸化位点JAK2(1001 - 1013)的结合方式相似。这些肽也与在Tyr(1007)磷酸化的JAK2肽pJAK2(1001 - 1013)结合。剂量反应竞争表明，Tkip和SOCS1-KIR对JAK2自磷酸化位点的识别相似，但可能方式并不完全相同。尽管Tkip抑制JAK2自磷酸化以及γ干扰素诱导的STAT1-α磷酸化，但SOCS1-KIR与SOCS-1一样，不抑制JAK2自磷酸化，但抑制STAT1-α激活。Tkip和SOCS1-KIR都抑制γ干扰素对Raw 264.7小鼠巨噬细胞的激活，并抑制抗原特异性脾细胞增殖。SOCS1-KIR结合pJAK2(1001 - 1013)这一事实表明，JAK2肽可能作为SOCS-1的拮抗剂发挥作用。因此，pJAK2(1001 - 1013)增强了次优的γ干扰素活性，阻断了SOCS-1诱导的对白细胞介素-6处理细胞中STAT3磷酸化的抑制，增强了γ干扰素激活位点启动子活性，并增强了抗原特异性增殖。此外，SOCS-1与SOCS1-KIR竞争pJAK2(1001 - 1013)。因此，SOCS-1的KIR区域直接与JAK2的自磷酸化位点结合，并且对应于该位点的肽可以作为SOCS-1的拮抗剂发挥作用。
