Cutting edge: IL-4 induces suppressor of cytokine signaling-3 expression in B cells by a mechanism dependent on activation of p38 MAPK

The signaling cascade initiated by IL-4 is classically divisible into two major pathways: one mediated by STAT6, and the other by insulin receptor substrates-1 and -2 via activation of PI3K. In murine splenic B cells, the suppressor of cytokine signaling (SOCS)3 is inducible by IL-4 via a mechanism independent of STAT6 and PI3K. SOCS3 expression increases 9-fold within 5 h of IL-4 treatment. This induction occurs normally in B cells deficient in STAT6 and is unaffected by pretreatment with the PI3K inhibitor wortmannin, or with the ERK pathway inhibitor, PD98059. However, the IL-4 induction of SOCS3 is blocked by inhibitors of either the JNK or p38 MAPK pathways (SP600125 and SB203580, respectively). Direct examination of these pathways reveals rapid, IL-4-directed activation of p38 MAPK, uncovering a previously unappreciated pathway mediating IL-4 signal transduction.     

Src family kinase-independent signal transduction and gene induction by leukemia inhibitory factor

Members of the interleukin-6 (IL-6) family of cytokines exert their biological effects via binding to their cognate ligand-binding receptor subunit on a target cell. The subsequent recruitment of the common signal transducer glycoprotein 130 and activation of the JAK/STAT and SHP-2/Ras/mitogen-activated protein kinase (MAPK) pathways are responsible for the majority of cellular responses elicited by IL-6 cytokines. Several types of experiments suggest that the Src family of kinases (SFK) also participates in IL-6 family cytokine-mediated signaling events. SYF cells, which lack expression of SFKs Src, Yes, and Fyn, were used to determine the role of SFKs in IL-6 family cytokine signaling and gene induction. SYF and wild type (WT) control fibroblasts displayed similar activation of signaling intermediates following stimulation with leukemia inhibitory factor (LIF). LIF-stimulated tyrosine phosphorylation of SHP-2 and subsequent activation of MAPK in SYF cells were identical to that seen in LIF-stimulated WT cells. Both LIF-stimulated tyrosine phosphorylation of STAT1 and STAT3, as well as LIF-stimulated DNA binding activity of STAT-containing nuclear complexes were indistinguishable when compared in SYF and WT cells. In addition, the phosphatidylinositol 3-kinase-sensitive Akt kinase and p38 MAPK were activated by LIF in both SYF and WT cells. Furthermore, LIF-stimulated expression of c-fos, egr-1, and suppressor of cytokine signaling-3 was retained in SYF cells. The IL-6 family cytokine oncostatin M was also capable of activating MAPK, STAT3, STAT1, Akt, and p38 in both WT and SYF cells. These results demonstrate that IL-6 family cytokines can activate a full repertoire of signaling pathways and induce gene expression independent of SFKs.     

The JAK-STAT signaling pathway: input and output integration

Universal and essential to cytokine receptor signaling, the JAK-STAT pathway is one of the best understood signal transduction cascades. Almost 40 cytokine receptors signal through combinations of four JAK and seven STAT family members, suggesting commonality across the JAK-STAT signaling system. Despite intense study, there remain substantial gaps in understanding how the cascades are activated and regulated. Using the examples of the IL-6 and IL-10 receptors, I will discuss how diverse outcomes in gene expression result from regulatory events that effect the JAK1-STAT3 pathway, common to both receptors. I also consider receptor preferences by different STATs and interpretive problems in the use of STAT-deficient cells and mice. Finally, I consider how the suppressor of cytokine signaling (SOCS) proteins regulate the quality and quantity of STAT signals from cytokine receptors. New data suggests that SOCS proteins introduce additional diversity into the JAK-STAT pathway by adjusting the output of activated STATs that alters downstream gene activation.     

人骨髓瘤细胞中两条IL-6信号转导途径的相互调控方式

首先利用凝胶阻滞电泳 ( electrophoretic mobility shift assay,EMSA )和免疫沉淀( immunoprecipitation,IP)方法观察两条 IL- 6信号转导途径—— JAK/STAT和 Ras/NF- IL- 6在人骨髓瘤细胞系 Sko- 0 0 7中的诱导激活状态 ;继而采用分别作用于两条途径的蛋白激酶抑制剂或激动剂以及转录因子的反义核酸与 IL- 6共同作用 Sko- 0 0 7细胞 ,观察一条途径激活信号上调 (或下调 )时 ,另外一条途径活化状态的变化 .结果显示 :1 .JAK/STAT和 Ras/NF- IL- 6信号转导途径都能够在 Sko- 0 0 7细胞中诱导激活 ;2 .与 JAK/STAT途径活化相关的某个酪氨酸磷酸化作用参与了Ras途径的诱导激活 ;Ras途径可通过蛋白激酶 MAPK( motigen- activated protein kinase)对 JAK/STAT途径的激活起正调控作用 .这说明在人骨髓瘤细胞 Sko- 0 0 7中两条 IL- 6信号途径可相互调控彼此的活化 .     

CDX2 can be regulated through the signalling pathways activated by IL-6 in gastric cells

The inflammatory infiltrate of the gastric mucosa associated with Helicobacter pylori infection increases the presence of the pro-inflammatory cytokine IL-6 that activates both the SHP-2/ERK/MAPK and the JAK/STAT signalling pathways. Furthermore, the ectopic expression of CDX2 is detected in pre-neoplasic lesions associated with decreased levels of SOX2, and we found that in gastric adenocarcinomas their expression is inversely correlated. To determine the role of IL-6 in the regulation of CDX2, MKN45 that constitutively expresses p-STAT3, and NUGC-4 gastric cancer cell lines were treated with IL-6, which induced the CDX2 up-regulation and SOX2 down-regulation. ChIP assays determined that in IL-6-treated cells, c-JUN and p-STAT3 bound to CDX2 promoter in MKN45 cells whereas in NUGC-4 cells, p-STAT3 binds to and c-JUN releases from the CDX2 promoter. Specific inhibition of STAT3 and ERK1/2 phosphorylation through AG490 and U0126, respectively, and STAT3 down-regulation using shRNA verified that the SHP-2/ERK/MAPK pathway regulates the expression of CDX2 in basal conditions, and the CDX2 up-regulation by IL-6 is through the JAK/STAT pathway in NUGC-4 cells whereas in MKN45 cells both pathways contribute to the CDX2 up-regulation. In conclusion, the signalling pathways activated by IL-6 have a crucial role in the regulation of CDX2 that is a key factor in the process of gastric carcinogenesis, suggesting that the inflammatory infiltrate in the gastric mucosa is relevant in this process and a potential target for new therapeutic approaches.     

IL-6 signal transduction and its physiological roles: the signal orchestration model

Interleukin (IL)-6 is a pleiotropic cytokine that not only affects the immune system, but also acts in other biological systems and many physiological events in various organs. In a target cell, IL-6 can simultaneously generate functionally distinct or sometimes contradictory signals through its receptor complex, IL-6Rα and gp130. One good illustration is derived from the in vitro observations that IL-6 promotes the growth arrest and differentiation of M1 cells through gp130-mediated STAT3 activation, whereas the Y759/SHP-2-mediated cascade by gp130 stimulation has growth-enhancing effects. The final physiological output can be thought of as a consequence of the orchestration of the diverse signaling pathways generated by a given ligand. This concept, the signal orchestration model, may explain how IL-6 can elicit proinflammatory or anti-inflammatory effects, depending on the in vivo environmental circumstances. Elucidation of the molecular mechanisms underlying this issue is a challenging subject for future research. Intriguingly, recent in vivo studies indicated that the SHP-2-binding site- and YXXQ-mediated pathways through gp130 are not mutually exclusive but affect each other: a mutation at the SHP-2-binding site prolongs STAT3 activation, and a loss of STAT activation by gp130 truncation leads to sustained SHP-2/ERK MAPK phosphorylation. Although IL-6/gp130 signaling is a promising target for drug discovery for many human diseases, the interdependence of each signaling pathway may be an obstacle to the development of a nonpeptide orally active small molecule to inhibit one of these IL-6 signaling cascades, because it would disturb the signal orchestration. In mice, a consequence of the imbalanced signals causes unexpected results such as gastrointestinal disorders, autoimmune diseases, and/or chronic inflammatory proliferative diseases. However, lessons learned from IL-6 KO mice indicate that IL-6 is not essential for vital biological processes, but a significant impact on disease progression in many experimental models for human disorders. Thus, IL-6/gp130 signaling will become a more attractive therapeutic target for human inflammatory diseases when a better understanding of IL-6 signaling, including the identification of the conductor for gp130 signal transduction, is achieved.