Boyle Kristy, Zhang Jian-Guo, Nicholson Sandra E, Trounson Evelyn, Babon Jeffery J, McManus Edward J, Nicola Nicos A, Robb Lorraine
The Walter and Eliza Hall Institute, 1G Royal Parade, Parkville, Victoria 3050, Australia.
Cell Signal. 2009 Mar;21(3):394-404. doi: 10.1016/j.cellsig.2008.11.002. Epub 2008 Nov 12.
The mechanism by which Suppressor of Cytokine Signaling-3 (SOCS3) negatively regulates cytokine signaling has been widely investigated using over-expression studies in cell lines and is thought to involve interactions with both the gp130 receptor and JAK1. Here, we compare the endogenous JAK/STAT signaling pathway downstream of Leukemia Inhibitory Factor (LIF) signaling in wild type (WT) Embryonic Stem (ES) cells and in ES cells lacking either the entire Socs3 gene or bearing a truncated form of SOCS3 (SOCS3DeltaSB) lacking the C-terminal SOCS box motif (SOCS3(DeltaSB/DeltaSB)). In SOCS3(DeltaSB/DeltaSB) cells phosphorylated JAK1 accumulated at much higher levels than in WT cells or even cells lacking SOCS3 (SOCS3(-/-)). In contrast enhanced activation of STAT3 and SHP2 was seen in SOCS3(-/-) cells. Size exclusion chromatography of cell extracts showed that in unstimulated cells, JAK1 was exclusively associated with receptors but following cytokine stimulation hyperphosphorylated JAK1 (pJAK1) appeared to dissociate from the receptor complex in a manner independent of SOCS3. In WT and SOCS3(DeltaSB/DeltaSB) cells SOCS3 was associated with pJAK1. The data suggest that dissociation of activated JAK1 from the receptor results in separate targeting of JAK1 for proteasomal degradation through a mechanism dependent on the SOCS3 SOCS box thus preventing further activation of STAT3.
细胞因子信号转导抑制因子3（SOCS3）负调控细胞因子信号转导的机制已通过在细胞系中的过表达研究得到广泛探究，并且被认为涉及与gp130受体和JAK1的相互作用。在此，我们比较了野生型（WT）胚胎干细胞（ES）以及缺乏整个Socs3基因或携带缺少C末端SOCS框基序的截短形式的SOCS3（SOCS3DeltaSB）的ES细胞中，白血病抑制因子（LIF）信号下游的内源性JAK/STAT信号通路。在SOCS3(DeltaSB/DeltaSB)细胞中，磷酸化的JAK1积累水平比WT细胞甚至缺乏SOCS3的细胞（SOCS3(-/-)）高得多。相反，在SOCS3(-/-)细胞中观察到STAT3和SHP2的激活增强。细胞提取物的尺寸排阻色谱显示，在未刺激的细胞中，JAK1仅与受体相关，但在细胞因子刺激后，过度磷酸化的JAK1（pJAK1）似乎以独立于SOCS3的方式从受体复合物中解离。在WT和SOCS3(DeltaSB/DeltaSB)细胞中，SOCS3与pJAK1相关。数据表明，活化的JAK1从受体上解离导致JAK1通过依赖于SOCS3 SOCS框的机制被靶向蛋白酶体降解，从而阻止STAT3的进一步激活。
