New functions of Suppressor of Cytokine Signalling-1 (SOCS1) dependent on its nuclear localization

这是一个名为“细胞因子信号1抑制因子（SOCS1）的核功能鉴定”的项目的更新申请，该项目之前由DFG （DA592/4-1）于2009-2012年资助。SOCS蛋白是Janus kinase (JAK)/signal transducer and activator of transcription （STAT）通路的诱导型细胞内反馈抑制剂。尽管SOCS1蛋白在抑制膜近端细胞因子受体信号传导方面的功能已经得到了充分的研究，但我们已经确定了SOCS1内的核定位信号导致SOCS1的核易位。在最近的资助期内，我们首次能够确定核SOCS1的功能，即通过p65的蛋白酶体降解来限制NFkappaB信号传导。为了进一步确定核SOCS1在原代免疫细胞中的新功能，我们现在已经产生了表达无核SOCS1突变体的BAC转基因小鼠（以及eGFP和荧光素酶报告基因），从而可以在回交SOCS1-/-小鼠时研究核定位的重要性。建议从三个方面探究SOCS1的核功能：i)假设核SOCS1通过蛋白酶体活性调节IFN诱导基因子集，从而促进IFN信号的终止。这种作用模式将为SOCS1调节干扰素（IFN）信号传导的已知机制增加一个全新的方面，并可以作为其他依赖JAK/STAT的信号传导模块的模板。ii)假设SOCS1易位进入细胞核是一个受调控的事件，依赖于分子内的蛋白质修饰。iii)通过无偏见的蛋白质组学方法确定核SOCS1的新相互作用伙伴。基于以往的工作，我们将首先研究核SOCS1与候选DDB1的相互作用及其在细胞周期调节中的作用。从实验中，它有望对核SOCS1迄今尚未明确的功能获得新的见解。

This is a renewal application for a project entitled 'Identification of nuclear functions of Suppressor of Cytokine Signalling-1 (SOCS1)' that was funded previously from 2009-2012 by DFG (DA592/4-1). SOCS proteins are inducible, intracellular feedback inhibitors of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway. Despite the well-studied function of SOCS proteins in inhibition of membrane-proximal cytokine receptor signaling we have identified a nuclear localization signal within SOCS1 resulting in nuclear translocation of SOCS1. In the last funding period we were for the first time able to assign a function to nuclear SOCS1 which is the limitation of NFkappaB signaling by proteasomal degradation of p65. To further identify new functions of nuclear SOCS1 within primary immune cells we have now generated BAC transgenic mice that express a non-nuclear SOCS1 mutant (together with eGFP and luciferase reporters) that allow studying the importance of nuclear localization when backcrossed to SOCS1-/- mice. It is suggested to interrogate the nuclear function of SOCS1 in three areas: i) It is hypothesized that nuclear SOCS1 regulates a subset of IFN inducible genes via proteasome activity thereby contributing to termination of IFN signaling. Such a mode of action would add an entirely new aspect to the known mechanism by which SOCS1 regulates interferon (IFN) signaling and could serve as template for other JAK/STAT dependent signaling modules as well. ii) It is hypothesized that translocation of SOCS1 into the nucleus is a regulated event that depends on protein modifications within the molecule. iii) New interaction partners of nuclear SOCS1 will be identified in an unbiased proteomics approach. Based on previous work the interplay of nuclear SOCS1 with candidate DDB1 and its role for cell cycle regulation will be studied first. From the experiments it is expected to gain new insight into hitherto ill-defined functions of nuclear SOCS1.