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

这是DFG(DA592/4-1)2009-2012年资助的名为《细胞因子信号抑制因子抑制因子-1(SOCS1)的核功能鉴定》项目的续展申请。SOCS蛋白是Janus激酶(JAK)/信号转导和转录激活因子(STAT)通路的可诱导的细胞内反馈抑制物。尽管SOCS蛋白在抑制膜-近端细胞因子受体信号转导中的功能已被充分研究，但我们已经在SOCS1中发现了导致SOCS1核转位的核定位信号。在上一个资助时期，我们第一次能够赋予核SOCS1一个功能，这是通过蛋白酶体降解p65来限制NFkappaB信号的。为了进一步确定核SOCS1在初级免疫细胞中的新功能，我们现在培育了表达非核SOCS1突变体(连同EGFP和荧光素酶报告)的BAC转基因小鼠，这使得我们能够研究当回交到SOCS1-/-小鼠时核定位的重要性。建议从三个方面探讨SOCS1的核功能：1)假设核SOCS1通过蛋白酶体活性调节干扰素诱导基因的一个子集，从而促进干扰素信号的终止。这种作用模式将为已知的SOCS1调节干扰素信号的机制增加一个全新的方面，并可以作为其他JAK/STAT依赖的信号模块的模板。Ii)假设SOCS1移位到核中是一个受调控的事件，取决于分子内的蛋白质修饰。三)将以无偏见的蛋白质组学方法确定核SOCS1的新相互作用伙伴。在前人工作的基础上，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控中的作用。从这些实验中，人们有望对核SOCS1迄今定义不清的功能有新的认识。

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.