Tob1 is a Constitutively Expressed Repressor of Liver Regeneration

How proliferative and inhibitory cell signals integrate to control liver regeneration remains poorly understood. A screen for antiproliferative factors repressed after liver injury identified Tob1, a member of the PC3/BTG1 family of mitoinhibitory molecules as a target for further evaluation. Tob1 protein decreases after 2/3 hepatectomy in mice secondary to post-transcriptional mechanisms. Deletion of Tob1 increases hepatocyte proliferation and accelerates restoration of liver mass after hepatectomy. Down-regulation of Tob1 is required for normal liver regeneration and Tob1 controls hepatocyte proliferation in a dose-dependent fashion. Tob1 associates directly with both Caf1 and the Cyclin/cdk complex to modulate kinase activity. In addition, Tob1 has significant effects on the transcription of critical cell cycle components, including E2F targets and genes involved in p53 signaling. These studies provide direct evidence that levels of an inhibitory factor control the rate of liver regeneration. Our data identify Tob1 as a crucial check-point molecule that acts by by modulating levels and activity of cell cycle proteins. Samples from wild type and Tob1 null mice as normal adults and 24 hours after 2/3 hepatectomy are used. Each experimental point used data from two chips, each having a different set of three pooled animals. In summary we had 8 chips: 2 for WT time 0, 2 for WT time 24, 2 for KO time 0, 2 for KO time 24.细胞增殖与抑制信号如何协同调控肝脏再生，目前仍未被充分阐明。通过对肝损伤后被抑制的抗增殖因子进行筛选，我们鉴定出Tob1——PC3/BTG1有丝分裂抑制分子家族的成员，作为后续研究的靶标。小鼠在接受2/3肝切除术后，Tob1蛋白的表达水平会因转录后调控机制而下调。敲除Tob1可促进肝细胞增殖，并加速肝切除术后肝脏质量的恢复。正常肝脏再生需要Tob1的表达下调，且Tob1以剂量依赖的方式调控肝细胞增殖。Tob1可直接结合Caf1与细胞周期蛋白-Cdk复合物，以调控激酶活性。此外，Tob1对关键细胞周期组分的转录具有显著调控作用，包括E2F靶基因以及参与p53信号通路的基因。本研究提供直接证据表明，一种抑制性因子的表达水平可调控肝脏再生的速率。我们的研究数据证实Tob1是一种关键的细胞周期检验点分子，其通过调控细胞周期蛋白的表达水平与活性发挥功能。本研究使用的样本取自正常成年野生型（wild type，WT）小鼠与Tob1基因敲除小鼠，分别采集其未手术的基础状态以及2/3肝切除术后24小时的组织样本。每个实验分组均采用两份基因芯片的数据，每份芯片对应一组由三只动物混合制备的样本，且不同芯片对应的动物组各不相同。综上，本研究共使用8份基因芯片：野生型0小时组2份，野生型24小时组2份，敲除型0小时组2份，敲除型24小时组2份。