Ubiquitin And SUMO Post-Translational Modifications In Development And Disease

泛素样SUMO蛋白的翻译后修饰调节了广泛的细胞过程。我们对脱苏酶SENP1的研究首次显示了这一途径在发育过程中的作用，特别是在胎盘的形成和功能中。相扑领域的一个主要问题是如何实现特异性。如何选择特定的靶蛋白进行summoylation或去summoylation ?是什么规定了SUMO1与SUMO2或SUMO3的结合？我们已经证明缺乏SUMO1的小鼠可以存活，这显然是由于SUMO2/3对SUMO1靶点的SUMO1化的代偿性利用。对不同SUMO蛋白的独特和共享功能的进一步了解来自对SENP1突变体的进一步分析。我们之前的数据表明，观察到的SENP1表型缺陷仅是由于较高的共轭SUMO1稳态水平，而不是SUMO2或SUMO3。因此，我们想知道降低SENP1突变背景中SUMO1的总水平是否会挽救这种表型。我们注意到，SUMO1突变的杂合小鼠显示出高分子质量SUMO1偶联物水平的显着降低。通过与SENP1突变体杂交，我们获得了SENP1纯合胚胎，而SUMO1突变体也是杂合胚胎。这些胚胎的SUMO1偶联物水平显著降低，接近野生型水平，尽管去氧化活性在这些胚胎中仍然受到损害。重要的是，这些胚胎存活到出生提供了确凿的证据，证明SENP1发育缺陷依赖于SUMO1。令人惊讶的是，从SENP1突变背景中完全消除SUMO1会导致更严重的表型，突变体在更早的发育阶段死亡。与SUMO1或SENP1突变体不同，双纯合胚胎积累了显著水平的SUMO2/3结合蛋白。这些发现进一步证明，在SUMO1缺失的情况下，正常被SUMO1介导的靶蛋白可以与SUMO2/3进行代偿性偶联。此外，在SENP1缺失的情况下，这些SUMO2/3偶联物的积累可能会对发育中的胚胎产生更严重的后果，这可能是因为不适当的SUMO平行物使用。

Post-translational modification with the ubiquitin-like SUMO proteins regulates a wide range of cellular processes. Our work on the desumoylating enzyme SENP1 was the first to show a role for this pathway in development, specifically in the formation and function of the placenta. A major question in the SUMO field is how is specificity achieved. How are specific target proteins selected for sumoylation or desumoylation and what specifies the conjugation of SUMO1 vs. SUMO2 or SUMO3? We have shown that mice lacking SUMO1 are viable, apparently due to the compensatory utilization of SUMO2/3 for sumoylation of SUMO1 targets. Additional insight into the distinct and shared functions of the different SUMO proteins has come from further analysis of the SENP1 mutant. Our previous data suggested that the observed SENP1 phenotypic defects were due specifically to higher steady state levels of conjugated SUMO1 only, and not SUMO2 or SUMO3. We therefore asked whether reducing total SUMO1 levels in the SENP1 mutant background would rescue the phenotype. We had noted that mice heterozygous for the SUMO1 mutation showed a significant reduction in the level of high molecular mass SUMO1 conjugates. By crossing to the SENP1 mutant we generated SENP1 homozygous embryos that were also heterozygous for the SUMO1 mutation. These were found to have a striking reduction in the level of SUMO1 conjugates, approaching wild-type levels, although desumoylation activity still is compromised in these embryos. Importantly, these embryos survived to birth providing firm evidence that the SENP1 developmental defects are SUMO1 dependent. Surprisingly, completely eliminating SUMO1 from the SENP1 mutant background causes a more severe phenotype, with mutants dying at even earlier developmental stages. Unlike SUMO1 or SENP1 mutants, the double homozygous embryos accumulate significant levels of SUMO2/3 conjugated proteins. These findings provide further evidence that target proteins normally sumoylated with SUMO1 can undergo compensatory conjugation with SUMO2/3 upon the loss of SUMO1. Further, in the additional absence of SENP1, the accumulation of these SUMO2/3 conjugates can have even more severe consequences for the developing embryo perhaps because of inappropriate SUMO paralog usage.