Ubiquitin And SUMO Post-Translational Modifications In Development And Disease

泛素样相扑蛋白的翻译后修饰调控着广泛的细胞过程。我们对脱苏糖化酶SENP1的研究首次显示了这一途径在发育中的作用，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专一性。如何选择特定的靶蛋白进行SUMO化或去甲基化？SUMO1与SUMO2或SUMO3的结合是什么指定的？我们已经证明，缺乏SUMO1的小鼠是存活的，显然是由于SUMO2/3对SUMO1靶标的SUMO1靶标的代偿利用。对SENP1突变体的进一步分析进一步揭示了不同相扑蛋白的不同和共同的功能。我们以前的数据表明，观察到的SENP1表型缺陷只是由于较高的稳态水平的共轭SUMO1，而不是SUMO2或SUMO3。因此，我们询问降低SENP1突变背景中的总SUMO1水平是否会挽救表型。我们已经注意到，SUMO1突变杂合子的小鼠显示出高分子质量的SUMO1结合物水平显著降低。通过与SENP1突变体杂交，我们产生了SENP1纯合子胚胎，这些胚胎也是SUMO1突变的杂合子。研究发现，这些胚胎的SUMO1结合物水平显著降低，接近野生型水平，尽管这些胚胎中的脱氨基化活性仍然受到影响。重要的是，这些胚胎存活到出生提供了SENP1发育缺陷依赖于SUMO1的确凿证据。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，突变株甚至会在更早的发育阶段死亡。与SUMO1或SENP1突变体不同，双纯合子胚胎积累了大量的SUMO2/3结合蛋白。这些发现提供了进一步的证据，证明通常与SUMO1相加的靶蛋白在失去SUMO1后可以与SUMO2/3进行补偿结合。此外，在缺乏SENP1的情况下，这些SUMO2/3结合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地使用相扑Paralog。

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.