Rockel Thomas Dino, Stuhlmann Dominik, von Mikecz Anna
Institut für Umweltmedizinische Forschung at Heinrich-Heine-University, Auf'm Hennekamp 50, 40225 Düsseldorf, Germany.
J Cell Sci. 2005 Nov 15;118(Pt 22):5231-42. doi: 10.1242/jcs.02642. Epub 2005 Oct 25.
The ubiquitin proteasome system plays a fundamental role in the regulation of cellular processes by degradation of endogenous proteins. Proteasomes are localized in both, the cytoplasm and the cell nucleus, however, little is known about nuclear proteolysis. Here, fluorogenic precursor substrates enabled detection of proteasomal activity in nucleoplasmic cell fractions (turnover 0.0541 microM/minute) and nuclei of living cells (turnover 0.0472 microM/minute). By contrast, cell fractions of nucleoli or nuclear envelopes did not contain proteasomal activity. Microinjection of ectopic fluorogenic protein DQ-ovalbumin revealed that proteasomal protein degradation occurs in distinct nucleoplasmic foci, which partially overlap with signature proteins of subnuclear domains, such as splicing speckles or promyelocytic leukemia bodies, ubiquitin, nucleoplasmic proteasomes and RNA polymerase II. Our results establish proteasomal proteolysis as an intrinsic function of the cell nucleus.
泛素蛋白酶体系统通过降解内源性蛋白质在细胞过程的调控中发挥着基础性作用。蛋白酶体定位于细胞质和细胞核中，然而，关于核蛋白水解的了解却很少。在这里，荧光前体底物能够检测核质细胞组分中的蛋白酶体活性（周转率为0.0541微摩尔/分钟）以及活细胞核中的蛋白酶体活性（周转率为0.0472微摩尔/分钟）。相比之下，核仁或核膜的细胞组分中不含有蛋白酶体活性。对异位荧光蛋白DQ-卵清蛋白的显微注射显示，蛋白酶体蛋白降解发生在不同的核质焦点处，这些焦点与亚核结构域的标志性蛋白部分重叠，如剪接斑点或早幼粒细胞白血病小体、泛素、核质蛋白酶体和RNA聚合酶II。我们的结果确立了蛋白酶体蛋白水解作为细胞核的一种内在功能。
