Medicum, Department of Biochemistry and Developmental Biology, Faculty of Medicine, University of Helsinki, Haartmaninkatu 8, 00290 Helsinki, Finland.
Cells. 2020 Aug 8;9(8):1858. doi: 10.3390/cells9081858.
The ubiquitin-proteasome system (UPS) and the autophagy-lysosomal pathway (ALP) are the two main eukaryotic intracellular proteolytic systems involved in maintaining proteostasis. Several studies have reported on the interplay between the UPS and ALP, however it remains largely unknown how compromised autophagy affects UPS function in vivo. Here, we have studied the crosstalk between the UPS and ALP by investigating the tissue-specific effect of autophagy genes on the UPS at an organismal level. Using transgenic expressing fluorescent UPS reporters, we show that the downregulation of the autophagy genes and , , and (mEPG5) by RNAi decreases proteasomal degradation, concomitant with the accumulation of polyubiquitinated proteasomal substrates in a tissue-specific manner. For some of these genes, the changes in proteasomal degradation occur without a detectable alteration in proteasome tissue expression levels. In addition, the RNAi-induced reduction in proteasome activity in intestinal cells is not dependent on /p62 accumulation. Our results illustrate that compromised autophagy can affect UPS in a tissue-specific manner, and demonstrate that UPS does not function as a direct compensatory mechanism in an animal. Further, a more profound understanding of the multilayered crosstalk between UPS and ALP can facilitate the development of therapeutic options for various disorders linked to dysfunction in proteostasis.
泛素-蛋白酶体系统（UPS）和自噬溶酶体途径（ALP）是参与维持蛋白质平衡的两种主要的真核细胞内蛋白水解系统。有几项研究报道了 UPS 和 ALP 之间的相互作用，然而，自噬受损如何影响体内 UPS 功能在很大程度上仍然未知。在这里，我们通过研究自噬基因对 UPS 的组织特异性影响，研究了 UPS 和 ALP 之间的串扰。使用表达荧光 UPS 报告物的转基因，我们表明，通过 RNAi 下调自噬基因 和 、 、 和 （mEPG5）会以组织特异性的方式降低蛋白酶体降解，同时多聚泛素化蛋白酶体底物的积累。对于其中一些基因，蛋白酶体降解的变化发生在蛋白酶体组织表达水平没有可检测到的改变的情况下。此外，肠道细胞中 RNAi 诱导的蛋白酶体活性降低不依赖于 /p62 的积累。我们的结果表明，自噬受损可以以组织特异性的方式影响 UPS，并表明 UPS 在动物中不作为直接的补偿机制发挥作用。此外，对 UPS 和 ALP 之间的多层串扰有更深入的了解，可以为与蛋白质平衡功能障碍相关的各种疾病的治疗选择提供便利。
