Graded Proteasome Dysfunction in <i>Caenorhabditis elegans</i> Activates an Adaptive Response Involving the Conserved <i>SKN-1</i> and <i>ELT-2</i> Transcription Factors and the Autophagy-Lysosome Pathway

The maintenance of cellular proteins in a biologically active and structurally stable state is a vital endeavor involving multiple cellular pathways. One such pathway is the ubiquitin-proteasome system that represents a major route for protein degradation, and reductions in this pathway usually have adverse effects on the health of cells and tissues. Here, we demonstrate that loss-of-function mutants of the Caenorhabditis elegans proteasome subunit, RPN-10, exhibit moderate proteasome dysfunction and unexpectedly develop both increased longevity and enhanced resistance to multiple threats to the proteome, including heat, oxidative stress, and the presence of aggregation prone proteins. The rpn-10 mutant animals survive through the activation of compensatory mechanisms regulated by the conserved SKN-1/Nrf2 and ELT-2/GATA transcription factors that mediate the increased expression of genes encoding proteasome subunits as well as those mediating oxidative- and heat-stress responses. Additionally, we find that the rpn-10 mutant also shows enhanced activity of the autophagy-lysosome pathway as evidenced by increased expression of the multiple autophagy genes including atg-16.2, lgg-1, and bec-1, and also by an increase in GFP::LGG-1 puncta. Consistent with a critical role for this pathway, the enhanced resistance of the rpn-10 mutant to aggregation prone proteins depends on autophagy genes atg-13, atg-16.2, and prmt-1. Furthermore, the rpn-10 mutant is particularly sensitive to the inhibition of lysosome activity via either RNAi or chemical means. We also find that the rpn-10 mutant shows a reduction in the numbers of intestinal lysosomes, and that the elt-2 gene also plays a novel and vital role in controlling the production of functional lysosomes by the intestine. Overall, these experiments suggest that moderate proteasome dysfunction could be leveraged to improve protein homeostasis and organismal health and longevity, and that the rpn-10 mutant provides a unique platform to explore these possibilities.细胞蛋白质维持生物学活性与结构稳定状态是一项涉及多条细胞通路的重要生命过程。其中泛素-蛋白酶体系统（ubiquitin-proteasome system）是蛋白质降解的主要通路之一，该通路功能减弱通常会对细胞与组织健康产生不利影响。本研究发现，秀丽隐杆线虫（Caenorhabditis elegans）蛋白酶体亚基RPN-10的功能丧失型突变体呈现中度蛋白酶体功能障碍，却意外地同时延长了寿命，并增强了生物体对多种蛋白质组胁迫的抵抗力，包括热胁迫、氧化应激以及易聚集蛋白质的存在。rpn-10突变体的存活依赖于保守转录因子SKN-1/Nrf2与ELT-2/GATA介导的代偿机制激活：该通路可上调编码蛋白酶体亚基的基因，以及参与氧化应激与热应激应答的基因的表达。此外，本研究还发现rpn-10突变体的自噬-溶酶体通路活性增强，具体表现为包括atg-16.2、lgg-1与bec-1在内的多个自噬相关基因表达上调，同时GFP::LGG-1阳性斑点数量增加。该通路的关键作用得到了验证：rpn-10突变体对易聚集蛋白质的抵抗能力依赖于自噬基因atg-13、atg-16.2与prmt-1。进一步研究发现，rpn-10突变体对通过RNA干扰（RNAi）或化学手段抑制溶酶体活性的处理尤为敏感。此外，该突变体的肠道溶酶体数量减少，且elt-2基因在调控肠道功能性溶酶体生成方面发挥了全新且至关重要的作用。综上，本研究结果表明，适度的蛋白酶体功能障碍可被用于改善蛋白质稳态、提升机体健康水平并延长寿命，而rpn-10突变体为探索这些潜在应用提供了独特的实验平台。